Important: These instructions require you to have followed the steps in rpi setup.
If this is the first time setting up the rover, you may want to take some precautions.
- put the rover's body on a box so that the wheels can spin without the rover hitting something by accident and the corner assemblies can rotate freely.
- alternatively you can take off the wheels
- Atach the USB dongle for your remote controller (xbox or Spektrum or other)
If you have any differences compared to the default build, you can change many parameters spread out over three files. Rather than modifying the original files, any changes should be made to the _mod.yaml files you made earlier. This way your changes don't get committed to git.
The files follow the same structure as the default. Just include the values that you need to change as the default values for other parameters may change over time. Say for example you installed bigger wheels on the rover. The software needs to know this such that it can control what speed to command to each motor. Start by opening the file you just created:
nano osr_params_mod.yaml
An editor (nano) should open, if not, you might have to install nano using 'sudo apt install nano'. You can also use an editor like VScode with an SSH extension so you can use a fully fledged editor while still working from a different computer.
Paste in the following snippet (compare with the contents of osr_params.yaml).
rover:
ros__parameters:
rover_dimensions:
wheel_radius: 0.082 # [m]The software will load in these changes and apply them. Take a look at the parameters for the roboclaws as well.
The servo motors at each corner have absolute encoders that will 'remember' where the wheels are even when power is turned off but we still have to calibrate them the first time so they know where the zero position is. Since the servo motors have a limited range of about 300 degrees, we'll want to make sure we are able to make use of the full range of motion. Start by unscrewing the M3 screw that connects the corner assembly to the servo output shaft using a 2.5mm hex wrench. Do this for all 4 corners. Detach the corner assembly from the servo so that the servo can spin freely.
First we'll send the servo motors to their zero positions. Since their range is from 0 to 300, we'll want the default position to be in the middle of that range at 150. Run the following commands:
cd ~/osr_ws/src/osr-rover-code/scripts
python3 calibrate_servos.py 0 150
python3 calibrate_servos.py 1 150
python3 calibrate_servos.py 2 150
python3 calibrate_servos.py 3 150
With each line, you should see the back right (0), then front right (1), then front left (2), and finally back left (3) servo motor move to an angle of 150. If the servo isn't moving, it either means that it's already at that angle or that there's a problem with the wiring, PCB, or PCA9685 connection. Try setting the value to some other angle like 200 for that motor and see if it moves. If so, it's working. Move it back to 150. If not, check if the other servo motors move.
When all servo motors where set to this angle, re-attach the corner assembly to the shaft using the M3 screw from before. When you do so, we recommend using a little bit of thread lock (e.g. loctite blue) so the screw doesn't unscrew and fall out while driving. In the following step we'll perform a finer calibration, so it's ok if the servo spline doesn't line up perfectly with the zero position of the corner assembly.
With each motor mounted, we can move ahead with aligning each corner assembly so that the wheels are pointing perfectly straight. We will do this by sending each corner assembly to different angles until it looks right. We'll use the same script for this. For one motor at a time, run the script with a slightly different value, for example we'll move the back right corner motor to 160 degrees:
python3 calibrate_servos.py 0 160
If it's moving farther away from the center, try 140, if it's getting closer, try 165 or 170. Repeat this until the wheel is exactly at zero. When you find the value where it's centered, write it down since we'll need it later.
tip: Make sure the servo motors are still free to spin without much friction by lifting the servo bracket until the wheel doesn't touch the ground. You can either prop it up or hold it up manually.
Repeat this for wheels at channel 1, 2, and 3. You should have 4 values, for example [135, 155, 125, 162]. Now we need to tell the software what these values are, so when you command the corner motors to turn, they will use these values as the true centers. Open the file osr_mod_launch.py:
nano ~/osr_ws/src/osr-rover-code/ROS/osr_bringup/launch/osr_mod_launch.py
Look for the line that says parameters=[{'centered_pulse_widths': [165, 134, 135, 160]}]. Replace the values using the 4 values you just found. Save and exit using ctrl+o then ctrl+x. The corner servo motors are calibrated and ready to go! Next we'll configure the gamepad to control the rover.
Not all controllers are the same and so we'll want to configure which remote controller axis and button does what. We'll be configuring how fast the rover can go, which axis makes it move forwards and backwards, which axis makes it move left and right, and which axis makes it spin in place.
We'll be making these changes in the file osr-rover-code/ROS/osr_bringup/launch/osr_mod_launch.py. These values in the node joy_to_twist are of interest:
{"scale_linear": 0.05}, # scale to apply to drive speed, in m/s: drive_motor_rpm * 2pi / 60 * wheel radius * slowdown_factor
{"scale_angular": 0.05}, # scale to apply to angular speed, in rad/s: scale_linear / min_radius
{"scale_linear_turbo": 0.05}, # scale to apply to linear speed, in m/s
{"enable_button": 0}, # which button to press to enable movement
{"axis_linear.x": 3},
{"axis_angular.yaw": 2}, # which joystick axis to use for rotating
{"axis_angular.pitch": 0}, # axis to use for in-place rotationStart by setting the scale variables (first three) low (e.g. 0.05) so you can easily confirm the rover moves as intended and avoid a potential crash. In the next steps once you have confirmed everything works ok, we'll set these scale values to more sensible settings.
Depending on which make and model of remote controller or gamepad/joystick you have, the buttons and axes (joysticks) may be represented differently. For that we'll launch the ROS 2 joy node and see what does what. Make sure your joystick is connected, then in a terminal run
ros2 run joy joy_node
It should confirm that is is able to connect to your gamepad. Check this by opening a new separate terminal and listening for any messages coming from the joystick:
ros2 topic echo /joy
You should see a constant flood of messages being printed. Move an axis or press a button on your controller and you should see a change in the output.
Tip: If the joysticks aren't sending through data in a separate terminal, make sure they have the appropriate permissions; sudo chmod a+rw /dev/input/event0. (The specific number may vary, run ls -l /dev/input/* to find out).
Then try again. You might want to consider using udev rules to automate this which you will need for automatic bringup using systemd services below.
If you need help, please post on GitHub Discussions or on the Slack forum.
Take a moment to choose which:
- button or switch on your controller you want to use to enable any movement to the rover. This switch/button is used so that the rover doesn't accidentally start driving when the controller falls or similar.
- axis you'd like to use to send the rover forwards/backwards
- axis you'd like to use to make the rover turn
- axis you'd like to use to make the rover rotate in place
You can always come back to this and change these later. In the window where the ros2 topic echo /joy messages are printing, for each of these axes and button you selected, write down which index in the list of axes/buttons changes when you move the axis. Open the file we looked at earlier osr_mod_launch.py and:
- when you move the axis that you'd like to use to control forward movement, take note of which number changes when you move the joystick. Counting starts at zero, so if the axis that changes is 3rd in the list, the axis number is 3-1=2. Enter this number (in this case 2) right after
axis_linear.x. - do the same for the axis you'd like to use for turning and for rotating in place, using
axis_angular.yawfor turning andaxis_angular.pitchfor rotating in place. - do the same for the button you'd like to use for enabling any movement in the first place. The button number (again count starting from 0) should go with
enable_button.
Now you're all set up to launch the full rover software stack!
In a sourced terminal (source /opt/ros/foxy/setup.bash && source ~/osr_ws/install/setup.bash, unless you added these to your ~/.bashrc file) already before, run
ros2 launch osr_bringup osr_mod_launch.py
This will start up the ROS 2 nodes to run the rover with the changes you made in the previous steps.
Any errors or warnings will be displayed there in case something went wrong. If you're using the Xbox wireless controller,
command the rover by holding the left back button (LB) down and moving the joysticks. You can boost as described in
the RPi setup by holding down the right back button (RB) instead.
If you have questions, please post on the Slack forum in the #troubleshooting channel or if you think there's a problem with documentation, submit an issue.
tip: If you notice the rover is moving in the opposite direction as your commands, add a minus sign to the appropriate scale_ factor in the osr_mod_launch.py file. ctrl-C to stop the currently running code, then re-run it for the changes to take effect.
If you want the code to calculate and publish wheel odometry, launch with the argument enable_odometry:=true.
Odometry is used for localization and SLAM.
In the [earlier section](#Mapping remote controller buttons and axes to rover movement)
The maximum speed your rover can go is determined by the no-load speed of your drive motors. The default no-load speed is located
in the file osr_params.yaml as drive_no_load_rpm, unless you modified it in the corresponding _mod.yaml file.
This maximum speed corresponds to scale_linear_turbo and can be calculated as drive_no_load_rpm * 2pi / 60 * wheel radius (=0.075m).
Based on this upper limit, later we'll set our regular moving speed to a sensible fraction of that which you can configure to your liking. This is because the motors will never reach the no load speed.
Start with e.g. 0.75 * scale_linear_turbo. If you think it's too slow or too fast, simply scale it up or down.
The turning speed of the rover, just like a regular car, depends on how fast it's going. As a result, scale_angular
should be set to scale_linear / min_radius. For the default configuration, the min_radius equals 0.45m.
note: At these speeds, the rover can be fast and strong enough to inflict damage or cause injury. Use caution and lower velocities to drive the rover in the presence of humans or obstacles.
In this section we'll see how we can have the RPi automatically launch the rover code when it launches. That way you don't have to SSH in to run the rover and it can be controlled completely offline. Any modified parameters in osr_mod_launch.py and in the config folder will be found automatically.
Note: We do not recommend enabling the service until you have verified that everything on your robot runs successfully manually. Once you enable the service, as soon as you power on the RPi it will try and run everything. This could cause issues if everything has not yet been fully tested and verified. Additionally, if you are doing development of your own software for the robot we suggest disabling the service and doing manual launch of the scripts during testing phases. This will help you more easily debug any issues with your code.
Starting scripts on boot using ROS can be a little more difficult than starting scripts on boot normally from the Raspberry Pi because of the default permission settings on the RPi and the fact that that ROS cannot be ran as the root user. The way that we will starting our rover code automatically on boot is to create a service that starts our roslaunch script, and then automatically run that service on boot of the robot. Further information on system service scripts running at boot.
There are two scripts in the ”init_scripts” folder. The first is the bash file that runs the roslaunch file, and the other creates a system service to start that bash script. Open up a terminal on the raspberry Pi and execute the following commands.
cd ~/osr_ws/src/osr-rover-code/init_scripts
# use symbolic links so we capture updates to these files in the service
sudo ln -s $(pwd)/launch_osr.sh /usr/local/bin/launch_osr.sh
sudo ln -s $(pwd)/osr_paths.sh /usr/local/bin/osr_paths.sh
sudo cp osr_startup.service /etc/systemd/system/osr_startup.service
sudo chmod 644 /etc/systemd/system/osr_startup.service
Your osr startup service is now installed on the Pi and ready to be used. The following are some commands related to managing this service which you might find useful:
| Description | Command |
|---|---|
| Start service | sudo systemctl start osr startup.service |
| Stop service | sudo systemctl stop osr startup.service |
| Enable service (runs on boot of RPi) | sudo systemctl enable osr startup.service |
| Disable service (doesn’t run on boot of RPi) | sudo systemctl disable osr startup.service |
| Check status of service | sudo systemctl status osr startup.service |
| View live service list | sudo journalctl -f |
Once you have fully tested the robot and made sure that everything is running correctly by starting the rover code manually
via ros2 launch osr_bringup osr_mod_launch.py, enable the startup service on the robot with the command below:
sudo systemctl enable osr_startup.service
At this point, your rover should be fully functional and automatically run whenever you boot it up! Congratulations and happy roving!!