Subject:
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Re: non-linear motor speed problem
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 11 Mar 1997 14:22:35 GMT
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Original-From:
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Fred G. Martin <fredm@SAYNOTOSPAMmedia.mit.edu>
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Viewed:
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2338 times
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The test isn't fair under no-load conditions, because then the motor
just spins when you give it any signal.
Are you sure the performance is the same when you have a full
operating load? This would not make sense; I would guess that this
would mean that your normal load is well beneath the load capacity of
the motors.
-Fred
--
This message was composed using Articulate Systems' PowerSecretary,
a Macintosh-based speech-to-text dictation system.
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In your message you said:
> I am using servos converted to plain gearmotors as the
> motive power for my baby bot. Finally I worked out how to
> add shaft encoders to them. (Found a small opto switch to
> poke through the inside of the case on the first gear).
>
> The servos I am using turn out to have a _very_ non-linear
> response to the speed set by the PWM routines. First, we
> note that there are only 8 discrete speed settings (ignore
> direction). Now, on speed setting one, I get nearly 50% of
> maximum revs and an overall response that looks like speed
> is proportional to the square root of the set speed. All
> this is under no-load conditions. Even under normal load
> the response is much the same. Driving the motors with good
> old variable DC seems to produce the desired response.
>
> So: why do I get this motor response?
> what can I do about it?
> would the frequency of the PWM make a big difference?
> should I build an external speed controller?
>
> I have no real low speed control and so can not get a PI
> control working smoothly.
>
> Many thanks
>
> Pete
>
> ----------------------
> Peter Harrison
> Peter.Harrison@cannock.ac.uk
>
>
>
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Message is in Reply To:
 | | non-linear motor speed problem
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| I am using servos converted to plain gearmotors as the motive power for my baby bot. Finally I worked out how to add shaft encoders to them. (Found a small opto switch to poke through the inside of the case on the first gear). The servos I am using (...) (28 years ago, 11-Mar-97, to lugnet.robotics.handyboard)
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