After showing the robots at PyCon.us, I had some great conversations about all the possible ways I could improve them. One particularly nice idea is to connect some extra wires to the servo pots, and by measuring the voltage on them get some idea about their actual positions and (indirectly) the force being applied to them. To do it with all 12 servos, I would need 12 analog input pins, though. I can think about several possibilities:

• Use two arduino pro minis, each controlling two legs, with 6 digital and 6 analog pins.
• Use a 16-channel analog multiplexer chip. That requires 1 analog and 4 digital pins.
• Use a 16-channel ADC chip, possibly through I²C.
• Use an additional board with lots of analog pins, like Teensy 3.1.
• Only do force-sensing on the 4 most important servos (the ones that carry the robot).

I think I will start with the last option, mostly because that doesn't require changing much and it will let me see how well this actually works. Then I can try one of the other options if needed.