Finding a ready-to-fly Taranis compatible, Eachine compatible, S4 compatible under 200€ drone The question
I'm looking for a drone under 200€, preferably 5" (as that's what I'm used to)  but other sizes are ok, that can be purchased/delivered to France, is compatible with a Taranis X7 and an Eachine EV800D. It needs to be as plug & play as possible because I'd rather have the opportunity to fly it at least once before spending another 10 hours Macgyvering the thing.
I have found some fairly interesting starter deals on getfpv.com:

https://www.getfpv.com/iflight-cidora-sl5-e-5-fpv-racing-drone-pnp.html
Only problem: according to the description I need to add a receiver which is, if I understood correctly, precisely what I couldn't get to work in my last build
https://www.getfpv.com/emax-hawk-sport-5-pnp-brushless-fpv-drone-1700kv.html
I can't determine if this one is compatible with the gear I already own.

Why not buy a complete package ?:
Because I already own the transmitter and the FPV goggles. And from what I understood the gear I got is decent enough, so I'd rather keep using.
plus I'm used to flying a sim with the Taranis so I'd rather keep it.
The Context, ignore if you don't care why I'm looking for such a plug & play solution:
Last year, after watching a few guys flying their quads, I decided to buy one. Having quite some experience with building computers and being pushed by the other guys to custom build it, I ordered a bunch of component (chosen by them) and bought some second hand from said friends. I got started building the drone and it was a mess. I had done soldering work a few years before but never had it required such precision so I messed up and burnt parts of my first FC. Replaced it, managed to solder everything, only to realize halfway through the build that I couldn't for the life of me pair the Taranis to the receiver and have no way to check if the Taranis is at fault for cheap. I did a lot of research, re-soldered using different connections, changed the settings in betaflight ... in the end I changed the receiver. Still the same problem, spent an other half dozen hours on it.
I spare you a whole lot more problems and research online...
conclusion: after a good 25 hours spent trying to get this drone working I got so frustrated that I put everything in a box and left it there.
note: during the year this group dissolved itself and I now have no contact with anyone that knows anything about quads, so I couldn't get help in building/troubleshooting anything.
Now, I want to fly, but I'd rather not have to build, flash & setup everything myself while going blind and with nobody to help me if need be. Thus, I'm looking for a ready-to-fly drone.

I think the Cidora SL5-E is a very good choice. What you need to look for is the "BNF" suffix in the description which stands for "Bind and Fly". In that case a receiver is already built in.
On the iflight website you can select this option.
If you have the choice, it's best to select the r-xsr because it comes with telemetry.
If you are browsing shops look for these acronyms:
BNF: Bind and Fly, you can pair it to your existing remote and goggles
PNP: Plug and Play, you install your own receiver
RTF: Ready to Fly: a complete kit with everything included such as remote and sometimes goggles.


Vibrating like a jelly when takeoff I have Kotleta 20 UAVCAN ESCs. When I trying to increase throttle, motors are vibrating like a jelly. How can I configure my ESCs via development port? What are best options for non vibrated flight? Is autotune good solution for that?Takeoff video

It might be a too high P-gain in the PID control loop. I assume you use Pixhawk so that document might be useful: PID tuning guide
The oscillation is from what i see on the roll axis so the MC_ROLLRATE_P might be a parameter to look into.
Regarding the Debug port: Your escs have a  Pixhawk Debug Mini connector and a serial console (with baudrate 115200 at 8 bit no parity 1 stopbit) should be available at pin 2 (tx) and 3 (rx) (pin 1: Processor voltage, pin 2: Console TX of ESC, pin 3: Console RX of ESC, pin 6: GND). See:  Pixhawk Debug Mini
You will need to connect your serial interface with the voltage.matching your controller (probably 1.8 or 3.3V) and the out pin of your interface with the in pin of the ESC and vice versa.
The commands you have available are described in the Sapog Reference Manual
Please provide more information about your setup to help others to help you with your question.


How does a quadcopter flip without falling very much? I have a quadcopter and it has a flip function (as do many other quadcopters).

I was wondering how this works. Say I am flipping it right (clockwise), I assume the motors on the left spin much faster than those in the right. If so, how does the quadcopter not loose too much altitude when doing this?

The trick is speed. The reason why multirotors don't lose (very much) altitude while performing quick mid-air aerobatics is because of the speed of the move and the skillful management of throttle by the pilot.

You're correct in presuming that a multirotor performs a flip by changing the speed of the motors on each side of the craft. Freestyle pilots usually make use of near-total stick deflection and extreme rate profiles targeting ~600-1200 deg/s of angular velocity. The fact that the flight controller speeds up motors on the side which needs to rotate "up" and slowing down those on the side which needs to rotate "down" ensures that the move occurs as fast as possible because all four motors contribute to the torque which rotates the multirotor.

The other factor which helps the multirotor not descend too much is the skillful management of the throttle during the move. By lowering the throttle to near idle while the craft is inverted, the pilot minimizes the amount of thrust the craft generates which acts to pull it down towards the ground. As I discuss in my answer to "What's the purpose of airmode and idle up?", the idle up and airmode features (of the RC transmitter and flight controller respectively) help ensure that the multirotor is in control during these times of low-throttle.

Because of these two factors, the duration in which gravity has the power to suck the craft towards the ground is often too little to matter, and the multirotor flips in-place.

Of course, there's nothing preventing you as the pilot from slowing down the flip and performing an "O"-shaped loop instead of a flip in-place. This can be done by easing off the roll/pitch axis and turning down rate profiles.


Learning how to fly a 3" quad Preface: I'm a newer pilot to the FPV world with limited stick time on 5".

I just built and flew a 3" for the first time. LOS is not a problem for verifying functionality. Then I put on the goggles and almost lost my mind! The throttle is super touchy. Seems like just a couple clicks off of minimum and it's climbing above the trees. All other controls seem reasonable.

My options as I see them:

Using a 3 cell battery (I'm using 4s) for a bit to get used to it.
Change to a lower pitch prop. Not sure what I have on there now but 4" pitch seems likely. I'll have to check when I can.
Throttle scaling in BetaFlight. An option but seems like training wheels, in a way. I feel like I should learn it as it is. Scaling seems like it would drag out the learning curve.
More stick time. Just fly it as it is and start in a big field and get the stick time.

What is the best option path? I'm guessing option 4 but I'm open to other's experience.

Thanks

Throttle scaling is not training wheels so don't feel back about using it.  It's never fun to fly a quad with a throttle that is too touchy.

Another option is throttle expo which you can turn on in the rates area of Betaflight.  Find the hover point for the quad and set that to be the center of your throttle curve. Then add some expo to soften the rate and give you some more resolution at the hover point.

Also keep in mind that with a 3" inch size, matching your motor kV and battery cell counts are very important. If your motors are up at 6000kv area you probably want to stay with 3s batteries.


How fragile are the SMA connectors used in FPV equipment? I've heard that it is a terrible idea to install and remove SMA antennae from my goggles every time I need to pack it away after a flight session. I know that this is because the SMA connector is fragile and wasn't designed for a high mating cycle rating, but how serious is the concern that the SMA connectors on my googles will break?

If I began taking off my antennae when I need to pack it away, how quickly would the connectors break or terribly attenuate the signal?

According to electronics-notes.com, the mating cycle rating for the SMA/RP-SMA connector is 500 cycles. However, it is important to note that this rating assumes that the connection and disconnection process happens as smoothly as possible, with the body of the connector not moving at all while the screw connection is tightened sufficiently to not allow the joint to shift while connected. Under nonideal conditions, the actual lifespan of the SMA connectors on FPV goggles is likely to be far shorter.

Under the best of circumstances, the connection would likely last: (assuming one mating cycle per flight session)

~19 years @ 2 sessions/month
~9.5 years @ 1 session/week
~5 years @ 2 sessions/week
~2.5 years @ 4 sessions/week
~1.4 years @ 7 sessions/week

From this, we can see that the answer likely depends on how often you fly and how long you would like your goggles to last. Although the attenuation (signal strength reduction) of the connector will increase with every mating cycle, if you fly infrequently enough it is possible that you may be ready to upgrade to a new goggle by the time that the SMA connectors begin to become a serious problem.

If you take care to make and break connections cleanly, casual pilots who don't fly very often might not see too much of a problem, but more serious pilots who fly more than once a week definitely shouldn't be removing their antennae on a regular basis.


What affects the total flight time for a drone? What factors would affect a drone's flight time? Battery capacity? Weight? Anything else?

I'd watch out for several factors:
1. Weight
Drop any additional weight that you don't absolutely need for functioning.  This may mean downsizing to smaller motors, which obviously means that you have to balance weight vs. power; you may be able to get your flight time much longer but at the expense of speed.
2. Battery
Obviously the more juice you got, the longer you can go for.  Again, though it's going to be a balance between the weight of your battery... go for lighter technologies like LiPo.
Also, make sure you've got new batteries on your drone; as your batteries age, they'll lose juice and capacity.
3. Motors
If you really want to increase the flight time... go for lighter less powerful motors.  Of course, you won't be able to go as far, so that may not be a tradeoff you want to make.
4. Weather
Make sure you're flying your drone in dry weather... Condensation or water droplets will both add resistance to any moving parts and weight.  Also, when the weather is well below freezing you'll notice that your batteries will start performing less well, as well as having increased friction.
5. Maintenance
Keep all moving parts well greased!  As friction increases, the amount of battery power you use will increase in consequence.
Also, make sure all contacts remain solid.  Though it's not a big issue with newer drones, rust in the contacts / loose contacts will eat power.


Why isn't my manual DSHOT600 programming of a HobbyWing ESC not responding to direction change? I wrote a firmware for an STM32L4 board to talk to a HobbyWing XRotor Micro 60A running BLHeli_32.
I can drive each motor indiviudally just fine using DSHOT600 by bit-blasting the signals out of GPIO with correct timings (based on NOPs for an 80MHz core). It works fine: I set up the packets for each motor, and then send them sequentially to each GPIO in a loop; until I set the throttle to zero, then I stop sending any packets.
However, the motors are not spinning in the proper direction so I am trying to issue ESC commands 7 and 8 and 20 and 21. My strategy is to STOP sending throttle packets entirely. Then I send command 7 (or 8, or 20, or 21) to each prop 10 times with 100ms between each command, and then turn the props back on with a nonzero throttle.
Documentation is super thin on this. I've found several sites saying special commands 7,8 or 20,21 should reverse the props, as well as different # of times the commands must be sent, etc. But I don't see a reversal.
Suggestions?

I would recommend taking a look at the source code for Betaflight to get some hints, since the DSHOT commands should be the same. More specifically the code for enabling turtle mode (flip over after crash), which reverses the motor directions.
It looks like the code that activates turtle mode is:
dshotCommandWrite(ALL_MOTORS, getMotorCount(), DSHOT_CMD_SPIN_DIRECTION_REVERSED, DSHOT_CMD_TYPE_INLINE);

Where DSHOT_CMD_SPIN_DIRECTION_REVERSED is the value 21 in an enum.
typedef enum {
    DSHOT_CMD_MOTOR_STOP = 0,
    DSHOT_CMD_BEACON1,
    DSHOT_CMD_BEACON2,
    DSHOT_CMD_BEACON3,
    DSHOT_CMD_BEACON4,
    DSHOT_CMD_BEACON5,
    DSHOT_CMD_ESC_INFO, // V2 includes settings
    DSHOT_CMD_SPIN_DIRECTION_1,
    DSHOT_CMD_SPIN_DIRECTION_2,
    DSHOT_CMD_3D_MODE_OFF,
    DSHOT_CMD_3D_MODE_ON,
    DSHOT_CMD_SETTINGS_REQUEST, // Currently not implemented
    DSHOT_CMD_SAVE_SETTINGS,
    DSHOT_CMD_SPIN_DIRECTION_NORMAL = 20,
    DSHOT_CMD_SPIN_DIRECTION_REVERSED = 21,
    DSHOT_CMD_LED0_ON, // BLHeli32 only
    DSHOT_CMD_LED1_ON, // BLHeli32 only
    DSHOT_CMD_LED2_ON, // BLHeli32 only
    DSHOT_CMD_LED3_ON, // BLHeli32 only
    DSHOT_CMD_LED0_OFF, // BLHeli32 only
    DSHOT_CMD_LED1_OFF, // BLHeli32 only
    DSHOT_CMD_LED2_OFF, // BLHeli32 only
    DSHOT_CMD_LED3_OFF, // BLHeli32 only
    DSHOT_CMD_AUDIO_STREAM_MODE_ON_OFF = 30, // KISS audio Stream mode on/Off
    DSHOT_CMD_SILENT_MODE_ON_OFF = 31, // KISS silent Mode on/Off
    DSHOT_CMD_MAX = 47
} dshotCommands_e;

Note that DSHOT_CMD_SPIN_DIRECTION_NORMAL has the value 20, and seems to be the command used to set the motor direction to normal. There is also DSHOT_CMD_SPIN_DIRECTION_1 and DSHOT_CMD_SPIN_DIRECTION_2 with the values 7 and 8 respectively, but I can't find anywhere where they are used.
Examining the definition for dshotCommandWrite we find that a variable repeats is set to 10 with the current input and that delayAfterCommandUs is set to 1000.
I would assume that this means that you should send the command 21 to the motors 10 times with an interval of 1000 μs. So I would try doing as you did before but with a delay of 1000 μs (1 ms) between each repetition instead of 100 ms.


Drone Controller, PID Is Enough, or ODE Modeling Required? I am planning to build a remote controlled dualcopter where I have two propellers, one on top and one on the bottom. The bottom rotor will be gimbal based for thrust vectoring. Something like this,
https://www.youtube.com/watch?v=b14_XQ5nd2A
I want to build the controller from scratch (the fella in the video used Multiwii Mega flight board controller). Do I need to get into ODEs, differential equations, etc. as the following paper has done?
https://andrew.gibiansky.com/downloads/pdf/Quadcopter%20Dynamics,%20Simulation,%20and%20Control.pdf
Or is this overkill? Could I simply use a PID based design for a target tilt, adjust control to reach it, and do the same for motor speed, etc?

You can certainly use a PID based design and tune it from there. This design is simple enough that if you just have XYZ PID controllers and proper output mixing it should work just fine.
I'd recommend doing something similar to his design where the motors are far from the center of mass which will increase the torque generated by tilting the motors.
Good luck!


At what point does drone insurance become worth it? Should the average enthusiast buy drone insurance?

I'm expecting it to be essential for commercial use, or if the drone was used in a busy area, but what if the drone was a collaboration between multiple people?

This is a personal approach, so like all financial advice it's only worth what you paid for it.
If you have worked with the insurance industry in the past, you will likely have learned that good insurance companies pay out almost (if not more) money than they take in. This is because what the insurer is doing is taking the premiums and lending them out, much like a bank. So when you spend \$100/yr across 10 years, and you get back a $1000 payout in the tenth year, the entire time the insurance company has been earning interest on the money you gave them. This 5-10% overhead is quite profitable when you have tens and hundreds of billions of dollars stockpiled.
The upshot is that insurance won't save you any money in the long-term, it only spreads the financial pressure of a decision across time. I only consider insurance worthwhile when the cost of throwing my hands up and walking away is unacceptably high. Put another way, I only get insurance when either required by contract or law (e.g. renters insurance or auto insurance), or when I cannot afford the consequences of not having the thing which is insured.

Worthwhile: I have a pet, and I don't want to have a financial consideration enter into whether life-saving surgery is an option.
Not worthwhile: I have a television which I don't really watch and wouldn't miss it if it weren't there anymore.

You'll have to decide for yourself the impact of losing your drone. If it's just a toy and you don't think you'll fly it again if you lose it, then maybe it's not worth the cost of insurance. If it's your livelihood and you can't afford to buy another one then insurance is a guarantee against catastrophic business failure.
Or if the amount of damage you could do with your drone could cause you to be personally liable for a ruinous amount, then you might want to protect yourself with insurance.
P.S. Drop a comment when you decide, I'd love to know how your reasoning went.


Why do most multirotors use outrunner brushless motors? I've noticed that most every quadcopter drone I see uses outrunner BLDC motors like this:

Why is that? What unique advantages to outrunners have that make them better than inrunners for multirotors?

The difference between outrunner and inrunner BLDC (brushless DC) motors is that an outrunner's rotor is outside the stator while an inrunner's rotor is inside the stator.

 (cit.)

In general, outrunners create more torque and rotate slower than inrunners, which usually have less torque and rotate significantly quicker. The two different designs are possible because it is relatively easy to conceptualize how to flip the order of the stator and rotor within the motor due to the fact that no mechanical commutation is necessary, unlike in a brushed motor.

Whichever side of the motor (outside or inside) that is the stator is far thicker than the other because the orientation of the coils on the stator contributes a lot of depth. Outrunners trade increased torque for decreased rotation rate because the electromotive force between the magnets and coils acts roughly at the air gap between them, which is further from the center of the motor in an outrunner, resulting in an increased moment arm and more torque. (remember that τ = F x r where τ is torque in Nm, F is the force, and r is the distance from the rotational axis)

This increased torque is critical because the BLDC motors have no gearboxes between them and the propellers, which require decent amounts of torque to spin. In other systems, motors could use gearboxes to trade speed for torque, but the requirements of multirotors to be as efficient and lightweight as possible don't allow for them to be installed.


What's the difference between the Spektrum DX6 and DX6e? Besides 90 bucks :-)
Looking through the specifications, they're both DSM2/DSMX radios with more model memories than you can use, 6 channels, wireless trainer, telemetry, 7 aircraft wing mixing types and 6 tail types.
The only differences I can see is 4 vs 5 programmable mixes, and 2 vs 7 helicopter swashplate types.
Is there a less-obvious feature that's missing, that would mean an average beginner would need to upgrade from one to the other? (and, yes, I know Flysky and Jumper offer great value, I'm just curious about how Spektrum differentiate these two transmitters.)
Links to Spektrum's website for comparison: DX6e DX6

I found this comparison chart in an rcgroups thread. The DX6e and DX6 (G3 in this case) are very similar, but the biggest differences that I could find is that the DX6e doesn't have voice alerts and that it doesn't support wired trainer, which will make it harder to use with for example a simulator on a PC. The DX6e also supports mode 5, where the throttle centers with a spring.
I see no compelling reason to upgrade from one to the other. If you want to use it with a simulator (which you probably want, at least as a beginner) it is cheaper to just buy a wireless adapter to be able to connect the transmitter to the PC via the wireless trainer link.


Please recommend a soldering iron for hobby use I'm frustrated with cheap irons that take ages to heat up, don't hold a consistent temperature, only have one size of tip and break after a year or so.
What sort of thing should I buy that can handle small wires on a flight controller and larger power connectors?
I think I want something with some sort of active temperature control so it heats up quickly and holds its temperature accurately, but does that mean I need one with a digital temperature setting and a bulky box? I'd rather it wasn't too large, if possible.
I only use it occasionally so I don't need industrial quality, but I would like it to last years.

Experience: I worked for HP R&D for 31 years soldering and building boards as an Electronic Engineering Technician.
First you need to decide if you are working on surface mount parts or through hole wire boards. The irons for each are completely different.
I always used WELLER soldering irons.
I used two irons, one was micro tip for very small parts and a standard iron for large parts and wiring.
The temp control is in the tip. It is magnetic and controls a switch in the tip holder.
You can buy tips from 600 to 800 degrees.
The standard temp is ~700 degrees. There are any tricks to use in soldering. the most useful trick is to use DISTILLED Water in the tip cleaner sponge. If you use tap water it leaves calcium on the tip and the tip won't wet properly.
Get D'water @ target for $1/gal and always use it for the sponge. I used a siphon bottle for the sponge.
Use the largest tip to do the job. It holds more heat and will speed the soldering process. I did lots of work with an 800 degree very fat tip, especially on IC's. It heats and solders quickly and very locally so you don't damage the board or parts. Do not cool the joint with water, it crystalizes the joint.
It takes lots of practice to learn to solder properly.
There are videos on proper soldering technique.
If you learn and practice you will move to larger tips and hotter tips but start with medium size 700 degree Weller.
READ: https://www.weller-tools.com/what-type-of-soldering-iron-do-i-need/


What should I look for when choosing a battery for my multicopter? There are many different kinds of battery, many of which have specifications such as capacity, S configuration, P configuration, C rating etc. How do I translate these into knowing what is best for my multicopter?

When looking for a battery, there are a number of factors to consider: the voltage (or S rating), the capacity, the C rating, the type of connector, and the weight:
Voltage
You will often see batteries having an ‘S’ rating on them, for example 6S or 4S. This is the number of cells, which directly impacts the voltage output of the battery. Just to be clear, I am specifically talking about LiPo batteries here as nominal voltages vary between battery chemistries.
Each cell will add a maximum voltage of 4.2V, and a nominal voltage of 3.7V to the battery, so to figure out the nominal voltage of a battery, just multiply the number of cells by 3.7, so a 3S battery has a nominal voltage of 11.1V and a maximum voltage of 12.6V. This is very important using a battery with too low an S rating will likely make the aircraft more sluggish, but using a battery with too many cells is likely to make the aircraft more on fire.
You may see batteries written in the format 4S1P or similar. This means that there are 4 cells in series that are treated as one parallel cell - i.e that there are no other parallel cells.
Capacity
The capacity of a battery is measured in mAh, or milli Amp-hours. This is the number of milliamperes the battery can output at the nominal voltage if the battery is discharged over the course of one hour. For example, a 1300mAh 4S battery could output 1.3A at 14.8V for one hour.
In general, a greater capacity will mean more flight time, however there are caveats, an important one being the battery’s weight (which I will talk about later).
C Rating
The C rating is the maximum discharge rating, and it acts as a multiplier of the capacity. For example, if I have a 1300mAh LiPo with a C rating of 100, the maximum current output will theoretically be 100*1.3=130A. Obviously, a higher theoretical discharge rate should give greater performance.
These metrics are very variable between brands, however. What Turnigy considers to be 100C may only be 75C for another brand, so there is in reality very little point comparing C ratings between brands.
C is also used when charging. You may have heard people say ‘charge at 1C’ or something similar, and this means the same thing. For example, charging a 1300mAh LiPo at 1C would be charging at 1.3A.
Connector Type
The way you get the power from your quad is also very important. There are many connectors currently in use, but here is a rundown of the most common used on a multicopter:

JST PH2.0: small white connectors most often used on Tiny Whoops, sometimes used in series on a toothpick.
BT2.0: small white connectors most often used on Tiny Whoops, sometimes used in series on a toothpick.
XT30: small yellow connectors, most often used on toothpicks and 2/3 inch quads.
XT60: medium-sized yellow connectors, pretty much the standard for 4-7 inch quads.
XT90: large yellow connectors, often used in parallel or series on larger Beast Class or X Class builds
Deans: not commonly used in multicopters, however many batteries you will see do have this style of connector, which often has burgundy plastic.

Weight
As mentioned before, more capacity usually brings more weight, which introduces the problem of balancing capacity and weight.
For example, a toothpick with a 5000mAh should be able to fly for an hour, but would in reality be unlikely to last a minute if it could even take off due to the large weight of the battery. Some people say that your battery should not make up more than a third of the weight of your drone, however, you can huddle this based on your motors’ thrust and your build’s weight.
Conclusion
There are many factors when choosing what battery to use for your drone, however, all of the above aspects are vital in ensuring good performance and longevity of your aircraft.


How to record footage from AcroBee Lite? I have an AcroBee Lite(linked to the site I bought it) that I've gotten okay with, and now I would like to record some footage with it. The only problem is, I can't figure out how to record. Any idea what buttons I have to push to start/stop recording? Where can I find the files after I record them?

I just scanned the manual for "record" and nothing. I looked at the build and I see no indication of recording capability.
There are 3 options (unless there is more information):

Record on goggle. Some goggles have a DVR built in, generally low quality.
Record on a dedicated DVR on device, goggle, or another receiver.  I have used all of these options, DVR's start at $20.
Mod it and put in a recording camera (if possible).  This will get you to 1080p fast (if possible).  RunCam, Caddx, and Foxeer all have models. I was working on this spreadsheet last week for our sub-250 units researching mounting trends - it is not complete but has a lot of the key players.

I know the New Bee guys and they should be able to help you out.


Why don't solutions exist for a 3-axis helicopter flight controller? So I've been searching around for a 3-axis flight controller for my 450-size helicopter. It seems that nearly every flight controller which is sold today is configured for solely the control of quad/hex/octo-copters, and have little options for helicopters.
Why don't helicopters have much options for flight controllers?

Beta flight has helicopter modes ("Heli 120", "Heli 90", etc. depending on your swashplate layout), as does pretty much every other programmable flight controller software.
The outputs from the flight controller are the inputs for the ESCs, which have the same signal protocol as servos. The exception are the flight controllers with integrated ESCs, where the outputs actually drive the motors directly.
This also allows most flight controllers to be used in a fixed wing, where most of the outputs drive servos.


When evaluating the weight of a multirotor, is there a standard way that the components are grouped? Let's say we can all agree on that the frame and landing gear are one group, would you group the motors, props, ESC, and Batteries together, or split them out as four separate items? Does the wiring get weighed as part of the powers system, or is the power wiring its own category? Are flight controls, radios, and camera/gimbal a single group, or are camera/gimbals, sensors or IR cameras considered in their own category like payload? Where does the FPV camera get weighed?

Or, does every designer/builder tally them up differently?

To me the only weight that matters is the total weight of the craft that is airborne.  Or commonly referred to as All Up Weight (AUW).  That is what performance depends on.  That is what regulations are based on ( mostly ).  Anything else is just the weight of individual components in my opinion.


How much does mounting an antenna near a carbon fiber frame degrade signal reception? By how much is signal reception degraded if I mount my RC receiver antenna next to the carbon fiber frame of my quadcopter?

I've heard that it's a major sin to do this because there is some sort of interference generated by the conductivity of the carbon fiber. Is this true?

This is a huge question, which is why a complete answer is not really possible without specifics on your drone frame, antennas, antenna placement etc.

Long story short - Carbon Fibre is pretty much opaque to 2.4GHz radio waves. It's not interference, as such, it just blocks it, which is why guidance is always given to ensure your antenna placement is such that the frame is not between them and you in normal flight.

For a camera platform drone, like an Inspire, you can be confident of the orientation of the drone so the antennas will always have line of sight to you, but for a racing drone you need to make decisions based on "least obscured" placement, as well as robustness, which is why they are typically in the plane of the frame (but not attached along frame members) or well above the frame.

Pic from getfpv.com showing antenna in the plane of the frame:

And a pic of one of mine with a mushroom antenna raised above the frame:


Can I replace the 433MHz modules on my homemade remote controller with an NRF24 transreciever? I built a simple 4 channel 433MHz transmitter and receiver because I can't afford a remote controller. The range is limited to 3 feet and NFR24 transreceivers have a longer range, so my question is: can I replace the 433MHz modules with an NRF24 transreceiver and it'll work?

Building your own radio system is a good exercise for understanding and appreciating the technology, but always remember to include a failsafe.
Regarding swapping modules, it looks like you are using the 432MHz modules which use On/Off Keying (OOK.) The work essentially by sending the state of a digital line, and support some serial formats like UART but also arbitrary pulses such as Pulse Width Modulation (PWM) and Pulse Position Modulation (PPM.)
However, the nRF boards communicate locally using SPI which is incompatible with the above. Without knowing more about your design it is difficult to say for sure how difficult this would be to integrate, but you will need a microcontroller at both ends. I can’t make out what the existing chips are – if you currently have a MCU you may just need to tweak a few lines of code but if you don’t, a more fundamental redesign may be needed.


DJI F450 ESC calibration fail everyone. I am building a DJI F450 clone. I've got everything attached except for the propellers. The Pixhawk connects to my mission planner via USB. The remote controller is paired with the drone. Now I need to calibrate my ESB. Unfortunately, this is not working. The drone seems not to be going into calibration mode. It just blinks yellow and beeps.
Here is a video of the issue: https://youtu.be/t6_HZAf62zw
Potential problems and fixes I've tried:

PWM vs PPM on the remote. I've tried it both ways, with no luck.

Power connection is backwards. In the tutorial I'm following, the connections seem to be a bit different from my hardware. I've got a female XT60 on my shield, a male XT60 on the battery, a male XT60 on the "in" side of my power board and a female on the "out" side (the one which also has the data cable coming out of it.) The only way I can plug this thing together is to plug the battery into the "out" side of the power board and the shield into the "in" side, as seen in the video above. To test this hypothesis, I made some female-female and male-male jumper cables and tried to connect things the way they are on the tutorial...but no luck, same result.

I have used the FS-i6, it was my first radio. The throttle is generally on the left, and it is generally mode 2. In your case, it doesn't appear to be the case. So it might be useful to check in the transmitter settings if you have channel assigned correctly.
You can always see the signals sent to the FC in the Mission planner Setup tap under RC calibration. Ensure throttle signal moves as you desire.
From what I can see, there is probably some issue with the RC link and the signal being sent to the Pixhawk.


Are there specific laws or regulations in the USA barring weapons on drones? Are there specific laws or regulations in the USA on operating an armed drone, or do armed drones fall under ordinary weapons laws? More specifically, is it legal to fly a drone with a weapon under the following conditions:

The weapon is one that the drone pilot can carry legally in the jurisdiction in which the drone is flown (e.g. pilot is not barred from having the weapon under Federal, State, or local law; they possess a license to carry the weapon if required under local law; etc.).
The weapon is not installed on the drone for the purpose of committing a criminal offense (e.g. performing a murder or assault), but for peaceful or at least lawful reasons.

Restated, is a drone considered an extension of a person's body for purposes of determining if a weapon is lawful, or is there a specific regulatory regime for determining if an installed weapon is legal for drone carry?

To be clear, I'm not asking for specific legal advice, but inquiring whether the USA has provisions specifically regulating weapons on drones or whether drone weapons fall under ordinary (non-drone) weapons law.

I’m not a legal expert, but according to the following link to an FAA page, it is illegal to attach any dangerous weapon to a drone: https://www.faa.gov/news/updates/?newsId=94424


How tight should the screws at the bottom of the motor shaft be? As I was replacing a shaft screw on a motor, I thought I'd check the other motor shaft screws.  I noticed that none of them were tight, so I tightened them.  As a result, the drone flew horribly.  So I loosened them up and it flew fine again.  What's the rule of thumb as to how tight/loose the shaft screws should be?

There are a few things that may be happening.
Tighter and flying bad screams bad mounting.  A prototype I was working on last week had this problem. As I tightened the motor, the c-clip on the base was rubbing on the arm and slowing down. Loosen the screw and it spins faster. To check for this, take the motor off and spin it with your hand and get a feel for how much it will "free spin". If you mount it and this "free spin" decreases then you want to look for friction.  Leave the leads disconnected when you are going to do this, as some motors will retain residual electricity and until drained they will spin slow (this is a false positive, so test everything unplugged)
Generally speaking motors are built to be bolted down REALLY TIGHT, so there is probably operator error going on.
Another very common problem is the mounting screw length.  There are 2 things I have run into related to mounting motors and screw length. First is the possibility that the screw is too long and is actually hitting something in the internals. If so, look for damage and/or compare amp draw with other motors, watch for higher heat, and be careful. The other more mystical problem is when the screw is too long, somewhat metallic or electromagnetic, and alters the magnetic field of the motor.  I have had his happen a few times and it is often not obvious.
Another possibility is that the motor and/or mount is warped. In this case, tightening can further disfigure or warp it and decrease performance.  Many elements on a motor should be parallel/perpendicular to other parts and that can help you see if a crash bent something.


What registration is required for 250g to 2kg drones in Australia? As some of you might know already, I'm planning to get into model aviation. I've been looking at the CASA rules and trying to get my head around them. So far, I've built a FliteTest Tiny Trainer with no electronics (it's just the foam airframe). Before I buy and fit the electronics for it, I want to know what registration I will have to do (if any). It looks like it will be in the very small category (250g-2kg) with battery and electronics. I'd just be flying it line-of-sight for recreation. I probably wouldn't be flying it exclusively at CASA-approved model airfields.
I've probably forgotten to write some information in there; if you need any just ask in the comments.

According to this page you don't need to register your drone "you’re only flying for sport or recreation, including model aircraft flown at CASA-approved model airfields". Since you're only intending to fly your drone in recreational purposes it seems like you don't need to register your drone even if it weighs over 250 grams.
I am no legal expert though, and if I were you I would contact CASA and ask for clarification if you are want to be absolutely certain about how you should do.


Advantages to having more rotors? I have a quadcopter drone, is there an advantage say of having a octocopter instead of a quadcopter. Will it improve performance?

Performance is unlikely to be improved, in terms of speed or agility, or even load-bearing capacity, as they are heavier, slightly less efficient aerodynamically, and more expensive.

What you do get is a degree of fault-tolerance.

With a quadcopter, losing one rotor means your drone will fall out of the sky. With an octocopter (or hexacopter, but an octocopter can lose more motors and still be able to fly) losing one rotor is not fatal - it will still fly, however, it will have a reduced control authority.

This makes them very desirable for carrying expensive loads - such as a £50,000 camera - you really don't want to drop that out of the sky if you have a fault.


Where can I find a list of all the model aircraft flying fields in the USA? Is there a comprehensive list of model flying fields that have operated or have been developed in the United States?  I assume the AMA has some of this data, but I am curious if there is a larger list that designates all places to fly both past and present?  Present is fine if past is too big an ask.

Does not exist, a few reasons.

AMA lists most of their fields, but that information is spotty and I have almost been arrested trying to fly at listed AMA sites that are not valid.
FAA has this list, but they have openly admitted that infrastructure and management problems have led to this data being in decay and not very useful.  This problem was exposed as 107 was coming into law and many commercial pilots raised a stink because airports on flight maps were never (EVER) updated, this led to LAANC and the apps becoming more of an authority.
No one shares spots. There have been several apps that try to get people to share and they all went belly up real fast.

This information ALL exists in the FAA, but their data is horrible (I work with this info, total nightmare).  Most of the good fields are private and invite only in my world. We run a few spots and you will be shot dead if you fly there with out permission (not an exaggeration, I often carry when flying).
Airmap and Kittyhawk will have reasonably good current AMA type fields.  That data is the best for "free".  You may want to check with Snowflake, but their data feed (last time I was involved) starts at $5k/year.
It should be noted that the FAAn NTSB, FBI, and other orgs all recognize the unstructured, uncoordinated, and non-unified nature of RC flight and use this to control airspace.  I mention this because there is considerable history on the record of the FAA trying to wipe all drone use from NAS and this is a declared strategy and we have seen it in action.  Dig into the DC restrictions of 2014-15 to understand why the FAA is an advisory and not an ally.


Picking the right prop pitch for my plane Sorry for all the questions, but I'm trying to figure out what I need before ordering a hundred dollars worth of stuff and then find out I got the wrong stuff.
So from what I understand of this site, which isn't much, if you want your plane to be slower you use a bigger propeller. I think that sounds good for my first plane so I'll get a big propeller(size is still up in the air until I figure out how big to make the plane, but I'm leaning towards a jumbo sized foam plane and modifying that), but then how do you decide what pitch to get on the propeller? I'll be using a low Kv motor (about 1500)so I guess I need a low pitch propeller, but I still have 0 experience with planes so some help would be appreciated.

The key here is to understand pitch speed. The pitch of a prop is how far it will advance in one rotation if there's no slip, so a 5" pitch prop spinning at 15,000rpm will advance 75,000 inches per minute, or about 70mph. That means that when your plane reaches 70mph, the prop cannot produce any thrust.
Now, exactly how much thrust is required to reach any particular speed is very hard to estimate, and how thrust drops off with speed is also hard to estimate, but it's safe to say that the above plane will have a top (level) speed of under 70mph.
The first step is to look at the recommended prop for your motor. Often it will say something like this:

Use on 2s with 9×4.7 slow fly or the GWS 9×5 direct drive propellers.
Can also be used on 3s with 8×4 or 7×3.5 propellers.

Here you can see how increasing battery voltage spins the prop faster and requires a smaller prop to keep the power within the motor's limits.
A larger, lower-pitch prop (or a smaller, high-pitch prop) will have roughly the same power requirements. The normal rule of thumb is to add an inch of diameter when you reduce the pitch by an inch, or the other way around. So if a motor can handle an 8x4, it could also handle 9x3, 7x5 or 6x6.
The larger prop will have more thrust, but the smaller, higher-pitch prop will have a higher pitch speed, and thus a higher maximum possible speed. Prop pitch is a lot like gears on a car of bicycle. Too low and the top speed will be very limited, too high and it'll be hard to get going.
Here you need to go back to rules-of-thumb. Props are made in a range of sizes that are useful for most models. Generally the highest pitch option is the same as the diameter (a so-called 'square prop') and is only useful to very fast, sleek models like pylon racers. Models with more drag will need more thrust, and won't need the high pitch speed.
For that motor, you'd use the following props on these types of model:
6x6 - pylon racer.
7x5 - 'sports' aerobatics or flying wing
8x4 - trainer
9x3 - 3D aerobatics (i.e. prop-hanging) or slow 'vintage' flight.
You can use the same proportions for other motors: a 'square' prop for speed, diameter = 2 * pitch for a trainer, etc.
If you're not sure, order a prop either side of what you think the ideal will be and see which you prefer. Props are relatively cheap and you'll probably need replacements at some point.
Ideally you should also test a new motor/prop combination on the bench with a Watt-Meter, so check it's not pulling more current than recommended (or the ESC can handle) but you can also just check how warm the motor gets when run for 30 seconds or a minute. Warm is fine, but if the motor gets hot, you'll have to be careful in the air until you're sure the extra airflow is enough to keep it cool.


How does the center of gravity affect a quadcopter? I have heard a lot about center of gravity for fixed wings, but very little about the CG in quadcopters. How does moving the CG forward or backward impact the flight characteristics of a quadcopter? For example, if I had a 5 inch drone, how different would it perform if I moved the CG from the center to a position right behind the front two motors?

Altering the location of the CG (center of gravity) also changes the CM(center of mass) because the force of gravity acts roughly on the CM. Normally, the motor arms are equally sized so that all motors have equal control authority and all contribute equally to providing thrust while in level flight when the CM is close to the center of the multirotor. Another way to say this is that multirotor frames are constructed so that the CG, CM, and CL (center of lift/thrust) are all as close as possible to one another.

However, this is no longer the case because now each of the motors now has a slightly different lever arm distance to the CM of the multirotor. Consequently, not all of the motors have the same control authority and some of the motors will have to remain at higher/lower throttle than others while in level flight.
This will manifest itself in diminished flight performance. If all motors are running at the same throttle, the multirotor will naturally begin rotating with the longer lever arm(s) going upward and the shorter one(s) going down. If the distance between the CG/CM and CL isn't too great so as to not make the multirotor immediately flip over after raising the throttle, the I term in the PID controller of your flight controller should be able to account for the discrepancy after takeoff. The ability to pitch/roll in different directions will be different due to the asymmetric thrust distribution around the CG/CM.
Even so, it isn't ever recommended to fly with a significant distance between the CG/CM and CL. All (half-decent) frames are designed to minimize the risk that component placement will move the three far from one another, but this is an important consideration for scratch-built frames.
In the example from the OP, a case where the CG/CM was moved from the center to a location right behind the front two motors, the effects would be quite severe indeed. It's difficult for me to come up with a practical setup to create such a situation, but this is a good example of a worst-case situation, with the CG/CM to CL distance being close to 2/3 the arm length. (depending on the angle between the arms on the frame)


What are the conditions for LiPo battery damage from undervoltage? It is widely known that Lithium-polymer cells are permanently damaged if their voltage drops below a certain threshold, around 3.0 volts, but I couldn't find much on the exact conditions and factors that regulate how this damage takes place (Which, I suppose, is related to the fact that few other applications dealing with lipos involve remotely as much recklessness as we subject them to).

The first of them is the contribution of voltage drop from internal resistance when the pack is under load. i.e. does the damage begin whenever a current (e.g. from a punchout) dips the pack's voltage, as observed from its terminals, below 3.0V/cell, or does the pack's "actual", resting voltage with no current drawn have to get that low?

Second, how fast does the performance of the battery degrade, and at what point does it stop? If voltage gets dropped (via IR) by a high current and it leads to damage, does it stop accumulating immediately as the current is removed and the voltage comes back up? What happens when a battery is discharged so that its resting voltage is below 3.0V, but is quickly charged back up or its voltage naturally bounces back somewhat?

Third, how significant is the time spent by the battery below the threshold versus the very fact of dipping down, i.e. what difference does it make if one rushes to charge an overdrained pack back to an acceptable voltage right after ripping it out of the aircraft (probably from another pack), versus doing it after getting home?

And finally, how does previously sustained damage from over-discharge contribute to further damage?

Note:
Some context regarding how this kind of damage relates to degradation from the other abuse that we subject our cells to would be very much appreciated, although the main focus is still the undervoltage-related damage itself.

Your questions are challenging to answer because (my opinion) I think there is a lot more that goes into a batteries longevity than voltage staying between a certain threshold.  In addition to keeping the voltage in specified ranges, the following also apply.

Do you fly in hot or cold or humid conditions?
Do you fly hard and fast all the time where your batteries come off the drone warm or hot, or do you take it easy and just fly for leisure?
How long do you let your batteries sit below or above storage charge (3.8V/cell)?
Do you charge your batteries immediately after using them or do you let them sit to cool down a bit (15 minutes or more)?
What brand of battery do you have?  Some are known to be junk, others have a great track record, but some bad batches now and then.
What charger do you use?  Is it reputable?
Do you balance charge?
How old are the batteries?
How often have the batteries been crashed?

My opinion is, and I've been tracking battery usage since 2011, is that despite the claim of 300+ cycles, most LiPos will only last about 100 cycles due to the factors that I mentioned above, which also includes the occasional oops moments when you fly your battery below 3V/cell or on the rare occasion when you forget to put them in storage charge.  On top of that, the number of cycles is highly dependent on the quality of the LiPo.

To make a long story short, a few mistakes with your batteries every now and then might "damage" them, but it shouldn't affect them as much as other factors involved in flying, like crashing and the others that I've listed above.  Generally speaking, if you take care of your batteries, they should last you a while.

I know it's a vague answer that doesn't really hit on your voltage questions, but it's based on many years of experience, so I hope it helps you out.


How to determine the largest LiPo I can use in a quadcopter? Multirotors can usually operate with a larger battery than recommended for longer flight times but slightly less performance. However, there is a point of diminishing returns at which increasing the battery size will just make a drone so heavy that it uses more power to stay in the air than the added battery size provides.

How do I know when a battery will be too big and won't provide significantly more flight time? Is there some way to calculate the diminishing returns of increasing the battery size for a freestyle quadcopter?

My goal is to get the longest flight time that I can while only losing the upper-end performance which I don't use anyways.

I've heard that you want to keep your battery weight no heavier than 1/3 your drone weight.


Is it possible to hijack a quadcopter? Is it possible to hijack a quadcopter?
Like an attacker would jam the controller's signals and send his/her own signal to controll the drone. If so, what would be the technical steps?

Is it possible to hijack a quadcopter?

A)Yes
B)No

If so, what would be the technical steps?

Find a flying drone. Intercept the communication. If encrypted go and get a quantum computer before they switch to quantum encryption.
I will not detail the step-by-step process to hijack a quadcopter. It's already on the internet. If you didn't find it yet, you didn't ask yourself the right questions.


Keep quadcopter steady when taking a video Whenever I take a video on my small quadcopter, it’s never steady. It always bounces up and down a bit rather than keeping level. How can this be stopped/prevented?

I'm going to assume that you don't need your videos to be stabilised realtime. In this case you need image stabilisation software.

I'm not an expert in this field particularly, so I'll copy the most relevant answers on this reddit thread.

  If it's a smoothing stabilisation like this, you can use VirtualDub
  and Deshaker (Tutorial), Ffmpeg (Tutorial) which are all free or you
  can use After Effects - Tutorial. There's also a Stabilization bot
  called stabbot which will do it for free. Check out r/stabbot. It uses
  Ffmpeg/vid.stab.


Affordable ways to crimp your own connectors Ever since PX4 and DroneCode came up with their connector pinout standards. I see more and more sensors and devices off the shelf adopting the same
This is particularly the JST-GH and Dupont connectors

I like to make my own cable harnesses (So that the cabling is clean and easier to debug) but I'm having trouble finding cheap ways to do my own harnesses now. Does anyone know how to crimp JST-GH connectors cheaply?
Here is my setup (which I don't like just because of how expensive it is):

Dupont:
Pins and housings $10
Amazon link

Crimper PA-09 $40

I find that it's easy to buy SN-28B style crimpers for DuPont connectors but those are garbage. I do not recommend. I will try the IWISS $16 and report back.

JST-GH:
Pins, only one kind $0.11 each
Digikey Link

Crimper YRS-1590 $1239
Digikey link

This crimper is awesome, it works like a machine gun, you load a reel of pins and you can go to town crimping left and right. But it's soo expensive!
Anyone know of better options?

I crimp my JST connectors using needle-nose pliers. It’s probably not be best way to do it, but it’s cheap and works well for me.

Place the wire with the stripped end in the metal connector piece.

Squeeze perpendicular to the tabs on the connector with the pliers.

Now squeeze parallel to the original direction of the tabs.

Finally, squeeze perpendicularly to the original position again.

Give the wire a tug to make sure it is held securely.

Like I say, probably not the best way and I can’t vouch for how reliable it is, but it hasn’t let me down yet.


Effect of Deadcat frame on performance? I've seen a lot of new frames with a Deadcat style because it keeps the props out of view for cinematic videos and such. Does the Deadcat shape of frame have any effects on flight performance?

I personally have never used a Deadcat frame, but I found this forum thread asking a similar question, the answer is:

  I was more interested in how the dynamics of a dead cat might affect efficiency.  But based on what some of the long-range guys have found, it doesn't appear to be an issue.  One thing that did come up with the SG+ at its genesis was instability while in steep dives, like down cliff faces, etc.  Guys were setting up in BF as a straight X design.  Once they started setting up as a custom in BF and used the program that Project Blue Falcon explains, the instability went away.


FPV lag on visuo xs812 I have a visuo xs812 but with a very slow lag. I know that for many people this is a problem, does anyone know a fix?

I found some information here which may be helpful to read through. They mentioned the issue of video lag and seemed to find a few potential solutions which were: to use a wifi extender, use a different app (mentioned in the link) to connect to the drone, or adjust settings of your phone like screen resolution and processor power if possible.
As I don't own this drone, I'm not sure that these solutions will fix the issue. But if the video lag persists, just know that you really can't expect very low-latency video from a drone this price.


My DIY Project - My motors and voltage regulator for water pump does not work at the same time I am working on a project to make a quadrocopter that can spray liquid material. Unfortunately, I had this problem: when I give full thrust and try to activate the water pump at the same time, the water pump won't respond. However, if I stop the rotors and then activate the water pump, it will work. What can cause this?
Flight controller: K++ Jivi
Voltage regulator: similar to this one
The water pump is being controlled by a voltage regulator that connects to the flight controller like a servo pin (for those who know this flight controller, the VR is attached to pin: EXT1 -> P2).

If you are using the same battery for everything, the drone rotors might be drawing too many amps causing your pumps to not spin. Try using an external battery for it, or get a bigger battery for the whole drone. And if this doesn't help, please explain your setup a bit better.


Alternatives to LiPo batteries LiPo is often the first choice of battery due to its high discharge rate and high specific energy (100 - 265 Wh/kg), defined as its energy per unit mass.

In terms of these two characteristics, what type of batteries are next best alternatives to LiPo?

Many people choose to use Lithium Ion batteries on long range builds.

They have a very large capacity and I have seen them give in excess of 20 minutes of flight on a quadcopter.

The reason that they aren’t often used for other purposes is that their current output is less than LiPo batteries.

This means that whilst they are good for long range flight, they lack the power for aerobatics and racing.


Does anyone have a manual for this radio? I ordered this JJRC JJPRO EM-16 2.4GHz 6CH AFHDS 2A Mode 2 RC Transmitter with Receiver Support P175 for RC Drone from banggood, and now I'm trying to figure out what the default settings are and how to program it. I did a bunch of google searches, but I cannot find any sort of manual or user's guide or even a youtube tutorial for this radio online.
Does anybody know where I can find a manual for this radio?

So the radio arrived, and I plugged in some servos and a motor and here's what I think everything is;
Ch1 is rudder, right stick right+left(I think, there was something weird with it)
Ch2 is elevator, right stick up+down
Ch3 was motor, left stick up+down
Ch4 was ailerons, left stick right+left
Ch5 and CH6 were switches


How can foreigners fly non-nano drones in India? According to some pages I found online, foreigners who want to fly non-Nano drones (drones over 250 grams) in India must lease their drone to an Indian entity who has authorizations from the Indian aviation regulator (DGCA).

How does this process work? Has anyone had experience with it? Can it be used only for commercial purposes, or also for recreational purposes?

Micro drones are between 250 grams and 2 kilograms:
Micro drones
These need registering, so therefore a foreigner will not be able to fly them. What you stated is for commercial purposes only. If you do want to fly commercially you will have to do some research before you travel, contacting an Indian entity and asking them to register it for you. This can be quite a hassle so I wouldn't do this unless it was really important.


Transmit video from drone to laptop via WiFi I recently decided to build my first drone and bought Eachine Tyro 129 KIT. It has a 5.8GHz video transmitter - xf5804 which is supposed to send video to 5.8GHz goggles. I don't have goggles and I'm not sure I want to buy it. My laptop (Debian10 Linux) has WiFi that can operate on 5.8GHz frequency.

How can I transmit video from the drone to the laptop directly? Which extra software and/or hardware do I need?
What maximal distance can I get with the video transmitter operating in the 600mW mode?

You have a few options. One is to switch to a digital video system such as the fat shark bytefrost and do something like this to convert the video to a format compatible with your laptop.
Essentially the above link documents how to convert a digital FPV feed into your laptop for doing low latency video calling, but you don't have to do the video calling part. You can skip the portions about the transmitter unless you want to control the whole drone from your PC.
Or, you can do something hacky that I have done before... which is buy the display and then pop it into a cheap pair of FPV goggles. Then put a USB webcam into the goggles where you would normally put your eyes. Then boom! You can see what the drone sees via a USB camera.
You can also utilize a analog to digital converter as other users have replied, but you are going to have at least 1-2 seconds of latency unless you get a converter in the 1000's of dollar range.


What are the benefits to different types of frame arrangements? When looking at different frames, there are lots of descriptions for different ways the arms are set up. Are there objective descriptions of how these arrangement change the flight characteristics rather than just "I like the way this one feels"?
For example, looking at the iFlight frames, the XL5 and SL5 are almost identical, except one is a "True-X" arrangement while the other is a "Squished-X" arrangement.
A few such terms that'd I would really like to see some solid description of the flight characteristics:

True-X
Squished-X
Stretch-X
Deadcat

Unfortunately it really seems to be a personal preference thing.
I tried logging the same move on both pitch and roll on a stretched x frame to determine exactly how much difference there was and I couldn't find any difference in the results.
Stretched x are generally preferred for racing, but Thomas Bitmatta decided on squished x for his JS-1 frame.
For definitions:

True X - Symmetrical in both X and Y dimensions
Squished X - Wider than it is long
Stretch X - Longer than it is wide
Deadcat - Wider on the front than the rear
Hybrid X - Wider on the back than the front (See XBEE MCK frame).

The primary advantage of squished X and Deadcat is that you can keep the props out of the frame of the camera if you are running low camera angle.


How do certified drone operators ensure they're not harassed by the police while filming from their drone? Lets say you get all your paperwork in good shape and have everything setup to film the city (or another scenic location) from a drone. How do you then ensure that the local police officers don't constantly come up to you and demand to see your paperwork, making it difficult to operate without interruptions?
I can imagine this being somewhat doable if you have an assistant but what about solo drone operators? Do they call the non-emergency police line and ask an officer to stay with them onsite? Do they put the permits up on a plaque before initiating the flight?

Look the part - wear a high-visibilty jacket with a company logo, "UAV Pilot" or other markings that makes you look like a professional.
Put up a sign which explains who you are and what you are doing - "Drone Filming In Progress - please wait until aircraft is landed before approachng pilot. Operator: SuperDronePics Ltd, Permit number: OP-4ME33NK."
Where possible, fly with an observer/helper who can intercept interested people (police, public, etc.)
If you are flying somewhere particularly likely to attract attention, it may be worth contacting the local non-emergency number in advance. I don't expect they'll post an officer with you thoughout the flight, but it could help to cover phone calls from the public - and perhaps a police officer who radios in before approaching you.

Finally, always have all your paperwork ready to show - if you are interrputed, it looks more professional to have a folder with your permits, insurance, etc. at hand. While police interest might become annoying (especially when repetitive!) you are almost always better off just answering their questions and being helpful.


Does FPV transmitter antenna need to match the goggle receiver antenna? So for a Fatshark, do I need to have both FPV transmitter and receiver antennas to be of the same brand and same specs? What about for a DJI goggle?

No, specific brand and specs don't matter for interoperability (aside from making sure that both antennae are built to transmit/receive the same frequency). Specific specifications about an antenna can help you figure out which will work best for your use case, like the antenna's gain, but mixing brands and types is fine.

However, there are certain mixes of antenna polarizations that will work better than others. You can learn more about this in Can circularly and linearly polarized antennae be used together for FPV? and about what antenna polarization is in What is circular polarization in antennae?.


How to debug a non-working Eachine E010? I have two Eachine E010 drones. One drone (green color) stayed outside for a night with rain. I inspected the circuit board and it shows no damage: no cut cables that I could solder, nothing corroded. Both the transmitter and the drone turn on and show light but the transmitter does not control the drone. I turn both on within 2 seconds of each other, push the left lever up and down and the transmitter beeps, but the controls have no effect. (Note: when the drone is turned off, the transmitter has the same behavior: beep when I push up, flashing light, beep when I push down, steady light, so the beeps do not indicate binding with the drone.)
The other drone (red color) works fine. The green transmitter can control the red drone, but neither transmitter can control the green drone. I could not find a way to reset both to factory settings.
What could have gone wrong, and how to fix it?
Update: Here are pictures of the drone. The drone was powered while in the rain: a child left it on a house roof upside down and I realized and took it the next day after a night of rain.

The beep from the transmitter indicates that it has linked successfully with the receiver on the drone, so at least part of the board is working. However without detailed knowledge of the design and a range of test tools it will be very hard to trace the fault accurately. Even if you did, you need specialist soldering tools to replace tiny surface mounted components, and the fault may be in a chip with proprietary firmware (i.e. not available for sale).
Really the only type of repair you could do is to replace the entire board, but I'm not sure they're available and given the price of these things I think you'd be best to buy a whole new drone and keep the frame, motors and props as spares because they are the parts that usually break.

What could have gone wrong

If it was wet when the battery was connected, it's likely that the water formed a galvanic cell between the copper traces of the circuit board and some of the other metals in the solder and component legs and cases. Galvanic corrosion is much faster than ordinary corrosion, and has probably caused an open circuit somewhere.
The other option is a short circuit that generated enough heat to melt some solder and break a connection.
If you dried it thoroughly before reconnecting the battery, then you did everything you could have, and that's normally enough - but small drones are made with the cheapest components and quality control is minimal, and sometimes they do just die unexpectedly.


Recommend safe distance from other drone flyers When going to fly my drone, I notice there are a few other drone flyers as well.

What is the recommended safe distance to be kept from other drone users in order to not cause an accident?

In this situation, I would approach the other flyer(s) to say hello and discuss this with them to prevent misunderstandings or differences of opinion - for example, if the other flyer is new they might want much larger separation than you think is enough, whereas if you are both experienced you might be happy flying in close quarters.

Also, it might make life easier if you stand close to each other; I've done this before (albeit with people I knew) and it is useful to regularly share information like "I'm at 200 ft by the tree on the left", "Thanks, I'm at 50 ft moving across to the right" - and of course warnings like "Unleashed dog approaching!" and "Helicopter!"

If you are looking for official guidance, you could check CAP 393 Article 95:

  95.—(1) The SUA operator must not cause or permit a small unmanned surveillance aircraft to be  flown  in  any  of  the  circumstances  described  in  paragraph  (2),  and  the  remote  pilot  of  a  small  unmanned surveillance aircraft must not fly it in any of those circumstances, except in accordance with a permission issued by the CAA.
  (2) The circumstances referred to in paragraph (1) are—
   (a) over or within 150 metres of any congested area;
   (b) over or within 150 metres of an organised open-air assembly of more than 1,000 persons;
   (c) within 50 metres of any vessel, vehicle or structure which is not under the control of the SUA operator or the remote pilot of the aircraft; or
   (d) subject to paragraphs (3) and (4), within 50 metres of any person.
  (3) Subject to paragraph (4), during take-off or landing, a small unmanned surveillance aircraft must not be flown within 30 metres of any person.
  (4) Paragraphs  (2)(d)  and  (3)  do not  apply  to  the  remote  pilot  of  the  small  unmanned surveillance aircraft or a  person under the control of the remote pilot of the aircraft.
  (5) In  this  article,  “a small  unmanned surveillance aircraft”  means  a  small  unmanned aircraft which is  equipped to undertake any form of surveillance or data acquisition. (b)

I am not aware of any specific rule for separation in relation to other drones, unless they were to be considered a vehicle for rule 95(2)(c) in the quote but elsewhere in CAP393 they use "flying machine" to refer to (any) aircraft.

However, as always, there is the 'catch-all' in Articles 94 and 241 should something go wrong:

  94.—(1) A person must not cause or permit any article or animal (whether or not attached to a parachute) to be dropped from a  small unmanned aircraft so as to endanger persons or property.
  (2) The  remote pilot of  a  small  unmanned aircraft  may  only  fly  the  aircraft  if  reasonably satisfied that the flight can safely be made.
  (3) The  remote  pilot of  a  small  unmanned aircraft  must  maintain  direct,  unaided visual contact with the aircraft sufficient to monitor its flight path in relation to other aircraft, persons, vehicles, vessels and structures for the purpose of avoiding collisions.

and

  A person must not recklessly or negligently cause or permit an aircraft to endanger any person or property.


Connecting 4 in 1 esc with power module I have a 4 in 1 iflight esc currently connected to my motors. I am attempting to interface it with my flight controller (Pixhawk 4), which comes with a power module (https://docs.px4.io/master/en/power_module/holybro_pm07_pixhawk4_power_module.html) in order to provide power to my escs and flight controller. This module has individual power outputs for every motor (each output is supposed to connect to a single esc, while the 4 in 1 esc only has one power input. Could I provide power to the motors by wiring all of the positive outputs together of the power module, and using them as the input to the esc, or would this create issues beyond losing the ability to track the power going to each motor? I am using a quadcopter. Thanks.

I think yes, this is doable. In this diagram you can replace the ESC Motor 1 with your 4 in 1 iflight ESC. Note that you will probably need to redirect the PWM outputs to your 4 in 1 ESC signal inputs.

Could I provide power to the motors by wiring all of the positive outputs together of the power module

No, no need to do that. Use a single power output of the power board (it is simpler and in certain cases more reliable).
EDIT
Following the discussion in comments, your 4 in 1 ESC already acts as a power distribution board. Depending on your situation, you may not need the power module at all. For example, one could split battery power output into two: one to go directly to 4 in 1 ESC, and another one to an UBEC to get 5V (to power the flight controller).


How can I run 2207 2450Kv motors on 4S with 7” props? I’m looking to use some spare motors I have to build a 7” rig.

The problem is that they are 2450Kv, and I don’t want to burn out my other components. As I understand it, if I set a motor output limit of 70%, this should give me similar performance to a 1700Kv motor. Is this the case, and are there any disadvantages to doing this?

7" props have a disk area that is almost twice as large as 5" props, so the motors will be heavily overloaded. (7 squared is 49, 5 squared is 25, the other terms in the equation for the area of a circle cancel out)

Assuming you use 5x4.5 3-blade props on a 5" quad, you could reduce the load 33% by switching to 2-blade props. You can reduce the load further with a lower pitch prop. 7x3 is about as low as you can find, and will give you another 33% reduction, so now the motors are only running at 133%.

I think that's worth a try, but if the motors get hot you may need to step down to 6" props. 6x4 props may work better than 7x3, giving you more speed.

Reducing throttle to 70% will reduce the maximum voltage, similar to switching to 3s batteries. However torque and heating are related to current. Reducing voltage will limit the maximum power and thus the maximum current, but won't make any difference at part throttle.


What are the available solutions for creating complex user-defined UAV behavior in autopilots? Most freely available autopilot-enabled flight control hardware and firmware for hobby/consumer-grade UAVs seem to have a rather fixed feature set. There are usually varying degrees of stabilization, position hold/loiter modes, automatic takeoff and landing, return to home and a waypoint-following "mission" mode, but little beyond that. There are sometimes specialized modes such as thermal soaring and terrain following. However, all of these are pre-programmed and non-extendable, by which I mean that there is no way (at least I could find none) for a user to program their own custom flight logic, e.g. via scripting. I may have missed this, though.

So, Is there, in any of the autopilot solutions currently available to hobbyists, a way for a user to define their own flight logic without rewriting the autopilot software itself, by instead building on top of existing software?

To be clear, I'm looking for a way to write logic outside of the main flight control/autopilot package, either via some kind of scripting engine native to the autopilot or as a program running on a device parallel to the autopilot that can communicate to it and get the necessary flight information/send commands.

I think your best bet would be Ardupilot. The communication protocol it uses, called MavLink, is documented and easy to use. Connect to the UART with an Arduino and you will have full control over the UAV.

There is even an Arduino library and a bunch of examples, like this forum post, of people doing exactly what you are looking to do. I did this once because I needed to grab the GPS and Compass information for a work project. You can research the various mission control programs that use MavLink to see the extent of control the protocol has. If I remember correctly you can even send direct stick commands over that interface to manually pilot the craft. This solution makes for lots of flexibility, especially when you consider the huge community writing Arduino libraries. It would be simple to add just about any sensor you could want.


LiPo battery charger remotely controlled? I spent hours trying to find a DC Li-Po charger that I can use to recharge my Drone's battery. I am looking for a DC charger accepting voltage between 24 to 48 V. This seems to exists.
However, I also would like a remote control port for monitoring the charge through a computer. USB/CAN/RS-232, Ethernet, any communication port would be fine.
All the chargers I can find have fancy designs and huge LCD displays. I don't want any user interface on the charger.
My goal is to make a charging platform for my drone. Solar panels recharge batteries (I have the system in place), then when the drone lends, it can be charged autonomously.
Any advice?

There are a few chargers with data ports but they may not work the way you want. These chargers have so many options that a remote interface would be quite complex, and the manuals often don't give much detail about the features available. Complex chargers always wait for you to confirm that it is set to the right type of battery before charging, and require you to press a button.
I think the way to go would be a really dumb charger that is set up specifically for your battery size. A charger like this will just start as soon as the battery is plugged in.
Lipo charging is pretty simple, you just provide a constant current until it hits a maximum voltage, then the charger reduces the current to the voltage constant.
You could build a simple circuit to do this, but you can also buy basic boards that do it for you. They're cheap and designed to be integrated into electronics projects.
You can monitor the pack voltage and individual cell voltages with an Arduino, Raspberry Pi or other device, depending what you want to do with the data. These all have inputs that are capable of measuring voltages sufficiently accurately to detect imbalances or tell when the battery is charged.


Would it be possible to inductively recharge a drone battery? Regular drones can only fly around 15-30 minutes before the battery runs out, which is annoying.
Newer smart phones use inductive loading, so it is possible to load a battery through such a field.
Super capacitors can be loaded in a very short time with high energy levels. (side question: are those used in drones?)

Would it be possible to get a drone close enough to a charge point to load the battery in flight? If yes, how close would that be? How long would it take?
Would it be possible to build a loading station with this principle, lets say to put it on my roof?

Given how close you would need to be to the charging system, it makes little sense to keep flying rather than simply land on a charger.
The question then becomes if the inductive power transfer scheme is worth the trouble vs having some sort of electrical contacts, possible with some kind of cam-driven capture in the base.
On the one hand a wireless power transfer scheme is weatherproof and may require somewhat less positioning precision; on the other, it adds weight to the aircraft, and a lot of complexity.


Difference between XM and XM+ receivers? I have seen both XM and XM+ receivers and am wondering which one would be better to get for a micro-drone build. What are the differences in specs? (range, reliability, weight, etc)

According to Oscar Liang, the XM+:

Is larger and heavier than XM (21.5 x 12 x 3.5 mm – 1.6 g)
Has diversity antennae, unlike XM
Has solder pads in addition to pin headers
Doesn't support Smart Port telemetry
Has RSSI channel support on a dedicated pad and 16th channel
Has a wider input voltage range than XM (3.7v-10v)


What are the typical methods of constructing a large airframe? When building a 5 feet wingspan UAV, what building techniques:

used on smaller aircraft can't scale to aircraft of this size?
are best used on aircraft of this size?

Ideally, I want a simple graphic that tells me approximately what techniques are best suited to my requirements. Heres an MS paint mockup:

While I'm far from knowledgeable enough to give you a chart like you requested, I can do a general overview of the methods commonly used in RC modelling for airframe fabrication.

I must begin with this: Almost all of these are applicable to an aircraft of about any size. It's even hard to tell which is better, they're all just different. So, without further ado, the list:

Extruded polymer foam. This is what most commercially manufactured models are made of. The manufacturing process involves CNC-machined molds, special extruding machinery, and a lot of money spent upfront. However, the models can be of any shape imaginable, are quite durable, light (although not the lightest) have excellent aerodynamics, and the unit cost is cheap once you get going. The load-bearing parts are usually reinforced/stiffened with carbon fiber inserts, although wooden reinforcements are not uncommon. There are several types of foam that can be used, each with different characteristics.
Hotwired polymer foam. This is the DIY method of making foam planes, although some commercially-available planes use it as well. It involves a resistive wire which is heated by a current and is used to cut a block of foam into the desired shape using a bow or other device that keeps the wire under tension. As with extruded foam planes, load-bearing sections are usually reinforced with carbon fiber for stiffness. The same types of foam can be used as with extrusion. The available shapes are limited by what can be achieved with straight cuts, although complex shapes can be created by gluing simpler sections together. See this video for an overview of the process. Sometimes (most of the time?) only the wing airfoil is wire-cut, while the rest of the airplane is fabricated using other methods. Planes made using this method are often covered with heatshrink film to add stiffness and durability.
Folded flat materials. Airplanes can be made from a variety of sheeted materials by cutting, creasing and folding them into shapes which are then glued together. The materials include (but are not limited to) foamboard (foam between two layers of paper/thin cardboard), depron (flat sheets of foam), corrugated cardboard or even paper. The very simplest models can even be made without folding, just by cutting the required outline out of a flat sheet, while the advanced builds feature smooth curved surfaces. While usually not especially sleek-looking, airplanes made using this method fly surprisingly well and are very durable! Most of this comes from the fact that they are also extremely light for their size, though. In any case, a foamboard (or cardboard, or depron) plane is very easy to build or fix and requires minimal tools (knife, ruler, glue) to do so. This type of construction is extremely popular in the RC community due to the simplicity and cheap price. The most prominent proponent of folded models is Flite Test, who publish free plans for all of their models. There are also countless plans for folded planes on various RC forums.
Wood and film. This is the "oldschool" method. It is very similar to the methods used for construction of early full-scale aircraft, and involves building a wooden "skeleton" for the plane out of precisely-cut thin pieces of wood (usually balsa) and covering it with a special heat-shrink film to form the surface of the airfoil. This method takes a lot of time and work, and involves cutting and gluing together hundreds of wooden parts. The method creates light, strong and stiff airframes, which can nonetheless be brittle if hit the wrong way in a crash and time-consuming to fix. While less common nowadays, this construction method remains moderately popular, with a great variety of plans available online.
Glass and carbon fiber composites. While carbon tubes, strips and sheets are used extensively together with all of the construction methods discussed above to add mechanical strength and stiffness in critical points to a weaker or more flexible material, some airframes are constructed entirely out of composites. This is arguably the most high-tech and definitely the most high-performance (if done properly) construction method of the ones discussed here. It is also the most expensive one, per unit, though it doesn't come anywhere near extruded foam in terms of upfront setup costs and thus is within reach of hobbyists who want to make only a small number of copies of their design. Creating a glass or carbon fiber airframe requires making a mold of the desired shape, carefully laying up the fiber, soaking (or impregnating) it with resin and curing under pressure, usually with a vacuum pump, to make sure that the absolute minimum of that resin actually stays in the part. Then comes sanding, polishing, and assembly of the parts. Carbon fiber, when properly done, is extremely strong yet light, and is used in high-performance thermal gliders and other planes which must withstand extreme forces while being as light as possible. While strong, such planes are often hard to fix when they do get broken (at least without compromising their original strength or lightness). Glass fiber, though somewhat outdated, is also still a popular choice for larger planes, as it is significantly less expensive and easier to fix. Sometimes DIY molded glass fiber reinforcements can be found on planes constructed from other materials, and usually made by laying the fiber directly on top of the fuselage, eliminating the need for a mold.


How does a quadcopter yaw? I've always wondered how a quadcopter actually yaws, when all propellers are horizontal. I know that two of the motors spins faster, but I don't understand how that generates thrust in the horizontal direction (I assume it has to?) to make the quadcopter turn.

Any vehicle yaws (i.e. turns) by having a net torque applied. What's interesting about a quadcopter is not just how it yaws, but how it yaws and doesn't roll, pitch, or climb at the same time.
To understand how this works, we need to briefly look at the math. We'll use a plus configuration, but really any mutirotor configuration works.

The thing to keep in mind is that thrusts and torques are related to propeller speeds. If you speed a propeller up, it's intuitively obvious that it will create more thrust. And likewise, if you spin it faster, you need more torque. So changing motor speeds changes the net forces and torques on the airframe.
(Pedantically, it goes with the square of speed. So if you double the speed you quadruple the thrust and torque. But that's not important to this analysis.)
Here's the high-level driving equation. If you've ever messed around with mixers, you'll notice that the 4x4 matrix in the middle looks really familiar:

What this does is it maps rotor speeds (squared) to torques about the roll, pitch, and yaw axes, as well as the net vertical thrust.
For hover, let's assume all motors are spinning at the same speed, W. So W = w1 = w2 = w3 = w4
Yaw
What happens if we speed up the first and third and slow down the second and fourth by the same (squared) amount dW?
torque_x = 0*(W^2 + dW) + 1*(W^2 - dW) + 0*(W^2 + dW) - 1*(W^2 + dW) = 0
torque_y = 1*(W^2 + dW) + 0*(W^2 - dW) - 1*(W^2 + dW) + 0*(W^2 + dW) = 0
torque_z = 1*(W^2 + dW) - 1*(W^2 - dW) + 1*(W^2 + dW) - 1*(W^2 + dW) = 4*dW
F_z      = 1*(W^2 + dW) + 1*(W^2 - dW) + 1*(W^2 + dW) + 1*(W^2 + dW) = 4*W^2

So the net force doesn't change (all the dW cancel out), and neither do the net rolls and pitches, but voila we have 4*dW worth of torque!

For completeness, here's what happens when you want to change the other axes as well.
Pitch
Let's change the front and back motors by the same (squared) speed, but we'll leave the other two motors alone:
torque_x = 0*(W^2 + 0) + 1*(W^2 - dW) + 0*(W^2 + 0) - 1*(W^2 + dW) = 2*dW
torque_y = 1*(W^2 + 0) + 0*(W^2 - dW) - 1*(W^2 + 0) + 0*(W^2 + dW) = 0
torque_z = 1*(W^2 + 0) - 1*(W^2 - dW) + 1*(W^2 + 0) - 1*(W^2 + dW) = 0
F_z      = 1*(W^2 + 0) + 1*(W^2 - dW) + 1*(W^2 + 0) + 1*(W^2 + dW) = 4*W^2

Notice that, again, z-thrust stays constant, but this time only a pitching torque appears.
Roll
Let's change the left and right motors by the same (squared) speed, but we'll leave the other two motors alone:
torque_x = 0*(W^2 + dW) + 1*(W^2 + 0) + 0*(W^2 + dW) - 1*(W^2 + 0) = 0
torque_y = 1*(W^2 + dW) + 0*(W^2 + 0) - 1*(W^2 + dW) + 0*(W^2 + 0) = 2*dW
torque_z = 1*(W^2 + dW) - 1*(W^2 + 0) + 1*(W^2 + dW) - 1*(W^2 + 0) = 0
F_z      = 1*(W^2 + dW) + 1*(W^2 + 0) + 1*(W^2 + dW) + 1*(W^2 + 0) = 4*W^2

As always again, z-thrust stays constant, but this time only a rolling torque appears.
Thrust
Finally, what happens if we speed up all four motors by the same (squared) speed?
torque_x = 0*(W^2 + dW) + 1*(W^2 + dW) + 0*(W^2 + dW) - 1*(W^2 + dW) = 0
torque_y = 1*(W^2 + dW) + 0*(W^2 + dW) - 1*(W^2 + dW) + 0*(W^2 + dW) = 0
torque_z = 1*(W^2 + dW) - 1*(W^2 + dW) + 1*(W^2 + dW) - 1*(W^2 + dW) = 0
F_z      = 1*(W^2 + dW) + 1*(W^2 - dW) + 1*(W^2 + dW) + 1*(W^2 + dW) = 4*W^2 + 4*dW

So only in this case do we see an increase in vertical thrust (by 4*dW). Notice how the net torques about each axis cancel out.


Does the FS-R6B receiver work with the JJPRO EM-16 transmitter? If I need a new receiver and can't find one that is exactly the same as the one that came with the radio, can I get one with the same amount of channels and from the same company and use it with the radio?
Specifically, I need to know if this receiver works with this radio.

There are various digital protocols, and many receivers are able to handle more than one protocol (and so can a few transmitters).
It looks like that transmitter uses "AFHDS 2A", so you need a receiver that can handle that.
That receiver (FS-R6B) says "AFHDS" on the label, and there's a big complicated chart (the 5th image) showing which receivers handle AFHDS 2A, but I can't see the FS-R6B on the chart so it's not much help. The binding instructions imply that it might do both.


What should I look for when choosing an FPV camera? I know that cameras are applicable to lots of fields, but FPV cameras are a special category with a very specific set of requirements - what should I look for when picking an FPV camera?

When choosing an FPV camera, there are several things that you need to look out for:
Sensor Technology
Most modern FPV cameras use a CMOS sensor. These are digital sensors that generally tend to have a higher resolution (measured in TVL or TeleVision Lines) than the alternative, which is CCD analogue sensors.
Pretty much every modern FPV camera uses CMOS tech, however, there are pros and cons to each:
CMOS positives:

They are generally higher resolution
They are very common so finding support should be easy

CMOS negatives:

They can introduce a shimmering effect in the image, especially around the edges of objects or in places of high contrast. Some people dislike this effect so strongly that they won't even consider CMOS cameras.

CCD positives:

They are less prone to jello, or warping of the image due to vibrations
They can have better dynamic range, although modern CMOS cameras tend to surpass CCD in this
They tend to create a "softer" image that is more pleasing to the eye, without any "digital" shimmer.

CCD negatives:

They are more expensive to make
They may have slightly higher latency
Very few new CCD cameras are being made, so there is less to choose from.

There are many more pros and cons, so I recommend reading the source of this pros and cons list.
Sensor size
The sensors used in FPV cameras can have different physical sizes.
Bigger sensor sizes perform better optically by capturing more light, so cameras with larger sensors are generally considered to produce a better image, but are also more expensive.
Format
There are two formats in our FPV cameras: NTSC and PAL. To know which camera you should get, make sure you check what format your goggles can use. Most modern cameras can be switched between NTSC and PAL, so
this isn’t too much of a big deal, but make sure you can check.
Size
Make sure you pick a camera that is an appropriate size for your drone.
The size classes commonly used today, defined by the camera enclosure's width, are Mini (22mm), Micro (19mm) and Nano (14mm). (The "full" size was 28mm).
Adapter brackets are available for mounting smaller cameras in frames with larger camera mounts, but there's nothing that would help you to fit a camera that's too wide for your frame.
For example, a CADDX Ratel which is 19x19mm would not be appropriate for a standard Tiny Whoop.
Aspect Ratio
Most modern FPV cameras will also have switchable 16:9 or 4:3 aspect ratios. Check which your goggles is designed for and which you personally prefer, though if you get a switchable one this likely isn’t a big deal.
Lens
The lens on your camera will affect the field of view. In general, a shorter lens will give a wider field of view (source). According to the same article, a wider lens can give better image quality.
Weight
If you’re going for an ultra-light build, every gram counts, and some cameras will be lighter than others. If this matters to you, be sure to check out the camera’s weight.
Software and other intangibles
There is more to a camera's performance than just the optics. The software that the camera uses to "prettify" the image is no less important, and can make or break the flying experience. Camera manufacturers each have their own WDR, sharpening, denoise, auto-exposure and other algorithms in their cameras, that all affect the picture. There are also some manufacturer-specific bugs in this software, which you may or may not care about. All of that can only be felt by looking at the actual imagery, which brings us to...
Personal Preference
This is the most important section. There are many videos and reviews online that let you see the actual image produced by the camera. Watch them and see for yourself. Do you like the look of its image quality? If so then you probably want that camera. If you don’t like the image then you probably don’t want it.


How to mount XM+ receiver antennas? I like to use XM+ receivers on many drones as they seem to work well and are small/light. What is the best angle and position to mount the antennas of an XM+ receiver in order to get the best signal?

I have often seen XM+ antennas mounted at a 90º from one another on the back of a quad. Is this a good configuration or are there other configurations that have better reception?

I really like the way the Joshua Bardwell does it.

He puts one on each rear arm facing forward with a zip-tie and heat-shrink over the top. It places the antennas at 90 degrees to each other and so you get good coverage from at least one antenna.

On the picture below, the yellow line is a zip-tie and red curve is the antenna from the XM+

Remember not to put too much of a tight angle on the antenna wire as it can deform the inside of the cable and have a negative effect on the signal receiving ability.


How does one hold the motor bell still when tightening prop nuts? Almost all of the brushless motors used in hobby-grade multirotors have a single threaded shaft and rely only on friction between the propeller and motor to keep the prop from slipping. This means that the nuts holding the propeller down must be tightened with considerable force.

When I try to do this, however, while I have a good grip on the nut (via a wrench), I can't hold on to the motor itself very well to keep it from spinning together with the nut, and if I try to hold on to the propeller, it cuts me with its sharp edges. What are the available tools and/or techniques that can aid in keeping the motor still while tightening or undoing the prop nut?

You know those rubber wristbands that are given out at lots of events?

You can wrap one of those around the motor bell to get better purchase on it, and then torque down the prop nut.

There are also specialised tools to hold motor bells, such as the one pictured below which can be found here, on Thingiverse.


Why do LiHV batteries degrade faster than an equivalent LiPo? There seems to be a lot of anecdotal evidence, at least on YouTube, that LiHV batteries degrade faster than LiPos. Is this true?

I own a couple whoops and only have 1s LiHV batteries since I can't find any decently priced non-LiHV 1s 300 mAh cells. My experience has been these LiHV batteries immediately begin to lose capacity and punch after only a few charge cycles. By 30 to 50 charge cycles the batteries are only good for about half a normal fight. What's all this I hear about people having multi-cell packs last a year or longer?

LiHV and LiPo batteries have different battery chemistry. If you were to charge a normal LiPo up to 4.35v per cell it would likely explode or at least puff up. The different battery chemistry in LiHV batteries allows the batteries to have a higher capacity to weight ratio. (For example, a 1500mah LiPo would be noticeably heavier than a 1500mah LiHV) A LiHV battery can hold more power and performance in a battery that weighs less.

This ability to pack more power into the battery does come at a cost though as it does reduce the longevity of the battery significantly. Any good quality standard Lipo should hold up to 300+ charge cycles (If taken care of properly) whereas a LiHV battery may begin to swell up at only 30-40 cycles.

LiHV batteries are very useful when it comes to serious racing though. The high performance and increased power per weight ratio give racers an advantage when racing, they will just need to replace batteries a lot more often.

It just depends on whether you want a little bit longer flight at the expense of needing to replace your batteries a lot more often.

You can read more about it here:
https://oscarliang.com/lihv-lipo-drone-battery-hvli/