Yes, it is possible to define a custom multibody joint in Simscape Multibody by implementing a Simscape-based custom component. This approach allows you to define the transformation between two frames explicitly, including both kinematics and dynamics, using your own equations. You create a custom Simscape component (`.ssc` file) where you specify how one frame moves relative to another, giving you full control over the joint behavior beyond the standard built-in joints.
You can refer to the following documentation for a better understanding: https://in.mathworks.com/help/sm/sm_examples_interface_block.html
Hope this helps!
