Subject:
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Re: Limited slip differential
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 31 Aug 2000 21:27:30 GMT
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Original-From:
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Simon Bogaert <simon.bogaert@advalvas.STOPSPAMbe>
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Viewed:
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750 times
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> Interesting. I assume you're talking about the white gear-looking
> thingy that comes with 8735. Where would you put it? In the center
> peg within the diff?
Actually, no. The white gear is known as the 'clutch gear'. It prevents
the frying of your motor in case it gets stalled. I don't know any way you
can prevent it from 'clutching' if the tension on the gear gets too high.
What I actually meant was a piece you can find in any later official Lego
gear box. It is used to make an idler gear (that can spin when its axle
isn't) turn when its axle is turned. Our part is a tube with two rings on
it. The tube's inner diameter is the same as the outer diameter of the
'axle joiner'. It has little rigs that make the part spin when the axle
joiner is spin. You can move it back and forth using a special piece that
fits between the two rings. Doing this, you move the piece in and out the
idler gear, toggling the 'axle following function' of the idler gear on and
off.
The differential is actually one big idler gear that's fully equipped to use
our special part. This way, you can fix one axle of the differerential to
the differential casing, so the possible difference between the two output
axles of the differential is made impossible.
When this 'differential lock' is engaged, you can force two wheels (on the
same differential) of a car to move at the same time. So if one wheel is on
slippery ground, because of the differentials' nature, this wheel will slip,
causing the other wheel to stand still and your car will eventually stop
moving. Now, if you want your car to move in such a situation there are two
possibilities: A) prevent the wheel from slipping by reinforcing the ground
(eg. put a piece of wood under the wheel) B) let the other wheel turn.
Possibility A is a good solution for a normal car that normally never gets
stuck in mud or other slippery ground. Possibility B is a good solution for
4x4 vehicles that often get stuck in mud.
B is achieved by 1) limiting the difference in speed between the two wheels
(limited slip differential) or by 2) eliminating the difference in speed
between the two wheels (differential lock). The first method is something I
haven't implemented yet (Jennifer Clark found someone who did; see her post
on lego-robotics/lugnet.robotics mailing list/newsgroup). The second method
is what I found out. It's just a temporary solution, because you can't make
turns with it engaged on solid soil, but in mud, it's not that much of a
problem, because this soil lets the wheel slip enough to let a difference in
speed between the two wheels exist.
You can also use the differential lock to come over obstacles (like entering
a carpet from the floor diagonally: the difference in height is just enough
to let one wheel spin, causing your vehicle to stop moving) without some
special form of suspension. A suspension is used to push all the wheels
firmly on the floor, which isn't the case with a fixed suspension on an
uneven soil: It's possible that a wheel turns in the air. When this
happens, just engage the differential lock and the other wheel, that's on
the ground, will propell your vehicle. If you don't have to use a special
suspension, you can eliminate a lot of friction and a lot of wheight,
causing your vehicle to ask less power of the motor that's propelling your
vehicle.
I hope this explanation is clear enough, and if you find any mistake
(spelling, grammar, or technical description), please do correct me.
Don't stop constructing...
Simon
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Message has 1 Reply:
 | | Re: Limited slip differential
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| Now I see it. I found the gear you were talking about on the Technica site. This if very serendipitous, as I have recently been pondering how to make a locking diff with Lego. Thanks for the intel! - Greg Simon Bogaert wrote: <snip> (...) (24 years ago, 2-Sep-00, to lugnet.robotics)
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Message is in Reply To:
| | Re: Limited slip differential
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| Interesting. I assume you're talking about the white gear-looking thingy that comes with 8735. Where would you put it? In the center peg within the diff? - Greg (...) (24 years ago, 31-Aug-00, to lugnet.robotics)
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