Subject:
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Re: Newbie needs Help
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 5 Jun 2006 22:40:39 GMT
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Original-From:
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steve <sjbaker1@airmail.*ihatespam*net>
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Viewed:
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3655 times
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Steve Hassenplug wrote:
> You can (A) add more weight (B) make it go faster, or (C) add more
traction.
> Considering you're already at the weight limit (out of parts), option
(A) is out.
>
> Making it go faster is a reasonable option. Geared down 5:1 should
still work,
> depending on the wheels.
>
> Adding more traction would mean using more wheels. It's likely
you're out of
> wheels, because there are only 3 wheels in a couple types in the RIS
kit. So,
> you're best option would be to increase the speed.
I guess a little sophistication might help traction.
(This is a little 'out there' - but maybe worth investigation)
Lego tyres and tracks are made of rubber - and presuming things work in
a similar way at the scale of Lego as they do at the scale of a full
sized car, there is the matter of sliding friction versus static
friction to consider.
Your car has probably has antilock brakes that make sure that the wheels
roll along the road rather than slipping when you brake hard. That's
because the coefficient of friction of rubber is much higher when it's
not slipping than when it is.
In the case of a tug of war, that would mean that you want to prevent
the wheels from spinning faster than the robot is proceeding across the
ground.
One way to measure that would be with a pair of rotation sensors (which
I presume you don't have - but bear with me). If you hade one wheel
connected to a rotation sensor but nothing else and another sensor on
one of your driven wheels then in theory you could compare their speeds
and if the driven wheel is going slower than the idler then you don't
have maximum friction because it's slipping and giving it a little less
power for a while might help.
Since you don't have a rotation sensor in the basic RCX kit, you have
to improvise. One approach is to use a switch to count revolutions of
a shaft with some sort of protusion that presses the switch once each
revolution - however that obstructs things and eats some power.
Using the light sensor with black and white bricks fixed to the shaft
is another way - that doesn't put a load on the shaft - which is nice,
but you only have one and it looks like you need two. Here is the
next trick - connect a differential gearbox between the idle wheel and
the driven wheel. The output shaft can be set up so it doesn't
rotate when the two wheels are moving at the same speed and it does
rotate when one of them is slipping. Hence you can simply look at
the output of the differential to let the RCX know whether the
driven wheels are slipping and adjust motor speeds accordingly.
I suspect it'll take a lot of work to actually make this work nicely.
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Message has 1 Reply:
 | | Re: Newbie needs Help
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| (...) Steve, One rotation sensor is allowed. There are also two light sensors, so your idea is definitely doable. The situations that are confusing are when the pull of the other robot prevents your robot from making any headway, as well as when (...) (18 years ago, 6-Jun-06, to lugnet.robotics)
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Message is in Reply To:
| | Re: Newbie needs Help
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| (...) I suspect you're far from breaking gears or axles. However, keep in mind it is always possible (so don't blame me if it happens) :) Keep the distance between gears & wheels small, so the axles don't twist. Sounds like you still have more (...) (18 years ago, 5-Jun-06, to lugnet.robotics)
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