Servo callibration?

pdmart

I have around 40 BoEs and Javelin Stamps, and about 10 of the robots are experiencing difficulties when trying to run the servos. The servos are calibrated when sending a pulseOut of 173, and they seem to be calibrated but on reset they become uncalibrated. In fact, on sequential resets the servos go one way and then the other way without changing any code. Any ideas? These robots are working fine with the BASIC stamp.

Thanks in advance.

Beau Schwabe

pdmart,

Can you send an example of the code that you are using?

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

pdmart

I'm writing this by hand from another computer rather than copying and pasting, so if there are any syntax errors
please ignore them.

import stamp.core.*;
public class ServoTest{
     public static void main(){

          // forward
          for(int i = 0; i < 1000; i++){
               CPU.pulseOut(220, CPU.pin13);
               CPU.pulseOut(130, CPU.pin12);
          }
          CPU.pulseOut(173, CPU.pin13);
          CPU.pulseOut(173, CPU.pin12);

          // still
          for(int i = 0; i < 1000; i++){
               CPU.pulseOut(173, CPU.pin13);
               CPU.pulseOut(173, CPU.pin12);
          }
          CPU.pulseOut(173, CPU.pin13);
          CPU.pulseOut(173, CPU.pin12);

          // backwards
          for(int i = 0; i < 1000; i++){
               CPU.pulseOut(130, CPU.pin13);
               CPU.pulseOut(220, CPU.pin12);
          }
          CPU.pulseOut(173, CPU.pin13);
          CPU.pulseOut(173, CPU.pin12);

          // calibrate
          for(int i = 0; i < 10000; i++){
               CPU.pulseOut(173, CPU.pin13);
               CPU.pulseOut(173, CPU.pin12);
          }
          CPU.pulseOut(173, CPU.pin13);
          CPU.pulseOut(173, CPU.pin12);
     }
}

Beau Schwabe

pdmart,

In addition to an "ON" time pulse ranging from 1ms to 2ms, you also need to have an "OFF" time of 15ms to 25ms (Typically 20ms). You may be setting the "OFF" time somewhere else in your code, but I don't see it in the code you have provided. The "ON" time looks ok to me.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Peter Verkaik

Normally servos are controlled by using the PWM VP.
Value 115 represents 1 msec
Value 173 represents 1.5 msec
Value 230 represents 2 msec
Value 2304 represents 20 msec

PWM servo = new PWM(CPU.pin0,173,2304)
servo.update(115,2304) 'full left
servo.update(173,2304) 'center
servo.update(230,2304) 'full right

Using pulseOut() is too awkward as pulses must be generated every 20 msec.
The PWM VP does that·for·you in the background.

regards·peter

pdmart

Thanks for the quick responses. I'll try this out.