Servo control is not that simple, there a lot in control theory that you
must deal of.
Closed loop instability is common and you must address it with a more
sophisticated algorithm.
It seems that a PID controller may be better suited for your problem.

Have you tried to add a dead-band to your logic (simply tolerate the 3
degree error. If the position is inside the 3 degree band, then stop
trying to correct it).


Isaac



Em 23/5/2012 00:11, yamanoor sairam escreveu:
> Hello All,
>
> I had written to the list long time back regarding the drive of servo mot=
or using a potentiometer and a PIC12F675. I was successful in doing driving=
 the same. I got back to working on this project and I am happen to face a =
new problem. =20
>
> When there is no load on the motor, it works perfect. When I load the mot=
or, it keeps wobbling. I think the motor is not able to drive the load or t=
here is a small slippage that is causing the problem. All I wanted to do wa=
s that the motor should rotate between 90 and 180 degrees when a switch is =
toggled.
>
> Should I just switch off the motor when it is near the desired position? =
It looks like the motor has reached 3 degrees and trying to correct the ang=
le and slipping off to -3 degrees. It keeps repeating this cycle.
>
>  I am posting a snippet of the code:
>
>  if(GPIO & (1<<3))
>                    {
>                    if(servoVal>=3D(1499))
>                    {
>                     servoVal =3D servoVal-(quotient*10);
>                     }
>                    // do_servo();
>                     }
>                  else         if(!(GPIO & (1<<3)))
>                                 {
>                                 if(servoVal<=3D(2300))
>                                 {
>                                 servoVal =3D servoVal+(quotient*10);
>                                  }
>                                   //do_servo();
>                                 }
>
> Sai
>

--=20
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