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 16:00:28 GMT
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Original-From:
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Daniel Miller <DANIELMI@EXPERTantispam.CC.PURDUE.EDU>
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Viewed:
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5453 times
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On Fri, 13 Nov 1998, Scott Furman wrote:
> > 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...
> 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.
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 decreases the frequency.
> * 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.
Hrm. Tried weighing down the chassis so the acceleration isn't so high?
Daniel "Dan'l" Miller Senior, School of Aeronautics and
danielmi@expert.cc.purdue.edu Astronautics, Purdue, Indiana
danielmi@cartoon.ecn.purdue.edu
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Message is in Reply To:
 | | Re: moving in a straight line with two motors?
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| (...) 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 (...) (28 years ago, 14-Nov-98, to lugnet.robotics)
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