Lab 7: Mobile Robot II

2.12/2.120 Intro to Robotics
Spring 2024¹

Table of Contents

• 1 Mobile Robot
  • 1.1 Understand robot/
  • 1.2 Understand Odometry
  • 1.3 U-Turn
  • 1.4 Circle
• 2 Joystick Control
  • 2.1 Get Robot MAC Address
  • 2.2 Get Controller MAC Address
  • 2.3 Validate Controller
  • 2.4 Run Controller
  • 2.5 Run Joystick Control
• 3 Custom Trajectory
• 4 Feedback Form
• 5 Optional Extensions
  • 5.1 IMU
  • 5.2 Mecanum Wheels

We have already written most of the code for this lab. We hope that you will use the extra free time to fully understand the mobile robot codebase and prepare for the final competition. Have a great spring break!

1 Mobile Robot

1.1 Understand robot/

Take some time to understand robot_main.cpp, robot_drive.cpp, robot_motion_control.cpp, and robot_wireless.cpp. At a high level:

• robot_main.cpp: Includes the setup() and loop() functions, telling the microcontroller exactly what to do and when.
• robot_drive.cpp: Sets up the motors and implements a PI controller to follow velocity setpoints.
• robot_motion_control.cpp: Calculates odometry and setpoints based on either joystick or a given trajectory.
• robot_wireless.cpp: Sets up two-way wireless communication with and sends messages to the microcontroller on your controller.

1.2 Understand Odometry

Open robot_motion_control.cpp and read through updateOdometry(). Make sure that you understand exactly how this function calculates odometry data. For reference:

1.3 U-Turn

Make sure your PlatformIO environment is set to be env:robot and upload the code to the microcontroller on your mobile robot. Once the code has finished uploading, unplug the robot from your computer, set it on the ground, power it on, and press RST. Your robot should now autonomously follow a U-Turn!

Your U-Turn will probably not be perfect! While odometry is straightforward to implement, it suffers from problems such as position drift due to wheel slippage. IMU data (or some combination of IMU and odometry) will likely be more reliable.

1.4 Circle

In robot_motion_control.cpp, comment out #define UTURN and uncomment #define CIRCLE. This will change the followTrajectory() function to follow a circle instead of a U-Turn. Your robot should now autonomously follow a circle!

2 Joystick Control

2.1 Get Robot MAC Address

In order to establish wireless communication, we first have to make sure that both microcontrollers know each other's MAC addresses.

Run lib/Wireless/examples/get_mac.cpp (you will have to temporarily move the existing files inside the src/robot/ folder and replace them with get_mac.cpp). Open lib/Wireless/wireless.h and change robotAddr to the MAC address being printed to the Serial monitor.

2.2 Get Controller MAC Address

Connect to the microcontroller on your controller and change your PlatformIO environment to be env:controller.

Forget how to change environments?

Please refer to the instructions from Lab 6.

Run lib/Wireless/examples/get_mac.cpp (you will have to temporarily move the existing files inside the src/controller/ folder and replace them with get_mac.cpp). Open lib/Wireless/wireless.h and change controllerAddr to this MAC address.

2.3 Validate Controller

Run src/test_controller/controller_test.cpp. You should see joystick readings being printed to your Serial monitor.

2.4 Run Controller

Upload controller_main.cpp and controller_wireless.cpp to the microcontroller on your controller. This will read the joystick and set up two-way wireless communication with the microcontroller on the mobile robot.

2.5 Run Joystick Control

In robot_motion_control.cpp, comment out #define CIRCLE and uncomment #define JOYSTICK. This will change the followTrajectory() function to follow a joystick instead of a circle.

Set your PlatformIO environment back to env:robot. Upload robot_main.cpp, robot_drive.cpp, robot_motion_control.cpp, and robot_wireless.cpp to the microcontroller on your mobile robot. At this point, you should be able to drive your mobile robot around with your joystick!

✅ CHECKOFF 1 ✅
Show your mobile robot in action to a TA or LA.

3 Custom Trajectory

In robot_motion_control.cpp, comment out #define JOYSTICK and uncomment #define YOUR_TRAJECTORY. In the followTrajectory() function, make your own path using a state machine, taking UTURN as inspiration.

✅ CHECKOFF 2 ✅
Show your mobile robot in action to a TA or LA.

4 Feedback Form

Before you leave, please fill out https://tinyurl.com/212-feedback.

✅ CHECKOFF 3 ✅
Show the feedback form completion screen to a TA or LA.

5 Optional Extensions

5.1 IMU

Integrate the IMU with your mobile robot! This will probably be very useful for your final project.

5.2 Mecanum Wheels

Replace the existing wheels with mecanum wheels! Mecanum wheels allow the robot to move in any direction. However, the odometry and controller will be slightly different.

Footnotes

1. Version 1 - 2016: Peter Yu, Ryan Fish and Kamal Youcef-Toumi
   Version 2 - 2017: Yingnan Cui and Kamal Youcef-Toumi
   Version 3 - 2019: Jerry Ng
   Version 4 - 2023: Joseph Ntaimo, Kentaro Barhydt, Ravi Tejwani, Kamal Youcef-Toumi and Harrison Chin
   Version 5 - 2024: Jinger Chong, Josh Sohn ↩