Load Transportation Simulator

We present a simulator in Gazebo to simulate Multi-agent load transportation tasks in a microgravity environment.

Fig. 1 Robot simulator

Requirements

• ROS 2 Foxy
• Casadi 3.6.5
• Gazebo ROS2 Control plugin
• Gazebo Plugins

NOTE: this package was tested on a Ubuntu 20.04 LTS with the packages above mentioned. Different versions of Casadi and ROS 2 may work, but it is not guaranteed.

Running Simulation

1. Create a ROS 2 workspace:

cd ~
mkdir -p ~/discower_ws/src
cd ~/discower_ws/src

2. Clone the repository:

git clone [email protected]:DISCOWER/discower_transportation.git

3. Build the workspace:

cd ~/discower_ws
colcon build --symlink-install
source install/setup.bash 

4. Start Gazebo simulation

ros2 launch discower_transportation launch_sim.launch.py 

5. Start PWM controller

ros2 run discower_transportation start_pwm_controller.py 

6. Run the Example controller. This controller is a simple controller that moves the load forward.

ros2 run discower_transportation example_controller.py 

Running Transport MPC

To run the Transport MPC controllers, clone into the workspace the Transport MPC:

cd ~/discower_ws/src
git clone [email protected]:pSujet/transport_mpc.git

Then, rebuild the workspace:

cd ~/discower_ws
colcon build --symlink-install
source install/setup.bash 

Then, run steps 4 and 5 from the previous section, followed by one of the following:

• Run centralized controller:

ros2 launch transport_mpc start_controller_cen.launch.py

• Run decentralized controller:

ros2 launch transport_mpc start_controller_decen.launch.py

Restart Simulation

We can reset the simulator by stopping example_controller and pwm_controller. Next, pressing Ctrl + R in the Gazebo window. Then we can restart the cable position by launching the following command line:

ros2 launch discower_transportation set_initial.launch.py 

Simulator

There are two robots and one load as shown in Fig. 1. The load is connected to the robots by cables. Each robot has four thruster pairs and is controlled by the PWM controller. Body wrench of each robot is calculated by the following equation:

$$\mathbf{F} = \mathbf{D} \mathbf{u} = \begin{bmatrix} F_x \\ F_y \end{bmatrix} = \begin{bmatrix} 1 & 1 & 0 & 0 \\\ 0 & 0 & 1 & 1 \end{bmatrix} \begin{bmatrix} u_1 \\ u_2 \\ u_3 \\ u_4 \end{bmatrix}$$ $$\boldsymbol{\tau} = \mathbf{L}\mathbf{u} = \begin{bmatrix} \tau_z \end{bmatrix} = l_{arm}\begin{bmatrix} 1 & -1 & 1 & -1 \end{bmatrix} \begin{bmatrix} u_1 \\ u_2 \\ u_3 \\ u_4 \end{bmatrix}$$