Subject:
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Re: positioning of robot
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 15 Aug 1997 17:26:21 GMT
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Original-From:
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Chuck McManis <CMCMANIS@FREEGATE.NETantispam>
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Reply-To:
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cmcmanis@FreeGate.+spamcake+net
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Viewed:
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1383 times
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I missed the first posting, I liked the summary posted by John Whitten.
Youcan take his posting one layer "up" to get at the abstractions if you
want.
These are:
1. Points of contact with the surface - More increases stability.
2. Drive Train considerations - power/traction/net torque
considerations.
3. Kinematics - Controlling BOTH position and attitude in your
robot.
Consideration for #1 affects generally how "tall" your robot can be
(that
is to say how far above ground you can tolerate the center of gravity)
and
how much "tilt" you can tolerate (or stated another way how steep a
surface
you could climb (assuming your power plant can handle it))
Consideration for #2 affects how much weight you can carry around and
for
how long. To some extent this is a self defeating proposition. The
larger the
batteries, the more they can power but the more they way. Efficiency of
the
drive train is the total torque available in relation to the net torque
available
to move the robot (net torque being total minus the torque required to
just
move the wheels and battery)
Consideration for #3 affects how easily you will be able to achieve
externally
motivated objectives. So if you have an objective to "plug in" to the
wall outlet,
then you have to be able to position yourself relative to the immobile
wall outlet
and kinematics are a big consideration. If on the other hand you are
simply picking
up balls as you find them, then by finding a ball you are pretty much by
definition
in a position to deal with the pickup.
So take these three things in consideration when making your locomotion
choice.
However, don't constrain yourself to necessarily existing examples.
Walking for
example can have a very good kinematic and torque content.
Here is an example.
One of the rovers at CMU used three wheels for its locomotion, however
instead
of the two driven wheels, one idler wheel design that many people adopt,
all three
wheels on the robot were both steerable, and powered. Using this
configuration
the robot got the advantage of using wheels (low power, high load
values) and
the kinematics of treads (independent control of attitude and direction)
The cost of course was more motors and thus a more complex mechanism but
the design was wonderfully useful.
Another opinion on Treads
I like treads, most of my robots use treads, they have nice kinematics
but they
suck when it comes to power utilization. Further since their drag
coefficient (friction)
goes up with weight, you can have a plaform which can turn on a smooth
surface
but can't turn on carpet. Generally, lightly loaded toy car chassis
don't have this
problem, but when they get loaded down they eventually get stuck.
--Chuck McManis
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Message is in Reply To:
 | | Re: positioning of robot
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| (...) Howdy- (...) No problem- as long as you get the relevant points across- that's what counts :) (...) Ok- that's a very good basic question. Here are the pluses and minuses for each type of drive system: 2 WHEELS: The two wheel drive system on (...) (27 years ago, 15-Aug-97, to lugnet.robotics.handyboard)
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