required pulse widths for servo motors

Lucifre · Mar 24, 2006

Hi, i need info on servo motors. To be precise i need to know how wide should i make the width of the pulse to make a servo motor turn to certain angle. I know it may vary from motor to motor, but most data sheets give you only neutral position what about other angles?. I do not need a controller because i am trying to build one my self. if any one could tell me how do i find out that info?

IanP · Mar 24, 2006

To control the servo, you command it to a certain angle, measured from 0 degrees. You send it a series of pulses. The ON time of the pulse indicates the angle to turn to; 1ms = 0 degrees, 2ms=max degrees(about 120) and anything in between gives a proportional output angle. 1.5ms is generally considered to be the "center". The 1~2ms limit is manufacturers' recommendations; you can usually use a wider range around 1.5ms for grater throw.
...
*Suppose I want to move the servo 30 degrees?
To command it to 30 degrees; you calculate the pulse length: 0 degree=1ms, 120 degree=2ms => 30 degree=1.16ms. Linear relationship. So if you keep sending it 1.16ms pulses, it will go and hold its position at 30 degrees. If there is an external force that tries to move it away, the servo will actively try to resist it (that is, if the arm is moved externally, the servo will give motor inputs to correct the error).

Quote from:
http://www.geocities.com/BourbonStreet/3220/servobasics.html

Regards,
IanP

Lucifre · Mar 24, 2006

so if i keep sending the pulses of the same width to the servo the servo will go to desired angle and be still? What do i do to make it rotate? do i send pulses of varying width? I also think there is an error in the calculation of the width for 30°, if this is linear relationship, than 30° would require .5 ms pulse. is there a way to modify a servo or any other motor that would behave as following...
motor receives a pulse of say .7 ms and it rotates its shaft to some angle, when it receives the same pulse again it rotates again with the same angle... so in other words it is rotating, but the rotational speed would be dictated by the angle, and angle would be controled by width of the pulse. i know i can power plain dc motor like that, but than it would be powered by 5V pulses, how about if i want to control a motor that requires 120V, with 5 V pulse without amplifing

IanP · Mar 25, 2006

If we are talking about these small servos used in radio controlled models (see picture below) then 1ms pulse will activate servo but will not cause any movement, and 2ms pulse will move the shaft to its other position ..
Without pulses or with pulses below 1ms servo doesn't work correctly ..
So, for, for exampe, 30° you need 1.16ms pulse (as was explained in the previous post) ..
Here is another brief on RC servo controlling:
https://www.epanorama.net/documents/motor/rcservos.html

The 120V servo that you mentioned in your post, what type of servo is it: AC servo? If yes, than all what has been said so far is almost irrelevant .. here are examples of AC servo amplifiers:
https://zone.ni.com/devzone/conceptd.nsf/webmain/8231FE168CB7B5B3862568460074FB8D

Regards,
IanP

Lucifre · Mar 27, 2006

more i do research on this more frustrated i get... I asked one of the proffesors at my school and he said that servos do rotate and that the width of the pulse indeed controls the angle, and therefore varying the widths of the series of pulses controll the speed (rpms). I guess there is a way to configure them thay way. i don't know if they are ac or dc, all i care about is how wide or how long should i make the width of the pulse to control their speed or angle. Now 0° is 1ms, 120° is 2 ms how about 180°? Do i interpolate? and also is that in general for all servos or just one in thousands of them? I really need to know this so if anyone could clearly describe it for me i can donate som points.
Thank you.

required pulse widths for servo motors

Lucifre

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IanP

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Lucifre

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required pulse widths for servo motors

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