I bought a bunch of AX-12A and XL-320 servos a while back and decided to design a custom controller board for them with an onboard IMU and also bluetooth and wifi capabilities. The first revision of the board can be found here: https://github.com/hansj66/automaton-xl320 (I am currently working on a new revision, since the BNO055 IMU has “end of life” status and has become incredibly hard to source)
So far, I have designed two robots with this board in mind. One is a hexapod with 18 AX-12A. This is still in development. The other is a balancing bot with 4 XL-320 servos. This is able to detect if it falls over and right itself.
The current firmware is running a web server. This allows the user to calibrate PID parameters via a browser. The display on the robot displays the url to the PID control web page as a QR code. This allows a user to just scan the QR code with a phone in order to open the PID tuning control page.
You can see a video of it in action here: