MG996R servo with Arduino Uno — external power, no jitter, smooth moves

The MG996R is the strong metal-gear servo (about 10 kg·cm) used in robot arms, steering linkages and pan-tilt heads, for about ₹300. It takes the same signal as a small SG90, but it needs far more current — and that is where most Uno projects with it go wrong.

The Uno only sends the control pulse on D9. The servo’s red and brown wires go to a separate 5–6 V supply that can give 3 A, and that supply’s negative is joined to the Uno’s GND. Without the shared ground the servo can’t read the pulse. Powered from the Uno’s 5V pin instead, it resets the board or jitters.

The sketch sets the start angle before attaching, so the servo doesn’t jump at power-up. It then moves one degree at a time between 0°, 180° and 90°, which also keeps the current spikes small.

Wiring

Board quirks

• The MG996R pulls about 0.5–1 A while moving and up to 2.5 A when stalled. On the Uno’s USB 5 V it resets the board or jitters wildly. A separate supply with a shared GND is not optional.
• The Servo library uses Timer1: PWM on D9 and D10 stops once a servo is attached. Up to 12 servos can run on any pins.
• Calling write(90) before attach() starts the servo at 90° instead of snapping to 0° at power-up.
• Many cheap MG996Rs only cover about 160–180° and buzz at the end stops. If it buzzes at 0 or 180, narrow the range (e.g. 5–175) — holding against the stop heats the motor.
• Some MG996Rs sold online are the 360° continuous kind, which spin instead of holding an angle. With those, write(90) means stop.

Code

// MG996R metal-gear servo on an Arduino Uno R3.
// SIG → D9. VCC and GND from a separate 5–6 V 3 A supply; supply GND joined to the Uno GND.
// Never power an MG996R from the Uno's 5V pin - it can pull 2.5 A when stalled.
#include <Servo.h>

const uint8_t SERVO_PIN = 9;
Servo servo;
int current = 90;

// Move in small steps so the servo doesn't slam and pull a big current spike.
void slowMove(int target) {
  int step = target > current ? 1 : -1;
  while (current != target) {
    current += step;
    servo.write(current);
    delay(10);
  }
  Serial.print(F("At "));
  Serial.print(current);
  Serial.println(F(" degrees"));
}

void setup() {
  Serial.begin(9600);
  servo.write(90);                  // set the start angle before attach() - no jump to 0
  servo.attach(SERVO_PIN, 500, 2500);
  Serial.println(F("MG996R on D9 - moving slowly between 0, 90 and 180"));
  delay(1000);
}

void loop() {
  slowMove(0);
  delay(1000);
  slowMove(180);
  delay(1000);
  slowMove(90);
  delay(2000);
}

// MG996R metal-gear servo on an Arduino Uno R3.
// SIG → D9. VCC and GND from a separate 5–6 V 3 A supply; supply GND joined to the Uno GND.
// Never power an MG996R from the Uno's 5V pin - it can pull 2.5 A when stalled.
#include <Servo.h>

const uint8_t SERVO_PIN = 9;
Servo servo;
int current = 90;

// Move in small steps so the servo doesn't slam and pull a big current spike.
void slowMove(int target) {
  int step = target > current ? 1 : -1;
  while (current != target) {
    current += step;
    servo.write(current);
    delay(10);
  }
  Serial.print(F("At "));
  Serial.print(current);
  Serial.println(F(" degrees"));
}

void setup() {
  Serial.begin(9600);
  servo.write(90);                  // set the start angle before attach() - no jump to 0
  servo.attach(SERVO_PIN, 500, 2500);
  Serial.println(F("MG996R on D9 - moving slowly between 0, 90 and 180"));
  delay(1000);
}

void loop() {
  slowMove(0);
  delay(1000);
  slowMove(180);
  delay(1000);
  slowMove(90);
  delay(2000);
}

Library: Servo (Arduino (on ESP32 use ESP32Servo by Kevin Harrington, John K. Bennett)) — compiled with Servo 1.3.0.

Expected serial output

MG996R on D9 - moving slowly between 0, 90 and 180
At 0 degrees
At 180 degrees
At 90 degrees

MG996R on D9 - moving slowly between 0, 90 and 180
At 0 degrees
At 180 degrees
At 90 degrees

Common errors