Grippers and end effectors

Learn

What you’ll learn

• What an end effector is
• Common gripper types and what each is good at
• How to build and protect a servo gripper

End effectors

The tool at the end of a robot arm is its end effector: a gripper, a suction cup, a magnet, a pen, a welding torch. Change the end effector and the same arm does a different job.

Gripper types

Type	How it holds	Good for
Two-finger (angular)	Jaws pivot closed	Simple, cheap, most hobby grippers
Parallel	Jaws slide closed, staying parallel	Boxes and blocks
Suction	A vacuum pump or cup pulls a flat surface	Flat, smooth items: phones, glass, card
Magnetic	An electromagnet	Steel parts only
Soft	Flexible fingers inflate or bend	Fruit, eggs, delicate items

Building a servo gripper

• A servo drives one jaw, and gears or a linkage close the other at the same time.
• Don’t stall the servo by commanding a “closed” angle tighter than the object allows. It will heat up and draw lots of current. Find the angle that just grips, and use that.
• Add rubber or foam on the jaws for grip.
• A limit switch or pressure sensor in a jaw tells the robot it’s holding something.

Examples

Example: tuning the close angle

Command	Result
write(140)	Servo buzzes and gets warm: it’s stalling against the block
write(110)	Holds the block firmly, no buzzing
write(100)	Block slips

Use 110°, and maybe a slightly lower angle for small objects.

Example: pick and place sequence

1. Open the gripper.
2. Lower the arm over the object.
3. Close to the tuned angle; wait 300 ms.
4. Lift, rotate the base, lower.
5. Open, lift, return home.

Practice

Try it in the virtual Arduino

Press Start simulator, open the diagram.json tab and replace its contents with the wiring below, then paste the sketch into sketch.ino and press the green ▶. 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": "servo1",
      "top": -100,
      "left": 180,
      "attrs": {}
    },
    {
      "type": "wokwi-pushbutton",
      "id": "btn1",
      "top": -90,
      "left": 40,
      "attrs": {
        "color": "green"
      }
    }
  ],
  "connections": [
    [
      "servo1:GND",
      "uno:GND.1",
      "black",
      []
    ],
    [
      "servo1:V+",
      "uno:5V",
      "red",
      []
    ],
    [
      "servo1:PWM",
      "uno:9",
      "orange",
      []
    ],
    [
      "btn1:1.l",
      "uno:2",
      "green",
      []
    ],
    [
      "btn1:2.l",
      "uno:GND.2",
      "black",
      []
    ]
  ],
  "dependencies": {}
}

sketch.ino

#include <Servo.h>

Servo jaw;
const int OPEN = 20, CLOSED = 110;   // tune these to your gripper
bool closed = false, wasPressed = false;

void setup() {
  pinMode(2, INPUT_PULLUP);
  jaw.attach(9);
  jaw.write(OPEN);
}

void loop() {
  bool pressed = digitalRead(2) == LOW;
  if (pressed && !wasPressed) {
    closed = !closed;
    jaw.write(closed ? CLOSED : OPEN);
    delay(50);
  }
  wasPressed = pressed;
}

A servo gripper with a buttonOpen full screen ↗

Start simulator

Runs on Wokwi, free, no account needed.

Tune itEasy

Change CLOSED to 90 and to 160. Which would be gentler on a real gripper? The smaller close angle (less squeeze) is gentler; 160 would probably stall a real gripper.

Slow closeMedium

Make the gripper close gradually (1° every 10 ms) instead of snapping shut. Replace jaw.write(...) with a loop: for (int a = OPEN; a <= CLOSED; a++) { jaw.write(a); delay(10); } when closing (and the reverse loop when opening).

Pick the gripperHard

Choose a gripper type for: a phone on a desk, an egg, steel washers, a cardboard box. Phone: suction. Egg: soft gripper. Washers: magnetic. Box: parallel two-finger gripper.

Quick check

1. What is an end effector?

The robot’s batteryThe tool at the end of an armThe last line of codeA type of sensor

2. Why avoid commanding a servo to close too far on an object?

It stalls, heats up and draws lots of currentIt opens insteadIt loses its angleIt becomes faster

3. Which gripper suits an egg?

MagneticSoftMetal parallel jaws at full forceNone

Check my answers