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 08:13:18 GMT
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Viewed:
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969 times
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In lugnet.robotics, lego-robotics@crynwr.com (Jim Choate) writes:
> > The representation of the space inside the bot is a simple Cartesian plane,
> > where the origin is the starting point. Distances are expressed in 10000th of
> > millimetre and angles in 10000th of radian. The bot is obviously not precise • up
> > to this point, but just to keep computation approximations as low as
possible.
> Jesus H. Christ, talk about over-kill. If all you're looking for is position
> sensing then the absolute highest resolution that is required is the
> dimension of the robot. Convert this to a integer multiple of wheel diameter
> and you can loose the floating point math, it's all integers; 1 body, 2
> body, 3 body, etc. You'll still need floating point to do the vector algebra
> but as you've discovered, tables are the way to do that.
That's true and clear. I'm not actually interested in such a precision, but as
you know very well the problem with odometry is that errors accumulates very
fast so I used four decimal digits in any computation to keep them as low as
possible.
> As to the smallest usable dimension, the question there is considering the
> smallest resolution in your A/D for wheel rotation and then using it as your
> base ruler for fine positioning, you can't get any finer than this.
Yes, this is what I did in my program. There are some constants which maps the
phisical properties of the bot (wheel size, base between wheels, resolution of
encoder, gear ratio between wheels and encoders). BTW, my arrangement is set
up to count 40 encoder ticks for every wheel revolution.
> 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.
That was not my goal.
> 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.
>
> This months EDN has a add in the rear for new products for just such a
> device.
Thanks the info. I'll have a look
Mario
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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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