obtaining different voltage output in l293d while giving same pwm signal to ic

Hi everyone
I am making a line follower but having a issue while providing same pwm to both l293d ic the output of ic is different for both the motors and bot move in a direction en1 and en2 are provided with same pwm signal. The voltage is different when measure between (out1 , out2) and (out3 , out4) and it also changes when measure next time my multimeter is all good and the connection is solid

#define left_1 9
#define left_2 8
#define left_pwm 10
#define right_1 13
#define right_2 12
#define right_pwm 11
int left__pwm = 128, right__pwm = 128;
char rd;
void setup() {
  // put your setup code here, to run once:
  pinMode(left_1, OUTPUT);
  pinMode(left_2, OUTPUT);
  pinMode(left_pwm, OUTPUT);
  pinMode(right_1, OUTPUT);
  pinMode(right_2, OUTPUT);
  pinMode(right_pwm, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(left_1, HIGH);
  digitalWrite(left_2, LOW);
  analogWrite(left_pwm, left__pwm);

  digitalWrite(right_1, HIGH);
  digitalWrite(right_2, LOW);
  analogWrite(right_pwm, right__pwm);

  Serial.print("left_pwm=");
  Serial.print(left__pwm);
  Serial.print("\t");
  Serial.print("right_pwm=");
  Serial.print(right__pwm);
  Serial.print("\t");
  Serial.print("\n");

}

Hi,

Usually there are differences in the motors and the driver ship so that a robot will not go straight with the same PWM to both motors. You need to add to your code separate adjustments for each motor.

Here is an example of doing that for a simple robot:

https://arduinoinfo.mywikis.net/wiki/RobotKitMenu-6

Find the section "TEST AND ADJUST MOTOR SPEEDS:".