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[DPRG] Why high resolution encoders are desirable

Subject: [DPRG] Why high resolution encoders are desirable
From: Dan Creagan dcreagan at bellevue.edu
Date: Fri Aug 24 15:58:31 CDT 2001

It will probably work. You can take large samples and then keep track of
the number of samples. However, 517 ticks per inch is way past the
useful stage for a hobby robot.

Having said that, if you've already figured out how to do it and have it
running, then rejoice! It would be a way cool setup even if it didn't
have a lot of practical use.  Nothing like experience - it may be useful
on your next project.

Dan

-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On Behalf
Of David Peterson
Sent: Friday, August 24, 2001 3:22 PM
To: Clay Timmons; dprglist at dprg.org
Subject: Re: [DPRG] Why high resolution encoders are desirable


I may be getting about 517 ticks per inch with the above encoders, would
it be a good idea to try and scale this, perhaps reduce the precision a
bit? That comes out to a 19 bit number for traveling 48 feet or so,
might be better to stick to word sizes, though it may work anyway, have
no real idea at this point. David P
http://www.geocities.com/robodave2000/
----- Original Message -----
>From: "Clay Timmons" <ctimmons at cadence.com>
To: <dprglist at dprg.org>
Sent: Friday, August 24, 2001 12:57 PM
Subject: Re: [DPRG] Why high resolution encoders are
desirable


>
>
> Dan Creagan wrote:
>
> > While I agree with your assessment, you have used the
extremes to show
> > your point. 1 tic per inch would be 9.4 tics per
revolution on a 3 inch
> > wheel.  Not likely a choice of patterns.
> >
> > With a 240 tics per revolution wheel, the wheel movement
is 4/100s of an
> > inch (less, actually) per tic.  So with a modest
encoder, you can have
> > enough accuracy that you *can* make those turns.  The
encoder tics won't
> > be the problem. Gear lash and wheel slip will now
overcome any accuracy
> > you gained by having an incredibly accurate encoder.
When I first
> > started this, I was using a 90 clicks per turn encoder
and it was
> > definitely getting accumulated error; however, running
on carpet, slopes
> > or running fast was always more detrimental to accuracy.
Much more!  I
> > have movies of the 90 clicks job doing perfect squares
on smooth
> > surface.  The errors tend to cancel one another for
short runs like
> > that.  They do accumulate over time.
> >
>
> My encoders work out to 40 tics per inch while David
Anderson has about 80 tics
> per inch.   4/100s would be 25 tics per inch.     These
are about the
> ballpark of accuracy for hobby robots.
>
> I can make turns to within +/- 0.5 degree.   A good way to
check your
> dead recokoning accuracy is to run the UBMARK test.   I
don't
> have the link handy but look for Johann Borenstien?  at
the University
> of Michigan.
>
> Later,
>
> -Clay Timmons-
>
> _______________________________________________
> DPRGlist mailing list
> DPRGlist at dprg.org http://nimon.ncc.com/mailman/listinfo/dprglist


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