Subject:
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Re: Questions about Differential
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 21 Dec 1998 05:38:57 GMT
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Original-From:
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Don Hewitt <donhewitt@worldnet.att=saynotospam=.net>
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Viewed:
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1381 times
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I've used the differential gear in two related ways:
1) As it is used in a car - to take power from one drive shaft and transmit
it to two wheels that may be moving at different speeds - a full-sized car
uses the differential to minimize wheel-slip as the car goes around a turn
(the outside wheel has to travel further (and thus rotate at a higher rate)
than the inside wheel.) If your robot has two drive wheels run from one
motor (and a separate mechanism for steering - like a car), then this is
what you need.
2) For other applications where you need to add or subtract shaft rotation
rates -
For example, let's say you want to measure the forward speed (or elapsed
distance) of a tank-style robot (with separate motors for each track.) Note
that the forward speed of the robot is approximately the average of the two
track speeds.
Just run the differential backwards - if you drive each of the "output
axles" of the differential (normally the outputs), then the "drive shaft"
on the center of the differential (normally the input) will run at a speed
that is proportional to the sum of the two driven shafts (the actual speed
is dependent on the gear ratios used).
In the tank example, drive the differential from both track motors, and
hook up an angle or rotation sensor to the center of the differential.
Count pulses from the angle sensor, and presto! you have an odometer for
the tank. Note that if you are spinning the tank in place (to turn it
around) then LeftTrackSpeed = - RightTrackSpeed and their sum is 0.
If this isn't clear, I could draw a quick sketch.
Also - in case anyone's interested, I've figured out a way to make a simple
rotation sensor using the standard Mindstorms light sensor coupled to the
light / fiber optic gizmo that comes in the "Extreme Creatures" add-on set.
This design can indicate distance (and thus speed, if you do some
computation), but not direction. I haven't taken the time to figure out
whether it can be programmed using the standard Mindstorms software, but it
is a snap using Spirit.ocx and VB.
Let me know (email or list posting) if you want instructions.
Don Hewitt
donhewitt@worldnet.att.net
======================
At 10:16 PM 12/20/98 -0700, Alan G. Smith wrote:
> Please excuse this ignorant question. I am a software guy that enjoys
> playing with Mindstorms and robotics.
> Can someone please point me to some explanations of different ways to use
> the differential gear that LEGO has?
>
> Thanks,
>
> Alan G. Smith
>
> +---------------------------------------------------------
> | Alan G. Smith
> | ags@poboxes.com
> | http://www.innovatus.com/ags
>
>
>
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Message is in Reply To:
 | | Questions about Differential
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| Please excuse this ignorant question. I am a software guy that enjoys playing with Mindstorms and robotics. Can someone please point me to some explanations of different ways to use the differential gear that LEGO has? Thanks, Alan G. Smith (...) (26 years ago, 21-Dec-98, to lugnet.robotics)
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