Subject:
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Re: Differentials on Tanks
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 15 Sep 2001 01:54:46 GMT
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Viewed:
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447 times
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If you use two differentials you can build a tank chassis that drives
very straight. The key is to have one side of one of the differentials
"flipped" in rotational direction. Its hard to do with ASCII art, but
here's a view from above....
---A-DDD-B---- <--- these axles drive the treads
-A
B-
-A
-A-DDD-B-
A = 16 tooth gear
B = 24 tooth gear
DDD = differential
Remember that axles don't go all the way through differentials.
If you apply power to the top differential, then it will try to turn
both treads (left and right) such that the sum of their rotation is
twice the rotation of the differential (ideally both treads moving at
the same speed). Now there are 3 gear meshes on the left side, and 2 on
the right side, so for the bottom differential the rotation of the
differential is twice the *difference* of the treads instead of the sum.
Use a second motor on the bottom one. In most cases (especially with
any gear-reduction at all), the physical resistance of a motor will
prevent the bottom differential from turning until you turn on the
motor, which means both treads will have to move at the same speed, and
the vehicle will move straight. Spinning the bottom differential will
cause the vehicle to turn (or even spin in place if you turn it at the
same speed as the top one).
Another option is to use two motors (one on each tread), but also use
rotation sensors on each side and use the RCX to adjust power to the
motors so that it drives straight. I prefer the differential approach
since it leaves my sensor ports free.
I hope this helps.
Dave Baum
In article <000a01c13d6b$9f3cee10$8c0e1a42@hal9000>, "Sean Watson"
<SeanWatson@ec.rr.com> wrote:
> I am having a real problem. I want to use a tank for my basic design,
> but I have to build one that can go perfectly straight. Well, not
> perfectly straight, but as close as possible. My problem is that I think
> one of my motors is much more powerful than the other. I have tried
> switching the motors to verify this. I have also tried many different
> gear ratios. I know that differentials are good for handling this sort
> of thing, but I can't seen to come up with a tank design that implements
> a differential. Anyone had any luck in this area?
>
> Sean Watson
> SeanWatson@ec.rr.com
> http://home.ec.rr.com/seanwatson/
>
> "There's a difference between knowing the path...and walking it..." -
> Morpheus
>
>
--
reply to: dbaum at enteract dot com
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Message has 1 Reply:
 | | Re: Differentials on Tanks
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| "Dave Baum" <dbaum@spambgoneenteract.com> wrote in message news:dbaum-A179A8.20...net.com... (...) If you want some visual information and specific building instructions you can use my page at: (URL) is a newish differential adder/subtractor and (...) (23 years ago, 15-Sep-01, to lugnet.robotics)
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Message is in Reply To:
| | Differentials on Tanks
|
| I am having a real problem. I want to use a tank for my basic design, but I have to build one that can go perfectly straight. Well, not perfectly straight, but as close as possible. My problem is that I think one of my motors is much more powerful (...) (23 years ago, 14-Sep-01, to lugnet.robotics)
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