Build your first robot arm

A robot arm brings together everything so far: servos, power, printed parts and code. Build it in small stages and test each one.

Safety: an arm can pinch fingers and move suddenly. Keep hands away while it has power, and have an adult with you if you are under 16.

What you need

• A Nano or ESP32 board.
• Four servos: base, shoulder, elbow and gripper.
• A 5 V supply of at least 3 A, not the board's 5 V pin.
• Printed arm parts and small screws.

Check the torque first

The shoulder works hardest, because it lifts everything. The further the load is from the servo, the more torque it needs.

Torque (kg·cm) = weight (kg) × distance (cm)

A 100 g load at 15 cm needs 1.5 kg·cm, and that is before the weight of the arm. Allow double, and pick a stronger servo for the shoulder.

Wire the power

1. Connect all servo red wires to the 5 V supply.
2. Connect all servo brown wires to the supply ground.
3. Connect the supply ground to the board ground.
4. Connect each signal wire to its own PWM pin.

Centre before you assemble

This is the step people skip, and regret. Set every servo to 90° first, then fit the arm parts. Otherwise a joint can drive into its own end stop and strip the gears.

#include <Servo.h>
Servo base;

void setup() {
  base.attach(9);
  base.write(90);
}

void loop() {}

Move it gently

Change the angle one degree at a time with a short delay, so the arm does not jerk.

for (int a = 90; a <= 120; a++) {
  base.write(a);
  delay(15);
}

On an ESP32, install and use the ESP32Servo library in place of Servo.h. Test one joint at a time. If a servo buzzes and gets hot at a limit, reduce its range at once.

Check your supply with the servo power checker in Tools. A weak supply is the most common reason an arm resets or shakes.