10:1 Herringbone Cycloid Gearbox

thingiverse

better / improved version at http://www.thingiverse.com/thing:1597419 I am the proud owner of two irreversibly crashed RC helicopters. The main drive gears were stripped (very cheap RC copters) but appeared to have a 10:1 ratio by measuring diameters. All the motors were fine. I started to wonder what one could do with them, maybe build a new RC vehicle given a better control board and frame. Such questions led to this, a mini 10:1 cycloid gearbox using printed gears large enough to feasibly survive some punishment. A herringbone cycloid in fact, something I'm not sure has ever been done before. It has four parts. 1) The flat platform with stub, which bolts to the motor. 2) The cam, which attaches to the motor shaft and gets stuck solidly to the inside of a 625 bearing. It's designed to jam there by getting wider towards the bottom. 3) The output gear, which holds the 625 bearing. The motor makes it wobble in a circular "rolling" motion around the inside of the output gear, but the slider to the side prevents it from turning, forcing the output gear to turn instead. A 3mm bolt with washer prevents it from popping off. 4) The output wheel, which fits onto the fixed gear. It contains a 7x3x3 bearing (7mm wide, 3mm thick, 3mm ID: Each copter had a pair) to center it on the motor shaft. This centering is what makes it actually move instead of just wobbling. Masking tape is needed to fit snugly on the motor's 2mm bore. The output gear is intentionally difficult to attach to the fixed gear -- it's supposed to stay on by itself while driving a pair of helicopter blades. I pry the notch apart with diagonal cutters to get the gear loose enough to install. Greasing it up nicely with white lithum before you snap it on couldn't hurt. This gearbox is only meant to turn counter-clockwise. The other can jam! To get a clockwise version of this gearbox, just mirror both gears on X or Y. I've printed this and it works. It sounds like a mini chainsaw, I had to epoxy the shaft to the cam, and if your tolerances are different than mine the gear might seize up immovably or pop right off without warning, but it works. Very much a work-in-progress nonetheless. Nothing flies at the moment. Further problems: The rotational speed of the output is not constant. Since I plan for the blades not to be fixed this might be okay. No, I don't know what kind of motor this fits. There's no markings on the motor at all. The screws are 17mm apart if that helps. It's from a "Sanhuan 8827 RC Helicopter", aka Pioneer X8, aka piece of trash that can't do anything but spin wildly and plummet.