Subject:
|
Re: 9v Gear Motors
|
Newsgroups:
|
lugnet.robotics
|
Date:
|
Fri, 9 Jun 2000 18:20:10 GMT
|
Viewed:
|
705 times
|
| |
|
|
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
|
|
Message has 2 Replies:
 | | Re: 9v Gear Motors
|
| =>From: "Jerry Kalpin" <jdkalpin@sympatico.ca> =>... =>if there are three states: on, off and float, there must =>be more than 2 terminals in use. No, with two terminals (A & B), you can get: * A positive with respect to B => motor runs in one (...) (24 years ago, 9-Jun-00, to lugnet.robotics)
| | | Re: 9v Gear Motors
|
| 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 (...) (24 years ago, 9-Jun-00, to lugnet.robotics)
|
Message is in Reply To:
| | Re: 9v Gear Motors
|
| 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 (...) (24 years ago, 8-Jun-00, to lugnet.robotics)
|
9 Messages in This Thread:
  
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
Active threads in Robotics
|
|
|
|
|
|
