Subject:
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Re: Problem with auto-steering mechanism.
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 29 Oct 2002 16:48:51 GMT
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Viewed:
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623 times
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In lugnet.robotics, PeterBalch <PeterBalch@compuserve.com> writes:
> > > The two wheels on the bogey are on a solid axle.
> > ...well...I used a single wheel.
>
> Hmmm. If it's a single wheel then why whould it prefer a straight line?
> ...
Well with all this discussion I couldn't resist trying it myself! :-)
If I understand the concept correctly, the front (single) wheel is driven thru
a freely rotating turntable. When the front wheel stalls due to the robot
hitting something in the direction of motion, the power to this wheel is
transferred into rotating the turntable via the locked up gears. The being the
case, I think you want the front wheel to be able to spin in place easily, i.e.
not have a wide grip.
The only thing biasing the robot to drive straight is the fact the the rear
wheels are connected (ie dont slip), therefore the whole device has a
preference to drive straight. If blocked, the front bogey will rotate and then
it becomes a fight between the grip of the front wheel vs the grip of the
locked back wheels as to whether it turns (causing the rear wheels to skid) or
the front bogey just keeps spinning till it reaches 180 deg the other way and
can drive both the rear wheels straight back.
My question is, I dont see how gear ratios make any difference? As best I can
tell it all comes down to the grip of the front vs rear wheels, which requires
carefully balancing the load over front and rear wheels. Too little weight over
the rear and the rear wheels just skid and the thing keeps turning in a circle
(ie lose the straight forward bias). Too little weight over the front and the
front wheel just skids when forward motion is blocked and the bogey doesn't
spin (ie friction of the front wheel is less than the friction to turn the
turntable).
As someone mentioned before, the device seems rather finicky, at least when
built in Lego. But maybe I'm missing something obvious...
Just my $0.02...
- Gareth
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Message has 1 Reply:
 | | Re: Problem with auto-steering mechanism.
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| (...) That's *not* entirely obvious. There is a tradeoff between ease of twisting of the turntable and ease of slippage in forward drive. A nice chunky tyre with tons of grip is hard to twist - which makes the robot drive forwards better without (...) (22 years ago, 30-Oct-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: Problem with auto-steering mechanism.
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| Steve (...) Hmmm. If it's a single wheel then why whould it prefer a straight line? Why did you abandon two wheels? (...) I bet their drive-trains are a lot more efficient. Frictional losses in Lego gears and axles are high. I've never seen one with (...) (22 years ago, 29-Oct-02, to lugnet.robotics)
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