Robot Arms

Hold out your arm right now. Look at all the things it can do! You can stretch it out long, bend it at the elbow, twist your wrist, and reach over, under, and sideways. Your arm is an incredible tool for reaching out and getting things done. Robots have arms too! Robot arms are one of the most useful parts an engineer can add to a robot. A robot arm lets the robot reach out into the world and work — just like your arm lets you reach for things on a shelf or give someone a high five.

How a Robot Arm Works

Your arm has joints — places where it bends. Your shoulder lets your arm swing in big circles. Your elbow lets your arm fold in half. Your wrist lets your hand twist and tilt. Robot arms work the same way! Each place where the arm can bend or twist is called a joint. The more joints a robot arm has, the more ways it can move and reach. A simple robot arm might only have two joints — like a straight stick that can fold at one spot. It can reach forward and pull back, but not much else. A more complex robot arm might have six or seven joints. That kind of arm can twist, turn, reach around corners, and get into tight spaces — almost like a human arm! Each joint is powered by a motor. When the computer sends a signal to the motor, the joint bends. When you move your elbow, your brain sends a signal to your muscles. When a robot bends its elbow joint, the computer sends a signal to a motor. Same idea, different machinery!

You see robot arms doing all kinds of jobs in the world around you. In car factories, giant robot arms weld pieces of metal together with sparks of electricity. These arms are huge, powerful, and incredibly precise — they do the same welding motion thousands of times a day without ever getting tired. In hospitals, smaller robot arms help surgeons perform operations through tiny cuts in the body — much more precise than any human hand could be on its own. In space, the International Space Station has a giant robot arm that reaches out to grab supply ships and help astronauts during spacewalks. That arm is longer than a school bus! At home, your video game controller might even have a tiny robotic arm inside that vibrates to give you the feeling of bumps and crashes.

One big difference between your arm and a robot arm is that your arm feels things. When you pick up a hot cup, you feel the heat and know to be careful. When you squeeze clay, you feel how hard you are pressing. Many robot arms do not feel anything at all! They just move to a position the computer tells them to go. Engineers are working hard to add sensors — little detectors — to robot arms so they can feel pressure and texture, just like your skin does. Robots with sensor-equipped arms can pick up fragile things like eggs or fruit without squishing them. That is a very tricky problem, and making it work is one of the coolest challenges in robotics today.