Lab 4: UR5 and Motor Control

2.12/2.120 Intro to Robotics
Spring 2024¹

• Lab 4: UR5 and Motor Control
  • 0 (Prelab) Software Setup
    • 0.1 Python
    • 0.2 UR5 RTDE
  • 1 Motor Modelling and Controller Design
  • 2 Validate Hardware Setup
    • 2.1 Validate Microcontroller
    • 2.2 Validate Motors
    • 2.3 Validate Encoders
    • 2.4 Validate Joystick
  • 3 Tune Controller
  • 4 Drawing Revisited
  • 5 Feedback Form
  • X Optional

0 (Prelab) Software Setup

Estimated time of completion: 15 min

Before coming in to lab, please download and install the following software.

0.1 Python

1. Download Python here: https://www.python.org/downloads/.

   What version of Python do I need?

   We recommend at least 3.8 to ensure compatibility with the packages we will use in this class. If you already have Python, you should be able to check its version by entering the command python --version in your terminal.

   Can I get Python via conda?

   We recommend getting vanilla Python. The staff may not be able to help troubleshoot issues relating to conda.

2. Make sure to check "Add python.exe to PATH".

   

3. Click "Install Now" and finish the installation.

4. Check that you installed Python correctly by entering the command python in your terminal. It should return Python X.X (tags....

   It's returning something else?

   If it instead returns python is not recognized as an internal or external command, operable program, or batch file or python: command not found, you may have forgotten to add Python to PATH during installation. You can fix this using the following instructions: How to Add Python to PATH.

0.2 UR5 RTDE

For Windows:

1. Open PowerShell in administrator mode by right-clicking and selecting "Run as administrator".

2. Enter wsl --install. This installs Windows Subsystem for Linux (WSL) with Ubuntu as the default distribution.

   Not working?

   Please refer to this tutorial: How to install Linux on Windows with WSL.

3. Restart your machine.

4. Open Powershell and enter wsl to open a WSL terminal window. You might be asked to create a username and password. This can be whatever you want as long as you remember it.

5. Enter the following sequentially:

   sudo apt update
   sudo apt upgrade
   sudo apt install python3-pip
   pip3 install ur_rtde
   

   Tip: You can paste text from your clipboard by right-clicking in Powershell.

For Linux:

1. Open Terminal.
2. Follow step 5 under "For Windows".

For MacOS:

1. Open Terminal.

2. Enter /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" to install Homebrew, a package manager similar to Linux apt.

3. Enter echo "export PATH=/usr/local/bin:$PATH" >> ~/.bash_profile && source ~/.bash_profile to add Homebrew to PATH.

4. Enter the following sequentially:

   brew update
   brew upgrade
   brew install boost
   brew install cmake
   
   git clone https://gitlab.com/sdurobotics/ur_rtde.git
   cd ur_rtde
   git submodule update --init --recursive
   mkdir build
   cd build
   cmake ..
   make
   sudo make install
   

   Not working?

   We are still debugging why this doesn't work especially for Apple chip Macs. Feel free to send the staff an email with the error you are getting.

Additional references:

• Github (Example Codes)
• RTDE API Doc

In lab, we will perform a supervised run-through of controlling the UR5.

1 Motor Modelling and Controller Design

Estimated time of completion: 20 min

Clone this repository. Open matlab/MotorModel.mlx in MATLAB and follow along the guided tutorial to find the nominal controller gains for the motors.

2 Validate Hardware Setup

Estimated time of completion: 10 min

Like in the previous labs, we first want to make sure the parts work individually! Faulty wiring or hardware can be very difficult to debug in complex systems.

2.1 Validate Microcontroller

Make sure that motor power is turned off any time you are uploading code to your microcontroller. The arm has a tendency to spin around and hit itself if motor power is on during upload. As a reminder, motor power should only be on when you expect the motors to move. Otherwise, please keep motor power off.

How to know if the motor power is on?

The yellow LED on the motor driver indicates whether motor power is on or off.

Clone this repository and run robot/blink_test.cpp. You should see the onboard LED change colors!

Forget how to clone?

Please refer to the instructions from Lab 1.

2.2 Validate Motors

Orient the arm straight up, in default starting position. Run test_code/motor_drive_test.cpp to validate your motor setup. You should see both motors oscillating back and forth. Remember, motor 1 is attached to the base and motor 2 is attached to the second link.

2.3 Validate Encoders

Run test_code/encoder_test.cpp to validate your encoder setup. Open the Serial Monitor to see the output and confirm that both the direction and the magnitude make sense!

2.4 Validate Joystick

Run test_code/joystick_test.cpp to validate your joystick setup. You should be able to see joystick readings within the range [-1, 1].

3 Tune Controller

Estimated time of completion: 20 min

We will be using lab_code/sinusoidal_input.cpp to tune our controllers. We will tune the two motors separately.

1. Uncomment #define MOTOR1 and comment out #define MOTOR2.
2. Update the parameters under the #ifdef MOTOR1 section to be the nominal parameters computed from MATLAB.
3. Run lab_code/sinusoidal_input.cpp.
4. Open matlab/TuningPlot.m in MATLAB. Update the COM port.
5. Run matlab/TuningPlot.m in MATLAB to visualize the performance of your controller.
6. Tune your controller by incrementally changing Ti1, Td1, Kp1, and alpha1 and seeing how that affects performance. Ideally, we want minimal overshoot, oscillations, and steady state error.
7. Once you are satisfied with the performance, repeat the process for MOTOR2.

4 Drawing Revisited

Estimated time of completion: 10 min

We will now use your tuned controllers to improve the drawing from last lab!

1. Open lab_code/drawing.cpp and update the parameters.
2. Set trajectoryType = HORIZONTAL_LINE.
3. Run lab_code/drawing.cpp and observe whether the arm performs better than last lab.
4. Open matlab/TrajectoryPlot.m in MATLAB. Update the COM port.
5. Run matlab/TrajectoryPlot.m to visualize the target and actual trajectories.
6. Set trajectoryType = JOYSTICK and run lab_code/drawing.cpp again.
7. Draw something awesome using your joystick!

✅ CHECKOFF 1 ✅
Show your work of art to a TA or LA so we can pin it up on the board!

5 Feedback Form

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

✅ CHECKOFF 2 ✅
Show the feedback form completion screen to a TA or LA.

X Optional

Here are some optional challenges you can try if you finish lab early!

1. Run lab_code/drawing.cpp with trajectoryType = VERTICAL_LINE.
2. Run lab_code/drawing.cpp with trajectoryType = CIRCLE.
3. Connect the joystick to a separate microcontroller and make it wireless.
4. Try using another type of input besides the joystick. For example, you can use potentiometers or an IMU!

Footnotes

1. Version 1 - 2020: Dr. Harrison Chin
   Version 2 - 2021: Phillip Daniel
   Version 3 - 2023: Ravi Tejwani and Kentaro Barhydt
   Version 4 - 2024: Joseph Ntaimo, Jinger Chong, Josh Sohn ↩