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part1_unity.md

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Part 1: Unity Setup

This part includes how to import the mobile robot in Unity scene, and control the mobile robot with your keyboard.

Open Unity Hub and click "Add" button. Navigate to the repository folder and select Mobile Robot Demo folder. Now you could open the added project Mobile Robot Demo.

In this demo, we are using robot freight robot base as demonstration. To import the robot in Unity

  • Navigate to Assets/Scenes and open scene Demo.
  • Navigate to Assets/URDF, right click freight.urdf and click Import Robot from Selected URDF file, then Import URDF. You will see the robot being imported in the scene.

As the robot is using ArituclationBody chain, we are not able to move the game object with Transform or Rigidbody methods anymore. In order to navigate the robot, we will need to actually move the wheels.

To ensure proper collision between wheels and the floor, the original mesh collider of the wheels need to be changed.

  • In the Freight hierarchy, navigate to .../freight/l_wheel_link/Collisions and delete the unnamed game object under Collisions.
  • Click Collisions, and in the Inspector window, under the Urdf Collisions script, select Sphere as Type of collision (The cylinder is not working), and click Add collision. A new unnamed game object is now generated.
  • Navigate to .../freight/l_wheel_link/Collisions/unnamed/Sphere, adjust the radius to 0.0605. You should see the collider surrounding the wheel.
  • Repeat the same process for the right wheel.

image

Now that we have the colliders properly set up, we will need to initialize and move the wheels. In the Pick & Place demo, they provide a sample controller Controller.cs, attached to the game object root "Freight". However, using its control logic to move the wheel will cause an undesired "moving-back motion" when the robot stops. Therefore, we will use different scripts to initialize and control the joints.

  • Remove or disable / unclick the Controller component in Freight.
  • Navigate to Freight/Plugins, click Add Component, search Articulation, then add Articulation Body Initialization and Articulation Wheel Controller.
  • The Articulation Body Initialization script will initialize all the non-fixed articulation joints by assigning stiffness, damping and force limit. In the Robot Root slot, drag and drop Freight, the game object root or freight/base_link.
  • The Articulation Wheel Controller helps to convert input linear velocity and angular velocity into wheel speed for differential drive robot. Drag and drop the two wheel articulation body objects in the slots, and enter the relative track length and wheel radius. In this case, they are 0.37476 and 0.0605 respectively.
  • After having scripts to initialize and control the joints, we need to send the control signals to the robot. Navigate to Freight/Plugins, click Add Component, this time, search keyboard, then add Keyboard Control. In the Wheel Controller slot, we need to put in the wheel controller, in this case, the Freight/Plugins.

image

  • Finally, we can now run the Unity, and try to control the robot with your keyboard. Also, by now, you will have the same setup as scene RobotImported.

image

Proceed to Part 2: Sensors