Jons correct with everything he says but I'll add to it.!!. . Mach Can't use Encoder feed back and correct for any error even with Servos. Also often Servos without Control participation don't correct for error they just have Encoder following Error value set in the drive software which they then give an output Fault signal if Encoder shows is outside this value. This is pretty much what the Am882 does.! Which by the way are great drives and worth paying the extra for even if your not using Stall detect.

If you want drive/Motors that actually correct for any error then look at the Leadshine Hybrid Servo system. These correct any position error internally to the drive so the Control is not involved. Nice bit of kit just not cheap but a lot less than Servos. (Some where on the Forum I posted a Link to a Video I made just do a search.)