Subject:
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Re: Advice on Rotation sensors and steering please.
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 21 Sep 2000 13:00:10 GMT
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Viewed:
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1426 times
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The solution is to float the motor. There is code in the NQC tutorial for
this. It works very well. the file is 9_rotation.nqc I will E mail it if
you do not have the file.
--
Bob Fay
rfay@we.mediaone.net
The Shop
http://users5.50megs.com/bobfay
http://www.geocities.com/Heartland/Bluffs/7900/
"Andy Gombos" <lego-robotics@crynwr.com> wrote in message
news:39C9482A.9EBCB1BC@yahoo.com...
> In my experience setting the motor to off has worked best. Constantly • check
> for differences in the counts. I was only using 2 sensors, and after 500 • or
> so steps(about 15 ft), there was only a 1 count differenece. The main • factor
> in determining what happens is if the robot is perfectly straight or not. • 1
> mm of non-straightness can lead to almost 1 foot of deviation at the end,
> relative to your reference line.
>
> Andy
>
> Steve Baker wrote:
>
> > OK - so I am now the proud owner of three rotation sensors.
> >
> > I've built a really basic two-wheeled robot with a caster at
> > the back for the purposes of getting in some programming experience
> > with these things. Each wheel has a rotation sensor (connected via
> > a gear train so I can play with the sensitivity)- each has it's own
> > motor.
> >
> > I'm using NQC.
> >
> > So, step one - steer in a straight line. Since two motors picked
> > at random don't go at anything like the same speed, I need to correct
> > for that.
> >
> > Here is some pseudo-code:
> >
> > zero both sensors
> > both motors full speed forwards
> >
> > while ( true )
> > {
> > if ( sensor1 < sensor2 ) {
> > full speed wheel-1 ;
> > slow down wheel-2 ;
> > } else {
> > if ( sensor2 < sensor1 ) {
> > slow down wheel-1 ;
> > full speed wheel-2 ;
> > } else
> > full speed on both wheels ;
> >
> > Wait(1);
> > }
> >
> > ...well, this (and MANY variations on this) fail miserably for a
> > variety of reasons. So I have some *basic* questions:
> >
> > * I heard that the rotation sensor can lose count if it rotates too
> > fast for software to keep up. Can anyone give me an idea of what
> > a 'sensible' rate is? I guess it's a compromise between precision
> > and risk of count lossage.
> >
> > * In the pseudo-code, I have 'slow down wheel-N'. There seems to be
> > a suprising variety of ways to do that..although there isn't actually
> > a 'speed' control! :
> >
> > + I can set the motor output to 'Off'.
> > + I can momentarily apply 'OnRev'
> > + I can reduce the 'power' from 7 to something
> > smaller...either suddenly or gradually.
> > + I can 'float' the motor output.
> > + I can do a combination of these things.
> >
> > Which of these things works best? Does the choice depend on the wheel
> > size/tyre type/gearing/robot weight - or this there simply 'one best
> > way' ?
> >
> > * The rotation sensor counts the total rotation measured in 22.5 degree
> > steps - right? If we drive more than 32767 steps, it'll wrap around • to
> > -32768 steps or something - right?
> >
> > Once I can get it to go in a straight line, I'll go on to figure out
> > how much I can accellerate/decellerate without tyre slippage, then write
> > code for turning, reversing, collision recovery, etc.
> >
> > * Has anyone ever written an RCX emulator? It would be nice to be able
> > to debug my code on the PC where I could print out variables and such.
> > With the limited 'byte code' that NQC uses, it seems like this • wouldn't
> > be so hard to do.
> >
> > --
> > Steve Baker HomeEmail: <sjbaker1@airmail.net>
> > WorkEmail: <sjbaker@link.com>
> > HomePage : http://web2.airmail.net/sjbaker1
> > Projects : http://plib.sourceforge.net
> > http://tuxaqfh.sourceforge.net
> > http://tuxkart.sourceforge.net
> > http://prettypoly.sourceforge.net
>
>
>
>
>
>
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Message is in Reply To:
 | | Re: Advice on Rotation sensors and steering please.
|
| In my experience setting the motor to off has worked best. Constantly check for differences in the counts. I was only using 2 sensors, and after 500 or so steps(about 15 ft), there was only a 1 count differenece. The main factor in determining what (...) (26 years ago, 20-Sep-00, to lugnet.robotics)
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