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Stepper Dynamometer: First Light

As a quick test of the stepper dynamometer, I lashed the larger stepper to that Pololu driver hairball, connected one winding of the smaller stepper to the oscilloscope, and recorded open-circuit voltages as a function of rotational speed:

Output voltage vs rps - open circuit

Output voltage vs rps - open circuit

Now, if that isn’t suspiciously linear, I don’t know what is!

The slope is 0.583 v/(rev/s).

I used the scope’s RMS trace calculator, which smushes out the non-sinusoidal nature of the lower speed waveforms. As expected, there are several nasty mechanical resonances that appear in the output waveform while they’re tormenting my ears:

Stepper Resonance - 4.82 rps

Stepper Resonance - 4.82 rps

Top trace is the winding output voltage, bottom trace is the drive input current, plus a line of junk I forgot to turn off.

Useful conversions:

  • Drive waveform frequency / 50 = rev/s
  • Drive waveform frequency * 6/5 = rev/min

So it works. Now I must figure out how to connect load resistors with something more reliable than crappy alligator clips.

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  1. #1 by Brian on 2011-08-30 - 12:48

    | So it works. Now I must figure out how to connect load resistors with something more reliable than crappy alligator clips. |

    Decide to really have a test platform and install plug points on your apparatus and connectors to your test loads. Next, just plug-n-play, plug-n-play, all the day. ;-)

    • #2 by Ed on 2011-08-30 - 13:20

      Aye! First see if it works, then make it pretty…

  2. #3 by david on 2011-09-06 - 00:59

    “Suspiciously Linear” would be an excellent name for a band…

    Don’t mind me, I’ve just returned from a week in the desert and my brain isn’t quite back to its usual abnormal.

    • #4 by Ed on 2011-09-06 - 08:08

      I’ll suggest that to our Larval Engineer, in the (highly unlikely) event she forms a band…

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