Need help with servo calibration

Update:

I'm making some progress on my own.  I found the Adafruit PDF file for the PCA9685 and it has some explanations for how to calibrate servos by trial and error method of just trying min and max values for the pulse width.    So I'll write up a small calibration program where I can just enter in pulse width values directly on the serial monitor until I find values that put the servos in the correct positions.   Then I'll have the numbers I'm looking for. ? 

In the meantime I'm going to bed at 3:00 AM.   This is too late for a 70 year old robotics nerd to be staying up trying to calibrate servo motors.  .

Yes, I think calibration that is the correct approach. Servos in the price range we use tend to need tweaking. Then you can add fudge factors to your code to compensate for irregularities in your hardware.

Not unlike a Harbor Freight tool... If you know what you are getting and willing the work around the quirks you can get some bargains.

I just posted this in my main Me Arm thread.  But since I also started this thread asking about how to calibrate these servos I figured I better post what I've done here too.   I think this will solve my problem.

Progress Report:

I wrote up a small program to find all my limiting pulse width numbers. The program is extremely crude, but I'll post it anyway just in case someone might find it useful in some way. It allows the control of 4 servos individually based on changing the pulse width in steps of 10 increments or decrements at a time. That was enough for me to find the limits of my Me Arm.

Unfortunately because of the mechanical design of the Me Arm things are not as simple as they could be. This has to do with the way the upper and lower arms of the Me Arm interact with each other. How they behave can depend on what position the other half of the arm is already in. So when programming the Me Arm we need to take into consideration what the optimal positions are for the upper and lower parts of the arm. The claw and the base rotation are independent and so they will be easier to deal with.

First the Results: (note that these results may be unique to my Me Arm)

For the Base servo I got the following:

The numbers are pulse widths to be used in the Adafruit command.

Base:
Left maximum travel = 140
Right maximum travel = 450
Centering the arm = 290

Upper Arm:
Fully Retracted = 230
Fully extended = 470
Midpoint = 350 * can depend on the position of the lower arm

Lower Arm:
Maxium up = 460
Maxium down = 190
Midpoint = 290 * can depend on the position of the upper arm.

Claw:
Fully open = 140
Fully closed = 220

So as you can see each servo will need to have its own mapping in the Arduino program.

Hopefully this will all work out and we can move forward with trying to program the arm to do some interesting tasks.

Here's the code I used to discover the pulse width limits of the Me Arm. It's a crude program that could use so prettying up. I just wanted to get these numbers and move forward.

/* Me_Arm_Servo_Calibration_V1
 * by Robo Pi
 */

#include  // Include Wire Library for I2C Communications
#include  // Include Adafruit PWM Library for using the PAC9685 board
#define FREQUENCY             50 // Variables for the PCA9685 board

// The PCA9685 board I2C address is 0x40
Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(0x40); 

String str_input = ""; // Used for Serial input from monitor
int int_Char; // Used for Serial input
int base_angle; //  Base angle
int u_arm_angle; //  Upper arm angle 
int l_arm_angle; // Lower arm angle
int claw_angle; // Claw angle

// Servo PCA9685 board pins
int servo_pin;
int base = 0; 
int u_arm = 1; 
int l_arm = 2; 
int claw = 3;

void setup() 
{ 
  Serial.begin(9600); // Use Serial monitor 
  pwm.begin(); // start Adafruit object
  pwm.setPWMFreq(FREQUENCY); // set frequency
} 
 
void loop() 
{ 
  Serial.println("Enter 0, 1, 2, or 3 for Base, U_arm, L_arm or Claw"); 
  while (Serial.available() == 0){} // wait for input
  str_input = Serial.readString(); 
    //  Add input rrror checking routine here ~~~ To be done later ~~~
  servo_pin = str_input.toInt();
  move_Arm(servo_pin);       
}

void move_Arm(int motorOut)
{
  int pulse_width = 300;
  while(true)
  {
      Serial.println("Enter 1 or 2 to inc or dec angle, or 3 to end");
      while (Serial.available() == 0){} // wait for input
      str_input = Serial.readString();
      int_Char = str_input.substring(0,1).toInt();
      //Serial.println(int_Char,DEC); 

    switch (int_Char)
    {
      case 1: 
        pulse_width = pulse_width - 10;
        Serial.print("Pulse Width = ");
        Serial.println(pulse_width,DEC);
        pwm.setPWM(motorOut, 0, pulse_width);
        break;
      case 2: 
        pulse_width = pulse_width + 10;
        Serial.print("Pulse Width = ");
        Serial.println(pulse_width,DEC);
        pwm.setPWM(motorOut, 0, pulse_width);
        break;
      case 3: 
        return;    
      }
    }
  }