Hello Jonghyeok Kim,
By default, the “rigidBodyTree” object represents rigid body trees with a fixed base. This means that the base body of the rigid body tree has a fixed position and orientation in the world. You can simulate robots with 6 degrees of freedom (DOF) by attaching a “floating” type rigid body joint to the base body of the robots. Floating-base robots can freely translate and rotate in space with six degrees of freedom.
The following code snippet demonstrates how to attach a “floating” base to the “rigidBodyTree” objects and visualize them using the “show” function:
% Create a rigid body tree object with data format specified as "row"
rbt = rigidBodyTree(DataFormat="row");
% Create a floating base body and assign it a floating joint
floatingBaseBody = rigidBody("floatingBase");
floatingBaseBody.Joint = rigidBodyJoint("j1","floating");
% Add the floating base body to the rigid body tree
addBody(rbt, floatingBaseBody, rbt.BaseName);
% Load the ABB IRB 120 robot model and set its data format to "row"
abbirb = loadrobot("abbIrb120", DataFormat="row");
% Set the base name of the rigid body tree to 'world'
rbt.BaseName = 'world';
% Add the ABB IRB 120 robot as a subtree to the floating base body
% ReplaceBase is set to false to keep the existing base of the ABB IRB 120 robot
addSubtree(rbt, "floatingBase", abbirb, ReplaceBase=false);
% Define the base orientation using ZYX Euler angles and convert to quaternion
baseOrientation = eul2quat([0 pi/3 pi/3]); % ZYX Euler rotation order
% Define the base position
basePosition = [-1.1 0.2 0.3];
% Combine the base orientation, base position, and the home configuration of the ABB IRB 120 robot
floatingRBTConfig = [baseOrientation, basePosition, homeConfiguration(abbirb)];
% Display the robot in the specified configuration
show(rbt, floatingRBTConfig);
axis equal; % Set axis scaling to equal
title(["Robot Joint Configuration With Base", "at Desired Position and Orientation"]); % Add title to the plot
For further understanding, kindly refer to the following MathWorks Documentation:
- Refer to the ‘Examples’ section to understand the details of the “floating” base to a “rigidBodyTree” object: https://www.mathworks.com/help/robotics/ref/rigidbodyjoint.html#mw_625b73a4-b5d8-4838-b9e5-e6162a3b219f
- Refer to this example to understand how to use robots with “floating” base and apply inverse kinematics to them: https://www.mathworks.com/help/robotics/ug/inverse-kinematics-for-robots-with-floating-base.html
I hope you find the above explanation and suggestions useful!
