"One Perfect Part at a Time"

It’s All Resonant?

I am having some thoughts that the HB2 stepper problem may be part of the stepper resonance phenomena. The two Y axis motors on separate channels but running in tandem may be creating a mechanical resonance between them. Kind of like tuning both engines to the same RPM in a twin piston engine aircraft. There is a “beat note” low frequency resonance between the engines as they approach the same speed. (I am a pilot.) The same effect occures in a twin engine boat.

The same holds true when tuning a CW frequency in amateur radio. Another frequency (BFO –Beat Frequency Oscillator) is offset about 600 Hz so the signal can be heard. In older radios it was possible to tune the BFO to the exact (beat) frequency and when very close you would hear “wow, wow, wow” beat frequency of a few Hertz beat. (I am also a ham radio operator)

That beat can get fairly strong and become resonant. I think this may be contributing to the stepper resonance sensitivity. The issue is the two Y axis steppers HAVE to run at exactly the frequency so they could be adding to each other’s mechanical feedback. Then suddenly one stepper falls into its resonance “hole” and quits, just stalls. All my crash stalls have been on the tandem Y axis. It doesn’t happen very often so it is hard to prove.

This is all wild and just slightly educated speculation. I can’t find any real data on the Internet about tandem drive resonance but will say it has to be there. Large machines may be able to absorb such resonant frequencies or damp them. My tandem Y stepper steps have ALWAYS sounded louder than the other single drive axis and I don’t mean just because of the sound of two motors running.

I have read and studied both mechanical and electrical solutions for damping resonance. Most if not all of the popular upper end stepper controllers have electrical damping built in. There is also a mechanical slipping flywheel type device that can be added to the motor shafts. The mechanical solution is bulky and somewhat intrusive and could be subject to accidental physical contact when running.

Worse case for me will be to replace the controller for one with electrical damping built in.

I am wondering if anyone else has seen or experienced this problem with tandem steppers. The clues are “louder” steps and very occasional stalls, especially around 500 RPM maybe + 100 RPM.

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