Cheap Diy easy Galvos based on the Tangent law of Magnetisim?

[MarioMaster]

Wow old thread - closed loop means the circuit has a feedback system so it knows the position of the mirrors.

Stepper motors are an example of open loop while servo motors are closed loop. Stepper motors do not know where they are in terms of a rotation unless you add an external encoder or limit switches for it to calibrate to.