steppers and DC motors as cheapo encoders ?
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steppers and DC motors as cheapo encoders ? pogo 04-04-2008
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Posted by pogo on April 4, 2008, 6:26 pm
I'm starting to accumulate quite a few DC motors and steppers from old printers
& scanners, etc.

Does anyone have examples of using them as cheapo encoders ? For example,
sometimes all I need to know is that a wheel is turning
& don't really care about how far or RPM, etc.

Thanks !
JCDeen


Posted by cadcoke4 on April 5, 2008, 12:19 am
I know that the kinds of uses you are talking about are done.
Specifically, there are some DC motor controllers that stop providing
power for a brief moment so that it can measure the "back EMF".
Essentially using the fact that the DC motor will continue to spin
from its own inertia, and become a generator. I know this is done in
some robotic wheel driver circuits.

Any DC motor can be used like a speedometer. Just measure the voltage
the motor generates while it is being spun in generator mode. (you may
need to filter the voltage to some extent)

I am sure any stepper (or AC) motor can be used in a comparable way,
but instead of a DC voltage, you get an AC waveform. You can use a
frequency counter to measure the speed. It may also be possible to
rectify the AC voltage and then meaure the resulting DC voltage.

Sorry, but I have not done any of the above, only read about them. I
don't have any sources for more info. A search for "robot" and "back
EMF" may be a good start.

Joe Dunfee

Posted by pogo on April 5, 2008, 1:26 am
>I know that the kinds of uses you are talking about are done.
> Specifically, there are some DC motor controllers that stop providing
> power for a brief moment so that it can measure the "back EMF".
> Essentially using the fact that the DC motor will continue to spin
> from its own inertia, and become a generator. I know this is done in
> some robotic wheel driver circuits.

Yeah my favorite motor controller to date - the Sabertooth 2x10 - works this way
(if I remember correctly).

Thanks !
JCD

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