Subject:
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Re: The Differential and One-Motor Turning
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 20 Jan 2000 05:06:07 GMT
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Viewed:
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737 times
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In lugnet.robotics, <kennep@mail.alum.rpi.edu> writes:
> ...I suddenly realized that you COULD use just one drive motor and still
turn. Combining this with a ratchet would let a robot turn one way in reverse,
or perhaps a mechanism like I mentioned before with the pivot wheel could be
used. Of course, a second motor could be employed to operate the turning
> in many ways.
Differentials are spiffy, huh? Even better, with two differentials you can
make a device known as an "adder-subtractor" which allows one motor to drive
two wheels at the same speed, in the same direction, and another motor can
drive the wheels in opposite directions. So you can drive straight ahead, or
pivot. Better still, you can use both motors at once to drive around curves.
The effect is basically the same as if you have a separate motor for each
wheel, but there are a couple of advatages: if your motors or you gear trains
aren't perfectly matched (as is the case mor often than not) the
adder-subtractor makes it easier to drive in a perfectly straight line. Also,
you can use a powerful motor to drive forward and a less powerful one (think
micro motor) to steer.
How is it built? Well, it's difficult to describe, and since I had so much fun
figuring it out for myself from a few clues, I'll let you work on it for a
while before I give it away. Here's your clue: you need two differentials
(two dark greys works best, two light greys is ok too, but I don't think you
can use one of each). I'll work on a description and post it in a few days if
no one beats me to it. I have a feeling that there are several quite different
solutions, which might be smaller or more elegant than mine, so if anyone works
one out, email me.
-Phil
ogstonpj@worldnet.att.net
P.S. "Adder Subtractor, what's that got to do with it?" I hear you ask...
Apparently this device was originally used in mechanical computers and adding
machines. You see, if you put motors on the wheel axles and wheels where the
motors were, one wheel spins at a rate which is the sum of the motor speeds and
the other spins at a rate which is the difference. So now you can be a
mechanical engineer _and_ a computer scientist.
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Message has 1 Reply:
Message is in Reply To:
 | | The Differential and One-Motor Turning
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| In response to several posts regarding driving and turning with only one motor... (Please excuse my very basic mechanical engineering knowledge!) Having only the two motors included with the RIS, I have also experimented with vehicles that are (...) (25 years ago, 19-Jan-00, to lugnet.robotics)
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