Originally Posted by
rvectors
Ok I did some more digging, and saw some informative posts by @mactec54. I must confess what little I do know, is more likely to be dangerous (and posts often contradict each other) but I don't think the feedback loop via the controller will be an advantage to me.
re the 7I83, the output is 13 bit (@2.5Khz), which may include a sign, + factoring in small errors, which will limit the potential resolution. I'm guessing having the PID loop closed via the DMM drive/motor, the processing will actually be quicker, & at the motors inherent resolution, vs PID loop via controller. (i'm aware my terminology is a bit pants but I'm still getting my head around it all)
As to Step/Dir, Torque, Speed modes, again, I get the feeling I probably wont see much difference. (at the moment, I haven't worked out if feedforward requires a particular mode)
Conclusion, Mesa 7I76E + LinuxCNC is tipping the scales at the moment. Its low enough cost to make it not painful if the decision was made to switch to another control setup.