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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Wed, 20 Sep 2000 23:28:43 GMT
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Original-From:
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Andy Gombos <GOMBOS_2000@YAHOOstopspam.COM>
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Viewed:
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611 times
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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 has 2 Replies:
 | | Re: Advice on Rotation sensors and steering please.
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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 (URL) Gombos" (...) (24 years ago, 21-Sep-00, to lugnet.robotics)
| | | Re: Advice on Rotation sensors and steering please.
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| (...) So you tell your system to drive both motors forward and if you do nothing else then you are only on count off! You must have better matched motors than mine! I see a 10 or 20% difference in their speeds that needs to be corrected to get the (...) (24 years ago, 21-Sep-00, to lugnet.robotics)
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Message is in Reply To:
| | Advice on Rotation sensors and steering please.
|
| 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 (...) (24 years ago, 21-Sep-00, to lugnet.robotics)
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