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Fw: [DPRG] Motor control, or how I quit worrying and learn to love radians

Subject: Fw: [DPRG] Motor control, or how I quit worrying and learn to love radians
From: Dale Wheat dale at dalewheat.com
Date: Mon Jun 9 12:58:00 CDT 2003

> Our medium is inhibiting our message.  I'll bet all this could be drawn
out
> and verified in 3 minutes at the whiteboard...  I'll buy a couple of 4'x8'
> whiteboard panels at Home Depot if someone with a truck will haul them to
> the warehouse.  Volunteers?
>
> The inside arc length is the radius minus half the wheelbase times the
angle
> (in radians), or (r - w/2) * theta.
> The outside arc length is the radius plus half the wheelbase times the
> angle, or (r + w/2) * theta.
>
> The velocities are those distances divided by the time.  I'm assuming that
> the inside, center and outside points all reach the destination at the
same
> time  :)
>
> I'd rather not depend on linearity in the motor drive, and instead use
some
> kind of feedback.  I got one quadrature encoder built and working last
> night.  Unfortunately, since it's measuring the wheel, the resolution is
> horrible.  I might have to switch to "timer ticks per encoder count"
instead
> of the other way around.  :(
>
> As far as the usefulness of these calculations go, it's important that *I*
> understand them so that I can make an informed decision as to wether or
not
> to use them in different applications.  I've already mentioned that my
trig
> skills are almost non-existent.  I'm delighted when I find out things like
> "right motor count minus left motor count divided by wheelbase equals
angle
> you just turned" (odometry) and "radius times angle equals arc length".
>
> I have a ton of other robot projects I want to work on.  I'm deliberately
> sticking with this issue until I can wrap my head around it, otherwise,
> knowing my nature, I'd just say "Hmmm... a mystery" and move on to
something
> with blinking lights.
>
> Thanks,
>
> Dale Wheat
> http://dalewheat.com
> (972) 486-1317
> (800) 330-1915, access code 00
>


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