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PICList Thread
'RC Servo PWM format'
1997\07\31@013152 by Sean Breheny

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Hello all,

I am trying to find out the specs on the servo control signal for radio
control servos (i.e. futaba servos for RC aircraft). I need to know how long
a pulse is for
neutral position, how long for each extreme of throw, what the pulse
frequency is, and what the voltage is. I am considering making several
PIC-based RC related projects, including a signal loss detector, autopilot,
and maneuver record/playback
device.

Thanks,
Sean

1997\07\31@094040 by Chaipi Wijnbergen

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Hi,

Interesting how is that two request came together for the same thing.

Futaba servos recieve a PWM signal to control the servo position.

Pulse duration is from 1mSec to 2mSec. If the servo goes from 0 degrees to
90 degrees then 1mSec pulse will put it in 0 degrees and 2mSec will put it
in 90 degrees. I use retract servos that goes from 0 degrees to 180
degrees and the same goes there (1mSec to 2mSec pulse). For all middle
positions use a pulse between 1mSec to 2mSec.

This pulse should be sent to the servo motor every 10mSec.

Chaipi

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On Thu, 31 Jul 1997, Sean Breheny wrote:

{Quote hidden}

1997\07\31@101248 by John Shreffler

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part 0 630 bytes


-----Original Message-----
From:   Sean Breheny [SMTP:.....sbrehenyKILLspamspam@spam@CSRLINK.NET]
Sent:   Thursday, July 31, 1997 1:08 AM
To:     PICLISTspamKILLspamMITVMA.MIT.EDU
Subject:        RC Servo PWM format

Hello all,

I am trying to find out the specs on the servo control signal for radio
control servos (i.e. futaba servos for RC aircraft). I need to know how long
a pulse is for
neutral position, how long for each extreme of throw, what the pulse
frequency is, and what the voltage is. I am considering making several
PIC-based RC related projects, including a signal loss detector, autopilot,
and maneuver record/playback
device.

Thanks,
Sean

1997\07\31@115817 by Peter Baines

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> This pulse should be sent to the servo motor every 10mSec.
>


This is actualy 18-20 mSecs.


I have some code that controls 2 servos from an old Sega joypad i can let
you have if you like, it is writen for the 16c84.

Cheers Peter..

1997\07\31@135811 by Andy Kunz

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At 10:03 AM 7/31/97 -0400, you wrote:
>I did some work on RC transmitters and receivers some time back.
>The format was AM, which was modulated by pulses which
>turned the carrier off.  Each frame consisted of 8 pulses, which gave
>7 channels of proportional control.  The space between each pulse
>in the train was 1.00 ms for neutral, .50 ms for one stop, and 1.50 ms
>for the other stop.  The frame rate is not critical, and was about 30
>per second.  The pulse train is clocks a 1 through a parallel out shift
> register,
>which separates the frame into the channels.  After the first pulse, the
>data returns to 0.  The pause between each frame resets the data to 1.
>Each SR output is a single pulse whose width is fed to its servo circuit,
>which positions both the flight surfaces, and a potentiometer so as
>to null out the difference in length between the data pulse and a locally
>generated pulse.  I would suppose that this system is still in use.

The actual measurements should have been 1000uS one end, 2000uS other end,
1500uS center.  The old Futaba G units were offset for a center near 1350uS
rather than 1500.

The frame rate varies from about 40 to 60 Hz, although more and less are
roughly valid.  The _real_ important factor was the synch period, which
needed to be 6mS by design in the early decoder chip NE5045 (encoder
NE5044, servo amp NE544).

Andy

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Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
         Hardware & Software for Industry & R/C Hobbies
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