After getting the first version of the mammal geometry leg working and jumping I worked on a second revision. At a minimum, I wanted to fix all the problems that required hand machining, however I also decided it was trivial enough to add a reduction ratio to the tibia through the belt drive, that I should just go ahead and do it. My inverse kinematics calculations showed that this would make a big difference in average power consumption.
The first revision of the leg in CAD looked like:
The second revision looks like:
The major differences are:
- The lower leg has a 44 tooth pulley, which combined with the upper 24 tooth pulley results in a 1.83x reduction ratio.
- The upper leg is taller to accommodate the belt path to the new lower pulley. This includes some weight reduction “truss” cutouts.
- The top of the upper leg is rounded off, expanded, and has observation cutouts. This facilitates installing the belt and giving it sufficient room to actually mate with the upper pulley.
- I actually included access holes so that you could fit a driver in to attach the upper leg to the BE8108 with bolts, while still leaving most of a mating surface for the pulley bearing.
- The lower leg clamp attaches with bolts instead of just pins.
- A lot of other tolerances were tweaked to make things fit better. These are all mostly specific to the Shapeways production machines.
Of course, I managed to mess up about a dozen things on the second revision, and had to spin a third. Here’s a video showing the process of replacing the leg with new parts in fast forward so that you can enjoy the two hour long procedure in mere minutes!