Subject:
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Re: Varying the output voltage?
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Newsgroups:
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lugnet.robotics.rcx.legos
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Date:
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Sat, 14 Jun 2003 02:35:00 GMT
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Viewed:
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2906 times
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In lugnet.robotics.rcx.legos, Aaron Goodman wrote:
> I was wondering if it was possible to control the speed/torque of the motor
> by varying the output voltage in brickOS. It seems that the speed parameter
> on the motors only changes the rate at which they pulse on and off. I am
> looking for something similar to how the standard firmware controls it with
> eight different power levels.
>
> Thanks,
> Aaron
The eight different power level pulsing is called "PWM", translation=Pulse width
modulation.
PWM is the way a digital chip cheats/mimics true analog without a D/A convertor.
Since the only output of a digital chip is on or off, there is no in-between
like analog.
The way the chip cheats is it turn the output on and off very quickly creating a
"flashing" signal. If you turn a light on, there is a delay in the amount of
time it takes for it to reach full brightness, and the same is for turning it
off. This combined with "persistence of vision" are used in PWM. As an effect of
the pulsing, the light level seems to hover at a light level that is not quite
on, and not quite off. The overall output is a semi lit light. It was learned
that by changing the width of the "off" period, a variable output of brightness
was attained. The same is also used with electric motors, where varying the
"off" period changes the overall strength and speed.
The overall answer is, the RCX is set up only to have three voltage levels: +9,
0, and -9. The basic options there are On, Off, and Reverse. Now by
electronically varying the Pulse Width you get 8/7 (not sure) levels of power in
each direction instead of the original 3, that is all you get.
The only option I can suggest is a RCX user who further modulated the levels of
the Pulses with the program he loaded. He did this to attain additional agility
of his robot. The name of it is: Legway
http://www.geocities.com/stevehassenplug/LegWay.html
I hope this helps!
A fellow member,
Timothy
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Message has 1 Reply:
 | | Re: Varying the output voltage?
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| (...) Actually there are four, sort of, as for 0 there are float (contacts separated, infinite resistance) and brake (contacts shorted, zero resistance). The standard firmware switches rapidly between on and float (each cycle takes 8ms), which (...) (21 years ago, 14-Jun-03, to lugnet.robotics.rcx.legos)
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Message is in Reply To:
| | Varying the output voltage?
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| I was wondering if it was possible to control the speed/torque of the motor by varying the output voltage in brickOS. It seems that the speed parameter on the motors only changes the rate at which they pulse on and off. I am looking for something (...) (21 years ago, 14-Jun-03, to lugnet.robotics.rcx.legos)
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