Two pin connections in series w

[jhansson]

Hello!

I am trying to assemble a mechanical device that contains one body (an axle, body A) that is free to rotate in relation to ground and then on this body there is a new body (a ring, body B) that is free to rotate in relation to the first body but with its axis coincident with the first axis.

My idea to model this was to constrain body A with a pin connection to ground and then constrain the body B to the first with a new pin connection. I am allowed to do this but it doesn't behave as expected because when I try to drag the body B around its axis on A it to starts to rotate around its own axis to ground so that both rotates in relation to ground. I understand that this behavior doesn't contradict the connections but it is still odd behavior and when performing a dynamic simulation later I don't want the extra mass of B to effect the inertia of A.

Do anyone know why it behaves like this and if there is anyway around it?

Kind Regards

[sdensberger]

I'm a little unclear of what your system looks like; can you provide some visuals? What's the goal of your simulation; what do you hope to learn? When you say, "dynamic simulation", do you mean rigid or deformable?

[mlindqvist]

I'm assuming you want to do this analysis in Creo Mechanism / Mechanism dynamics, i.e. rigid body motion, correct? If you assemble components using mechanism constraints, just make sure you connect the right thing with the right thing. I.e. when connecting part A with part B, make sure you only use references from A and B. When you "click and drag" components, they might always not move as you intuitively would expect. If you impose the motion using motors/forces on joint axes / parts, you get a better idea if your components are properly connected.

If you are anlayzing this in Creo  Simulate (i.e. FE-analysis), I prefer to use beam elements and links to create "joints" where I can control what degrees of freedom to release or not. Just as with Mechanism Design/Mechanism dynamics, you need to be careful what you connect to what.