Servo motors: precise angles for grippers and arms

Where a DC motor just spins, a servo moves to a specific angle and stays there. Inside it there is a small motor, gears, and electronics that constantly correct the position. You tell it "go to 90 degrees" and it does, holding against a load.

How you control it

A hobby servo has three wires: power, ground, and signal. You command the angle with a special PWM signal, but libraries hide the detail:

#include <Servo.h>
Servo arm;
arm.attach(9);
arm.write(90);   // go to 90 degrees

Two things the datasheet does not tell you loudly

• Real range: a servo advertised as "180 degrees" often reaches a bit less in practice. Test the actual limits before you design a mechanism around them.
• Current draw: servos pull a lot of current under load, in bursts. Power them from a dedicated supply, not from the controller's pins, or you get resets and jitter.

Where servos shine in robots

• Grippers: open and close to pick up an object.
• Arms: lift, lower, rotate a mechanism to a known position.
• Sorting mechanisms: move something to one of a few fixed positions.

Standard vs continuous

A normal servo moves within a limited angle. A continuous rotation servo spins freely and you control speed instead of angle, useful as a simple geared motor with built-in control. Pick the one your mechanism needs.

The key idea: a servo gives you repeatable position. When a robot must do the exact same motion every time, a servo is usually the answer.