Arduino Nano Robot with MG90 Servos

[Ricochet76]

I have designed and built a small educational robot using and Arduino Nano and a Nano servo Shield (HiLetgo 5pcs Nano I/O Expansion Sensor Shield). I am using 4 MG90 360degree servos for the wheel motors. Power is supplied to the board via a rechargeable 9v battery pack.

In my code, a speed value of 90 is full stop. I program the servos to drive forward or backward by adding or subtracting a value of +/- 90 (closer to 0 or 180, the faster it turns). However, If I ever go above a total of 130 or below 50 the nano resets. Any ideas?

#include <Servo.h>

Servo FrontLeftServo;
Servo FrontRightServo;
Servo BackLeftServo;
Servo BackRightServo;

const int FrontRightServoPin = 5;
const int FrontLeftServoPin = 4;
const int BackRightServoPin = 7;
const int BackLeftServoPin = 8;

const int echoPin = A1;
const int trigPin = A0;
const int MaximumRange = 30; //Value in centimeters
const int MinimumRange = 0;
long Duration, Distance;

const int BuzzerPin = 2;

void setup() {
  FrontRightServo.attach (FrontRightServoPin);
  FrontRightServo.write(90);

  FrontLeftServo.attach (FrontLeftServoPin);
  FrontLeftServo.write (90);

  BackRightServo.attach (BackRightServoPin);
  BackRightServo.write(90);

  BackLeftServo.attach (BackLeftServoPin);
  BackLeftServo.write (90);

  pinMode (BuzzerPin, OUTPUT);

  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  Wait(); 
}

void loop() {
  // put your main code here, to run repeatedly:
  CheckObstacles();
  if (Distance > 15)
  {
    Forward();
  }

  if (Distance < 14)
  {
    Stop();
    delay(500);
    Backward();
    delay(1000);
    turnRight();
    delay(400);
  }

}

void Stop() {
  FrontLeftServo.write(90);
  FrontRightServo.write(90);
  BackLeftServo.write(90);
  BackRightServo.write(90);
}

void Forward() {
  FrontLeftServo.write(90 + 50);
  FrontRightServo.write(90 - 50);
  BackLeftServo.write(90 + 50);
  BackRightServo.write(90 - 50);
}

void Backward() {
  FrontLeftServo.write(90 - 50);
  FrontRightServo.write(90 + 50);
  BackLeftServo.write(90 - 50);
  BackRightServo.write(90 + 50);
}

void turnRight() {
  FrontLeftServo.write(90 + 50);
  FrontRightServo.write(90 + 50);
  BackLeftServo.write(90 + 50);
  BackRightServo.write(90 + 50);
}

void turnLeft() {
  FrontLeftServo.write(90 - 50);
  FrontRightServo.write(90 - 50);
  BackLeftServo.write(90 - 50);
  BackRightServo.write(90 - 50);

}

void Wait() {
  Buzz();
  delay(2000);
  Buzz();
  delay(2000);
  Buzz();
  delay(2000);
}

void Buzz() {
  digitalWrite (BuzzerPin, HIGH);
  delay (90);
  digitalWrite (BuzzerPin, LOW);
}

//Use Ultrasonic Range Finder to check for obstacles
void CheckObstacles() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  Duration = pulseIn(echoPin, HIGH);
  Distance = (Duration / 2) / 29.1; // Get Distance
  delay(10);
}

[DaveX]

Maybe the rechargeable 9V battery pack doesn't have enough amperage? How does the Nano get its power?

[Ricochet76]

The Nano is mounted directly on the servo shield and gets power from the shield. The shield distributes the power to the servos as well. I was dubious about the 9v power cell as well. However, the code I uploaded is for allowing students to do autonomous programming. I have a second setup in which I use an Arduino Nano controlled remote to drive the robot and I am able to get the servos to run full speed with that setup.

[xfpd]

Observe the power LED on the shields during maximum power usage. Any indication of power flicker/brownout? My guess is the capacitors on the power lines are not holding a charge long enough during maximum usage.

[Ricochet76]

I think you might be right. It seems to perform better with some kinds of 9v than others but I suspect 4 360degree servos all pulling continuously are too much for that board regardless of the battery I use. Thanks much!