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From: nahshon@vnet.ibm.com (Itai Nahshon)
Subject: Re: RC Servo Characteristics?
Sender: news@austin.ibm.com (News id)
Message-ID: <NAHSHON.95Apr28142708@rs3bt-01.haifa.ibm.com>
In-Reply-To: nagle@netcom.com's message of Wed, 26 Apr 1995 00:40:33 GMT
Date: Fri, 28 Apr 1995 11:27:08 GMT
References: <v01510100abc32cfe0b8f@[158.152.22.215]> <nagleD7M9vM.4zC@netcom.com>
Organization: IBM Israel Science and Technology, Haifa, Israel
Lines: 37

In article <nagleD7M9vM.4zC@netcom.com> nagle@netcom.com (John Nagle) writes:

>francis@pinza.demon.co.uk (Francis Knight) writes:
>>I'm considering a project using RC servos as cheap off-the-shelf
>>actuators.
>>I'm wondering if there's an 'industry standard' as far as response to
>>PWM signals goes. That is, will a similar duty-cycle control signal
>>produce the same response from any servo? What are typical duty cycles
>>for 'full left' and 'full right' responses?

>    Once again...

	   RC servos have three wires, which are power, ground, and control.
>The control signal is a CMOS signal (0 to +5 works fine) with a period
>of about 13ms and an ON time of about 0.5 to 1.5ms.  The ON time controls the
>servo position.  OFF time isn't critical.
>
>					   John Nagle
The pulse width should be 1 to 2 milliseconds and the period anything between
14 to 20 millisecond. The position is determined by the pulse width and not
by the period between pulses.

Different servos are different in their characteristics. "Standard" servos 
will turn 90 to 120 degrees over full pulse width range. Retract servos usually
turn 180 degrees and have a "step" or hysteresis rather than linear response
DIfferent types may be different in the direction of rotation.

You can expect difference in response time, speed, torque, accuracy, rigidity,
dimensions and weight and off course, price. I'd say there's no industry
standard. Just chose the servo which is best matched to your application
(and to your budget).

Servos from different manufacturers (Airtronics, Futaba, JR, Tower, RCD and more)
may have different connectors but they are electrically compatible.

Itai Nahshon
Haifa, Israel
