@poppyrate I’ve done some testing and it should be possible to run the AX-12A at 7.4V (or a 2S lipo). I’ve hooked one up on an DXL interface with a 2S lipo and works fine - I can scan the bus, I can send commands and the servo moves in position. I can’t talk yet about the torque you can get at this voltage - but I will try to test that in the next days.
If that will work all well it means you don’t need any voltage changers - just a couple of custom cables that change from the XL connector to the AX one. Or if you have a board that is custom and has both XL and AX connectors, and you position it in the chest (with a raspberry A+? maybe) it’s even better.