Is there a way to get the Centroidal Momentum Matrix in Robotics Toolbox?

In Robotics toolbox centerOfMass function returns center of mass of the robot and center of mass Jacobian of it. When I look inside the function I have realized that centroidal momentum matrix (written as cmm) is also being calculated but not returned, and I want to get that matrix. I cannot overwrite the file to change the outputs, and cannot write a wrapper due to class property being private. The error:

'No public property 'TreeInternal' for class 'RigidBodyTree'

Is there a way to get the Centroidal Momentum Matrix in Robotics Toolbox somehow? Thanks

Answer 1

[Amal George M]

Hi Yigit,

In order to access this variable, you can edit the 'RigidBodyTree.m' file outside of MATLAB. At the location "<Matlabroot>\toolbox\robotics\robotmanip\+robotics" (Write permission required). You can add 'cmm' in the list of output variables to the function 'centerOfMass()'. The modified line will be:

function [com, comJac, cmm] = centerOfMass(obj, varargin)

Restart MATLAB for changes to take effect.

Full disclosure: If there is a dependency associated with this function it might result in an error in future. Also, there is no guarantee that the file will be accessible in later releases.

[Marijn Peters]

Hi Amal,

Do you happen to know if this is still possible in matlab 2020a? Or maybe another way to find the CMM in simscape?

kind regards,

Marijn