Low-Cost Robot Arm

The finish line

What you will build

The arm moves through a programmed pick-and-place cycle and relocates a 20-gram foam block between two marked zones five times.

Before you build

Materials, tools, and safety

Reuse-material cost: Usually under $5 with an existing kit. Supervision: Adult guidance recommended for wiring and cutting.

Build it

Step-by-step instructions

1. Step 1

   Build the base

   Laminate a wide base and add ballast away from moving links.

   Mark the shoulder axis at center.

2. Step 2

   Make equal link pairs

   Laminate two 15 cm beams and add reinforced servo-horn holes.

   Keep left and right faces parallel.

3. Step 3

   Mount the shoulder servo

   Capture its body between side plates and support the output horn.

   Do not use the servo shaft as the only frame support.

   Builder checkpoint: After mount the shoulder servo, the first subassembly should stay aligned when handled gently.

4. Step 4

   Add the elbow

   Attach the second servo at the first link end and route its cable with a loose loop.

   Check full motion by hand with power off.

   Watch for: If this stage binds or drifts, inspect off-axis loading before adding more parts.

5. Step 5

   Build the claw

   Create two lightweight jaws driven by the third servo horn and a connecting link.

   Add soft pads and hard stops.

6. Step 6

   Wire power correctly

   Power servos from the 5 V supply and join its ground to controller ground.

   Do not draw servo current from a controller logic pin.

   Builder checkpoint: After wire power correctly, operate the build slowly and confirm that shoulder, elbow, and claw position begins without binding.

7. Step 7

   Calibrate safe angles

   Upload a slow one-joint-at-a-time sweep and record non-binding limits.

   Stop before links touch the frame.

8. Step 8

   Program pick and place

   Move through home, approach, close, lift, target, release, and home.

   Run first with no payload, then a 20-gram block.

   Builder checkpoint: At the final checkpoint, The arm moves through a programmed pick-and-place cycle and relocates a 20-gram foam block between two marked zones five times.

See the engineering

Why it works

Input

microcontroller pulse commands

Output

shoulder, elbow, and claw position

Motion

electrical commands-to-multi-joint angular motion

Energy losses

servo backlash, link flex, joint friction, off-axis loading

#include <Servo.h>
Servo shoulder, elbow, claw;
int shoulderPos = 80, elbowPos = 95, clawPos = 35;
void moveServo(Servo &motor, int &current, int target) {
  int direction = target > current ? 1 : -1;
  while (current != target) { current += direction; motor.write(current); delay(20); }
}
void setup() {
  shoulder.attach(3); elbow.attach(5); claw.attach(6);
  shoulder.write(shoulderPos); elbow.write(elbowPos); claw.write(clawPos);
  delay(1000);
}
void loop() {
  moveServo(shoulder, shoulderPos, 62);
  moveServo(elbow, elbowPos, 120);
  moveServo(claw, clawPos, 72);
  moveServo(elbow, elbowPos, 82);
  moveServo(shoulder, shoulderPos, 110);
  moveServo(elbow, elbowPos, 112);
  moveServo(claw, clawPos, 35);
  moveServo(elbow, elbowPos, 95);
  moveServo(shoulder, shoulderPos, 80);
  delay(2500);
}

Make it behave

Test, troubleshoot, and tune

Keep experimenting

Try another version

Build together

Classroom and access options

Reflect on the design

1. How did one link length or motion speed change the measured result?
2. Where did servo backlash affect the build most strongly?
3. What evidence shows that serial-link manipulation explains the motion?
4. Which change would improve shoulder, elbow, and claw position without creating a new problem?