Subject:
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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 09:13:19 GMT
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Original-From:
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Peter Harrison <peter.harrison@cannock.ac.uk{NoMoreSpam}>
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Viewed:
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2334 times
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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 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 has 2 Replies:
 | | Re: non-linear motor speed problem
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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 (...) (28 years ago, 11-Mar-97, to lugnet.robotics.handyboard)
| | | Re: non-linear motor speed problem
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| (...) Several reasons. Understand that PWM has the effect of controlling the amount of power fed to the motor, power is related to current in a quadratic (p = i^2r), and your current is related to the voltage applied and the motor parameters (...) (28 years ago, 11-Mar-97, to lugnet.robotics.handyboard)
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