Alt-BEAM Archive
Message #04912
To: beam@sgiblab.sgi.com, JVernonM@aol.com
From: Bruce Robinson Bruce_Robinson@bc.sympatico.ca
Date: Sun, 27 Jun 1999 17:03:54 -0700
Subject: [alt-beam] Re: Photopopper problems
JVernonM@aol.com wrote:
>
> Bruce,
> Everything you say is true. You only forgot one thing. Friction. The
> shaft of the pager motor must be pressed with sufficient force to turn
> the wheel without a lot of slippage. This requires the motor to lose
> torque through the application of lateral friction on the shaft.
Hey, no fair, Jim. I didn't forget it -- look at my note again. Down
there, near the bottom. See, I mentioned it. Admittedly, I didn't give
it much air play.
Anyway, the point of my note was, there's alternatives to setting your
motors at an angle. I figured James might have already mounted his
motors (rather securely) parallel to the ground, and it might have been
easier for him to rearrange the wheels.
Pager motors work well when mounted at an angle. Other types of motors
may have too large a diameter, or too short a shaft for this
configuration to work. Also, many motors will generate excess friction
if you load them with a side thrusting force at the very ends of their
shafts. This may be as bad as using an idler wheel. Pager motors aren't
likely to experience this problem, because they are designed to handle a
high imbalance force from the eccentric weight normally attached to
them.
Starting from scratch, with a solar powered 'bot I would most definitely
consider some form of direct drive. Only if that proved difficult would
I resort to indirect drive, and I would make every effort to minimize
friction.
Regards,
Bruce
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