Simscape: how to simulate trajectory/motion in my assembly

Hi, I have been struggling with simulation the motion of my assembly in Simscape: I would like to simulate a trajectory/motion of said asembly to then read the positions from the joints. I cannot figure out how to import this trajectory/motion. How can I do that?

Can I move rigid assembled parts in space to simulate the trajectory of the whole assembly?

[Yifeng Tang]

You may add a 6 DOF joint to the part and send the motion signal to the joint. You can set up the joint to receive prescribed input motion signal.

[Elia]

Hi, I have tried that, but for some reason it changes the initial position of my assembly. I used a simple ramp as signal so that the part would move "smoothly" to the right position in the world frame during the simulation. Why does that happen?

[Yifeng Tang]

The 6DOF will try to honor the input signal you send in even at time=0. So if the input is indicating a different starting position, the 6DOF may just do that.

A trick you can play is to let the 6DOF joint sense its position, while you run the simulation from the initial condition you want without a position input. You'll then know what is the correct initial position (and orientation) of the 6DOF. Set up your signal to add on to that initial value.

[Elia]

Hello, this worked, but I have another issue now. Only the parts after the joint moved accordingly, but the rest of the assembly did not follow together.

I want to use this to simulate a circular motion of the tip of my assembly and then read the position of the joints in my cardano joint at the base of the system.

Do you have any input for this?

[Yifeng Tang]

Sounds like the assembly isn't put together correctly, or you have some extra DOF that you weren't expecting.

Is it possible to share the model? Hopefully a simple one :)