Subject:
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RE: Batteries?
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 17 Dec 1998 03:32:11 GMT
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Original-From:
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Tilman Sporkert <[tilman@nscale.activesw.com]NoSpam[]>
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Viewed:
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1512 times
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> On Wed, 16 Dec 1998 RSKSMBMS@aol.com wrote:
>
> > Hello All, Is there a rechargable batteries that anyone can suggest to
> > use with the RCX? How long does a group of batteries usually last? What
> > happens to the programs stored in the RCX when the batteries rundown?
Sorry, I have no experience with rechargables in the RCX.
> The RCX uses a six-pack of AA batteries. Its voltage range is 9-12 volts,
"9-12 volts" applies to the external power jack, and is for AC. That is not
the same as the battery voltage.
> which puts the onboard power with alkies at the lower end. A six-pack of
> nicads or nimhs puts out about 7.2 volts, possibly enough to work but
> definitely below range.
No, it's not below range at all. The Mindstorms manual clearly states that
rechargable batteries may be used, but with reduced power output.
The processor in the RCX requires 5V to operate. As long as the battery
voltage is high enough to operate the 5V voltage regulation circuit, it will
work just fine.
The voltage to the motors is probably not regulated. Which means that if you
switch from Alkaline batteries to rechargables (lower voltage, see above),
the voltage for the motors will be lower as well. Hence, "reduced power
output". In other words, your robot will be slower.
> Something that might make a difference: nicads can dump a lot faster than
> alkies. This means, for a direct-to-motor application, that a stalled
> motor (which is shorted out) is a Bad Thing for the pack and motor both.
> I don't know how the RCX does speed control;
The RCX does simple PWM (pulse width modulation).
> would someone wiser than I say if this is an issue?
It shouldn't be an issue for three reasons. First, the manual says you can
use rechargable batteries. Second, a stalled motor is not shorted out. It
just draws a lot more current than usual. According to
http://www.enteract.com/~dbaum/lego/motors.html, the geared motors draw only
250mA when stalled. Third, the motor driver chips used in the RCX have a
built-in current limit of 500ma (see
http://www.melexis.com/site/10402/f_10402.htm).
Tilman
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Message has 1 Reply:
 | | Re: Batteries?
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| (...) Cool... that means that unless the train regulator does PWM too, you're bvetter off using an RCX to control your train than the regulator :) Jasper (26 years ago, 21-Dec-98, to lugnet.robotics)
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Message is in Reply To:
| | Re: Batteries?
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| (...) The RCX uses a six-pack of AA batteries. Its voltage range is 9-12 volts, which puts the onboard power with alkies at the lower end. A six-pack of nicads or nimhs puts out about 7.2 volts, possibly enough to work but definitely below range. It (...) (26 years ago, 17-Dec-98, to lugnet.robotics)
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