Subject:
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Re: mindstorms NXT
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 8 Jan 2006 01:15:26 GMT
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Viewed:
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7656 times
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In lugnet.robotics, Ross Crawford wrote:
> In lugnet.robotics, Yann Vernier wrote:
> > In lugnet.robotics, Matthew Ruschmann wrote:
> > > Actually, the RCX outputs 0's and 1's to power the motors as it is right now.
> > > So all all you have to do is crimp your lego wires into a RJ11 and connect it to
> > > the NXT and send it a digital PWM signal. Voila! Your old motor works again.
> >
> > I doubt that will do what you want. The RCX motor ports are equipped with motor
> > drivers - ICs that can provide rather a lot of current, switch direction, and
> > even short circuit the port. The digital wires would be I/O, not meant for
> > noticeable current, and only 1 or 0. So you'd wind up with an NXT shutting
> > itself off as the signal lines draw too much current.
> > No, what will be needed in the adapter will be such a motor driver, speaking the
> > appropriate serial protocol. Probably that means the device will contain a PIC
> > or PLC along with one or more motor drivers, and will be inefficient to build
> > for less than two motors per port. Personally I'm hoping for such a device with
> > separate power input.
>
> I see no other wires into the motors, which means all the current is coming from
> that one connection. Whether or not there is separate supply and control lines
> in that connector is debatable until we get our hands on one - I would prefer
> not, because that may make it harder to use the motor for non-NXT applications.
>
> ROSCO
From the LEGO NXT FAQ...
"An electric motor whose speed or position is controlled by a closed loop
feedback circuit that can sense its position. The speed of the motor is measured
by a tachometer. The tachometer produces a voltage that is proportional to the
speed. This voltage is compared to a reference point and the difference, or
error, is used to adjust the speed of the motor, either up or down."
http://www.lego.com/eng/service/faqs.asp?section=ConsumerService-FAQ-Products&catid=E8D0CD47-16B8-4B2F-900C-8FC40C163598&faqid=17251#17251
So the motors operate in a variable voltage/current mode, where a target RPM in
the objective. Two wires for the tach (as a sensor), two for the motor current,
two for something else.
Ray
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Message is in Reply To:
 | | Re: mindstorms NXT
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| (...) I see no other wires into the motors, which means all the current is coming from that one connection. Whether or not there is separate supply and control lines in that connector is debatable until we get our hands on one - I would prefer not, (...) (18 years ago, 6-Jan-06, to lugnet.robotics)
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