Subject:
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Re: a couple of new-bot questions from a generally quiet lurker
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 21 Sep 1999 09:06:25 GMT
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Original-From:
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S. Crawshaw <sc10003@eng.+NoMoreSpam+cam.ac.uk>
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Viewed:
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1931 times
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On Tue, 21 Sep 1999, Ian Warfield wrote:
> In addition, I'm happy to say that it meets all the criteria of another post
> on this subject:
> > 1) Like the single rotation sensor system, you can monitor the
> > difference in wheels in forward/backward movement
> > 2) You can monitor Forward/backward DISTANCE
> > 3) You can monitor turning distance.
> > 4) You can detect stalling. (if no pulses are coming in, the robot is
> > not moving, and something else must be done.)
> > 5) You can calculate speed.
>
> The only thing I don't like about this design is having to correct "drift"
> every few feet, although with this design you know about it and can fix it
> easily on the run. Other than that, it works pretty well.
You can achieve all 5 of these criteria with the standard differtrans, if
you put a rotation sensor directly on each motor shaft...
[ I've build such a 'bot, and it appears to work pretty well (ie it
measures distance accurately, and drives in a straight line without
drifting) Unfortunately I don't have a good surface to test it on (only
the RIS test mat on carpet!), so I can't (yet) promise that I can do
accurate distances _and_ angles using the sensors. ]
...although if you _really_ want to know where you are, then you wouldn't
turn while driving (the calculations get really tricky!) - in which case
you only need one motor, since you're only doing one thing at a time.
That sounds like an interesting challenge: build a *compact* differtrans
which runs off one motor, ie only forwards and rotate right (or left, if
you prefer!) It can presumably be done with 3 differentials, but can it
be done with 2? 1?? (I only have 2 diffs [unless you count an old-style
one], so I'll be trying the 2-diff version...!)
Stuart
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