continuous rotation of servo problem

Question

I am making a solar tracker using MG995 servo motors. The problem I am facing is that as soon as I run the program the servo starts continuously rotating. Can someone please help me to figure it out?

I am using an Arduino Uno and external power supply for 2 servos.

Below is my code:

#include <Servo.h>
//defining Servos 
 Servo servohori;
int servoh = 0;
int servohLimitHigh = 160;
int servohLimitLow = 20;

Servo servoverti;
int servov = 0;
int servovLimitHigh = 160;
int servovLimitLow = 20;
//Assigning LDRs
int ldrtopl = 2; //top left LDR green
int ldrtopr = 1; //top right LDR yellow
int ldrbotl = 3; // bottom left LDR blue
int ldrbotr = 0; // bottom right LDR orange

void setup ()
{
Serial.begin(9600);
servohori.attach(5);
servohori.write(0);
servoverti.attach(6);
servoverti.write(0);
delay(500);
}

void loop()
{
servoh = servohori.read();
servov = servoverti.read();
//capturing analog values of each LDR
int topl = analogRead(ldrtopl);
int topr = analogRead(ldrtopr);
int botl = analogRead(ldrbotl);
int botr = analogRead(ldrbotr);

// calculating average
int avgtop = (topl + topr) / 2; //average of top LDRs
int avgbot = (botl + botr) / 2; //average of bottom LDRs
int avgleft = (topl + botl) / 2; //average of left LDRs
int avgright = (topr + botr) / 2; //average of right LDRs
Serial.print("avgtop = ");
Serial.print(avgtop);
Serial.print("\n");
Serial.print("avgbot = ");
Serial.print(avgbot);
Serial.print("\n");
Serial.print("avgleft = ");
Serial.print(avgleft);
Serial.print("\n");
Serial.print("avgright = ");
Serial.print(avgright);
Serial.print("\n");
delay(500);

 if (avgtop < avgbot)
{
servoverti.write(servov +1);
if (servov > servovLimitHigh)
 {
  servov = servovLimitHigh;
 }
delay(10);
 }
else if (avgbot < avgtop)
{
servoverti.write(servov -1);
if (servov < servovLimitLow)
{
servov = servovLimitLow;
}
delay(10);
}
else
 {
servoverti.write(servov);
 }

if (avgleft > avgright)
{
servohori.write(servoh +1);
if (servoh > servohLimitHigh)
{
servoh = servohLimitHigh;
}
delay(10);
}
else if (avgright > avgleft)
{
servohori.write(servoh -1);
if (servoh < servohLimitLow)
 {
 servoh = servohLimitLow;
 }
delay(10);
 }
else
{
servohori.write(servoh);
}
delay(50);
}

Answer 1

You simply have the wrong servo for your application. Google MG955 and you will find that some are labelled "continuous rotation" or "360°". It means that you can not set it to a particular angle.

Arduino Servo library tells:

Writes a value to the servo, controlling the shaft accordingly. On a standard servo, this will set the angle of the shaft (in degrees), moving the shaft to that orientation. On a continuous rotation servo, this will set the speed of the servo (with 0 being full-speed in one direction, 180 being full speed in the other, and a value near 90 being no movement).

A standard servo motor uses a potentiometer to acquire the shaft angular position. Then a feedback loop controls the position.

If your servo is new, it must be a simple DC motor with a reduction stage (like here). If it is not new, it also could be a standard servo that has been hacked to break the position control loop (like here).