Servo robot arm

Learn

What you’ll build

A small robot arm with a rotating base, a shoulder, an elbow and a gripper, each driven by a servo. First you control each joint with a knob; then the arm learns to replay a sequence by itself.

Parts

Part	Qty	Notes
Servos (SG90 for a light arm, MG90S/MG996R for stronger joints)	4	Metal gears last longer
Arm kit or 3D-printed / cardboard links	1
Potentiometers (10 kΩ)	4	One per joint
5–6 V supply, 2 A or more	1	Servos must not run from the Arduino’s 5V pin
Arduino UNO, breadboard, wires	1

Wiring

Joint	Servo signal	Knob
Base	9	A0
Shoulder	10	A1
Elbow	11	A2
Gripper	6	A3

All servo red wires go to the external 5–6 V supply; all grounds (supply, servos, Arduino) are joined.

Build tips

• The shoulder carries the most load: use your strongest servo there.
• Keep the arm light, especially near the end: every gram at the tip loads the shoulder.
• Set each servo to 90° before attaching its horn, so the arm’s middle position matches the code.
• Limit each joint’s range in code so it can’t crash into itself.

Examples

Knob control for four joints

arm-knobs.ino

#include <Servo.h>

Servo joint[4];
const int SERVO_PIN[4] = {9, 10, 11, 6};
const int KNOB[4] = {A0, A1, A2, A3};
const int MIN_ANGLE[4] = {0, 20, 20, 30};     // safe ranges: tune for your arm
const int MAX_ANGLE[4] = {180, 160, 160, 110};

void setup() {
  for (int i = 0; i < 4; i++) joint[i].attach(SERVO_PIN[i]);
}

void loop() {
  for (int i = 0; i < 4; i++) {
    int a = map(analogRead(KNOB[i]), 0, 1023, MIN_ANGLE[i], MAX_ANGLE[i]);
    joint[i].write(a);
  }
  delay(15);
}

Record and replay (idea)

Store the four angles in an array every time a button is pressed (up to, say, 20 poses). On a second button, play them back in order, moving each joint smoothly from pose to pose.

Practice

Try it in the virtual Arduino

Press Start simulator, replace diagram.json, paste the sketch and press ▶. Each knob moves one joint. If Wokwi says a library is missing, click its Install button and press ▶ again.

diagram.json

{
  "version": 1,
  "author": "RoboLearn",
  "editor": "wokwi",
  "parts": [
    {
      "type": "wokwi-arduino-uno",
      "id": "uno",
      "top": 0,
      "left": 0,
      "attrs": {}
    },
    {
      "type": "wokwi-servo",
      "id": "base",
      "top": -110,
      "left": 160,
      "attrs": {}
    },
    {
      "type": "wokwi-servo",
      "id": "shoulder",
      "top": -110,
      "left": 300,
      "attrs": {}
    },
    {
      "type": "wokwi-potentiometer",
      "id": "pot1",
      "top": -100,
      "left": -40,
      "attrs": {}
    },
    {
      "type": "wokwi-potentiometer",
      "id": "pot2",
      "top": -100,
      "left": 50,
      "attrs": {}
    }
  ],
  "connections": [
    [
      "base:GND",
      "uno:GND.1",
      "black",
      []
    ],
    [
      "base:V+",
      "uno:5V",
      "red",
      []
    ],
    [
      "base:PWM",
      "uno:9",
      "orange",
      []
    ],
    [
      "shoulder:GND",
      "uno:GND.1",
      "black",
      []
    ],
    [
      "shoulder:V+",
      "uno:5V",
      "red",
      []
    ],
    [
      "shoulder:PWM",
      "uno:10",
      "orange",
      []
    ],
    [
      "pot1:GND",
      "uno:GND.2",
      "black",
      []
    ],
    [
      "pot1:VCC",
      "uno:5V",
      "red",
      []
    ],
    [
      "pot1:SIG",
      "uno:A0",
      "green",
      []
    ],
    [
      "pot2:GND",
      "uno:GND.2",
      "black",
      []
    ],
    [
      "pot2:VCC",
      "uno:5V",
      "red",
      []
    ],
    [
      "pot2:SIG",
      "uno:A1",
      "green",
      []
    ]
  ],
  "dependencies": {}
}

sketch.ino

#include <Servo.h>

Servo base, shoulder;

void setup() {
  base.attach(9);
  shoulder.attach(10);
}

void loop() {
  base.write(map(analogRead(A0), 0, 1023, 0, 180));
  shoulder.write(map(analogRead(A1), 0, 1023, 20, 160));   // limited range
  delay(15);
}

Two-joint arm with knobsOpen full screen ↗

Start simulator

Runs on Wokwi, free, no account needed.

Safe rangesEasy

Change the shoulder range to 45–135° and check that the knob can’t push it further. shoulder.write(map(analogRead(A1), 0, 1023, 45, 135));

WaveMedium

Replace the knob code with an automatic “wave”: the base swings 60°→120°→60° while the shoulder stays at 90°.

Show an answer

void loop() {
  shoulder.write(90);
  for (int a = 60; a <= 120; a++) { base.write(a); delay(10); }
  for (int a = 120; a >= 60; a--) { base.write(a); delay(10); }
}

Record and replayHard

Add a button: each press saves the current two knob angles (up to 10 poses). After 10 presses, replay all poses in a loop. Use two arrays, int baseA[10], shoulderA[10]; and a counter. Detect presses with the edge-detection pattern from the button lessons.

Quick check

1. Which joint usually needs the strongest servo?

GripperShoulderBaseAll the same

2. Why power the servos from an external supply?

They need more current than the Arduino’s 5V pin can giveIt looks tidierIt makes them quieterIt doesn’t matter

3. Why limit each joint’s angle in code?

To stop the arm crashing into itself or stallingTo save memoryIt makes servos fasterNo reason

Check my answers