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Mini Robot Arm

Builder · Ages 10–12

1Read the conceptLearn the big idea behind this project.
2Check the partsSee which parts the robot needs.
3Follow the build stepsBuild it step by step, then test it.
4Answer the quizTap one answer for each of the 10 questions to earn XP.

💡 The concept

A robot arm is made of joints moved by servo motors. Each servo turns to an exact angle (0°–180°), so by setting angles for the base, elbow and gripper in order, the arm can pick up and drop an object. The order of steps is called a sequence.

Parts you need

3 servo motors
Arm pieces (card or plastic)
Gripper
Microcontroller
Battery

🔎 Parts specification

Exactly what each part is, which models to buy, and what it does.

Microcontroller▸

Suggested models: Arduino Uno R3 or BBC micro:bit V2

Features: Sends angle commands to each servo. Needs 3 PWM-capable output pins (on the Uno: pins 3, 5, 6, 9, 10, 11). The Arduino Servo library makes this easy.

Servo motors▸

Suggested models: SG90 micro servo (×3)

Features: Turns to an exact angle between 0° and 180° and holds it. Three wires: red = 5V power, brown/black = ground, orange/yellow = signal. SG90 is light, cheap and strong enough for a card arm.

Arm pieces▸

Suggested models: Pre-cut kit pieces, or cardboard/foam board cut with a grown-up

Features: The skeleton of the arm. Keep them light — the SG90 can lift about as much as a small sponge at the end of a 10cm arm.

Gripper▸

Suggested models: 3D-printed or kit gripper, or two curved card 'fingers'

Features: Opened and closed by the third servo. Soft foam tips help it grip without squeezing too hard.

Battery / power▸

Suggested models: 4×AA pack (6V) or USB power bank

Features: Three servos moving together can need more power than USB gives. Power servos from the battery pack and share ground with the board.

💻 Program the microcontroller

📲 App to use: Arduino IDE with the built-in Servo library, or MakeCode's 'servo write pin' blocks

No download needed for the Servo library — it comes with the Arduino IDE (Sketch → Include Library → Servo).

// Arduino IDE (C++) — Mini Robot Arm
#include <Servo.h>
Servo base, elbow, gripper;

void setup() {
  base.attach(9);
  elbow.attach(10);
  gripper.attach(11);
}

void loop() {           // pick-up sequence
  base.write(60);       // rotate over object
  delay(600);
  elbow.write(120);     // lower the arm
  delay(600);
  gripper.write(30);    // close gripper
  delay(600);
  elbow.write(60);      // lift
  base.write(150);      // rotate away
  delay(600);
  gripper.write(90);    // drop!
  delay(2000);
}

🧠 How it works: Each servo.write() moves a joint to an exact angle, and delay() gives it time to get there before the next step. The order matters — that is the sequence. Change the angles a few degrees at a time until the arm picks and drops cleanly.

🛠️ Build it step by step

Press Play to watch every part go into place and every wire connect. Ask a grown-up to help with real wiring!

Step 1 of 6

⚙️ Build the base joint

Screw the first servo onto a flat, heavy base. This servo rotates the whole arm left and right, so the base must not wobble.

🧠 Project quiz

Question 1/10⭐ 0