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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Fri, 9 Jun 2000 21:04:48 GMT
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Viewed:
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2216 times
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Ah, that's why it changes the speed. The motors have a flywheel so pulses of
on/float with no motor load will not appreciably change the motor speed. The
inertia of the flywheel keeps the motor running during the float times.
However, pulses of on/off will actually apply a braking force during the off
times and thus the motor will slow down.
Neat!
If you want to see what they look like inside, try this...
http://www.pressroom.com/~wesm/mStorms/Motor/Motor.html
Conrad.
In lugnet.robotics, Jerry Kalpin writes:
> 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
> difference from a setting of 7.
>
> The program in the NQC Tutorial actually switches on and off (not float)many
> times a second. It's neat to watch: has high-speed clicking and is
> definitely slow at no load.
>
> After re-reading the code I think that's all it does. It does an OnFwd for 1
> tick and an Off for 1 tick. It would be great for rotating a scanning sensor
> slowly or erecting a crane arm slowly.
>
> Anyway, thanks for the response. I would still like to know what those little
> motors look like inside and how they're wired!
>
> Jerry
>
>
> In lugnet.robotics, Conrad Venn writes:
> > 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 is in Reply To:
 | | 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 (...) (26 years ago, 9-Jun-00, to lugnet.robotics)
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