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.
The Smell of Molten Projects in the Morning 
Comments
6 responses to “Stepper Dynamometer: First Light”
| 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. ;-)
Aye! First see if it works, then make it pretty…
“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.
I’ll suggest that to our Larval Engineer, in the (highly unlikely) event she forms a band…
[…] larger (480-ish mN·m) stepper in 1/8 step mode while recording the short-circuit current from the smaller (anonymous) stepper. Slowly cranking the step frequency upward produced this trace when the stepper […]
[…] All of that depends on the motor current, of course, and that depends on the amount of heat you’re willing to generate in the motors. I really must build a better dynamometer. […]