Subject:
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Re: ROM stuff: Better than PWM
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 19 Dec 1998 13:39:55 GMT
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Original-From:
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Markus L. Noga <markus.noga@inrialpes.IHATESPAMfr>
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Viewed:
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3648 times
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Kekoa Proudfoot wrote:
> You can avoid the O(n^2) table cost by keeping a counter. Count p cycles
> on, then count n-p cycles off. This works. But as n gets large, the
> period of n ms drops low enough that the motor becomes ineffective. For
> example, if n is 1000 and p is 500, the motor is on for 1/2 sec then off
> for 1/2 sec. That won't drive the motor the way you want it to be driven.
> Even for n = 100, things are very jittery.
>
> So here's my solution:
>
> every 1/1000th sec:
> count += p
> if (count >= n)
> turn motor on
> count -= n
> else
> turn motor off
>
> That's it.
>
> I'm sure this algorithm has been thought of before; I got the idea from
> Bresenham's line drawing algorithm and from the Floyd-Steinberg error
> diffusion dithering algorithm, but I believe this algorithm is a typical
> one used in one-bit D/A converters.
In fact, I'm using exactly this algorithm to drive the motors for my
laser scanner - though the host platform is an embedded PC, not the RCX.
I'm currently rewriting the motor drivers to:
* keep an 1ms resolution system clock
* call the task scheduler every 20 ticks, thereby making it IR
compatible
I'll integrate the Bresenham algorithm with a practical n of, say, 256,
too.
--
Markus L. Noga noga@inrialpes.fr
INRIA Rhône-Alpes http://www.inrialpes.fr/
IPR Universität Karlsruhe http://wwwipr.ira.uka.de/
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Message is in Reply To:
 | | ROM stuff: Better than PWM
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| So I was thinking about writing a motor driver that is better than what is in the ROM already. Here's the problem: You have a function called once every 1/1000th of a second. You want to allow n speeds of the motor at minimal cost in lookup tables. (...) (28 years ago, 19-Dec-98, to lugnet.robotics)
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