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From: WELLS <WELLS@CTSD2.JSC.NASA.GOV>
Subject: Re: How to control hobby servo with computer ????
Message-ID: <1993Feb16.193450.12049@aio.jsc.nasa.gov>
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Date: Tue, 16 Feb 1993 19:34:50 GMT
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In article <TPgTyB2w165w@sys6626.bison.mb.ca> baden de bari, 
baden@sys6626.bison.mb.ca writes:
>                Remember, all you really need to control servos is a 
>control pulse width between 580 and 3000 micro-seconds, oh yeah, and a 
>clean pulse would help as well.

Just thought I'd post some related info.
We measured the pulse character sent from the receiver of a Futaba 
PCM1024A R/C system to its servos (over the white signal wires). This is 
a pulse code modulated system so the pulses are very clean and 
consistent as they are generated in the receiver from code received 
instead of in the transmitter. The update rate is about once every 14280 
sec. Eight of the nine channels are started in pairs, with pulse starts 
at 2360 sec intervals. Under power of a four cell ni-cad pack, "On" 
state pulse voltage is typically 2.96v open circuit, 2.7v while driving 
a servo and about 2.6v if driving an HP6N139 optocoupler with just 
enough current to saturate.

Individual pulse characteristics:

Pulse width (Usec)			Condition
2120				+110% stick, +110% trim
2070				+100% stick, +100% trim
1980				+110% stick, 0% trim
1940				+100% stick, 0% trim
1680				0% stick, +100% trim
1520				0% stick, 0% trim
1380				0% stick, -100% trim
1115				-100% stick, 0% trim
1075				-110% stick, 0% trim
980				-100% stick, -100% trim
925				-110% stick, -110% trim

Note that different systems may vary and that servo travel is not used 
up at the max and min pulse widths.here. This allows for manufactuing 
slop in the servos and the PWM type transmitters. Longer and shorter 
pulses will allow increased travel; You just have to avoid motor stall 
at the ends of travel.
