Subject:
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Re: moving in a straight line with two motors?
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 14 Nov 1998 06:09:48 GMT
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Original-From:
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Scott Furman <fur@netscape.*nospam*com>
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Viewed:
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2336 times
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> Here's an exercise for someone with an RCX: Create a chassis that
> consists of one drive motor to the wheels and an angle sensor geared to a
> 2-d inverted pendulum on top. Write a program that moves the chassis to
> keep the pendulum straight vertical.
Believe it or not, I've been working on exactly this problem for the last few
days. I built an angle sensor using a 500K potentiometer wired directly to an
RCX input port. (Lego's angle sensor doesn't have sufficient angular
resolution unless it's geared down and adding those gears adds too much
mechanical resistance for the pendulum to swing freely.)
The problems I am still facing are:
* The acceleration provided by two motors isn't sufficient to keep the
pendulum erect if it's only slightly perturbed from vertical. Partly,
this is due to the tires slipping when the machine accelerates from rest,
but I think that, even with that corrected, the motors may not be
powerful enough.
* Although there's programmatic control of the motor power, there doesn't
seem to be control over the motor velocity. As a result, the motor tends
to jerk when it starts or changes direction. When the pendulum is
leaning slightly, the motor turns on briefly to correct it, but the
application of full velocity tends to cause overcompensation and the
pendulum swings the other way. In a few cycles, the pendulum
oscillations increase beyond the motor's ability to compensate.
Incidentally, there's a good description of the control loop required for an
inverted pendulum in Siebert's "Circuits, Signals and Systems".
-Scott
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Message has 2 Replies:
 | | Re: moving in a straight line with two motors?
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| (...) Perhaps you're asking too much of them. Try toning down the pendulum; that is, give it some length below the hinge point as well. As long as it's still top-heavy you're still technically an inverted pendulum, and the added mass below the pivot (...) (26 years ago, 14-Nov-98, to lugnet.robotics)
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Message is in Reply To:
| | Re: moving in a straight line with two motors?
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| (...) 1) You've been playing too much Carmageddon. 2) Control theory is relatively new (it paces the development of computers). There are quite a few good textbooks available, but a professor is a much greater help. Familiarity with calculus and (...) (26 years ago, 14-Nov-98, to lugnet.robotics)
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