Lab 4: The Motors and Open Loop Control

Prelab

In order to deliver enough current for the car to go fast, we are parallel-coupling the motor drivers, so essentially two channels will drive each motor.

Soldering

Before starting the tasks, I soldered both motor drivers to the Artemis board.

This is my wiring diagram:

Tasks

Task 1: Power and Signal Inputs to One Motor Driver

For this task, I connect the necessary power and signal inputs to 1 dual motor driver. I keep the motor driver powered from an external power supply with a controllable limit, for easier debugging.

Task 2: Generating PWM Signals

First, I wrote setup code for the A1IN, B1IN, A2IN, and B2IN pins for the LEFT motor control board.

#define AB1_IN_LEFT 16
#define AB2_IN_LEFT 15

void setup() {
    pinMode(AB1_IN_LEFT, OUTPUT);
    pinMode(AB2_IN_LEFT, OUTPUT);
}

Next, I connected the Artemis board to the oscilloscope – this is what it looks like.

Zoomed in view of probes with the motor control board. The ground clip is connected to the GND pin of the motor control. The sharp probe is used to check the A1IN, B1IN, A2IN, and B2IN pins.

Now, with the pins set up, I send the following PWM signals to the 4 pins. A1IN and B1IN should get readings, while A2IN and B2IN should not.

void loop() {
    analogWrite(AB1_IN_LEFT, 100);
    analogWrite(AB2_IN_LEFT, 0);
}

Now I can visualize the signals on the oscilloscope!

Task 3: Taking the Car Apart

Here is the car without anything removed.

This is the car with the control PCB removed.

Task 4: Running Motor in Both Directions

For this task, I had to demonstrate that I can run the motor in both directions. I wired the first motor control board to the motor and got the wheels spinning.

Then, I wrote code to loop between driving one direction then switching.

Task 5 & 6: Second Motor Driver and Powering With Battery

Next, I finished soldering the second motor driver, then connected the 850 mAh battery. Now, both wheels can spin.

Task 7: Installing Boards Into Car

Using a lot of electrical tape, I attached all the boards into the car. A detailed picture of the car with all sensors and boards labeled is below.

Task 8: Lower Limit PWM Signals

I tested the minimum PWM signal to get the car moving forward on the lab room tile. It was 35.

void forward() {
    analogWrite(AB1_IN_LEFT,  35);
    analogWrite(AB2_IN_LEFT,  0);
    analogWrite(AB1_IN_RIGHT, 0);
    analogWrite(AB2_IN_RIGHT, 35);
}

To get the car spinning, I used a PWM signal of 200, a lot higher. This is partially because the battery had a lot less power from testing.

void spin_in_place() {
    analogWrite(AB1_IN_LEFT,  35);
    analogWrite(AB2_IN_LEFT,  0);
    analogWrite(AB1_IN_RIGHT, 35);
    analogWrite(AB2_IN_RIGHT, 0);
}

Task 9: Wheel Calibration

To test if the motors spin at the same rate, I did a straight line driving test. A good result would be if the car can drive in a straight line for at least 6 ft. As you can see in the video, the car stayed in a straight line for a lot longer than 6 ft, so no calibration necessary.

Task 10: Open Loop Control

For this task, I demonstrate open loop control of the car. It can drive forward, backward, and turn with programmatic inputs.

void open_loop_demo() {
    forward();
    delay(3000);
    spin_in_place();
    delay(2000);
}

Collaboration

This lab involved a lot of soldering and making sure I connected the right pins to the motor control boards. I referenced Aidan Derocher's website for the overall wiring. I also used his website to understand how to test the motor boards for power with the oscilloscope. During Open Lab hours, I also got a lot of help with understanding how to use the oscilloscope and the power source for testing. Finally, I used Claude to style my website by providing my lab report text and images/videos.