edu_drive

This package comprises a ROS interface for EduArt's generic drive concept. It covers several kinematic concepts: Differential drive, Mecanum steering and Skid steering. All three can be used in dependency of the mounted wheels and the configuration of YAML parameters.

Launching the Robot

In order to run the robot, you need to launch the appropriate launch file. In the launch folder, there is a prepared template. Configure the correct kinematic concept and motor parameters. A description of the YAML file can be found below.

roslaunch edu_drive edu_drive.launch

When everthing is initialized well, one should see the following output:

# Listener start
CAN Interface: can0
[ INFO] [1651663592.994224328]: Instanciated robot with vMax: 0.366519 m/s and omegaMax: 0.733038 rad/s
...

After startup, the drive system is in the deactivated state.

Please notice also, that the ROS variables ROS_MASTER_URI and ROS_IP should be set properly. If you have a changing IP-address of the robot, you might consider to use the following bash code in your ~/.bashrc:

MYIP=`hostname -I | awk '{print $1}'`
export ROS_MASTER_URI=http://${MYIP}:11311
export ROS_IP=${MYIP}

YAML file parameters

tag	description
canInterface	SocketCAN interface, e.g. can0
frequencyScale	Divider of PWM frequency, Base frequency: 500kHz (Divider=1)
inputWeight	Low pass filtering, setpoint = inputWeight*setpoint_new + (1-inputWeight)*setpoint_old
maxPulseWidth	Limitation of pulse width, meaningful values [0; 100]
timeout	Dead time monitoring of communication (in milliseconds)
kp, ki, kd	Controller coefficients
antiWindup	Enable anti windup monitoring of closed-loop controller
invertEnc	Invert encoder signal
responseMode	Activate transmission of RPM or position measurements of motor controller
controllers	Number of motor controllers used
canID	Motorcontroller ID (set by DIP switch on motor controller PCB)
gearRatio	Gear ratio of connected geared motors
encoderRatio	Encoder pulses per motor revolution (rising and falling edge evaluation)
rpmMax	Maximum revolutions per minute of geared motor pinion
channel	Used channel of motor controller. There are single-channel motorshields and dual-channel motorshields. Meaningful values are 0 or 1.
kinematics	Three-dimensional vector describing the conversion from Twist messages in motor revolutions. See explanation below.

Calculation of the kinematic parameters

The kinematic concept uses a conversion matrix for the conversion of twist parameters and wheel speeds.

, where ω_i are the wheel's angular velocities and v_x, v_y and ω are Twist values. The matrix T can be calculated as follows:

for a four-wheeled robot. kx_i, ky_i and kω_i are the translation parameters from one space to the other. These parameters include the wheel radius r as well as the robot length l_x and robot width l_y.

Example for a Differential drive

Example for a Mecanum drive

Setting up a Raspberry PI4 SBC from scratch

1. Install Basis OS, Raspbian GNU/Linux 11 (bullseye) has been tested
2. Update and install necessary packages

sudo apt update
sudo apt upgrade
sudo reboot
sudo apt install can-utils build-essential cmake git

3. Add the following entries in /etc/rc.local

ip link set can0 up type can bitrate 500000
echo 16 > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio16/direction

echo 22 > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio22/direction
echo 1 > /sys/class/gpio/gpio22/value

4. Install ROS

sudo apt install python3-empy libboost1.71-all-dev libtinyxml2-dev lz4 libroslz4-dev liblz4-dev libbz2-dev lbzip2 libgtest-dev libgpgme-dev libspnav-dev python3-rosdep python3-rosinstall-generator python3-vcstools ros-cmake-modules libpoco-dev 
rosdep update
mkdir ~/ros_catkin_ws
cd ros_catkin_ws
python -m rospkg.os_detect
rosdep install -ay --os=debian:bullseye
rosdep update
rosinstall_generator ros_comm geometry_msgs sensor_msgs joystick_drivers diagnostic_updater --rosdistro noetic --deps --tar > noetic-ros_comm.rosinstall
sudo ./src/catkin/bin/catkin_make_isolated --install -DCMAKE_BUILD_TYPE=Release --install-space /opt/ros/noetic -j4
sudo reboot
mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/src
catkin_init_workspace
git clone https://github.com/EduArt-Robotik/edu_drive.git
cd ..
catkin_make
source devel/setup.bash

Now, the launch file should be started. Please adjust the parameters in edu_drive.yaml before.

roslaunch launch/edu_drive.launch