Subject:
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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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Sun, 27 Oct 2002 13:52:11 GMT
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Original-From:
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PeterBalch <PeterBalch@{ihatespam}compuserve.com>
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Viewed:
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600 times
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Steve
You shouldn't have a differential.
The front bogey can rotate about its vertical axis about (let's call it)
the steering shaft - which also doubles as the drive shaft.
The two wheels on the bogey are on a solid axle.
The idea is that it's "easier" for the two wheels to go in a straight line
than to turn because of the gear ratios (and perhaps because the axle is
solid). But when they meet an obstacle, the bogey prefers to rotate.
I've seen designs where the bogey wheels axle is directly under the
steering shaft and (more rarely) where the bogey wheels are (one
wheel-diameter) in front of the steering shaft.
The only example I could find in my son's toy box has a steering shaft
pinion with ten teeth and a crown wheel on the bogey axle with twenty
teeth. So the bogey wheels are geared-down relative to the steering. The
bogey wheels are 20mm dia and 25mm apart. The rear axle is 65mm behind the
bogey.
In general, the rear wheels shouldn't be on a solid axle but, in this
example, they are but are made of slippery plastic (whereas the bogey
wheels are rubber).
I used to work in the Artificial Intelligence department here in Edinburgh
and my boss was fascinated by these toys. They could find their way out of
corners far better than any of the "intelligent" mobile robots. He had one
hidden under a cardboard box with fake antennae, etc. and would ask
students what they thought the algorithm might be.
His view was that it is very difficult to get the whole machine to behave
properly. The factors you have to adjust are the ratio of the gears, the
diameter of the wheels vs. their distance apart, the loading on the front
and rear wheels and the distance from the bogey to the rear wheels. Once
one works, it works well but if you try adding extra weights to a
shop-bought toy, you'll see how sensitive they are.
Peter
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Message has 1 Reply:
 | | Re: Problem with auto-steering mechanism.
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| (...) Yes - I realised that and posted a photo of the new mechanism yesterday. (URL) The front bogey can rotate about its vertical axis about (let's call it) (...) ...well...I used a single wheel. (...) Right. The problem with making it work (...) (22 years ago, 27-Oct-02, to lugnet.robotics)
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