Things worth knowing

Staging and committing are separate on purpose

One packet can carry all four joints, and that is the only way to move them in step. Sending a packet per joint makes the movement visibly ragged.

robot.arm_left.to(1800)   # staged
robot.arm_right.to(1200)  # staged
robot.commit()            # one packet, both joints

ServoFaultError means a power cycle, not a bug hunt

When every joint reads position 0, the servo controller has stopped. Unplugging USB will not fix it: Eilik has an internal battery, so it has to be switched off at the power switch.

Only one process can hold the port

A second connection raises PortBusyError. Use the context manager so the port is always released.

Every command waits for its acknowledgement

The firmware parses one frame at a time. Sending a second command while it is still reading a 1032-byte display frame drops the device off the USB bus entirely. The library waits, so you do not have to — but it is why a display write is not instant.