Leg zeroing fixture

As part of provisioning a quad A1, or anytime the mechanical configuration has been changed, I need to go and record where the zero position of all the joints is.  The “0” position for the software now is with the shoulders perfectly horizontal, and the upper and lower leg sticking straight down.

Up until now, every time I’ve done this it has just been by eyeballing and with lots of foam and bubble wrap to shim things into place long enough to record the level.  Sometimes I had to go back and try a few times, as even determining when something is straight is not, well, straightforward.

So, I made two new fixtures to help with this process:

One that rests on a flat surface and supports the shoulder to be exactly level, and forces the upper leg to be exactly at a 90 degree angle.  This assumes the robot is flipped over on the same flat surface.  The second snaps between the upper and lower leg, forcing them to be exactly straight.

With these two fixtures, I was able to get repeatability of my calibrations down to less than half a degree, which should be good enough for now.