Today I finally adapted all the code for IK and walking, and realized that practically everything I did yesterday is wrong.
First, the cheap WiFi dongle that I soldered to the mini-hub is really bad. It gets hot and eats enough current to make the Pi Zero restart when the servos move. I had to switch to console over serial.
Second, before you laboriously trim all the servos to the right positions, make sure the new servo library that you wrote takes the same range of angles as the old one. In this case, the old one took -90° to 90°, and the new one takes 0° to 180°. The result is that all the servos are wrong by 90° and I have to redo the trimming.
Of course the board has a tendency to restart when all the servos are switched on simultaneously anyways, so I had to add some code that switches them one by one, with some delays. Nothing new here, old #Tote had the same thing, and it's a good idea anyways.
I still have to figure out which pins are for servos on which legs -- I didn't keep track of that when connecting them, and I figured it would be easier to just go one by one in software and see which leg moves.
Hopefully I can get the first walk by the end of the month.