Author Topic: Encoder mounting on this sort of short motor backshaft?  (Read 2261 times)

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Offline Infraviolet

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Encoder mounting on this sort of short motor backshaft?
« on: January 03, 2022, 05:25:02 pm »
https://m.media-amazon.com/images/I/51LQC3TLA4L._AC_SL1001_.jpg

That is a type of motor with a very short backshaft and a big gearbox. Encoding from the backshaft would let you get a lot more precision than putting an encoder on the main output shaft. And there is a bit of backshaft exposed, but it is very short, barely comes a mm above the surface of the white plastic. Any suggestions on how I might fit either a magnetic encoder disc to that stubby backshaft, or otherwise find a way to use some other form of QUADRATURE* encoding from it?

Thanks

*I know one can count voltage spikes on the casing from brush sparks, but these don't tell direction the way quadrature does, and in some applications I've had a very nasty time trying to keep counts when I can't be entirely confident in direction.
 

Online thm_w

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Re: Encoder mounting on this sort of short motor backshaft?
« Reply #1 on: January 04, 2022, 11:39:47 pm »
The problem with putting the encoder on the rear motor shaft is now you are not taking into account backlash of the gears.
It looks way too small for me. You probably want a servo or stepper motor, or give a better description of what you are trying to accomplish.

What precision is needed on that main gear shaft?
 

Online Benta

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Re: Encoder mounting on this sort of short motor backshaft?
« Reply #2 on: January 06, 2022, 06:00:47 pm »
That is a type of motor with a very short backshaft and a big gearbox. Encoding from the backshaft would let you get a lot more precision than putting an encoder on the main output shaft.

Logic flaw in your thinking: you'll get increased resolution, but not increased precision. It's two different things.

As @thm_w says, the gearbox backlash will be in the way.

 

Offline Infraviolet

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Re: Encoder mounting on this sort of short motor backshaft?
« Reply #3 on: January 12, 2022, 09:09:27 pm »
Thanks both, should have thought of that limitation. The back end encoder idea use was really to measure exact speed rather than position, and I had planned on placing a second encoder on the driven items to get position better, but thought I'd get a betetr speed estimate by measuring the quickly moving backshaft.
 


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