"Hip Joint" Worm Drive Gearbox

grabcad

Designed for university Mars rover competitions and intended to power a 42" leg (attached at the bolt circle at end of the long hollow shaft). The rover has two of these legs, which are intended to increase mobility over rough terrain by allowing the rover the ability to lift either end of itself if caught, right itself it tipped, and increase stability on steep grades or drops. Each leg is designed to lift a maximum of half the rover's total weight of 50kg in order to provide a factor of safety for more realistic situations. To achieve this, a gear motor with a nominal torque output of 1.5 N-m is attached to a worm gearing with a 50:1 reduction. The worm drive allows the large ratio needed to obtain the appropriate output torque to occur within the limited space that was allocated to this design, as well as protects the motor by ensuring that the large loads placed on the leg cannot back-drive the system. To avoid over-constraint, increase serviceability, and reduce material costs, the top-supported geometry of and downwards-only nature of the radial loading introduced by the worm drive are taken into consideration and the shaft is held in the gearbox housing by two half bearings, while full bearings are used only to support the shaft in the rover's frame. The position of the leg is measure using a potentiometer with a 3D-printed gear which meshes with the worm.