Subject:
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Re: compensating battery level
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 10 Dec 2001 13:25:26 GMT
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Original-From:
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Steve Baker <SJBAKER1@antispamAIRMAIL.NET>
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Reply-To:
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sjbaker1@airmail.STOPSPAMMERSnet
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Viewed:
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588 times
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Mathias Uhr wrote:
> now i want to let the program calculate the parameters auto-
> matically from the current battery level.
>
> and now (finally... :-) my questions:
>
> - has anyone tried this before?
> - does anybody know if the torque of a motor is proportinal to the
> voltage? or does it rise "in the square"? or how?
> - is it better to adjust the power level of the motor or the time
> it runs? (currently, i'm using the latter)
Well, I don't know the actual answer to your question - but I do know
that there is a tremendous variability from one motor to another *and*
from one construction of a particular mechanism to another.
(See my report here: http://www.sjbaker.org/steve/lego/motor_speed.html)
Given that this amount of variability will probably carry over into your
torque-versus-battery-state curves, you'll probably need to do actual
experiments with each robot you build in order to figure them out. If
you take the robot apart and put it together again, you may need to
re-test too!
You might also note that the RCX current-limits - so when the batteries
are fully charged, there will be a flat part to the torque curve where
the batteries *could* provide more current but the RCX electronics
don't allow them to.
Finally, you *might* get better results from NiCd batteries than regular
disposable or NiMH batteries. NiCd's produce a pretty constant voltage
right up to just before the point where they die. The other kinds tend
to drop in voltage gradually over their entire life-span - which is annoying
if you are relying on dead reckoning. However, since NiCd's only produce
1.2 volts instead of the usual 1.5, some devices don't work well with them.
----------------------------- Steve Baker -------------------------------
Mail : <sjbaker1@airmail.net> WorkMail: <sjbaker@link.com>
URLs : http://www.sjbaker.org
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