Motor Control - CourseReps/ECEN489-Fall2015 GitHub Wiki

#Motor Control Motor control is a very general term that involves many different types of motors and aspects, this tutorial will briefly cover just a few. In general, there are four main types of electric motors, AC, DC, Stepper and Servo.

##DC Motors ###PWM PWM (Pulse Width Modulation) is a simple way to control the speed of most basic DC motors (and other components, like the brightness of LEDs), by simulating an average, constant DC value with modulated digital pulses. The pulses have a constant period, but the thing being changed is the width of the "High" pulse.

The idea is to have a period fast enough to where a 50% duty cycle just appears like a DC voltage with half the power. This becomes a problem with small enough pulse widths or periods that are too long, as the friction during the low pulses becomes higher than what power can be delivered in the high pulse, so it will slowly stop.

###H Bridge PWM is a good way to control motor speed, but often more precise control is required. An H bridge is a control circuit for a DC motor that can control the direction of the motor as well as force it to stop. By controlling for switches, usually transistors or relays depending on the power requirements of the motor, it is possible to force voltage in either direction on the motor, let it spin freely, or apply the same voltage on either side and force it to stop.

##Stepper Stepper motors are very precise motors that move at exact angles. They do not move continuously, but from step to step individually. However, they have no way of knowing exactly where it is in the rotation at any given time. Some have a home position that is checked at every full rotation, but that doesn't fix anything immediately if it somehow skips a step. Stepper motors require a software controller to function correctly and control its movement.

##Servo A servo motor is similar to a stepper motor in its precision, however it has the benefit of feedback to know exactly where it is located in its rotation. The downside is that most servos are limited to 180 degress of rotation. Servos also require software control. Servo control is a special type of PWM, with a set standard period, and the desired position is dictated by the length of the high pulse.