The removable driveshaft is a telescoping spring-loaded bar with a socket wrench at each end. At one end of a tube (nominal 3/4" stainless waterpipe) a 32mm deep socket wrench is welded, at the other end another 32mm deep socket wrench can slide axially on a bonze bushing but is kept from rotating by a 1/4" pin with rounded ends that catches the corners of the socket (inside, where the corners of a nut would be). a spring (not visible--inside the yellow moped suspension boot) pushes the socket outwards, the socket is kept from falling off by the pin mentioned above (the pin is pressed in after the socket is assembled). the other end of the spring hits a bike seatpost clamp collar which can be repositioned to adjust spring force to arm strength of rider. The sockets engage knobs with pins on the pushrim and the wheel that similarly engage the corners of the sockets (see next photo). The combined "slop" of all three pins in the sockets results in a total 20mm of play at the 17" diameter pushrim after 1 year of use (20 mm measured from pushing forward to pushing backward). Ralf Hotchkiss of Whirlwind Wheelchair has described another method of creating a FOLDING rather than REMOVABLE drive axle, using ball bearings at each of the three pivots to create a system with essentially zero free play, this would be advantageous in situations where the extra non-removable weight was tolerable. If anyone makes one, please email me a pic, mccambridge@hotmail.com