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:

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:

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.

6 thoughts on “Stepper Dynamometer: First Light”

1. Brian says:

| 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. ;-)

1. Ed says:

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

2. david says:

“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.

1. Ed says:

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

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