Measure RPM with video camera

[ProgramThyself]

Others have described ways to measure motor RPM without a tachometer:
Acoustically: https://endless-sphere.com/forums/viewtopic.php?t=7477
Bike speedometer: https://www.endless-sphere.com/forums/viewtopic.php?f=2&t=65311

It is also possible to put white tape around half of the wheel circumference and analyze a video recording of the spinning wheel. The black and white tire acts as an optical encoder.

Analysis code (using Octave): View attachment RPM_analysis.zip

Video and more info for the above graph is here:
https://ffuser.blogspot.com/2019/07/rpm-measurement.html
and here:
https://drive.google.com/open?id=1HDR7m3I3oTboHEsaelmvrsaIOG02XJ52

 

[kcuf]

many phone apps

strobe measurement

 

[flat tire]

It does take a smart person to overcomplicate something to this degree.

 

[neptronix]

Sounds like it'd be difficult to measure a couple thousand RPM this way. The camera speed is a limit.

$10 ebay laser tachometer will do the job when the camera won't.

 

[ProgramThyself]

@kcuf: How many phone apps provide source code? Do they give 4 digits of stable resolution and a nice graph?

@flat tire: It's a sign of ignorance to think simple things are complicated and complicated ones simple.

@neptronix: True, camera speed is a limit. You'll want at least 2 frames per rotation to be within the Nyquist limit. But 240 Hz cameras (which could measure 7200 rpm) are becoming a thing. I'd rather build an RPM meter from things I have lying around the house and a little homebrew computer code, than add another rarely-used gadget to my overflowing toolbox.

 

[flat tire]

Lots of IQ points going to waste here.

 

[neptronix]

@neptronix: True, camera speed is a limit. You'll want at least 2 frames per rotation to be within the Nyquist limit. But 240 Hz cameras (which could measure 7200 rpm) are becoming a thing. I'd rather build an RPM meter from things I have lying around the house and a little homebrew computer code, than add another rarely-used gadget to my overflowing toolbox.

That's a good point. I wasn't aware that 240 fps cameras were becoming so common. I imagine they are still a bit spendy. But yeah, the environmental impact of a lot of 1-2 use items is kind of ridiculous when we have this awesome thing called a desktop computer and/or mobile phone that can serve so many purposes.