High Ratio Eccentric Gearbox 483:1

thingiverse

## How it Works The design of this gearbox is a modification of a planetery gearbox. The input sun gear is replaced by a hollow gear and the stepped planets are reduced to a single one with almost the same number of teeth as the ring gears. With this, the transmission ratio is proportional to the number of teeth of one of the gears (the number sia lmost the same for each) squared. - carrier-> ecc shaft -forumlas -low efficeincy -> not used for power transmission -look for my second design with 100 teeth, 1:10000 The cycloidal and harmonic drive gearboxes are kinematically equivalent improvements on this design. For the harmonic drive, a wave generator instead of the eccentric shaft works together with an elastic planet to get a higher contact ration and remove all backlash. Cycloidal gearboxes improve the efficiency by eliminating all sliding contacts with the help of bearings. This makes them backdrivable, which this gearbox is not. ## Some Design Choices If you want to design such a gearbox yourself, you have to watch out for some things. Because the difference in the number of teeth is so small, interference between the inner and outer gears is a problem. This can be fixed by using a profile shift or increasing the tooth difference a bit. This comes at the cost of increased eccentricity, therefore more vibrations. -stronger or weaker teeth? Because in my case, the mainlimit to the maximum output torque was slipping gears because of shaft deflection, it was important to keep the distance between the shaft bearings short and use a large diameter. Furthermore, the shaft has to be split, which required a stiff coupling between both halfes. I chose to insert a steel rod to transfer the bending moments. Another remedy i used, was to use a shallower pressure angle for the gear teeth. While nowadays almost all gears use a pressure angle of 20°, smaller pressure angles have some advantages, such as lower tangential forces which translate into smaller bending moments. Because i used 3D printing, it is easy to use an arbitrary pressure angle, as i am not limited by the available tooling. -counterweights ## Printing This gearbox is very small, with teeth of module 1. Therefore it is advisable to print it on a resin printer. Additionally, the tolerances must be kept low. To position the parts, they should be prtined upright on the buildplate, with the symmetry axis aligned with the z-axis. I did however not print them directly on the buildplate, but used supports. For some parts,such as the ring gear and the housing, this can cause problems with layer seperation from the suction cup effect. My remedy for this was to use a slow lift speed and heating of the printer to 40°C. ## Tests -failure mode -efficiency -max torque out