README.md

Servo Experiment

The GPIO library provides the set_servo_pulsewidth method to control the width of a pulse signal within the range of [500-2500]. We conducted an experiment to measure the steering angle of the servo induced from this pulse width range:

Objective:

• Determine the relationship between pulse width and the induced steering angle on a servo

Materials

1. Protractor
2. Ruler
3. 8.5"x11" Printing Paper
4. Pencil
5. Car Prototype

Setup:

1. Make sure the hardware connection is established between a GPIO pin and the servo
2. Place the car prototype on a standard 8.5"x11" printing paper
3. Place the servo on a neutral position and align a ruler with the axis of the wheel (simply place the protractor on the face of the wheel).
4. Draw the line along the ruler
5. Call set_servo_pulsewidth(GPIO_PIN, PULSE_WIDTH) where GPIO_PIN is the pin connected to the servo and select PULSE_WIDTH from the range [500-2500].
6. Align the ruler with the axis of the wheels and mark the position of the two wheels after turn
7. Measure the steering angle with a protractor.
8. Repeat Step 5-8 for each desired pulse width.

Result

There is linear relationship between pulse width and the induced steering angle.

• Left Turn (width: 1200 - 1450): 17.9x + 1439
• Right Turn (width: 1550 - 1800): 15.9x + 1561

Through more test on the hardware, I found it more fitting to use one linear mapping, particularly 17.9x + 1439, as it produce more balanced steering angle around the range between [-18, 18] for steering angle degree and [1200, 1780] for pulse width.