Subject:
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Re: Received my RIS 2.0 - the two motors run at different speed! :-(((
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 11 Jan 2003 17:47:17 GMT
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Original-From:
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Steve Baker <SJBAKER1@AIRMAILavoidspam.NET>
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Viewed:
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931 times
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Stephane Simard wrote:
> It's definitely higher than 10%. When my rover is running far enough, it's
> turning right enough to form a triangle whose side ratio is about 1 length
> for every 6 traveled, so it's somewhere between 15% and 20% difference.
Is it? Did you do the math or are your just guessing?
There isn't enough information to figure the math from what you've told us...
It depends on how wide your robot is and what units that triangle is
in (feet? meters? miles?).
But let's make some guesses (using nice round numbers so my poor little
brain can do the math):
If your robot went 1 meter off to the side for every 6 meters it went forwards,
then that's an arc of a circle with an 18 meter radius.
Let's guess that your robot was 10cm wide, then if we let it drive around
a complete circle back to it's starting point (an 18m radius circle)
we know that the inside wheel wheel have travelled 2 x pi x 18meters and
the outer wheel went 2 x pi x 18.1 meters - which is a difference of 1 part
in 180...about a HALF a percent difference in speed! ...not "between 15% and 20%"
It doesn't take much of a motor speed error to cause massive error!
You certainly can't return motors that are mismatched by just half a percent,
that's totally unreasonable!
But - without knowing how wide your robot is - and the actual radius of
the circle it would eventually have covered, I can't compute the actual
motor error - and it could very well be higher.
> I will call Lego monday and ask if I can send back *both* motors, to ensure
> they will send me back two motors, hopefully they will have tested them.
No - they won't go to that much trouble - they'll just ship two new
motors - and the odds are that they'll be just as mismatched as the ones
you've got now. You don't seriously imagine they have some guy there
with a techometer who'll sort through the motors looking for two that
match do you? Nah - they'll just pick two new motors at random and
ship them back to you.
Unless you actually have a FAULTY motor, you gain nothing by returning
them.
I think you have two pretty normal motors and it would be unethical
of you to waste Lego's money by making them replace them.
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://www.sjbaker.org
Projects : http://plib.sf.net http://tuxaqfh.sf.net
http://tuxkart.sf.net http://prettypoly.sf.net
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