Are you sure it is a positioning servo?
For a speed controlled motor the hall sensor is not needed. By monitoring the Back EMF, the drive can decide when the poles pass the commutation points. The problem is that this BEMF is small at low speed, and absent at standstill. So startup of these motors is not trivial. I guess it can keep account of the commutation points even at standstill after having been up to speed by using the encoder. |