question: How do machinery such as diggers transfer power to the tracks or wheels when the top half spins?
comment: Caterpillar trained mechanic here. Modern era excavators do have hydraulically powered tracks, along with all the other moving parts. The engine is only there to provide power to the hydraulic pumps. There is a component called a rotary manifold that allows the hydraulic fluid to flow through multiple separate galleries while being able to rotate indefinitely via its two separate halves. URL_0
passages: Parry People Movers have also been demonstrated on narrow gauge railways (Welshpool and Llanfair Light Railway, Ffestiniog Railway, Welsh Highland Railway).
  
  Section::::Technology.
   While friction can be reduced, it can never be eliminated, and sometimes hundreds of tons of force are required to push the machine and liner into the ground. A large “jacking frame” containing hydraulic rams is required to produce these forces. In most cases the entrance must be modified to support this frame and the forces it generates. 
   BULLET::::- Both flanks of the worm shaft will now be coated with spotting color. Then rotate the shaft by hand in both directions by at least 2 x 360°, so that the marking ink is transferred from the worm flanks to the flanks of the teeth of the wheel. This creates the load pattern in the contact region.
  
  BULLET::::- The wheel has to be displaced axially, up to an optimal position where the load pattern on front and back flank are approximately equally distant to the center of the wheel.
   In order to go over a vertical obstacle face, the front wheels are forced against the obstacle by the center and rear wheels. The rotation of the front wheel then lifts the front of the vehicle up and over the obstacle. The middle wheel is then pressed against the obstacle by the rear wheels and pulled against the obstacle by the front until it is lifted up and over. Finally, the rear wheel is pulled over the obstacle by the front two wheels. During each wheel's traversal of the obstacle, forward progress of the vehicle is slowed or completely halted. This is not an issue for the operational speeds at which these vehicles have been operated to date.
   HO slot cars work on a similar principle, but the current is carried by thin metal rails that project barely above the track surface and are set farther out from the slot. The car's electrical contacts, called "pickup shoes", are generally fixed directly to the chassis, and a round guide pin is often used instead of a swiveling flag.
   On the east end is the outrigger. It consists of two joined arms connected by gears and chains to the appropriate engines. At the end is the bucket, with a capacity of . Beneath it is a small pile of rocks.
  
  Section::::History.
   Machines with continuous blocks differ from single block machines by having a series of dies through which the wire is drawn in a continuous fashion. Due to the elongation and slips, the speed of the wire changes after each successive redraw. This increased speed is accommodated by having a different rotation speed for each block. One of these machines may contain 3 to 12 dies. The operation of threading the wire through all the dies and around the blocks is termed "stringing-up". The arrangements for lubrication include a pump which floods the dies, and in many cases also the bottom portions of the blocks run in lubricant.
   The player uses a joystick to slide a piece of the track into the vacant square and can use a button to accelerate the locomotive. However, it is always in motion and cannot be stopped. The player must avoid running into a dead-end barricade, a barrier at the playfield edge or the edge of the empty square; doing so costs one life. As the player moves the pieces of track around, the route the locomotive will take is highlighted in yellow up to any dead end.
   BULLET::::- Step 1. All even numbered columns (2,4,6,8) are added to all odd numbered columns (1,3,5,7) simultaneously. An interior sweep arm turns each even column to cause whatever number is on each wheel to count down to zero. As a wheel turns to zero, it transfers its value to a sector gear located between the odd/even columns. These values are transferred to the odd column causing them to count up. Any odd column value that passes from "9" to "0" activates a carry lever.
   Catch points may consist of a full turnout or a single switch blade. In some cases, on a track that is only traversed by uphill traffic, trailing point blades are held in a position to derail any vehicle travelling downhill. However, any traffic travelling in the correct (uphill) direction can pass over the turnout safely, pushing the switch blades into the appropriate position. Once the wheels have passed, the catch points are forced back into the derailing position by springs. In these cases, a lever may be provided to temporarily override the catch points and allow safe passage down the gradient in certain controlled circumstances.
   Early S&C allowed only a very slow speed on the subsidiary route (the "turnout"), so geometrical design was not too important. Many older s&c units had a loose joint at the heel so that the switch rail could turn to close to the stock rail or open from it. When the switch rail was closed, a reasonable alignment was secured; when it was open, no wheel could run on it so it did not matter.
   We seemed very near the ground and the small wheels made an unusual tapping noise as they almost sank into the rail joints. The Sentinel did well enough but we did wonder what would happen if the chain drive failed as, quivering with energy, she made the final steep hill into Methven.
   When using this method, the tower operator positions A point anchorages according to existing track geometry measurements taken beforehand. Once A point has been positioned, it is then assumed that both A and C are in correct position as if machine were sitting on corrected track. The machine then uses the lifting lining unit to move the rail and B point in line with A and C.
  
  Section::::Standard tamping machine arrangement.:Tamping units.
  
  The Tamping units of most Tamping machines will consist of:
   Trains feature a single lap bar in each row actuated by depressing a foot pedal near the front of each car, done by a station attendant. Unlike many roller coasters, though, there are no upstop wheels to prevent the trains from leaving the track; instead there is only a flange (upstop pad) which achieves the same result. This is common on "mine train" type roller coasters.
  
  Section::::Ride experience.
   Diesel-electric arrangements are used on many railway locomotives, ships, large mining trucks, and some bulldozers. In these cases, each driven wheel is equipped with its own electric motor, which can be fed varying electrical power to provide any required torque or power output for each wheel independently. This produces a much simpler solution for multiple driven wheels in very large vehicles, where drive shafts would be much larger or heavier than the electrical cable that can provide the same amount of power. It also improves the ability to allow different wheels to run at different speeds, which is useful for steered wheels in large construction vehicles.
   The push arm type stair climber have an arm fitted to the bottom of the truck that folds out and down, pushing on the step above and in so doing lifting the truck up in an arc to rest on that step. Repetitions of this movement allow the truck to move up the stairs. The mechanical opposite of this motion allows the unit move down stairs, many units also employ a forward only braking system to stop the stair climber rolling of the edge of a step. There a few notable variants of this type.
  
  Section::::See also.
  
  BULLET::::- Wheelbarrow
   The shuttle featured in this gallery was also used from the 1940s until 1983 to take salt from the mine face to the loading station at the main rail line. Powered by a DC extension cord, the car reduced labor and increased efficiency because miners no longer had to lay rails to get the salt from the blast site to the main rail lines.
  
  Section::::Galleries & Exhibits.:The Geology Gallery.
   When the Helix Dumper wagon enters the unloading area, a wheel at the top of the wagon makes contact with the spiral-shaped rigid guide that constitutes the unloading station. As the wheel travels along the path of the guide, the wagon chassis remains on the rails while the body of the wagon is rotated 148 degrees to dump its load. After the rotation, the direction of the guide changes and the wagon body is returned to its normal position. The Helix Dumper has a discharge rate of up to 25,000 tonnes per hour.
   The 18-step flat track BBC stepping switch was mounted on the transformer. It was driven by a battery supplied direct-current motor. Initially the stepping switch was controlled by a crank handle, later by a control wheel. It was possible to operate the stepping switch by hand, but only by someone actually at the switch inside the centre locomotive body.
   In a patent dispute involving rival crawler builder Best, testimony was brought in from people including Lombard, that Holt had inspected a Lombard log hauler shipped out to a western state by people who would later build the Phoenix log hauler in Eau Claire, Wisconsin, under license from Lombard. The Phoenix Centipeed typically had a fancier wood cab, steering wheel tipped forward at a 45 degree angle and vertical instead of horizontal cylinders.
  
  Section::::Patent history.:Linn.
   The very earliest motors (p/n x469b) were 4.5 volt, and consisted of a modified "Electric Train Motor" (p/n x469) and along with the 4 driven bushes for wheels added an axle hole enabling axles of different lengths to be used. While these were released in kits with Technic parts they were not sold as Technic motors.
   At the Fair, the drive wheels operated under the locomotive's own steam power ran continuously on the roller platform at 60 mph (97 km/h) all day long . Film footage shows that all the wheels on S1, besides the drive wheels, were also placed on rollers powered by electricity; every time S1 started its performance by moving the drive wheels, all the wheels were rolling, including the wheels on the tender's truck.
   K-3 cart
  
  The K-3 cart is a 2-wheel, strongly constructed wire cart, similar to artillery caissons, but equipped for carrying and reeling out wire; used together with Signal cart, type K-4, to form the wagon formerly called "Pintle wire wagon, model 1910." 
   Section::::Operation of a mule.
  
  BULLET::::- Watch video demonstration #1
  
  Mule spindles rest on a carriage that travels on a track a distance of , while drawing out and spinning the yarn. On the return trip, known as putting up, as the carriage moves back to its original position, the newly spun yarn is wound onto the spindle in the form of a cone-shaped cop. As the mule spindle travels on its carriage, the roving which it spins is fed to it through rollers geared to revolve at different speeds to draw out the yarn.
   "Krummen Zapfen") and transmitted over twin flat rods, several hundred metres long, to the shaft. Here, reciprocating motion was re-converted into rotary motion.
  