2.12/2.120 Intro to Robotics
Spring 20251
Table of Contents
In this lab, you will be working together as a small team of 3 or 4 to drive a mobile robot! Some parts of this lab can be performed in parallel, so please skim through the handout and delegate to get through the lab faster.
Estimated time of completion: 5 min
Clone this repository.
In past labs, we asked you to move files into the robot/ directory in order to run them. This is because we have set the default environment in PlatformIO to be robot. Today, we will teach you how to change environments so that you can separate code for the mobile robot and the controller.
Click the button at the bottom of the screen that says Default (lab6_2025). Then, select env:joystick. PlatformIO should reconfigure the project. Once it finishes, you can now click the upload button as usual and it should compile and upload code in the joystick/ directory!
To switch back, you can repeat the process above but select env:robot.
For this lab, we will not remind you to switch environments every time we switch between the controller and the mobile robot. You should do this automatically. Since you are working in a team, it may be easier to keep one laptop connected to the controller and the other connected to the mobile robot, so you don't have to switch environments.
Estimated time of completion: 10 min
First, we need to wire and program a controller. All wiring and code in this section should be on the controller. We have written this lab assuming you will use one joystick as the only input on your controller, but you are welcome to use other sensor/s as well.
Run test_basic/blink_test.cpp. You should see the onboard LED change colors!
If needed, wire the joystick and update include/pinout.h. We recommend you wire U/D to Y_PIN and L/R to X_PIN.
Run test_sensors/joystick_test.cpp and open the Serial Monitor. You should see values in the range [0, 4096) print.
Estimated time of completion: 30 min
Now, we need to set up wireless communications between the controller (sender) and the mobile robot (receiver) so that the mobile robot can move using controller input. Since the other half of your team should be going through the motor validation on the mobile robot, please use a plain ESP32 on a breadboard as the receiver for this section. See this tutorial for more details.
On the receiver, run test_basic/blink_test.cpp. You should see the onboard LED change colors!
Tip: on the mobile robot, you can use the large RST and BOOT buttons on the PCB.
In order to make sure your controller doesn't accidentally command the other mobile robots, the sender needs to broadcast to the MAC address of the receiver.
On the receiver, run test_wireless/get_mac.cpp. Copy the MAC address to the TODO in test_wireless/esp_now_sender.cpp.
How exactly do I copy it?
In the curly brackets, type 0x before each pair of characters and separate them with commas. For example, if the MAC address is 30:AE:A4:07:0D:64, you should set
uint8_t broadcastAddress[] = {0x30, 0xAE, 0xA4, 0x07, 0x0D, 0x64};
We will then use test code directly copied from the tutorial to send and receive some data.
On the receiver, run test_wireless/esp_now_receiver.cpp.
On the sender, run test_wireless/esp_now_sender.cpp.
On the machine connected to the receiver, open the Serial Monitor. You should see received messages in the form
THIS IS A CHAR
3
1.2
false
where 3 is a random integer that changes every message.
Now that we can send data wirelessly, we can change the data we send to be the controller inputs.
Using test_wireless/esp_now_sender.cpp and test_sensors/joystick_test.cpp as references, fill in joystick/joystick_wireless.cpp. struct joystickData is defined in wireless.h.
On the sender, run joystick/joystick_wireless.cpp.
To validate that your code works, we have provided code to receive and print messages. On the receiver, run robot/robot_drive.cpp and robot/robot_wireless.cpp. Open the Serial Monitor and confirm that joystick data is received correctly.
| ✅ CHECKOFF 1 ✅ |
|---|
| Show your Serial Monitor with joystick data printing to a TA or LA. |
Now, follow section 3.2 to change the MAC address so that the sender sends data to the mobile robot microcontroller. You may have to work in parallel with the other half of your group.
Estimated time of completion: 30 min
With wireless communications set up, we can now focus on using controller inputs to command the mobile robot. We have already assembled and wired the mobile robots. All the code in this section should be on the mobile robot.
Make sure the wheels of the mobile robot are all elevated off of any surface. If the robot falls off of the table, please try to catch it before it hits the ground.
Run test_basic/motor_drive_test.cpp. You should see each motor drive at two different speeds, in two different directions, one-by-one. Confirm that the wheels spin in the following order: front-left, front-right, back-left, and back-right.
Wheels not spinning?
Check the motor wiring. Try changing Serial.begin(); to Serial.begin(115200);. Serial may have trouble initializing without an explicit baud rate.
Run test_basic/encoder_test.cpp and open the Serial Monitor. You should see each motor's position and velocity printed. Make sure that E1 is front-left, E2 is front-right, E3 is back-left, and E4 is back-right. It is very important that the motors and encoders are in the same order!
Fill in robot/robot_drive.cpp to implement velocity control on all motors. Define the setpoints to all be 2 rad/s. Remember, each motor needs its own PID controller! You may use test_basic/motor_drive_test.cpp, test_basic/encoder_test.cpp, and test_basic/motor_velocity_control.cpp as references.
Hint: You may have to input the negative of controlEffort to motor.drive() for some motors since they are wired in the opposite way to motor 1. You may also have to negate the setpoint value.
Run robot/robot_drive.cpp and robot/robot_wireless.cpp and confirm that all wheels spin at about 2 rad/s and in the direction that would make the mobile robot go forward.
Modify robot/robot_drive.cpp so that the setpoints are depedent on joystick.x and joystick.y instead of just being 2. Think carefully about how you want to map joystick readings to the individual velocities of the motors.
Now it is time for both halves of your group to come together. While you have not confirmed that your code works, make sure the wheels of the mobile robot stay elevated off any surface. Run robot/robot_drive.cpp and robot/robot_wireless.cpp. Confirm that the wheels spin reasonably with respect to the joystick.
You should not need to upload new code on the joystick. Just supply power via the USB-C port of the microcontroller by plugging it into your laptop or a power brick.
| ✅ CHECKOFF 2 ✅ |
|---|
| Show your mobile robot in action to a TA or LA. |
Please clean up your group's station and return everything to an orderly arrangement.
Estimated time of completion: 10 min
Only attempt this portion if there are more than 10 minutes until the end of lab (5 mins before the hour). At this point, you should be able to use your joystick to drive your mobile robot around. You will recieve extra credit if you successfully drive your robot along the white u-shaped path on the floor. You may need to tune your controller gains or make other modifications to make sure robot can follow your commands.
Footnotes
-
Version 1 - 2024: Jinger Chong, Josh Sohn
Version 2 - 2025: Roberto Bolli Jr., Kaleb Blake ↩