Subject:
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Re: RCX Output
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 15 Dec 1999 18:48:56 GMT
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Original-From:
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Joel Shafer <joel@connect.ANTISPAMnet>
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Viewed:
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411 times
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So if you need a 1, 1.5 & 2ms pulse for controlling a servo and you said
the low setting in NQC = a 1ms pulse, are there other matching motor speed
settings to get a 1.5 or 2ms pulse?
At 05:14 PM 12/15/99 +0000, you wrote:
> Hi F'Amos,
> I just now put a scope on the motor output ran an NQC motor test
> program. At OUT_FULL the motor output is about +7V DC. At OUT_LOW
> the motor output is a pulse train of 1ms 7V pulses at about 125Hz.
> The low level depends on the motor load ... almost 7V with no motor
> connected and approaching 0V with a stalled motor. NQC provides
> seven motor speeds ... and by increasing the duty cycle of the pulse
> train the average DC level to the motor is changed.
>
> RC servos are also controlled by varying the pulse width. For most
> servos a 1.5ms pulse tells the servo to go to the center position.
> Increasing the PW toward 2.0ms turns the servo CW and decreasing
> toward 1.0ms turns the servo CCW. The exact pulse width determines
> the exact stopping position. Servos that are modified for use as
> motors can never find a null position so they continue to turn
> seeking the nonexistent null. Unless the PW sent to the servo is
> very close to the null PW, the servo will turn at full speed. If
> the null PW is 1500us, then a 1550us PW will result in a slower
> speed.
>
> Hope this helps,
> - Nick -
>
> "Avery, Amos E." wrote:
> >
> > --- Nick Taylor <ntaylor@iname.com> wrote:
> > > If I'n not mistaken, the RCX output is pulse width
> > > modulated to control motor speed, while the train controller
> > > varies the DC voltage.
> >
> > Can anyone confirm the output characteristics of the RCX?
> > It is my understanding that PWM is used to control RC servos
> > and not to power them. Has anyone put a scope on the RCX's
> > outputs to see what they look like? If the info is available,
> > I'd be interested to know the exact output specs (eg. 0-9v 200ma).
> > F'amos
Joel Shafer joel@connect.net
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Message has 2 Replies:
 | | Re: RCX Output
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| Hello Joel, Attempting to drive an RC servo directly from the RCX is NOT a good idea! The servo is a three wire device; +4.8V to +6.0V for power (usually the red wire), an approximately 40Hz pulse train of 1.0 to 2.0ms pulses at 0V and +5V logic (...) (25 years ago, 15-Dec-99, to lugnet.robotics)
| | | Re: RCX Output
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| (...) The pulses are 1ms, 2ms, 3ms....7ms, 8ms. The 8ms case is sort of a degenerate case since the period itself is 8ms, so an 8ms pulse winds up being continuous power. Dave Baum (25 years ago, 16-Dec-99, to lugnet.robotics)
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Message is in Reply To:
| | RCX Output
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| (...) Can anyone confirm the output characteristics of the RCX? It is my understanding that PWM is used to control RC servos and not to power them. Has anyone put a scope on the RCX's outputs to see what they look like? If the info is available, I'd (...) (25 years ago, 15-Dec-99, to lugnet.robotics)
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