ServoMotor

The purpose of this library is to create a custom servo motor. To use it you will need:

• An H-bridge
• A DC motor that can be reversed by flipping the voltage across it.
• An analog sensor that can measure the position of the motor.

You will also need a single analog pin and two pins capable of pwm output. See this page to find out what pwm pins are available on your arduino board:

Wiring

Each of the components must be connected in the following way:

• The motor leads connect to the H-bridge.
• The H-bridge input pins are connected to the chosen pwm pins of the arduino.
• The sensor is connected to the chosen analog pin of the arduino.

The schematic below provides an example for the required conections:

Usage

The available functions are:

• initialize(): sets the input and output pins and calibrates the servo.
• readSensor(): returns the unfiltered sensor signal.
• setPosition(int): sets the target position of the servo.

Note that the library uses analogRead() to measure the sensor. As such, the entire range of motion will be divided to 1024 individual steps. For a 180 degree rotation this means a maximum precision of 180/1024 ~ 0.18 degrees.

The motion of the servo is controlled via a PID loop. The associated coefficients are set when a sketch is compiled and cannot be changed once the arduino is running.

References

The library uses an alpha-beta filter to smoothen and differentiate the signal from the analog sensor.