Subject:
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Re: A robot who knows his position (fwd)
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 28 Apr 1999 11:43:11 GMT
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Viewed:
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988 times
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In lugnet.robotics, lego-robotics@crynwr.com (Jim Choate) writes:
> ----- Forwarded message from Mario Ferrari -----
>
> From: "Mario Ferrari" <mario.ferrari@edis.it>
> Date: Tue, 27 Apr 1999 22:12:25 GMT
>
> I had some success in my first experiment with odometry. My goal was to build
> and program a bot that at every moment knows where he is.
[ talk of Dead Reckoning ]
> What you want is two levels of precision. The first used for gross
> positioning and obstacle mapping. The second fine-scale used for close in
> maneuvering and goal completion (ie dropping a can in a bucket).
That's a useful idea; I'll take note of that.
> If you're talking about a free-roaming bot that could live in the outdoors
> (ie unlimited world dimensions) then you want to get rid of the
> dead-reckoning vector math and go to some sort of inertial guidance. Wheel
> slippage, precision errors, motor fluctuations, battery drain, etc. make it
> less than effective. The errors pile up so fast the bot gets lost pretty
> quickly.
I've been doing some robot building aimed at dead reckoning and have found
that even the home or flat environment is enough to f*&k things up; the
bumpy slippery floor in my kitchen is particularly bad. Given slippage and
so on, the technique I was testing was one of timing ie move or rotate by a
given amount, but sense when you have stopped moving/rotating. Use the time
moving or rotating as an indication of distance or degree actually turned. The
reasoning behind this is that you don't need sensors which directly tell you
the distance or degree, only ones that can react quickly in telling you when
you've stopped moving/turning. I've managed to make sensors which can do this
to a limited degree. I'll put up some piccies of them when I get round to it
:-)
For my next robot I'm going to abandon dead reckoning (at least on it's own)
in favour of some external sensing relative to a landmark. My flatmate has
informed me of a way the Chinese used to navigate before they had compasses.
Basically, you get a two wheeled vehicle, take the output of each wheel and
feed it into a differential such the differential is still when they are moving
in the same direction. Take the output of the diff. and arrange it so that it
makes an arrow sticking out of the top of the contraption (think "weather
vane") turn. Down-gear this turning a bit. The result of this is the fact that
when you move the vehicle around, the "arrow" always stays pointing in a
direction parallel to it's original direction. I reckon you could use this
effect to tie into something external. Don't ask me what just yet ;-)
> Current small-scale, single-unit purchase, accelerometers are going for about
> $300 now. Real popular with the high-performance and experimental (go bird, • go)
> rocketry crowds.
Sounds great, except I don't have $300 kicking around.
> This months EDN has a add in the rear for new products for just such a
> device.
What's EDN?
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Message has 1 Reply:
 | | Re: A robot who knows his position (fwd)
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| (...) Looking forward to seeing them :) (...) Dead-reckoning should be used BETWEEN two consecutive (artificial) landmark sensing. When you get any external reference point you can zero your accumulated errors. (...) moving (...) Seems interesting. (...) (26 years ago, 28-Apr-99, to lugnet.robotics)
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Message is in Reply To:
| | A robot who knows his position (fwd)
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| ----- Forwarded message from Mario Ferrari ----- From: "Mario Ferrari" <mario.ferrari@edis.it> Date: Tue, 27 Apr 1999 22:12:25 GMT I had some success in my first experiment with odometry. My goal was to build and program a bot that at every moment (...) (26 years ago, 28-Apr-99, to lugnet.robotics)
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