DC Motor Controller and Tachometer

Controlling the speed of a motor is very important in many situations especially in robotics. There are many techniques of controlling the speed of motors, each with their advantages and disadvantages. This document will show you how to build a motor controller which controls the speed of a motor by varying the input voltage. Along the same lines,
DC Motor Controller and Tachometer - schematic

it is useful in many situations to know the exact speed of the motor (in rotations per second for example). By knowing the exact speed of the motor, we can then adjust the motor`s speed to exactly what we want. Once again, there are many ways to do this, the method shown in this document is purely electrical and requires no additional sensors. From the outside, the 3 look almost identical. They all have a rotating shaft running through the centre. For our purposes, we will be designing our components for DC motors only. DC motors are commonly used in hobby situations and robotics. They are cheap and robust and easy to use. DC motor are made by wrapping coils of wire around a post. These windings are placed inside a magnetic field (created by permenant magnets or electromagnets). When a voltage is applied to the windings, a current will go through the coil, which will create another magnetic field. The two magnetic fields may attact each other (like two opposite poles of magnets) or repell each other (like two similar poles of magnets). This will cause the the windings to move and rotate the central shaft of the motor. After making a half a rotation, the current going through the windings will go in reverse (due to a switch known as the commutator ring) and the motor will continue spinning. Far better descriptions can be found here: The purpose of the speed controller is to vary the speed of the motor. The name "speed...

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