Moving Frames in Simscape Multibody without associated mass and moment of inertia

Hi,

I'm currently building a nonlinear model of a motorcycle in Simscape Multibody. I have the following problem:

• The rear frame of the motorcycle is connected to the world coordinate system with a 6 degrees of freedom joint, so that it can move freely in the world
• For sensing and camera purposes, I want to create a frame, which has the same alignment of the x-axis as the moving rear frame of the motorcycle, but itself is not translating and thus has its origin in the world coordinate system.

I've already tried several ways:

• Sensing the rotation of a rotation joint and connect the physical signal to the actuator port of another rotation joint, which leads to the error, that this type of physical connection is not allowed
• Adding a rotation joint between the camera frame and the world coordinate system and an angle constraint between the camera frame and the motorcycle. But this leads to the error ".. degenerate mass distribution on its follower side.". If I connect a mass with a moment of inertia to the camera frame, everything works, but this doesn't correspond to the reality, as the motorcycle then has to put on a moment to move the camera frame.

There has to be a way to solve this properly!

Thanks for your help.

Best regards,

Maximilian

[Yasmin Khattab]

If you want to connect the sensing port of a joint to actuator port of another just add a gain (K=1 in that case) between them

Answer 1

[Steve Miller]

Hi,

When you define a dynamic camera in Simscape Multibody, you can specify its location and aim axis independently. You can choose to have it located at world and have its X-axis along the axis of the frame attached to the motorcycle. The vertical axis of the camera can be associated with yet another frame, though I expect you would pick World or the frame of your motorcycle. You should not need any additional joints.

--Steve