Custom Motor Driver


Posted on Feb 5, 2014

This is a chapter that was cut from Applied Robotics 2 because of space issues. It discusses motor control issues in general and then moves on to build a 5-amp motor driver. The principles involved can be applied to much larger motor controllers. Though it is probably cheaper and easier to use the readily available Electronic Speed Control (ESC) s


Custom Motor Driver
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ystems on the market, a home-built ESC gives us (in theory) more control over the specifications. We can control the power rating (within reason), the PWM frequency, braking and regeneration features, acceleration curves, and other fine details. Also, many microcontrollers provide a nice PWM signal generated by hardware timers while the R/C control signal typically has to be created in software, using precious MCU cycles. There are two variables in the motor control state space - the actual motion of the motor, and the direction of the applied torque (from power applied to the motor). When the motor is stopped or moving forward and the power across the motor is in the forward direction (forward torque), then the control is said to be in Quadrant 1 (Q1), forward acceleration. A motor controller that only supports Q1 may consist of a single switch (transistor, IGBT, or MOSFET) and a clamp diode to protect it. When the motor is stopped or moving in reverse and the torque is in reverse, it is being driven in Quadrant 3 (Q3), reverse acceleration. A simple two-quadrant motor controller will operate in Q1 and Q3 and will consist of four switches in an H-Bridge configuration. This will be explored in more detail later. The motor moving forward with a reverse applied torque puts the control into Quadrant 2, reverse braking. Reverse motor motion with forward torque is Quadrant 4, forward braking. Motor controllers that support the...




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