Subject:
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Re: r/c servos
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 20 Aug 1999 15:20:38 GMT
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Original-From:
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Greg Mrozek <Greg.T.Mrozek-1@tc.umn.edu/spamless/>
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Viewed:
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676 times
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I love the idea of controlling an R/C servo with the RCX, but I don't think it
is possible with only software. On the other hand, a relatively simple
circuit could be made to convert a duty cycle to a R/C servo signal. Is
anyone out there interested in something like this? If there is enough
interest I will take the time to draw up a circuit and post it somewhere. Let
me know.
A few comments on the questions asked.
> Since RC servos use pulse width as the input, there is already potential
> here. Does any one, with a deeper knowledge of the insides of the RCX code
> know if the squarewave duty cycle is being controlled by software or a
> hardware based PWM?
I am almost positive that the PWM is done in hardware. There are three output
driver chips, seperate from the microcontroller. The microcontroller sends
duty cycle commands to these chips, but I believe the PWM frequency is fixed
by an RC network extenal to the driver chip.
> In response to the question about RC servos, I noted, while probing
> the signals on the I/O ports with a scope, that the motor power settings
> result in varying duty cycle square waves from 1:7 through 7:1 and finally
> full on as the parameter value sweeps 0 -7.
I believe these output controllers are also capable of much more than 3 bits
of resolution. I just got my RIS and have not done much programming yet, but
I have been doing lots of research. If you look at the documentation for
LegOS (an alternate firmware for the RCX, found at http://www.noga.de/legOS/),
the motor speed can be set from 0 to 255. That's 8 bits! Does anyone else
have more experience with LegOS?
Zeke
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message is in Reply To:
 | | r/c servos
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| In response to the question about RC servos, I noted, while probing the signals on the I/O ports with a scope, that the motor power settings result in varying duty cycle square waves from 1:7 through 7:1 and finally full on as the parameter value (...) (25 years ago, 20-Aug-99, to lugnet.robotics)
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