Would anyone consider there to be a speed or accuracy advantage to using some form of encoded feedback for the linear movements of CNC machines like there often is for the rotational aspects? I know pulsed laser rangefinders aren't accurate enough at short distances, but perhaps ultrasonic transducers could be used. Alternatively some kind of laser/linear CCD triangulation setup. I've seen some people use the resistive tracks on digital calipers/rulers, though that seemed to be as a safeguard in development rather than an intrinsic part of their machine. Given that brushless motors operate rather like AC motors and not entirely unlike stepper motors, but deliver far more power at lower prices, are we all going about this the wrong way by trying to assume the driver's behaviour rather than actually measuring the driven's? Can we massively increase the precision of off-the-shelf parts by implementing feedback systems? Like the micromachining thread, I'm not necessarily coming down on either side, just looking for discussion and opinions.