Servo-Powered Claw

The finish line

What you will build

The claw grips and releases five different 10-30 gram foam or paper objects without stalling or crushing them.

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 claw frame

   Laminate a base with two equal pivot positions.

   Mark center grip line.

2. Step 2

   Make matched jaws

   Cut two mirror-image jaws and add broad padded tips.

   Drill or punch pivots with adult help.

3. Step 3

   Install pivots

   Attach jaws with free-running gaps and hard open stops.

   Confirm equal manual swing.

   Builder checkpoint: After install pivots, the first subassembly should stay aligned when handled gently.

4. Step 4

   Connect the jaws

   Use a tie link so one driven jaw mirrors the other.

   Adjust hole positions for symmetric closure.

   Watch for: If this stage binds or drifts, inspect pad compression before adding more parts.

5. Step 5

   Mount the servo

   Fix its body rigidly and align the horn near the drive-jaw link.

   Keep load sideways forces off the shaft.

6. Step 6

   Wire safe power

   Use regulated 5 V and common ground, then connect signal and buttons.

   Test servo unattached at 40 and 120 degrees.

   Builder checkpoint: After wire safe power, operate the build slowly and confirm that symmetric jaw opening and closing begins without binding.

7. Step 7

   Calibrate limits

   Attach the linkage at midpoint and approach open and closed stops slowly.

   Record safe angles before gripping.

8. Step 8

   Run object trials

   Grip, lift 5 cm, hold five seconds, and release each soft object.

   Stop on buzzing or stalled motion.

   Builder checkpoint: At the final checkpoint, The claw grips and releases five different 10-30 gram foam or paper objects without stalling or crushing them.

See the engineering

Why it works

Input

button or potentiometer command

Output

symmetric jaw opening and closing

Motion

servo rotation-to-opposed jaw rotation

Energy losses

linkage backlash, jaw flex, pivot friction, pad compression

#include <Servo.h>
Servo claw; const int openButton=2, closeButton=3;
int position=45; const int openAngle=45, closedAngle=112;
void setup(){ pinMode(openButton,INPUT_PULLUP); pinMode(closeButton,INPUT_PULLUP); claw.attach(9); claw.write(position); }
void loop(){
  int target=position;
  if(!digitalRead(openButton)) target=openAngle;
  if(!digitalRead(closeButton)) target=closedAngle;
  if(position<target) position++;
  if(position>target) position--;
  claw.write(position); delay(18);
}

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 closed servo angle change the measured result?
2. Where did linkage backlash affect the build most strongly?
3. What evidence shows that servo-linkage actuation explains the motion?
4. Which change would improve symmetric jaw opening and closing without creating a new problem?