Why does a pin connection physically link two parts during an analysis?

[markdensul]

I am using Creo Parametric Release 10.0 and Datecode10.0.3.0

Assembling one part with a pin connection to ground. Assembling a second part with a pin connection to the first part. There are no other connections between the two parts. Using a velocity motor the rotate the first part. When running the analysis, the second part rotates as well. It should stay still since there are no connections or forces / motors on it. Why does the second part rotate?

[Abhiram_Pande]

Hi @markdensul 

Is it possible for you to share a sample file for better understanding and clarification.

Thanks, 

[markdensul]

Hi, sure, attached.

Thanks,

Mark

[ToddKraft]

Hi Mark,

The rotation of disk2 occurs since you reference disk 1 to make the disk2 pin joint.  The rotation dof is open and it moves since disk1 moves.  If you assembly disk2 with a pin joint that only references the ground part...then it won't rotate.  

In addition, you can lock disk2 when defining the dynamic analysis with one of the 'Locked entities' methods.  Many options will work there.

Regards,

Todd Kraft

[markdensul]

Hi Todd,

Thanks, but my actual analysis connects the two disks via a torsion spring from one to the other.

I'm investigating the relative motion between the two when the first is accelerated.

To do the torsion spring I need the axis to be between disk 1 and 2, but want to make sure the only thing turning disk 2 is the spring force, not some 'artifact' of the software.

I tried custom forces on each disk to mimic the spring, based on the rotational angle difference between them, which seemed to work.

However, I also need to create a gear-like connection between the two, again based on the angle difference.  I can't find a way to do this gear without disk 2 being assembled to 1.

Ideas?

Regards.

[markdensul · Accepted solution]

Hi,

Just an update -

Tried more things with the test assembly I provided.

The second disk only turns with a velocity motor applied to the first disk.

It does not turn when I apply an acceleration motor, a force load (to generate rotation), or a torque load on the first disk.

I will go ahead with my model having disk 2 connected to disk 1, since I am applying accelerations and forces, not a velocity.

Thanks!