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Linear Pot to control a servo how to adjust the travel of the dial from left to right

e14 Contributor

Hello....

My supplies:

Arduino UNO

TowerPro Servo

Linear Pot. (radio shack 271-1715 ( http://www.radioshack.com/product/index.jsp?productId=2062354#inTheBox ))

Sketch being used: Arduino / File / Example / Servos / Knob

*******************************************

Ok hope the supplies help you, help me image

 

Everything works wonderful using this example, but my question is:

The lineear pot turns from left to right about, maybe 350°, in laymen terms picture a clock 7 being the start, 5 being the stop.

The servo will turn, when the pot is turned, but it seems as though the servo does NOT star moving until (using the example above until 11, and completes its travels upto 1) sorry for using this as an example, but its the best way to paint the picture.

So can someone tell me what I need to do in order to get the servo to start turning say around 8 and stop right around say 4?

here is the code if you are unfamiliar with it:

// Controlling a servo position using a potentiometer (variable resistor)
// by Michal Rinott <http://people.interaction-ivrea.it/m.rinott>

#include <Servo.h>

Servo myservo;  // create servo object to control a servo

int potpin = 0;  // analog pin used to connect the potentiometer
int val;    // variable to read the value from the analog pin

void setup()
{
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop()
{
  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 0, 179);     // scale it to use it with the servo (value between 0 and 180)
  myservo.write(val);                  // sets the servo position according to the scaled value
  delay(15);                           // waits for the servo to get there
}

 

Thanks for your help...

Tony

Parents
  • 0

    I discovered what I consider a valuable piece of data at http://arduino.cc/en/Reference/ServoWriteMicroseconds.  It notes that some servo manufactures do not follow standards very closely so that servos often respond to values between 700 and 2300 instead of the standard 1000 to 2000.

     

    What does this mean?  Well, 1500 may be the center point for both types of servo; but, Sevro.h is only going to be sending out PWM that corresponds to 1000 to 2000.  Doing the math quickly in my head tells me that your non-standard standard servo will only travel 62.5 percent of its capacity.  Therefore you loose 37.5 percent of its capacity. 

     

    Yes, I realize that the way you have described it the servo is apparently set up to do 0 to 3000.  Maybe it is.  I really don't know.

     

    And that, my friend, explains the particular difficulty you are having with your servos.

Reply
  • 0

    I discovered what I consider a valuable piece of data at http://arduino.cc/en/Reference/ServoWriteMicroseconds.  It notes that some servo manufactures do not follow standards very closely so that servos often respond to values between 700 and 2300 instead of the standard 1000 to 2000.

     

    What does this mean?  Well, 1500 may be the center point for both types of servo; but, Sevro.h is only going to be sending out PWM that corresponds to 1000 to 2000.  Doing the math quickly in my head tells me that your non-standard standard servo will only travel 62.5 percent of its capacity.  Therefore you loose 37.5 percent of its capacity. 

     

    Yes, I realize that the way you have described it the servo is apparently set up to do 0 to 3000.  Maybe it is.  I really don't know.

     

    And that, my friend, explains the particular difficulty you are having with your servos.

Children
  • 0 in reply to billabott

    Funny while looking at the other servo issue, I had the same idea....

     

    You can specify the max and min pwm values, and this may be a way of overcoming the problem.

     

    You'll need to either find someones elses code that dealt with them, or experiment yourself, by plugging the value into the sketch, and observicng when it stops moving.

     

    I'd start at the nominal centre of 1500 and slowly step it back until it no longer moves.

    Then repeat the other way.

     

    This should give you a range the servo works over.

     

     

    Mark