Quadcopter Stability Modelling We know software like XFLR5 to model fixed-wing aircraft to determine aircraft dynamics and stability. Is there any software which we can model our quadcopter geometry in so we can know it's CoG, thrust, lift, stability, etc?

Solidworks works great and is very intuitive for beginners for a CAD software. Given that you have the entire simulation suite it can perform stress analysis and automatic optimization for the frame, air flow simulation for the propellers, etc etc (nice video to start with here: https://www.youtube.com/watch?v=6y_G6om74Mc). If you want to go deeper in the analysis of a custom flight controller, then you should investigate solutions through Matlab - a bunch of mechatronics students have produced a lot on the subject and you can buy drone focused video courses like this one to get up to speed: "Model, Simulate and Control a Drone in MATLAB & SIMULINK" on Udemy.
But unfortunately I'm yet unaware of a dedicated piece of software to do all this; my approach is to use engineering "general purpose" CAD softwares and model everything because I've learned these tools at work.


How do I safely dispose of my LiPo batteries? I have an old LiPo battery that is nearing the end of its life, how can I dispose of it safely?

First is to discharge the battery to zero volts which can be done by using a LiPo charger or a light bulb. It can then be thrown into a recycle bin, but check with your municipality before doing so as some will not take them. There may be a local or regional centre where they can be dropped off.

It is not advised to use salt water as it takes a long time and its corrosive nature to metals can lead to incomplete discharge.


Where to find model aircraft with moving parts? I came across a model F22 raptor here and here but I am looking for a place where I can get one with moving parts, e.g retractable landing gear, canopy and the likes with a sizable scale, maybe 1:48 or thereabouts.

I have had no such luck online, do such models exist without having to get RC models?

I don't have any models from this site, but it appears from their product descriptions that they have what you're looking for on themotorpool.net. They have a plethora of models of all nationalities, classes, and time periods.

For example, their Bf 110E-2 model is described as having "spinning propellers"
and the "ability to display the model with landing gear in either extended or retracted mode".

From what I can tell, almost all of their models have movable parts of some sort.


How to fix OSD flickering? I just changed my Diatone R349 flight controller because the old one broke. On my first test flight, I noticed the OSD is flickering very bad, sometimes losing it for more than 1 second, even when not armed.

The video feed is good, just the OSD flickering.

The VTX and camera are powered by an external 5v regulator. The rest is powered by the FC.

I've read that it could be a ground issue.

Could it be something else?

EDIT:
This is my current hardware and wiring diagram.

I fixed it by adding a common ground between the 5v regulator and the flight controller. I can't explain the science behind this, but I took the answer from this video from Painless360

The flickering is completely gone, even when I punch the throttle.

New wiring diagram:

EDIT: I will leave the post unanswered until someone intelligible explains this, and maybe other OSD flickering causes just to keep the post general to the question and not specific to my hardware and wiring.


multi-protocol transmitters -- difference between stm32 4-in-1 and stm32 c2500 only ? [tx16s Vs. tx12] Searching on the radio controllers radiomaster TX16s and TX12,

I found that video https://www.youtube.com/watch?v=ekrG5meNZOU%3F&t=5m47s
that warns me that Tx16s has an internal stm32 4-in-1 protocols chip, whereas Tx12 has an stm32 c2500 "only", according to this opensource project website : https://downloads.multi-module.org/

What are the cons with the c2500 chip ? Does it handle less protocols ? Does it provide less power to the 2.4GHz antenna and thus reduces the range for sending commands?
What is spectrum protocol ? A brand of drones ? I often hear about these recceivers for not being compatible with universal radio transmitters

1> The "4 in 1 chip" does handle more protocols than the CC2500. It has the CC2500, nRF24L01, A7105 and CYR all integrated in one package and allows you to bind with and use Flysky, Spektrum, HUBSAN, DSM2, DEVO, J6PRO, ESKY, HISKY, KN, V2X2 and ASSAN receivers which you won't be able to do with just the CC2500.
2> Spektrum is basically a brand of high end radios. (At least they are high end for me)


What should I use to cover this plane with? Unsatisfied with the weight of my first model (a FT Tiny Trainer), I decided to build something lighter. Since overweight foamboard was the downfall of my first model, I decided to try reducing amount of foam by building a rib-and-stringer balsa design at with foamboard. I scaled down these plans to half scale and have assembled the fuselage and tailplane. When complete, the plane will have about 85cm wingspan and will be 65cm long.
Initially, I was planning to cover the plane with thick, semi-waterproof paper of about 300gsm thickness, and created a test section of the fuselage using the paper. Unfortunately, after putting together the ribs I found that the thick paper was too heavy and would bring no significant weight loss. I've been thinking for some weeks, but I haven't been able to come up with anything good to cover my plane in.
These are some of the things I've considered using:

Conventional covering film (specifically this brand. This would be light enough, but I'm not sure if it would adhere to foamboard. I also don't wish to buy a heat gun (apparently a hairdryer isn't enough), considering that I probably won't make more covered models in the near future.
Office paper (about 90gsm). It would be very light, but the paper would rip easily and fail on contact with any moisture. In addition, it would add almost no strength to the body.
Plastic tablecloth material (similar to this. It's light and waterproof. However, it would probably be a bit baggy and wouldn't add any strength to the body.

I'd also like the material to come in opaque white color, as the plane I'm modelling is normally white.
So, the question is: What material would work best to cover my plane?

How about the thin white polythene/polyethylene from carrier bags or bin liners? I think you could stick it on with a foam-safe contact adhesive such as UHU POR.
Alternately, you can save weight from your Tiny Trainer by peeling the paper off the foam.
It sounds like what you really want to build is an old fashioned balsa model, covered in tissue and dope. They're really no harder than the model you have just built, and the balsa for that size of model is only $5-10. The tissue shrinks when you wet it, and then the dope makes it rigid, adding significant strength to the airframe.


Why does motor not want to go above 2/3 thrust? This is related to my past ESC troubles. See link for some flight history.
I tried the recalibration as suggested by ifconfig, which sadly didn't work. But now the motor will not go above 2/3rds thrust(slight improvement), no matter the calibration range. I did do one calibration where I used full throttle as max and the center as none, and the ESC would stop working once I got above 2/3rds of the calibration range.
What it is not;

ESC overheating/overloading(it is cool to the touch and I even ran it in our deep freezer, same results)
broken ESC(I used a new ESC as well as an old one I fixed. Both have the same problem)

What I'm not sure about;

the receiver has been in some crashes, perhaps it got shaken around and is messing with the signals?
the transmitter is cheap so it might be messed up, but it was working fine before.
motor might be broken but I don't think so, it's not even scratched up.
battery(charger) might be to blame. The charger I have (also cheap) has 3 lights for the cells, and the cell 1 light never turns green(ive left it charging overnight, still red). I just thought the charger was broken, but maybe cell 1 isn't getting charged?

hardware specs;

ESC is rated for 30A, uses T-plug to connect to battery.
Battery is a 3S 2200 mah 30C from Mirahobby
Motor is 2200 kv, is using a 9050 prop(slightly outside plane and motor recommendations)
Plane is an FT Spitfire from flitetest
The only modifications I have made to any of these pieces is when I globbed some hot glue onto the antennae on the receiver to strengthen it some

What do I need to fix to get the motor/esc to work properly? Do I need to replace any of my hardware? Should I just build a lighter plane that only needs 2/3 thrust?

It was the battery.
Bought a new battery, charged it, all 3 lights turned green, and motor/esc has no trouble going to full thrust. Lots of power now, so that should really help the plane fly.
Problem solved!
And on the bright side, I get to tear apart the broken 3s battery and see how to fix it or turn it into a 2s. I'll probably put a question on electrical engineering SE about that later.


Can a receiver get damaged if you power it up without an antenna? My r-xsr receiver short circuited after a crash recently. When investigating the reason, I found two things; The filtering capacitor had come loose, as well as one of the antennae on the r-xsr.
Since the reviver can handle up to 10 volts, and it was connected to a 5 V output on the FC, I assume the capacitor isn't the problem. So my question is therefore: can this problem have been caused by the drone being powered up when the antenna came loose?

Running a receiver without an antenna should not cause any damage to the receiver, as no RF power is sent to the antenna (if your receiver has an active antenna there may be a DC bias present, but this does not cause problems - you will often see this in GPS receivers.)
However, for completeness, it is worth noting that some modern RC receivers actually do transmit, to send telemetry and other data back to the controller; in this case 'receiver' is a misnomer, used to mean "the radio part in the aircraft" - and it is possible for damage to occur. The correct term would be 'transceiver', a portmanteau of 'transmitter' and 'receiver'.
The reason a transmitter can be damaged when run without an antenna is because the power sent to the antenna has nowhere to go. When a (matched) antenna is connected, the power is transferred to the antenna but without it the energy is reflected back down the transmission line to the output transistors. These transistors are not designed to handle that much power coming back, and can fail. The likelihood of this happening generally increases with transmit power, but it also depends on the rating of the output transistors so this is just a crude approximation.
(Transmission line theory deviates somewhat from the normal models of power transfer, where having nowhere for the power to go would create an open circuit, and no current flows.)


How can I reverse the direction of a brushless motor? I have a brushless motor on my RC plane. After connecting it to an ESC and testing it I've found that it is spinning in the wrong direction.

How can I reverse the direction the prop is spinning?

Swapping any two of the wires connecting a brushless DC motor to its ESC will reverse the direction it spins.

Despite the name BLDC which implies that the motor runs on DC power, each of the three wires (connected to one of the three phases in the motor) is driven by the ESC with a phase-shifted AC waveform. Each wire's waveform is shifted by 120 degrees from the other two.

This offset is what allows the swapping of two wires to reverse the direction of the motor's rotation.

Because nothing special is required to reverse the motor direction, it is also possible to fix this by editing the software configuration, which will do the same thing but in software. e.g. in the BLHELI32SUITE software for ESCs with the BLHELI_32 firmware installed


Binding DX5e (or any other hobby controller) to generic "toy" drone - protocol compatability I picked up a really cheap generic drone mostly for the purpose of tinkering and testing with something that I wouldn't mind losing or destroying. However I can't seem to bind to it with any of my controllers. The main one that I use is the DX5e (DSM2, as it says on the front), but I don't think it's working. Is there a standard/universal procedure that I can use to be fairly sure that the drone is incompatible or broken? Does a difference in rx/tx protocol always make it completely incompatible? I have a few other "toy" transmitters that I tried a little as well.
It's something like this RCtown SH5 (Wish.com).

There are many different communication protocols used for radio controlled models and even for the same vendor the parts/versions are not always compatible. While most use the same chips to build their systems everybody uses a different protocol and so the different parts do not understand each other.
Most of the companies do not release official information how the protocols works and are not interested to make their products compatible with a competing vendor.
So if a drone claims to be DSM2 compatible there are two options: a genuine spektrum receiver is used or somebody found out how the protocol is working by reverse engineering the system.
Most cheap drones do not use genuine receivers since the product costs less than the receiver alone. The drone you linked does not state DSM2 compatiblity so I'd say the problem is that you have no compatible tx. But information on the product page is not sufficient to tell what they are using.
You could try to find out what protocol the drone uses and check if the multiprotocol project supports it: https://github.com/pascallanger/DIY-Multiprotocol-TX-Module/blob/master/Protocols_Details.md
But even in that case you would need to buy a multiprotocol module and make sure it works with your DX5e.


Does the Meteor65 Acro support Spektrum RSSI? I have a BetaFPV Meteor65 Acro with a built-in DSMX receiver. I'm wondering if the F4 1S Brushless Flight Controller V2.2 (DSMX) supports RSSI. I've seen DVR of people flying and they have an RSSI value on the OSD but mine just flashes 0. I checked the product page for the quad and the FC that is in the quad and I do not see anything mentioning RSSI. Maybe this is not supported with an FC with a built-in RX and only supported with an external RX.

Most serial receivers support RSSI through a feature called RSSI channel.

This means, unlike in receivers with a dedicated RSSI output, you can map one of the channels to carry the RSSI signal.

For example, on a FrSKY receiver, the telemetry channel is channel 16, or aux 12.

So you would go into the receiver tab in Betaflight and set RSSI channel to aux 12, and then place the RSSI icon in the OSD.

It is likely a similar process for Spektrum, so I would recommend consulting your transmitter’s manual.


Is there a way to estimate battery discharge duration from mAh and C-rating? Lots of batteries are out on the web, and I understand what the values mean. But I would like to get a battery with a good discharge duration, so is there a way to tell an approximate battery life based on mAh and C-rating?

The capacity and C-rating don't tell you how long the battery will last, just how quickly you could discharge it if you really wanted to do it as fast as possible.
It's perhaps analogous to the top speed of a car - just because your car can reach 120mph doesn't mean that a journey of 120miles will take an hour. Most of the time you'll never reach that top speed.
A high C rating is like having a really big fuel hose on a car. You might need it on a dragster but it won't make an ordinary car any faster, or use fuel any faster.


Disposing of a drone safely Related:

How do I safely dispose of my LiPo batteries?

If my drone crashes and I want to dispose of it, how can I do so safely? Is it necessary to disassemble the drone into different parts: motors, batteries, propellers, shell etc. ?

In the UK a drone would almost certainly be considered WEEE waste (Waste Electrical and Electronic Equipment.)

You can take WEEE waste to your local waste handling/recycling facility; alternatively, there are "Take back Schemes" where some distributors will accept WEEE waste. This is often geared more towards white goods (fridges, washing machines, etc.); unfortunately you will need to check locally.


Is it possible to get a FAA Part 107 drone license if one has had a pilot license revoked or suspended? A Part 107 license (which requires a knowledge test and background check) is required in order to use a drone commercially in the US. If one has lost an FAA aircraft pilot license (that is, a license to fly human-piloted aircraft), does that make one ineligible to hold a Part 107 license or is drone licensure based only on whether one is capable of operating a drone?

If only certain types of license loss (e.g. medical disqualification versus revocation for violating regulations) count, under what conditions would a prior loss result in ineligibility to hold a drone license?

I can't find anything that says losing your general aviation license would prohibit you from being unable to obtain a drone pilot's license. In fact, the two seem separate in every regard but one: The Integrated Airman Certification and Rating Application (IACRA) . Per the Part 107 page you need to make an IACRA application. That application will ask if you have ever had an IACRA revoked

  Have you ever had an Airman Certificate Revoked?

It's unclear what answering Yes will do (they want you to explain why it was revoked), but it doesn't seem to be an automatic disqualifier.


How to determine the correct specification of servo for a control surface Servos come in a large range of sizes, torque values, etc. and the servo to use depends on a number of factors such as control surface size, aircraft speed and desired manoeuvrability.

While there is some intuitive correlation (as an aircraft gets larger, usually so do the servos), is there a way to calculate or determine the 'right' servo to use, sufficient to safely and reliably control the aircraft while keeping the 'downsides' (cost, weight, power consumption) as low as practical?

Most forces in aerodynamics are proportional to area, speed squared, air density and a 'coefficient' that describes how efficient your object is. There's also usually a 1/2 for obscure theoretical reasons.

If you work in metric, the density of air at sea level is basically 1, which takes that out of the equation.

The maximum lift coefficient of an average wing is roughly 1. The drag coefficient of a non-aerodynamic object is also (very) roughly 1 (see link for examples), so for a first approximation, we'll use 1.

Now you've got to guess the maximum speed of your model, maybe by multiplying the motor Kv, battery voltage and prop pitch.

That should give you the maximum force on the control surface. We've no idea how it's distributed but we'll assume it's in the middle. Multiply the force by half the chord to get the torque.

Then allow for differences in the length of control horns. If they're the same, the servo needs the calculated torque. If the servo horn is half as long as the control surface horn, the servo will only need half the torque.

Finally, double or triple that value to give yourself a safety factor.

Alternately, just copy a similar model.

Then when you test fly, don't try any high-speed dives until after you'd tried a level full speed pass. If the controls feel sluggish at speed, you need larger servos.


Can circularly and linearly polarized antennae be used together for FPV? I have a few spare antennae of mixed polarizations I'd like to be able to reuse for my FPV gear.

Is there anything I need to know about incompatible configurations of mismatched polarizations between my transmitting and receiving antennae?

The compatibility of mixed polarity antennae depends greatly. For a little background in RF polarity, this diagram shows the difference between the four main types of antenna polarization available: (mixed/elliptical polarization do exist)

 (cit.)

In general, it is best if the TX and RX antennae match in polarization, but some other combinations are possible while minimizing signal strength loss.

Linear → Linear

Linearly polarized antennae are interchangeable, as long as they are oriented in the same direction. Signal reception between linearly polarized antennae oriented with an angle between them of θ will fall off with a polarization loss factor (PLF) of PLF = cos^2 (θ) and reception will be zero when the antennae are perpendicular to one another.

Circular → Circular

As long as the circular polarization is identical (RHCP or LHCP) between the two antennae, no signal loss will be observed due to the polarization of the antennae. Signal strength isn't dependent on the angle between the orientations of the circularly polarized antennae. However, if you aren't using omnidirectional antennae (e.g. mushroom)¹ and instead have a directional antenna (e.g. patch, helical), you must point the directional antenna in the direction of the other antenna to have the most gain. (see "What is antenna gain?"). Within the beam width of the directional ciruclarly polarized antenna, orientation doesn't matter.

As pointed out by @FlashCactus, only circular → circular polarization matches benefit from the multipath interference reduction effect. This is because circularly polarized waves switch polarization when they bounce off of an obstruction (i.e. RHCP → LHCP and vice versa), so duplicate signals taking an odd number of bounces to reach the receiver will be ignored by the antenna. (they will be recieved as the opposite polarization with which they were transmitted)

For more details on how circular polarization works, I (and @FlashCactus) recommend having a look at this question: What is circular polarization in antennas?

¹: Omnidirectional antennae are also not truly omnidirectional; they have a region of low gain along their axis, and will transmit/receive poorly in that direction. It is best to face them sideways towards the other antenna for best reception. The same is true for linear antennae; they receive&transmit best from their sides and worst along the antenna.

Circular → Linear

Because a circularly polarized wave can also be represented by two 90° out-of-phase perpendicular linearly polarized waves, the linear antenna will receive with a signal strength reduction (PLF) of half (or -3dB). Signal strength isn't dependent on the angle between the orientations of the linearly polarized and circularly polarized antenna.

This configuration can be useful if you want to spectate someone who has the opposite transmitting antenna handedness from you (LHCP while you use RHCP, for example), or to scan the radio spectrum that might contain signals of different polarization (RHCP, LHCP or linear) without switching the antenna: A linear antenna will receive both RHCP and LHCP signals equally well.

Linear → Circular

Likewise from before, because the circularly polarized antenna is built to receive both perpendicular components of the circularly polarized wave, it will receive a linearly polarized wave with a signal strength reduction (PLF) of half (-3dB). Signal strength isn't dependent on the angle between the orientations of the linearly polarized and circularly polarized antenna. As with the opposite configuration, RHCP and LHCP antennae will receive linearly polarized signals equally well.

This configuration can be commonly seen in the case of micro-quads like Tinywhoops which only come with linearly polarized transmitter antennae. Here, the orientation-agnostic benefits of receiving a linearly polarized signal with a circularly polarized antenna (and the convenience of not replacing the antennae on your goggles) are often worth the signal strength reduction.


Possible to use Eachine E160 with Futaba T6EX transmitter/receiver set? I've inherited a Futaba T6EX transmitter with a Futaba R6106HFC receiver, and now I'm planning to buy an Eachine E160 RC helicopter (BNF version), to be bound to this Futaba set.
However, I'm not sure if the receiver can actually be connected to the motherboard of the E160:
I've found a video that shows how to connect a receiver to the E160's motherboard, but I'm afraid that available DSM and SBUS/PPM ports are not suitable for my Futaba receiver.

The product page of the helicopter states it is compatible with: FUTABA S-FHSS, expandable satellite receiver, and supports DSMX DSM2 PPM S-SUS
Your TX/RX are from Futaba but from the older FASST system so S-FHSS is no option. DSMX and DSM2 are from Spektrum and not compatible with Futaba.
There are two options remaining: PPM and S-BUS. Both do basically the same: send the signal of all channels via one cable. As far as I can tell your TX does not support either and only allows to send one channel via one output.
S-Bus is also from Futaba so you could try to find a FASST receiver that supports S-Bus output. Frsky also has compatible FASST receivers with PPM output (like FrSKY TFR4-B). Then you could solder a connector from the outputs from the RX to the E160 motherboard. The yellow cable in the picture is the S-BUS/PPM wire, red is 5V and black is ground. To find the correct matching pins on the RX I'd look in the manual. Usually you have some labels on the case.
A PPM enconder is also an option. This is a small board that encodes the servo signals to a single ppm stream. The downside is that you still have many cabels between the encoder and the RX and you need space for an additional board.


Can drones/uav's fly over international waters without FAA's regulations? Can UAV's or drones (consumer/commercial scale) operate over international waters (12 miles out from the shore) without being regulated by the FAA?

Just wondering if companies can do things like BVLOS* testing out in international waters if they wanted to, instead of getting exemptions or leasing private airspace.

* Beyond Visual Line Of Sight

My conclusion is yes, the FAA regulations do not directly apply. However ICAO takes over and the FAA is in charge of enforcing ICAO rules. Thus, while you can fly without FAA jurisdiction, High Seas Airspace is not a Wild West where anything goes.

The FAA remains in charge of all US civil aircraft even in High Seas Airspace:

Sec. 91.703 - Operations of civil aircraft of U.S. registry outside of the United States.
Each person operating a civil aircraft of U.S. registry outside of the United States shall--
(1) When over the high seas, comply with annex 2 (Rules of the Air) to the Convention on International Civil Aviation and with Secs. 91.117(c), 91.127, 91.129, and 91.131;

Note that all US drones are required to be registered with the US, so they would fall under this clause.
The upshot is that ICAO regulations are in force in international waters. A circular can be found here: https://www.icao.int/Meetings/UAS/Documents/Circular%20328_en.pdf. It describes required BVLOS navigation aids.

RADIO NAVIGATION AIDS AND AIRBORNE NAVIGATION EQUIPMENT
6.26 As a general statement, all aircraft, whether manned or unmanned, must meet the navigation performance requirements for the specific airspace in which they will operate.
6.27 RPA that utilize VLOS as the basis for navigation would not require an on-board means for determining position or the ability to fly an instrument approach. Operations of these aircraft are usually conducted under VMC to ensure the remote pilot can maintain continuous and direct visual observation of the RPA and its surrounding environment.
6.28 RPA that traverse several airspace volumes may operate for the most part under IFR. Such RPA will have to meet the communications, navigation, and surveillance requirements and have an appropriate aircraft operational certification associated with the airspace.
6.29 In cases where small RPA have a requirement to fly beyond VLOS, they will need a means to meet navigation capabilities for the airspace within which they are operating. This could involve an alternate means of achieving the navigation performance.

In addition,

LICENSING AND TRAINING FOR PILOTS AND OTHER MEMBERS OF THE REMOTE CREW
7.8 Remote pilots and other members of the remote crew shall be trained and licensed in accordance with Annex 1.
7.9 Licensing and training requirements will be developed similar to those for manned aviation and will include both the aeronautical knowledge and operational components. Specific adjustments may be needed considering the particular and unique nature and characteristics of the remote pilot station environment and RPA applications (from both a technical and flight operations perspective, e.g. VLOS or beyond VLOS) as well as aircraft type (e.g. aeroplane, helicopter). In that context, qualifications for certain categories of remote crew (e.g. VLOS helicopter) may be  significantly different from those pertaining to the traditional qualifications pertaining to manned aviation.
7.10 On the basis of the foregoing, current and previous notional designations for personnel piloting RPA will need to be replaced with applicable terms as contained in Annex 1, appropriately modified to indicate their position being external to the aircraft, such as “remote pilot”, “remote navigator” and/or “remote engineer”, each of which is a member of the remote crew. A new crew position unique to some VLOS operations is “RPA observer”, an individual who, by visual observation of the RPA, assists the remote pilot in the safe conduct of the flight. Additional crew positions unique  to remote pilot station/RPA operations may be identified over time. These new positions will need to be incorporated into Annex 1 for international standardization.


In what situations do puffy batteries pose a risk of ignition? In this Drones and Model Aircraft SE question, Is it safe to fly LiPo batteries after they get "puffy"?, David O. asked if it is safe to use puffy LiPo batteries.
Gparyani provided an excellent answer, which was upvoted and accepted.
To further understand the issues and risks involved, I would like to ask:
Does the potential for ignition exist during storage, charging, or use (or more than one of those)?  Is it more prevalent in one of those conditions?

The risk of a puffy battery exploding during storage is still comparatively low, you shouldn't underestimate it however.
During charging the risk of explosion is at its peak. This is also the reason why you charge your batteries slower than you discharge them (i.e. to lower the risk of puffing and explosions, as well as to keep wear and tear low).
During use, the risk is quite high as well, though I'd say it's lower than while charging.
Always, always get rid of them as quickly as you can. Exploding LiPos are not a joke. Besides, a puffy LiPo has a far lower total capacity, rendering it basically useless for flying anyway (though don't be fooled - the explosion is still more than dangerous).


How do aerodynamics for small model aircraft differ from that of larger aircraft? I am reading an aerodynamics textbook (Introduction to Aerodynamics by Anderson). I am still in the chapters that deal with subsonic aerodynamics, which seems to have a focus on life-sized manned aircraft. I am wondering: are there major differences in the consideration of aerodynamics when designing model aircraft as opposed to life-sized manned aircraft?

The largest difference is that in Reynolds number, which is the same issue that wind tunnel models have. The Reynolds number is linear in length, which for the wing is the chord length. So for example, a quarter-scale model will have a Reynolds number equal to one-forth that of the full-scale aircraft (in the same atmospheric conditions). The reason this matters is that airflow tends to transition from laminar to turbulent at a specific Reynolds number, so if one uses the same airfoil on the model as in the full-scale aircraft, then usually the performance will be different near stall (usually much worse). That is why reduced-scale models usually change to an airfoil that is designed for lower Reynolds numbers.
BTW, Intro to Aerodynamics by Anderson is excellent. That was my first textbook when I started aero engineering over 30 years ago.


How to secure the screw on a BLDC motor shaft I lost the screw that holds the motor bell to the base of the motor.  I replaced it and flew, but it came loose and I lost it again.  I used blue thread lock to secure it.  Do I need to use red thread lock?  What's the trick to keeping the screws on?

Use red or better. Blue and sub-red are explicitly designed to loosen with low to medium heat. (in the manual)
FWIW, thread lock is little more than an increasingly heat resistance paint, close in composition to latex paint (depending on the brand).  I have used latex paint and also nail polish in a pinch (an old trick from a car mechanic).
If you want a screw to stay, and are okay with possibly never getting it out again, there are a number of advanced and possibly no bueno tricks. All of these are from decades of mechanic work and caution is advised.

Toothpick:  Shred it, thin it out, stick it in and screw away and grind the fibers in.
Tooth pick with thread lock, glue, or paint.
Metal shavings, grind them in
Damage the correct end of the screw or thread so you get a fused connection (may never come loose >> aka >> danger zone).
In some cases, you can cover the screw with a proper cap to stop it from spinning and falling out, similar in theory to the use of a c-clip.  For example, drop solder on the top and let it "cast" into the head, then put electrical tape over it (not recommended, many reasons like motor may be off balance).
Copper braid or similar, just jam it up.
Re-tap and get a new screw

Your problem is most probably a combination of these factors:

heat
hot/cold expand and contract cycle
vibration
possible weakened threads (cut wide from friction).

The trick is context, experience, knowing the tools and materials, and not buying cheap stuff.
Now to the meat of the issue - BLDC motor, that is a broad designation (https://en.wikipedia.org/wiki/Brushless_DC_electric_motor), so you could be using an in- or out-runner. Big/low Kv versus smaller high Kv demands a different solution possibly. Each motor has a unique footprint on vibration, heat, operational range, expand/contract margins, etc.  So there are a number of factors that will help you decide what is best, I would contact the company if possible (probably Chinese and ZFG, but always an early consideration if possible).


What LiPo C-rating is best for a small 65mm quad? I have a small 65mm quadcopter which uses 2s batteries. Is there a recommended LiPo C-rating to get for a drone like this? Or is there some way to figure out what C-rating I should get?

C rating is very much a non-science. There’s no real way to compare between brands, so just go off the idea that the higher the C value, the better.

If you want to do it a little more mathematically (though it still won’t be completely accurate), find out the maximum current draw of each of your motors and other electronics, add them up and then add a bit (maybe 20%) for some extra safety, and this will be your maximum current draw.

Divide this by the capacity of your battery in amp-hours (so 0.45 for a 450mAh battery) and this will give you your ideal C rating.


How should one chose the correct motor KV for a build? For a 5 inch, 4S build, the general advice is to go 2300-2750KV. For the same size but 6S, it should be ~1800KV. However the same motors could be used on a 4S 7 inch quad. And all of this scaling seems to go into the window when moving onto something like whoops or toothpicks, and up to X-class.

How should one choose the most appropriate KV for their intended build? Is there a formula to use, or is it just learned through experience?

I think it’s learned through experience and it can also be roughly figured out using this table based on frame and propellor size:

    ╔══════════════════╦═══════════════╦═════════════════╦══════════════════╗
    ║ Frame size       ║ Prop size     ║ Motor size      ║ KV               ║
    ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
    ║ 150mm or smaller ║ 3" or smaller ║ 1306 or smaller ║ 3000KV or higher ║
    ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
    ║ 180mm            ║ 4"            ║ 1806            ║ 2600KV           ║
    ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
    ║ 210mm            ║ 5"            ║ 2204-2206       ║ 2300KV-2600KV    ║
    ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
    ║ 250mm            ║ 6"            ║ 2204-2208       ║ 2000KV-2300KV    ║
    ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
    ║ 350mm            ║ 7"            ║ 2208            ║ 1600KV           ║
    ╠══════════════════╬═══════════════╬═════════════════╬══════════════════╣
    ║ 450mm            ║ 8", 9", 10"   ║ 2212 or larger  ║ 1000KV or lower  ║
    ╚══════════════════╩═══════════════╩═════════════════╩══════════════════╝

(table source)


What propellers should I get for my drone? How do I know what type of propellers to get for my drone and what do the specific numbers for each propeller mean?

The first step to getting the right propellers is to figure out what size propellers will fit your drone. What you can do is measure the distance from the center of the motor to the closest thing (probably the frame) that would block the propeller. Multiply that by two, and a few millimeters smaller than that is the maximum prop size/diameter. (smaller props can also work)

For example: if the center of a motor is 2.6 inches away from a frame, I would get 5'' props.

The next thing to look at is the pitch and number of blades. This is where most of the numbers come in for props. Let's use the example of 5143. the first part, 51, is the prop diameter (5.1'') and the second part is the pitch of the prop, 43, which would mean that the pitch of the prop is 4.3''. A higher pitch generally uses more power but can result in faster flying to some extent. (sometimes the prop pitch is not entirely accurate, as it depends on what the manufacturer thinks) The number of blades of the prop will be listed separately when the dimensions of the prop are listed like this.

Another way you may see prop dimensions formatted is like this: 5.1x4.3x3. That essentially says the same thing except it also includes the number of blades, which in this case, is 3. The 5.1 is 5.1'' diameter and the 4.3 is 4.3'' of pitch.

What I would recommend is to try many different types of propellers because many props that have the same measurements will perform differently.


Do I need CW or CCW props for my plane? So I'm making an airplane with a motor at the front, do I use CW or CCW props?
Pretty sure this is what counts as a puller plane (is that the right term?).

The decision between CW (clockwise) and CCW (counterclockwise) propellers has to do with the direction your motor/engine will spin, not really in regard to where you're putting the engine on the plane. CW props will create thrust behind them when spun in a clockwise direction, and CCW props will create thrust behind them when spun in a counterclockwise direction. It's that simple. :)
For an electric motor driven plane, it probably doesn't matter which kind you get because it's highly likely that you can reverse the motor direction in the ESC (electric speed controller), but I'm not aware of any ability to do this with model plane gas engines. If you're using a gas engine, inquire to figure out either what kind of propeller the specs say to use (if this is listed) or what direction the engine spins and get the appropriate CW/CCW propellers.
If the model airplane plans/kit you have calls for a specific kind of propeller, like for example if the plane was designed to fly better with one propeller rotation direction, I'd recommend abiding by their recommendations. There are quite interesting aerodynamic and physical phenomena like P-factor which the designer may have taken into account in the aircraft layout, resulting in the design requiring a specific kind of propeller.


How to drive a servo for a tricopter with a flight controller? Is there any way to set up a servo with full control for a tricopter using a normal flight controller and normal drone parts? Are there any other things that I should use or consider?

This servo will be used to roll the rear motor (there will be two front motors). The prop size will probably be around 6-7'' so the servo will require a decent bit of power.

Essentially, I'm asking if a servo can be powered from a flight controller (does the flight controller have the ability to output 3a 5v) and can I control the servo? Are there only specific flight controllers that can output that?

This has likely been answered here: https://drones.stackexchange.com/a/230/50, but to paraphrase:

A standard flight controller can easily be set up to control a servo, as per your edit.

You first need to plug in your flight controller (with props off, if you’re using one with motors already attached) and enable ’servo tilt’ in the configuration tab, then go into the CLI.

You then need to type ‘resource’ (assuming you are on the latest version of Betaflight.)

As you want a tricopter and your flight controller is likely for a quadcopter at least, you can reassign a motor output (or any other PDB with a built-in timed) to become a servo output. If you don’t know how to re-map resources in Betaflight, the answer I have linked gives an excellent rundown.

You should then see a servo tab appear in Betaflight, and from there you should be able to configure everything you need.


EU Citizens: range settings of DJI Digital FPV system (FCC vs CE)? I'm looking to buy the DJI Digital FPV System and I'm now looking at the range. In the specs it says:
Max. Transmission Distance
FCC/SRRC: <4 km
CE: <0.7 km
MIC: <2.5km

I'm living in the EU, but I obviously would like the long range 4km version. So I was wondering; are these versions different in hardware, in software or is it simply a setting in the software? And if I buy this in the EU, could I switch it to the FCC version so that I could enjoy full range?
Is there anybody from the EU here that has the Digital FPV system and can tell more about it? Is there a menu setting for this? And what is your experience with the range?

The difference is due to regulation - in the EU, the permitted radio power output is lower than that allowed under the FCC regulations, which results in reduced range.
Without a licence from your countries telecoms regulator, it would be illegal to operate the FCC equipment in Europe.
It is likely to be a software setting, but there might be hardware differences if the costs make business sense (possibly cheaper hardware Vs. different production process.)


How do thrust requirements change as a multirotor leaves ground effect? Assuming either a quadcopter or a hexacopter, is there any published data on how much more energy is expended to escape the ground effect?

Is it a function of the thrust being produced to lift the multirotor? And is it different for a quadcopter than for a hexacopter? Is the requirement lower when the props are higher off the ground?

To fly above ground effect, you need thrust equal to the weight of the aircraft (or slightly more, as you want to climb).

Ground effect doesn't hold aircraft down, it just makes it easier to fly when they are close to the ground. The exact amount varies quite widely depending on exactly how close the wing/rotor is to the ground. For a plane or helicopter it may only be 10% extra lift, but a vehicle designed to maximise ground effect (like a hovercraft) can fly with vastly less power than would be required to fly without ground effect.

Ground effect is particularly noticeable if you hover a model helicopter inverted over a smooth surface. As it descends towards the floor, it looks as if it lands in a big soft cushion - decelerating and bobbing around at about half to a third of rotor diameter. You can hover without the constant adjustments in collective pitch that are normally required, and need to drastically reduce thrust to go lower. When you're half an inch or less off the floor, it's probably only using 10-20% of the pitch required for normal hovering, and there's a self-levelling effect so it's much easier than it looks!
For a typical FPV quadcopter with 5" props on top of the motors, you almost can't feel ground effect if you put the battery under the frame. With the battery on top you can feel a noticeable cushion and you can find a throttle setting that holds the quad off the ground but won't climb out of ground effect. I'd estimate that it's flying at about 80-90% of normal power.

While the power may be reduced, it can be harder to hold a multi-rotor or helicopter in place when in ground effect. The bubble of higher pressure tries to escape out from underneath the aircraft, pushing it in the opposite direction.

A general rule of thumb is that the reduction in power due to ground effect starts to be noticeable when the altitude is less than around half or a third of the wing span or rotor diameter. The 'air bubble' effect on position holding while hovering is noticeable one or two diameters above the ground. Both tail off gradually so there's no hard limit.

See also:
* What is ground effect?
* How high does the ground effect last?
* Does ground effect scale 1:1 with wingspan?
and lots more, over at the Aviation stack-exchange.

Also this excellent academic paper:
Characterization of the Aerodynamic Ground Effect and Its Influence in Multirotor Control


S800 Reptile Matek F411 auto launch question I just built my first wing a S800 Reptile V2 using a Matek F411 Wing flight controller.
Here is the video of the behavior:
https://www.youtube.com/watch?v=muoECu_lvKs
I just checked that my Servos are well trimmed and calibrated so when turned my Radio transmitter on both of them are in a 90 degre angle so my flaps are flat. If I have horizon mode enabled and I angle the the wing to the right or left I can see a small compensation of each servos so that’s also good. Also the sticks of my transmitter moves the servos in the right position, already checked that.
I wanted to test Autolaunch without the propeller installed. So I waited for the gps to get enough sats and then I armed and push throttle up and then grabbed the wing with my hand and simulate a launch and I could get the motor spin fast. So all that working flawlessly. The only thing that I noticed is that when I simulate launch by moving fast the wing is that right flap had a bigger angle than my left one, even if keep the plane with my hands completely horizontal with no tilt I could see that.
So don’t know if this is a normal behavior because I didn’t throw the wing in real life and then GPS is not updating altitude or maybe other thing.
Any clue? Does simulating autolaunch without throwing the wing could result in flaps not getting the right position becuase the wing is not in real air? Because what I was expecting is that when launching both of flaps went into up position having the wing prefectly horizontal.
Appreciate any feedback

A possible explanation is the flight controller compensating for propeller torque.
When a propeller spins, there is a counter-rotation applied to the aircraft (Newton's third law.) Assuming your propeller spins clockwise (viewed from behind the aircraft) this would be corrected in the air with a small amount of right roll - which is what is shown in your video. The amount of surface deflection will vary by airframe, so it is hard to judge from a  video if the amount of movement is correct.
More info: http://ffden-2.phys.uaf.edu/webproj/211_fall_2016/Collin_Lasley/collin_lasley/torque.htm


Implementing object detection in DJI Mavic 2 pro in real time I have developed a model in python (pytorch)  for detecting specific kind of objects,
Now I'd  like to embed and load this model into the my DJI Mavic 2 pro,
According to posts I understand I need to to write code on the drone which should be c++,
Is there any suggestions how can I start capturing live footage and pass those frames into the model?
Any helpful resources/examples/github repos will be helpful

That's a fascinating project, but I'm not sure it's possible on a DJI drone. The firmware is closed source and not designed for easy modification.
I don't know if it's possible to replace the DJI firmware with an open source project like iNav or if you would need to build a new drone from scratch around an iNav capable flight controller.
You might also find that you need a more powerful processor to run real-time image analysis.


Is there a way to override the distance limit on a DJI Mavic Mini without a mobile phone app? I recently bought a DJI Mavic Mini.

It seems to me, that DJI wants me to fly it with a mobile app, but I currently don't have access to a mobile phone (extremely weak battery only). It looks like I can only fly some 50 meters without the app.

I'd like to override this because I am on a wide field with (almost) no obstacles. I looked into the app, but the distance limits there seem to apply only for the flight with the app.

The instructions given along with the drone are quite minimal and not helpful in this case.

Is there a way to override the distance limit on a DJI Mavic Mini without using the mobile phone app?

Currently no, barring exploiting vulnerabilities on the platform (which DJI are pretty quick at fixing) there is no way around the distance limit. The wide field really won't be your issue here. At 60m you can't see it safely line of sight.

Why not get a cheap phone just for this purpose? Doesn't need to be fully featured, or indeed that current - just check compatibility with DJI first.


How do I tell when to replace the motors on my tinywhoop? I own a brushed micro quadcopter, more commonly known as a tiny whoop. I've read that brushed motors in general, and especially those used in such quadcopters, have a limited lifetime and that you should replace them when they near the end of that lifetime.

However, as far as I can tell, there are no obvious signs that the motors have become too old to fly, as they don't break but instead their performance decreases over time. There's a maximum total runtime in hours listed for the motors, but I can't imagine any way to track how many hours the current set has been flown for besides writing down the length of each flight, which would be extremely tedious.

So how do I figure out whether my motors are worn out and should be replaced, or are still okay to fly with?

As someone who loves collecting data for analysis, I do track all of my flights.  I have found that, under normal conditions, brushed motors should last for at least a few hundred flights.  You can get higher if you don't fly hard or get things caught in the props or motor shaft that will make the motor heat up more than normal.

How to determine whether a brushed motor needs to be replaced is a tough question and it really depends on your willingness to fly with a drone that isn't operating perfectly.  With mine, the telltale indicator is that I notice less power than usual and yaw is off a bit (twitchy or lethargic).  This makes sense since all motors perform to the level of the least capable motor.  If you experience less performance, first, ensure that it's not just the battery.  This is easy to do - just use a newer battery, or one that you know is still providing good power.  The next thing to do, if the battery checks out, is to replace the motors.  I recommend replacing all of the motors at once for brushed motors since they are all getting some form of wear while in use.  Replacing them all ensures that you are starting with peak performance.


Why does a brushless drone fly longer? I have noticed that drones with brushless motors fly longer than those with brushed motors. Why are drones with brushless motors able to fly for longer amounts of time?

Brushless motors (aka BLDC) are typically[*] more efficient than brushed DC motors. Higher efficiency equates to longer flight times for a same battery pack.

Amongst other reasons:

The inrush current at the moment of commutation can involve sparks (which is an inefficient waste of energy), and in any case is a free-running operation without the possibility for optimization.
The carbon brushes have a somewhat higher resistance, which is an electrical energy loss
The carbon brushes involve a certain amount of drag, which is a mechanical energy loss
The EM field is not easily controllable to reduce torque ripples, resulting in mechanical energy losses. Anecdotally, you can hear these ripples, especially when comparing power tools using universal motors (i.e. brushed AC wound in series) vs BLDC. Sounds represents energy, all other things being equal a noisier drive is a less efficient drive.

Brushless motors also are easily built into outrunner applications, which is appropriate for high-torque direct drive applications, such as a propeller. An inrunner needs an inefficient gearbox to develop the torque required to spin a blade (which might also be complex, costly, and weighty).

An oftentimes overlooked consequence of brushless efficiency is heat generation. Fundamentally, what limits a motor's power is heat, and producing less of it means that more energy can be supplied from a smaller package. The smaller package means lighter weight, which equates to longer-runtime.

Each of these on its own is small, but summed together they result in a far superior drone operation from brushless than brushed.

[*] There are some extremely efficient (>95%) brushed motors out there. However, the engineering required to get that high efficiency is costly. Cheap mass-produced brushed motors will never have those kinds of tolerances, but brushless motors are much less sensitive to manufacturing imprecision.


How to charge LiPo batteries in series? Is there any way to use my main charger, which can charge 2-6s batteries, to safely charge multiple 1s batteries in series? (assuming all of the batteries are the same capacity)

How would I go about doing this?

Huh. I never thought about this before, but charging identical LiPo batteries in series with one another seems logical enough. In fact, here's an article which discusses how to do it, which I'll summarize here.

Prerequisite requirements:

The charger must support the series battery (e.g. for 2x 4s batteries, the charger must work with at least 8s)
You must create a balance lead adapter (and separate main discharge lead adapter) that combines the leads from the batteries into one. The highest voltage cell on one battery will have the same balance connector pin as the ground wire in the next battery's balance lead. (graphic below shows this in more detail)
All batteries MUST be the same capacity, but not necessarily the same cell count. (e.g. not 1s 1000 mAh and 1s 1500 mAh, but 1s 1000 mAh and 4s 1000 mAh is fine)
All batteries MUST have per-cell voltages that are close to one another. A difference of 0.05 V is usually okay.

Advantages

Time savings from charging all at once and hooking up batteries fewer times
Can allow for faster batch charging than parallel charging if the charger's power limit is less of a bottleneck than the current limit
Unlike parallel charging, each individual cell is monitored and balanced separately by the charger

Disadvantages/Risks

If something were to go wrong during the charge cycle it would effect multiple packs. (e.g. an internal cell short in one pack could light all packs on fire)
All batteries MUST be properly connected to both the main discharge lead adapter and balance connector adapter, (and connected in the right order) or funky stuff like short circuits and fires could happen!
Can be a slower batch charging method than parallel charging if the charger's power limit is more of a bottleneck than the current limit


Are these methods of Drone Localization Techniques for a dark environment plausible? I am working on a project where I need a quadcopter to accurately know its location relative to a starting point in a GPS denied environment in the dark.
A quick overview of the project:

The drone will be mounted on a vehicle in a docking station
When prompted, the drone must hover above the vehicle by ~30 m
The drone must be able to accurately locate its position relative to the docking station in the dark without GPS
The drone must also be able to react to the movement of the vehicle (very small movements in nature)
When finished, the drone will return to the docking station

Given the requirements of the problem I have been looking at a couple of solutions:

Use around 3 infrared beacons on different parts of the vehicle with a camera on the drone to perform localization (looking at the IR-LOCK sensor and beacons for this purpose)
Use ultra-wideband communication with a similar setup of three or so anchors and one receiver on the drone (looking at the Pozyx anchors and tag)
Use Bluetooth of some sort (haven't looked into this one as much)

Any suggestions or tips you may have would be greatly appreciated. My main concerns are the range/feasibility of each option.

With sufficiently accurate and stable IMUs (think ADIS 164xx) on both vehicle and drone you should be able to calculate the relative offset between the two. In any way this will have to be a custom solution.
What GPS denied environment are you referring to?


What obstacles are there in making ultra long range model aircraft? As far as I am aware, there have not been any model aircraft that have successfully circumnavigated the Earth without stopping. Few trans-Atlantic attempts have succeeded (see: The Spirit of Butts' Farm). My question is: what makes long-range model aviation so difficult? Is the small size of model aircraft disadvantageous when traveling long distances? Or is success just a question of improving the materials and propulsion, and flying during good weather?

So many different issues, I study a lot of the FAA regulations closely but have contemplated this same question a few times.

The power and weight of gear is heavy, so to make it all the way around is not going to happen without a lot of hacking. (solar proof of concept or similar notwithstanding)
Efficiency of solar (power and weight) is a problem. The square feet of solar needed is quite large and disproportionate to how we conceptualize "RC planes".  These vehicles are really flying solar arrays.
Data, control, tracking, and safety assurance is much harder half way around the globe, even with satellite assistance
Satellite data and connectivity hardware is still big leaving this type of task to the larger military units.

From a regulatory perspective

FAA would rather cut their hand off than issue BVLOS waiver
Patchwork problems internationally exist not only for aviation, but also frequency use . EU radio freqs are very different.  When traveling to fly internationally it takes a while to make sure I am legal or have legal gear.
Clearing airspace for these attempts is a serious undertaking of budget and politics.

Weather is a huge concern for small craft.  Variations in the strata of the atmosphere are no joke. Be it thin air at altitude, winds, cold/hot temperature, all of this is hard for a small craft to manage.

"At heights of 7 to 16 kilometres, the air in jet streams moves at constant speeds of over 25 metres per second or 90 kilometres an hour." source

The US Military is one of a few orgs with advanced programs for this type of use.  The U.S. military UAS groups has Tier 2+ with a '3,000-nautical-mile (6,000 km) radius'. These devices range from sub-55 pound to 2+ ton vehicles.
For what it is worth, I know some people with ties to a successful cross Atlantic RC plane flight.  The stories they tell underscore how hard this task is to pull off.
In the end our number one obstacle for extended UAV flight of this type (and in general) is the same problem we have for phones and laptops.  Our current battery tech is 20-30 years behind the technology it powers.  The physics community engaged with this part of the equation frequently try to move the ball forward but the person to make a lighter and better battery will win the internet.  Other fuel types are out there too, for example Hydrogen where the MFD3000 by Bobby Watts is available with a hydrogen fuel cell providing some interesting performance and represents good progress.
I think anyone with some expertise in mechanical, electrical, aviation, fuel and power train, etc could stop by and add a few more reasons why this is generally out of reach right now.


What is the advantage of a stretched-X frame over a true-X or squished-X design for racing? Most racing frames on the market appear to be stretched-X (longer than they are wide).

I have heard the argument that a stretched-X allows better airflow to the rear props due to physical distance, but in a racing environment, the quads are usually flying at a much steeper pitch angle than any other form of flying which should give the rear props much cleaner air.

In my experience flying line of sight, stretched-X frames seem to have more pitch authority than roll which would seem to be the opposite of what would be desirable in a racer.

Other than the fact that they are a little narrower so they fit through the gates better, can anyone offer any advice as to why stretched-X frames are so popular?

I'm not a frame designer, but one distinguishing characteristic comes to mind as to why stretched-X frames are more common.

As you mention, a stretched-X frame has a longer front-to-back dimension than its left-to-right dimension. In addition to providing the rear propellers with cleaner airflow when in forward or backward motion, this results in the moment of inertia about the pitch axis being higher, which means that it requires more work for an external force (e.g. wind) to change the pitch of the quad inflight.

 (cit.)

This also means that, as you noted, the pitch axis has greater control authority (due to the longer moment arm) which allows the quad a more quickly accelerated response to the pilot's commands. The differences in control authority accessible to the pilot can be smoothed over with rate profiles and PID tuning so that the quad maintains the stability it gets from the stretched-X design while responding uniformly to pitch and roll commands.


New Prebuilt Drone flipping on takeoff I have a small quadcopter drone, immediately on takeoff it flips upside down, this happens all the time.

What could be a potential problem?

Edit: It is prebuilt and bought from a shop and has never flown

There are several things that can be causing this with different likelihoods.

The first thing to check is - are your propellers on correctly? It is an easy mistake to make and always worth a check.

The next thing to check is that all of your motors are working correctly. Start by spinning each of the motors by hand and see if anything feels obviously wrong, for example, a magnet out of place. If nothing feels wrong, remove the props and individually spin up the motors in Betaflight to test them. Make sure that they spin the direction that betaflight shows in the configurator.

The next port of call is your gyro. Plug your quad into Betaflight or whatever firmware you use and move it around - does the virtual representation of the quad match up with your movements in real life? If not, that is almost certainly the cause.

If all of these have failed, swap two of your motors and see if the quad flips in the same direction. If the problem follows the motor, you have a faulty motor. If the problem stays in the same place, you have a faulty ESC.


Are there any brushed outrunner motors? The most common motors on drones are brushless outrunner motors. I´ve also seen some brushless inrunner motors. Are there any brushed outrunner motors? If so, why are they so uncommon?

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 have 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.

Almost all brushed DC motors would be classified as inrunners and very few brushed outrunner designs exist, as you note. The Wikipedia page for Brushed DC motors makes no reference to an "outrunner" brushed motor and almost no search results appear for them.

I'm not a designer of electric motors, but I have a theory for why this might be the case: the usefulness of brushed motors is mostly because they are inrunners.

 (cit.)  (cit.)

The above images show "inrunner" brushed motors and the commutation mechanisms they require. If you were to make them into outrunners, the only difference they would have with brushless outrunners would be the swapped location of the coils/magnets. This setup would also increase the size of the commutation mechanism and forcing the brushes to be crammed inside the commutation ring, making it more complicated and susceptible to breaking.


Why are quadcopters inherently unstable? I have heard it mentioned that quadcopters are inherently unstable and only become stable due to control. What does inherently unstable mean in this context, and why are quadcopters inherently unstable?

A stable system is one where there's a force that pushes the system back towards it's original state when the system is moved from its balance point.

For example, when the driver gets into a car, there's more weight on one side of the car than the other but the car doesn't flip over. The springs on that side of the car compress and push harder on the wheels. The tyres push harder on the ground and the ground pushes back. The extra force from the ground exactly balances the extra weight and (after possibly bouncing for a moment) the car stops moving.

In an unstable system, say a broom balanced vertically, once it moves from the perfect balance point gravity will pull it further away and it accelerates.

For a quadcopter, there is no force that returns it to its original location, holding it horizontal, or even preventing a gradual roll.

Even if the thrust from each motor was exactly the same, and the weight was perfectly balanced, it's very unlikely to be perfectly stationary. If there's even the slight amount of pitch or roll, the angle from horizontal will gradually increase. As the angle increases, the sideways thrust increases and the drone accelerates.

So the roll rate is constant, the angle and acceleration increase linearly, the horizontal speed increases faster as the acceleration builds, and the distance from the starting position increases even faster as the speed builds. To the pilot, it looks like the drone is accelerating away from its original position much like the broom falling over.

To a systems engineer, the rotation of the drone is neutrally stable - there are no forces increasing or decreasing the rotation rate. However the speed and position are unstable - once it starts moving, it accelerates.

I should mention that there are second-order (i.e. relatively minor) forces too. If you had a large fin on top of the drone, aerodynamic drag on the fin would return the drone to upright as the speed builds and limit the maximum speed - in practice this isn't useful as it doesn't return the drone to its original position.


How to update the firmware of a T16 Pro's internal multiprotocol module? How should I go about updating the internal multiprotocol module firmware of my Jumper T16 Pro?

The first thing to do is to check that you have the bootloader. Newer radios should have it installed. (Just check that you have Multiprotocol Module firmware v1.2.1.85 or later) If you don't have the bootloader installed, here is a video on how: Jumper T16 "Update Recommended" Fix (how to flash internal multiprotocol module).

Assuming you have the bootloader, the next step is to go here: MULTI-Module Firmware Downloads. Here, you can get the latest firmware for any multiprotocol module, so this works for more than just the T16. On the left, find the module that you want to update. In this case, the Jumper T16 Pro Internal module.

After that, most of the information is filled out so just fill in the rest (in this case just channel order)

Get the file that corresponds to the channel order of your radio:

Put the file onto the FIRMWARE folder of the micro SD card from the Jumper T16 and then put the card into the T16 and power it on. Long press the system key, press the page button once, scroll down to [FIRMWARE] and click it, long-press the new file, and then Flash Internal Multi.

If you need a more comprehensive guide, check out Joshua Bardwell's video: Jumper T16 "Update Recommended" Bootloader Method (how to flash internal multiprotocol module).


How to determine the minimum thrust to weight ratio for a fixed-wing aircraft? I am considering building a fixed-wing aircraft with foam board, and I'm unsure what the necessary thrust to weight ratio is. With quads, it's easy to determine the necessary thrust. Just find a motor/prop combination that can provide more thrust than the weight of the quadcopter. With a fixed-wing, it isn't as simple because the aircraft can fly with less thrust than the total weight of the aircraft.
Is there any way to determine the minimum amount of thrust that can keep a fixed-wing airborne? The reason I'm trying to figure this out is because the goal of this aircraft is to be as efficient as possible.

I'm afraid it's not that simple. As you mention, planes can fly with a fairly low thrust to weight ratio. Obviously gliders can fly with no power at all, so there's no critical lower-limit.
The other issue is that pitch-speed is important - the prop needs to be producing thrust when the plane is moving, not stationary. Measuring static thrust only tells you half the story.
Instead of thrust, it's better to look at power. Assuming that your motor and prop are reasonably efficient (and most are) measure the power going into the motor with a watt meter (or run it for a minute and see how much energy your charger puts back into the battery). Then weigh the complete model, including the battery.

50 w/lb is about the minimum for gentle cruising and slow climbs.
100 W/lb is 'sporty', say for a warbird. You don't have to worry about conserving energy and can easily climb out of trouble. It might not have unlimited vertical climb though.
200 W/lb is unlimited vertical climb, hovering and climbing vertically out of the hover.

For ducted fans, you should double these numbers. i.e. at 100 w/lb you'll need to be careful to conserve energy.
However foam board planes aren't super-efficient or super-fast, so you can usually do a simple thrust test to check it'll be OK. Dangle it by a wing tip and gradually apply power.

If the model has enough power to support its own weight, it's probably around 100 w/lb
If it can only reach about 45 degrees, its about 50 w/lb and will fly if you're careful.

About pitch speed
If a prop has 6" of pitch and is turning at 1000rpm, under no load it would advance 6000 inches per minute. Or to put it another way, if the model reaches that speed, it won't be producing any power!

'Slow' props have a pitch of about half their diameter (e.g. 8x4")
'Sport' props are 2/3 to 3/4 of the diameter (e.g. 8x6")
'Speed' props are 'square' with the pitch equal to the diameter (8x8)

If you find your plane accelerates well from the launch but has a low top speed, you might need a higher pitch prop.
If it doesn't have enough thrust to take off, go to a larger diameter.
If you change the prop, you should measure the current drawn to check you're not exceeding the limit of the ESC. Also check that the motor and battery don't overheat.


How to reduce propeller tip losses? I have heard that tip losses in propellers can occur when a propeller is highly loaded (when there is a much higher pressure under the prop blade than above it). This can happen with drones that fly quickly and create a very highly loaded prop. Are there any prop designs that can remove or lessen the drag caused by tip losses on drones?

Propeller tip losses are a function of, or perhaps we could say it is a side effect of the propeller design itself. The designer of a propeller can influence the tip losses, but a user is unlikely to find a practical way to accomplish it for a propeller they already own. So this question is theoretical.

The overall size and geometry of a propeller can influence the tip losses, but for any particular multirotor, the size or length of the propeller is most likely to be at its maximum size already. Or, if it is not at the maximum size, the length of the propeller is at the optimum size for the multirotor it is installed on. Making the propellers any longer than the airframe can accommodate makes the question morph to one of: "What changes to a multirotor influence the tip losses of the propeller." Ok, now the answer can include making the prop longer.

In the real world, the answer is: "Buy a better propeller".

In the theoretical world, redesign the propeller. And one could also add a well designed shroud with a very precise gap (very narrow) between the tip of the propeller and the shroud. And to accomplish this, the tip of the propeller would then need to have a shape that is different than one designed for free air. It would fit precisely with the shroud just a fraction of a millimeter away. This prevents the tip vortexes from rolling off the end of the propeller. But if this theory were practical for multirotors, one or more drone maker would have employed it already. And so far, it is not being done. I have not yet seen it. They are also claimed to be quieter and more efficent, but that too is not proven with any experimental evidence on an entire drone. It is all laboratory results. So there must be trade-offs that make that solution unattractive.

And to actually add a shroud, we are back to changing the entire multirotor to reduce the tip losses. I am not sure that is what the question was.

Most prop manufacturers make claims that their props are better, but provide little proof or clues regarding how they did it. We can see unique shapes used on the tips, but there is little published data that helps us replicate it for ourselves.
Was this question one of theory or a practice?


Quality of transmitted image and electrical problems There is a question already regarding a flickering OSD, but I wonder how other image quality problems relate to electrical problems. What's the first thing one has to look for when the transmitted image is jumping or features vertical running lines or the quality of the image seemingly depends on throttle value? What are common wiring strategies to avoid these kinds of problems and what are their respective root cause?

What I usually do is power the VTX from BEC/ESC (or directly from battery if it is rated for it) and power the camera from the VTX 5V out and braid the wires, but I think there must be more to know about image transmission issues.

There’s a lot to unpack here, so I’m going to give a general kind of advice that should be helpful for anyone trying to get cleaner video:
Electrical Power
There are two main aspect to the image transmission: the camera and the VTX.
Whenever you have noise, the first step would be to increase power filtering as much as possible.
The easiest way to do this is to add a capacitor to the battery pads to filter out the voltage spikes.
If that doesn’t work, try powering your VTX from a BEC on your flight controller instead of VBAT (if that’s what you already have).
Also try powering your camera from a BEC on your VTX if it has one.
Then try adding a common ground between the camera and the VTX to avoid what is called a ground loop.
There are other sources of power noise, which could include oscillations that cause voltage spikes in the motors.
Antennas
The antenna you use also has a big impact on video.
The best way to ensure good video link quality is to have two circularly polarised antennas with the same polarisation, for example RHCP with RHCP and LHCP with LHCP.
You can also use a patch antenna to increase the reception of your goggles at the expense of the number of directions from which you can receive a signal.
VTX
Have you ever powered on your VTX without an antenna? This can sometimes cause the VTX to become damaged.
If you have a spare VTX, try using that and see if quality improves.
VTX Settings
If you’re flying in a wide area, you can try increasing your VTX power (as long as it is legal).
If you’re flying in a tight space like a bando, sometimes having a higher power output can actually make the video signal worse due to multipath interference. If you experience that, you may want to try lowering the power output.
Frequency
Make sure your goggles are on exactly the same frequency as your video transmitter.
People often use the auto-scan function on their goggles, however this is known to be inaccurate and often goes to a close channel, but not the exact one.
The wrong frequency will introduce static, but it is unlikely to create the lines you describe.
It is also possible that lines may be caused by RF interference from WiFi, power lines etc. You may be able to get around this by changing your frequency.


r-xsr won't bind to qx7s I'm trying to bind an r-xsr to a qx7s, but the receiver shows a solid red, green and blue light and won't bind.

I have updated the receiver to version 2.1.0 LBT and the transmitter to the EU version of OpenTX 2.3.7.

Is there a known problem with any of this firmware, or is there another problem?

Okay, I solved it: I had installed the EU version of OpenTX, but I hadn't flashed the internal module on the transmitter. When I did that it worked flawlessly.


Taranis x9d plus se 2019 malfunctioning My taranis suddenly stopped working properly. When I turn on the taranis it does not read my crossfire module anymore (sometimes the crossfire turns on/off randomly) and then the taranis screen goes blank.
The taranis is still on when the screen goes blank. I've replaced the internal 3v battery and the issue still continues.
I've also made sure my connections are connected properly.
What is the best way to troubleshoot this?
Where can I buy spare parts such as a backboard or front board for the taranis, cannot find a vendor in the US.

Sounds like a hardware issue, you might want to RMA it to FrSky.

The best way to get advice for troubleshooting and replacement parts is directly from FrSky.


What is the advantage of SBUS over IBUS? Flight controllers have to implement an inverter to process the SBUS signal. Why is SBUS not just uninverted?

SBUS and IBUS are both digital protocols and for a digital protocol, you define two voltage values to represent an active state and one inactive state. This is done for every digital protocol.

You can specify that 0V is inactive and 1V is active (this is called active high). But you can also define that 0V is active and 1V is inactive (active low).

Many bus protocols are active low and SBUS is also such a protocol. The reason for this choice is that active low signals can handle noise better. This is probably the reason why Futaba designed SBUS this way.

The ARM chips used on the flight controllers have the hardware to decode serial signals (both SUBS and IBUS are serial protocols). This decoder also is built for active high or active low signals. If you want to decode an active low signal (SUBS) with a decoder that is built for active high you have to add an inverter between so that both "talk the same language". This is the case for the F4 chips since ARM did not include an inverter on the chip. For F3/F7 this problem does not exist since ARM included the inverter in the chip and the software can enable/disable the inverter.

You get similar performance from SBUS and IBUS since both are a serial protocol with comparable frame times.


What are controllers of Parrot AR drone 2? I have a few questions about Parrot AR drone 2. Here is the official website
Q1:What are the controllers for the AR drone 2? Is there a position controller (GPS), velocity controller (accelerometer), attitude controller, heading controller (compass), and/or altitude controller (barometer) in the microchip of AR drone 2?
Q2:If there are some of the controllers that I mentioned above, and these controllers may need the current states for feedback control purpose, do the current states form the estimation based on IMU data?
To be more specific, if there is a PID position controller, we need the desired position and current position information for feedback controlling. Is the current position from the estimation algorithm (like EKF) based on IMU sensor data?
Q3:Is there any way that I can control the motor speed for AR drone 2 directly and use my own controllers?
any suggestions and comments would be helpful! Thanks in advance!

After reading relevant materials, i think I have find the answers for this question.
Q1:Since AR drone2 is a proprietary system,  this company didn't publish any documentation about the internal structure.
Q2:According to my understanding and guess, the controllers will use the estimated states of AR drone2 and the estimated states may from EKF(I am not 100% sure)
Q3:Since AR drone2 is a proprietary system, it seems there is no way you can control the motors directly by using your own controllers. But there is an alternative way:
using Simulink and Optitrack to control AR Drone
using Simulink and Vicon to control AR Drone


Ftd driver for 3dr telemetry radio I have been attempting to connect my pixhawk 4 to qgroundcontrol using an old 3DR telemetry radio set. The connection works fine over usb, but qgroundcontrol shows disconnected when I plug in both telemtry radios. I know the radios are connected properly, and both show a solid green light and flashing red when connected the telem 1 port. When connecting to telem 2 it shows solid green but no red. According to the docs, solid green means the radios are connected, and blinking red means data is being transmitted. Therefore, I thought the issue resided in the usb connection. I'm pretty sure I was correct, as when opening the devices menu (I am using Windows 10), there was a yellow triangle next to the device icon, and it could not find a driver. The device was titled F231x usb uart, so I tried to find drivers online, but am struggling to install them. I read they were the same as arduino usb drivers, so I downloaded that. However, there are two inf files, 'ftdibus' and 'ftdiport'. Which do I choose, and how do I install it properly so that the radios will work?

FTDI drivers can be downloaded from the FTDI Website.
You should then be able to install the driver using "Update Driver -> Browse my computer for driver software" and selecting the folder containing the extracted files.


Differences between brushed and brushless motors - advantanges and disadvantages of each When buying a drone I have 2 options to consider: brushed and brushless motors. Are they much different from each other? Does one have advantages over the other?

They are very different.
Brushed motors
Brushed motors are good for toy grade drones for a couple of reasons: they are cheaper and don’t require ESCs, which would add extra cost and complexity.
Brushless motors
However, in almost every way brushless motors are better: they produce much more power, are more efficient, produce more torque and, my favourite part, they don’t have physical brushes and so, unlike cheaper brushes motors which are only designed to run for a number of hours, brushless motors can take a lot of abuse and can last for years. Additionally, they are very water-resistant.
There are downsides: to a brushless motor - they require ESCs and, due to the torque, can do more damage in a crash.
For info on how each works, see my answer here: https://drones.stackexchange.com/a/87/50


How do I test if my DX5e antenna is still good? I have a second hand DX5e tx that I haven't really used a ton yet, just on a little Blade Inductrix, within my house. However, the upper plastic end is broken off and the actual antenna seems pretty beaten up. Is there a way to check the reliability of the antenna before I risk it on a more expensive/larger drone? I hear that replacing this particular antenna is a pain and I'd rather just 3d print the upper cap out of PLA if I can. I have a cheap multimeter, if that helps at all. Thanks!

That's probably OK, but you should do a range test.
All transmitters have a mode that transmits a much lower power than normal, and if that is sufficient to control the model at 30 paces, full power will be enough to fly further than you can see.
From page 9 of the DX5e manual:

Face the model with the transmitter in your normal flying position. Pull and hold the trainer switch while toggling the HI/LO Rate Switch four times. The LEDs will flash and the alarm will sound indicating the system is in range check mode. note: The trainer switch must be held the entire time during the range check process; releasing the trainer switch will exit the range check mode.

You should  have    total   control of  the model   with    the trainer switch  pulled  at  30  paces   (90 feet/28 meters).

Now an Inductrix probably won't have the range of a normal receiver so don't worry if it's a little short, but you should range test every receiver you buy every time you install it in a different model. Ideally from a range of angles to make sure the antenna can't be hidden behind a large metal or carbon-fibre part.
Before doing a range test, it's important to either remove the props or ensure that the model will shut down if it loses signal, to prevent it flying away.


Drone tipping over when attempting to fly (possible accelerometer problem?) This is my first time building a drone, so sorry if this is a stupid question or I use the wrong words. When I attempt to fly my drone, it immediately tips over (link to video here: https://youtu.be/og8w9KjhzBI). I know its not a problem with the motors themselves because when i turn the motors on using Betaflight Configurator, they all spin at the same speeds. I made sure my accelerometer was properly calibrated through Betaflight, and have searched the web for hours attempting to find an answer to no avail. Any help would be much appreciated.

Some simple things to look for before we go deeper:

Did you check that all four props are mounted correctly? (CW on top left + bottom right, CCW on top right + bottom left)
With your props off(!), your drone connected to the Betaflight Configurator, and your control inputs neutral, are all three control axes all centered (at $1500$) in the Receiver pane?


Why are larger propellers generally more efficient than smaller ones? In almost every case, long-range drones use larger propellers than other drones that don't need to travel very far or don't need to fly for very long. I have heard that a major reason for this is because a drone with larger props can be much more efficient than a drone with smaller props. If this is the case, what is the reason that larger props are generally more efficient to use?

Thrust is proportional to the change in momentum of the air passing through the prop - i.e. how much the prop speeds it up.

The power required to do this is proportional to the kinetic energy of the air, which is proportional to speed squared. That 'squared' is the problem.

A smaller prop acts on less air, so it has to speed it up more to generate the same thrust. Half as much air moving twice as fast generates the same thrust, but takes twice as much power.

This explains why helicopters can hover relatively economically, propeller planes only if they're powerful aerobatic models, jets only if they're extremely powerful and carrying a minimum of weight, and no one uses rockets unless they have to.


Do propellers at different angles work the same? And do intersecting flows of air work the same? Say a propeller pushing thrust downwards generates 70 lbs of force. If you tilted the angle of the system to 45 degrees would it generate the same thrust?
If you had each rotor angled inwards of a system like this, assuming that the system is on the ground, would the airflow be the same or cancel each other out a bit? (the arrows is airflow direction)

Thanks

The amount of force generated remains the same, however it is applied in a different direction; you therefore get an effective reduction in force for a given axis. To use the two extremes:

If the airflow is straight down, all of the force is used for lift
If the airflow is completely horizontal, none of the force is used for lift

Aligning the motor at angles between these splits the force between horizontal and vertical. The 'best' angle for your design of course depends on the type of aircraft; for a rotary wing aircraft you need to generate a lot of lift from the rotors but for a fixed wing you want thrust, while the aerofoils create the lift.

In your image, the airflow would remain the same but the two motors would be pulling against each other - this decreases efficiency, however the advantage can be improved manoeuvrability in flight as rather than just relying on gravity to roll and pitch the aircraft you can use the angled thrust to 'push' the aircraft around.


What would a basic fixed-wing electronic setup look like? I'm building an FT Tiny Trainer. Currently it's just a chuck glider, but now that I have tested it, I want to add electronics. At first, the plane would be a controlled glider, but then I'd probably add a motor. So far, I've figured out what transmitter/receiver I want.
However, I am clueless about motor/servos/battery. FliteTest have "power packs" on their store, but I don't live in America and the shipping would be horrendous. I also don't want to just buy the parts in these packs from other places - my local hobby shops wouldn't have the specific ones I need, and I'd rather avoid buying online altogether. Instead, I want to find what parts I need (servos, motor, etc) and then go down to my local hobby shop and buy them.
My question has two parts, but they link together into one answer.

The first half of my question is: What electronic components do I need to make a plane fly?
The second half is: How are they linked together? What plugs into what?

A diagram would be lovely.
Also, I presume I'd need to learn to solder to do this, please correct me if I'm wrong.
EDIT:
Two months after I asked this, I went to my hobby shop and bought all of the components. I managed to avoid soldering (for now) by getting the guys at the shop to attach the connectors. Thank you to everyone who answered this question - you are the people who convinced me to make the leap and buy this stuff. The plane flies great and has enough power to hover on the prop.

The main things you need are a motor, battery, electronic speed controller (ESC) and servos.
The ESC sits between the battery and motor, and it also has a thinner cable that goes to the receiver. The wires from ESCs are often labelled, but if not, there will be two big wires on one end that are the input from the battery (red for positive, black for negative), and three big wires on the other end that supply the motor. The motor wires can be any colour and it doesn't really matter how you connect them. If the motor runs backwards, switch any two motor wires. The cable to the receiver will be three wires joined together in a ribbon, similar to the cable on servos (and with the same plug)
The ESC also provides 5v to power the receiver and servos. All the positive and negative pins in the receiver are connected. The part of the ESC that does this is known as a BEC or 'battery eliminator circuit' because 'back in the day' you needed a separate 5v battery for the radio.
Servo cables have three wires, positive, negative and signal. Positive is in the middle so that plugging it in backwards doesn't cause short circuit. Servo plugs are pretty standard, although some have a little tab on one side to prevent them being reversed - but this requires that the receiver has a slot for the tab (and many don't, and the tabs get cut off).
Servo plugs are small and need a special crimp tool to make, so they are nearly always done for you - and they all use the same pins, so different brands are compatible.
You might also want plugs to connect the motor and ESC, either because the design routes the motor wires through the firewall, or so you can move components between models. 3.5mm bullet connectors are pretty standard here, with the male plugs on the motor (so you can safely power up an ESC without a motor).
If you shop carefully, you can probably find an ESC and motor with all the relevant plugs already attached but many only have the servo plug, either to reduce cost or to provide you with more choice. If it comes without plugs, or you need to change a plug, you will need to solder.
The Tiny Trainer is just about able to use the little red JST battery plugs that use the same pins as servo plugs, but it's right at the limit and old plugs tend to overheat, melt and short circuit. XT30 plugs would be a safer choice. XT60 plugs are much bigger than you need but a common standard for chargers and larger models. There are lots of other types of plugs these are the most common now.
Beware that the connectors such as the motor plugs or XT60 battery plugs require a larger soldering iron than the 20w irons that are usually sold for hobby electronics. Also, if you're soldering, you'll need some heat shrink tube to cover the joint. 5mm diameter fits XT60s and 3.5mm motor plugs. Remember to put the tube on the wire before you solder the joint, and slide it away from the heat or it'll shrink before you are ready.
If you are lucky enough to have a local hobby shop, they are usually very helpful in finding parts that will work together. Take a list of the recommended gear and they'll find equivalents, and may even do the soldering for a small fee.
When you're in the hobby shop, buy some spare props, some piano wire for the pushrods, control horns and swing keepers to make the attaching the push rods easier, and some Velcro strap to hold the battery in place. And a battery charger (with power supply). And some screws to hold the motor to the firewall.


Can I power the VTX and FC from the same vbat pad on the ESC? I have the Hobbywing x-rotor 60A 4 in 1 ESC and the TBS Unify pro hv race.

Since neither my FC or ESC has a 10V regulator, I need to power both from the battery voltage. There is however only one battery pad on the ESC; will this be okay?

Yes, you can.  Generally, you want to have your VTX and Camera on the same ground (in order to avoid video noise), so this approach will definitely work.  There is continuity on pretty much every VBAT pad, as well as ground, so having a single pad or multiple pads don't really matter much.
If you're seeing EMI noise effects, I would still highly recommend running a large capacitor directly on the pads of the ESC.


Suitable ready-to-fly micro copter for a beginner I read several docs on the ardupilot website, in particular about building a copter. It was suggested that total newbies (like me) should buy a small inexpensive copter first and learn how to fly/use it. That's what I want to do. However the copters listed there are no longer available. Can you, please, advise which Ardupilot-based micro drone is available in USA and/or Germany? Before I buy/build a bigger copter I would like to learn...

how to fly,
how to update firmware,
how to use QGroundControl Software,
how to use DroneKit, etc...

I'm on Linux... (I'm not interested in FPV/racing, but I do want some basic video camera.)

Looking through that page, the F450 FlameWheel style kits are still available, and a reasonable choice for a DIY Ardupilot drone. These are about twice the size of a typical FPV quad and will give you more room for sensors and/or a gimbaled camera. Alternately, if you think everything you want will fit on a 250mm FPV frame (they can carry GPS and a fixed GoPro), there are lots of cheap components due to the popularity of FPV.

I would agree with the advice to also buy a cheap toy quad to learn the reflexes you need to fly, and for when your friends want to try flying. They're so cheap now that it's a tiny fraction of the cost of a bigger multi-copter. You won't find any running Ardupilot though, as the flight controllers are too expensive.

The Hubsan X4 H107 is still available - watch out for the different versions, there's a basic version, one with a recording-only camera (that's a bit pointless) and an expensive one with a low quality FPV camera.

The Blade nano has been replaced by the Inductrix - they're quite expensive but their customer service is good.

Eachine's range of toy quads are pretty good and very cheap. The E010 or E011 both work well and can often be found for $10-15. The E012 is smaller but only flies for a minute or two. The protected props make them strong enough for beginners to learn to fly indoors, but they can be flown outdoors in light winds. I would suggest ordering a few spare batteries - one is never enough.

Some of Eachine's range (like the E016) have altitude-hold, which seems like a great idea, as holding a constant altitude is one of the first challenges to learning to fly (especially indoors) - however I've found these need extra trimming to hover accurately and really aren't suitable for a beginner unless you've got an experienced helper to trim it each flight.