Servo loop control (NOT stepper) Tachometer needed?

"If you mean me, then yes, I have probably been on the LinuxCNC mailing list that long, but the rest of the things sound more like Charles Steinkuehler who works on LinuxCNC / Machinekit but was also involved in the Video Toaster. "

I used to work with Charles - I showed him how to use an early PCB CAD system - he went on to program the insides of FPGAs - really smart guy.

I looked you up - Could be there is another guy with a similar name? Really liked your video clip of fixing the pewter mugs.

BTW - one of my favorite Youtube channels is
www.youtube.com/user/ROBRENZ/videos

If you want to close the velocity loop in LinuxCNC, then you could use those tachometer OUTPUTS from the drive, derived from the resolvers. But, then you'd need a high-resolution ADC to convert the analog output to digital. LinuxCNC normally computes the velocity by subtracting the last position from the current position reading, but this has both time and positional quantization, and is therefore quite noisy. But, then, the drive probably does exactly the same thing. Many of the encoder systems on LinuxCNC have a smoothing algorithm on the encoder input using timestamps of the last position change that produces a smoother velocity.

As for the linear scales, belts are not likely to be a problem, but backlash in the leadscrews and sticktion in the slides may be, These can make the servo tuning a bit difficult.

Jon