Subject:
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Re: 9v Gear Motors
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 8 Jun 2000 22:33:18 GMT
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Viewed:
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577 times
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Just went back and re-read the book, and in fact the RCX does do pulse width
modulation and not voltage amplitude to set different power levels.
In which case I'm not sure why effectively doing the same thing in NQC code
works any better, but it does seem to.
Conrad.
In lugnet.robotics, Conrad Venn writes:
> There's nothing specially clever about the 9v geared motors.
>
> There are in fact only 2 terminals. The 4 connectors you see are just LEGO's
> clever way of supplying power to the motor regardless of the orientation of
> the power connector wire.
> So forward is one polarity, reverse is the opposite, off is short-circuit and
> float is open circuit.
>
> I presume that the different power levels that the RCX can set are simply
> different supply voltages (but this is just a guess). However, the actual
> speed depends on the load, so the power levels are not really a very good way
> of driving the motors at varying speeds.
>
> That is why the power pulsing method is used. Driving the motor at full power,
> but in short on/off bursts gives you much better speed control regardless of
> the motor load.
>
> Hope this helps.
>
> Conrad.
>
> In lugnet.robotics, Jerry Kalpin writes:
> > I have been searching lugnet for more info on the standard Lego 9v
> > gearmotors. I know there are 4 terminals. I know there is forward, reverse,
> > off (with braking) and float (without).
> >
> > Mark Overmar's NQC tutorial which is included with Dave Baum's book/CD has a
> > scheme to vary the speed by turning it off and on many times a second. I
> > absolutely do not understand the code, but it works anyway! He says: "It
> > constantly checks the variable speed to see what the current speed is." But
> > is there speed monitoring, or current monitoring, or even something that • would
> > tell the RCX motor direction?
> >
> > If anyone knows how the motor works, or has any good links, let me know.
> >
> > Thanks, Jerry
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Message has 1 Reply:
 | | Re: 9v Gear Motors
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| Conrad, if there are three states: on, off and float, there must be more than 2 terminals in use. Yes, there is PWM. According to the experts that changes the torque more than the speed. Under no load and a setting of (say) 2 you should see little (...) (24 years ago, 9-Jun-00, to lugnet.robotics)
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Message is in Reply To:
| | Re: 9v Gear Motors
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| There's nothing specially clever about the 9v geared motors. There are in fact only 2 terminals. The 4 connectors you see are just LEGO's clever way of supplying power to the motor regardless of the orientation of the power connector wire. So (...) (24 years ago, 8-Jun-00, to lugnet.robotics)
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