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Archive for September 12th, 2011

Stepper Dynamometer: Mechanical Resonance

Here’s a howling 1200 Hz mechanical resonance excited by a full-step drive at 290 rpm, with the resonance running at 5 cycles for every 4 full steps.:

1 Step Res 240 Hz

1 Step Res 240 Hz

[Update: top trace is voltage from big stepper-as-generator, bottom is small stepper winding current = 1 A/div.]

Switching to 1/2 microstepping at the same rotational speed pretty well tamps it down:

Half Step Res 240 Hz

Half Step Res 240 Hz

However, here’s the same resonance excited by 1/2 microstepping at half the rotational speed, oscillating at 9 irregular cycles for every 8 half-steps:

Half res 120 Hz

Half res 120 Hz

The resonance was strong enough to back the setscrew completely out of the generator end of the shaft, leaving me wondering why the output was dead when the motor was obviously running. Yes, several times…

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