There's a little bit of feedback: Each belt has a rotary encoder to track position, and the motors apply positive torque rather than positive position. This is in contrast to how stepper motors work on a 3d printer, for example.
Heh, nice, from the guy who also made a wacky hair cutting robot.
I think his approach can be improved if indeed he replaced the guiding rails by a system with corner-points only. That would make it more user-friendly.
Anyway, I want a machine like this that can paint.