M542 driver - motor vibration at low speeds

[Jonathan]

Slides 22 onwards in this document give a good explanation of how resonance affects machine frames. If you read that then what is happening here should be obvious. The other lecture notes in that series are well worth reading too.

The question is - should the motor be smooth throughout the range or will there be inherent "bad" spots due to the Chinese drives and motors?

You can't blame this on the Chinese (or in John S's case linux), since the Chinese also sell drivers with resonance damping functions (e.g. AM882). That doesn't mean you need to change drivers though. I'd try testing cutting something at the speeds where it sounds bad and see if it affects the finish noticeably. Also, thoroughly test the motor tuning, e.g. by running random G-code. If it doesn't stall, goes fast enough and gets an acceptable finish then you can safely ignore the 'problem'.

At what step frequency do you start getting the real time error? Unless you're very unlucky with the computer it should be fine around 25kHz - quite likely more.