standard Parallax servo

Tom N.

Hi everyone,

I'm fairly new here and from what I understand so far about the Parallax (unmodified) servo motor is that it should only receive a pulse signal between 1 ms and 2 ms.

Well, when I send a 1.5 ms signal to the servo, it doesn't stop at it's center position. It's actually far from it. The same happens when i send a 1 ms signal. The servo doesn't rotate clockwise all the way.

So my question is, is this ok? or do I have to calibrate it in order to function like it's described in the text.

Chris Savage

Tom,

1ms to 2ms is the 'standard' however many servos travel well outside that range. Sending a 1.5ms pulse should put it at roughly center either way if you send the pulse every 20ms. Sending a single pulse won't do much of anything. Also, which model BASIC Stamp are you using? Some have different values for the PULSOUT command. Take care.

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Chris Savage
Parallax Tech Support

D Faust

Usually you have to loop the position more than once to get it there. In another thread it was calculated to be about 38 loops of

pulsout 1, 750
pause 20

until the servo actually reaches the desired postion.

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Tom N.

I have the HomeWork Board and the servo that came with it. I also loop the signal pulses no less than 75 times.

Mike Green

Make sure you have an adequate power supply. Servos can draw a lot of current and that can use up a 9V battery pretty quickly.

Servos are not precise devices. If you need an exact center position, you will have to calibrate them. Usually this is done by having a program that puts out a 1.5ms pulse and mechanically adjusting what's attached to the servo so it's centered. Alternatively, you can have a program that lets you vary the pulse width around 1.5ms, perhaps using a pair of pushbuttons to let you step the pulse width up and down until the servo is positioned the way you need it and you'd use the debug window in the Stamp Editor to show you the current PULSOUT value.

Tom N.

Thanks Mike. I appreciate the help.