This is a tutorial on using ROS with a Donkey Car.
- Follow instructions on https://downloads.ubiquityrobotics.com/pi.html and Ubuiquity Robot network instructions to get ROS running on your Donkey Car.
Assumes it is in the mode where it connects to a home wifi (see switch_to_wifi_mode.sh below)
- Turn on donkey car
ssh ubuntu@ubiquityrobot.local(password:ubuntu)
Assumes it is in the mode where it provides an access point (see switch_to_ap_mode.sh below)
# To run this:
# sudo bash
# nohup ./switch_to_ap_mode.sh
echo "y" | pifi remove GWifi
echo "Removed GWifi"
# sleep 30 # just to see if a reboot even needed
reboot
# To run this:
# sudo bash
# ./switch_to_wifi_mode.sh
pifi add GWifi YOUR_WIFI_PASSWORD
echo "Rebooting, wait 30s and ssh ubuntu@ubiquityrobot.local"
reboot
In order to control the motor and steering, you go through the i2cpwm_board ros node. This assumes that you've already installed https://gitlab.com/bradanlane/ros-i2cpwmboard.
Start the ros node by running:
$ rosrun i2cpwm_board i2cpwm_board
and you should see output:
[ INFO] [1571265047.816527752]: I2C bus opened on /dev/i2c-1
[ INFO] [1571265047.832949932]: Setting PWM frequency to 50 Hz
This step is useful to validate that the i2cpwm_board is properly working. You probably want to put your donkey car on a "rack" so that you don't end up chasing it.
To set the throttle to make the wheels spin:
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray <TAB> <TAB>
and change the default values to:
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 366.0"
After hitting enter, the wheels on your donkey car should be spinning.
To set it back to idle, redo the above command but use 333.0 as the value.
The ESC operates just like a servo where forward/stop/reverse is mapped to right/center/left. To go into reverse, you will need to specify a value less than 333.0 (i.e. stop/center).
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 290.0"
The above will work as expected for some. For most people using an entry-level ESC it will not, at least not yet. There is a catch.
To prevent drivers from accidentally reversing during a race, many ESCs require the user to "double tap" the throttle controller into reverse. The user moves the throttle stick to reverse, then back to stop/center, then again into reverse.
For ROS, we accomplish the same thing like this:
# First reverse "tap"
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 320.0"
# Back to stop/center
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 333.0"
# Second reverse "tap"
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 320.0"Now your wheels are spinning in reverse. Once in reverse driving mode, you can continue to change the throttle without going back to stop/center again:
# After the Second "tap", accelerate in reverse
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 310.0"
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 300.0"
$ rostopic pub /servos_absolute i2cpwm_board/ServoArray "servos:
- servo: 1
value: 290.0"This is the bridge between teleop twist messages and the i2cpwm_board controls. It reads teleop twist messages from the cmd_vel topic and controls the motor accordingly. It assumes you've downloaded the code, see Appendix / Build donkey_llc below.
In a seperate terminal, run:
$ cd ~/catkin_ws/src/donkey_llc
$ rosrun donkey_llc low_level_control.py
$ rosrun teleop_twist_keyboard teleop_twist_keyboard.py
Now you can type i to accelerate and k to stop.
This assumes you've built the https://github.com/dganbold/raspicam_node module. See Appendix / Build raspicam_node.
$ roslaunch raspicam_node camera_module_v2_640x480_5fps_autocapture.launch
On a linux laptop with ROS installed:
$ export ROS_MASTER_URI=http://ubiquityrobot.local:11311
$ rosrun rqt_image_view rqt_image_view
and you should see a window popup that shows the video stream from the donkey car camera.
On the raspberry pi do the following one-time install:
$ sudo apt-get install ros-kinetic-web-video-server
Then start the streaming server via:
$ rosrun web_video_server web_video_server
and in your browser open http://ubiquityrobot.local:8080/stream_viewer?topic=/raspicam_node/image_raw.
$ cat donkey_ros.launch
<launch>
<include file="$(find i2cpwm_board)/launch/i2cpwm_node.launch"/>
<include file="$(find raspicam_node)/launch/camera_module_v2_640x480_5fps_autocapture.launch"/>
<node pkg="donkey_llc" name="donkey_llc" type="low_level_control.py" output="screen" >
</node>
<node pkg="web_video_server" name="web_video_server" type="web_video_server">
</node>
</launch>
$ roslaunch donkey_ros.launch
135 git clone https://github.com/tizianofiorenzani/ros_tutorials.git tizianofiorenzani_ros_tutorials
136 cd tizianofiorenzani_ros_tutorials/
137 ls
138 cd donkey_car/
139 ls
140 cd src/
141 ls
142 rosrun donkey_llc low_level_control.py
143 cd
144 cd catkin_ws/
145 ls
146 cd src/
147 catkin_create_pkg donkey_llc
148 cd donkey_llc/
149 ls
150 cd ..
151 rm -rf donkey_llc/
152 catkin_create_pkg donkey_llc rospy
153 cd donkey_llc/src/
154 ls
155 cp ~/tizianofiorenzani_ros_tutorials/donkey_car/src/low_level_control.py
156 cp ~/tizianofiorenzani_ros_tutorials/donkey_car/src/low_level_control.py .
157 rosrun donkey_llc low_level_control.py
237 git clone https://github.com/dganbold/raspicam_node.git
238 catkin_make --pkg raspicam_node
239 ls
240 cd ..
241 catkin_make --pkg raspicam_node
242 source devel/setup.bash