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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Fri, 6 Jan 2006 20:44:53 GMT
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Viewed:
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7754 times
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In lugnet.robotics, Matthew Ruschmann wrote:
> Actually, the RCX outputs 0's and 1's to power the motors as it is right now.
> It uses Pulse Width Modulation (PWM). Basically for 1/3 power 1/3 of the pulse
> is 1 and the other 2/3 is 0. For full power, the signal is all 1. This creates
> a non-linear input/output curve, but works.
>
> http://www.restena.lu/convict/Jeunes/ultimate_stuff/speed.htm
>
> 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.
>
> Of course, someone will have to build a block in "LabVIEW" to send the PWM
> signal to the motor. Easy as pie if the software allows this.
I think that saying the RCX outputs 0's and 1's to the motor may be a bit
misleading with respect to considerations of digital signalling.
It is true that the CPU inside the RCX creates a logic level (1's and 0's) PWM
signal intended for the motors. But there is a key element between the RCX's CPU
and the motor outputs - an H bridge chip. This converts the switching logic
levels to switching power outputs. These switching power outputs are what makes
the motor go. Regular logic outputs are typically limited to a few tens of
milliamps at most, so a "digital" (ie; logic level) output would not be adequate
to drive the motor. But the H bridge outputs can handle upto about 800mA at
above logic level voltages, 9v for the RCX which is perfect for small DC motors.
JB
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Message is in Reply To:
 | | Re: mindstorms NXT
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| (...) Actually, the RCX outputs 0's and 1's to power the motors as it is right now. It uses Pulse Width Modulation (PWM). Basically for 1/3 power 1/3 of the pulse is 1 and the other 2/3 is 0. For full power, the signal is all 1. This creates a (...) (19 years ago, 5-Jan-06, to lugnet.robotics)
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