Error in calculating path to workspace goal region in robot's path planning algorithm

Hi there, I'm having an issue in calculating a path for my rigid body tree object to follow to the specified goal region. I'm developing a script to find the path from from the home position of the robot to a specified goal region - much like the "Plan Path to a Workspace Goal Region Example" demonstrated in the manipulatorRRT documentation page. My issue specifically is that the plan function can not find a suitable path (outputing IsPathFound = 0, and ExitFlag = 2 - meaning that the maximum number of iterations was reached without finding a suitable path).

I have been following the prevously cited MATLAB example nearly word-for-word and my inputs to the plan function (the rrt object, the initial robot configuration, and the goal region) all function correctly and are passed without any errors.

I checked the following areas to try to fix this issue:

The robot (the rrt object) has the joint position limits set to [-inf, inf] and therefore can be rotated manually through the script to any angle - I believe that the joints have available freedom to rototate during the pathing calculations.

I have placed the goal region very close to the final link and set the bounds to have a very large positional and angular tolerance - I believe this should clear up any issues with difficult to reach angles.

Perhaps my lack of an end effector is affecting the pathing algorithm but every link (and frame of each link) resides in the goal region.

I have attached the URDF file and the smallest working example of the code as a .zip file to demonstrate the issue I'm having. Any help and/or advice would be greatly appreciated.

Thank you, Scott Brown.

Cal Poly SLO - Mechanical Engineering Master's Student

Answer 1

[Scott Brown]

With some fiddling and adjustments I found my error. To generate a path for a rigidBodyTree object there has to be at least six joints in order to work properly - my issue stemmed from using sub-6 joint models.