Issue with multiple rod end mates in assembly

[Anonymous]

Hi.

I'm a new user of Inventor. I'm trying to put together a model of a pick and place robot to model forces, etc.

Each of the connecting arms has a rod end/universal joint on it. This is causing a lot of issues.

I managed to draw all the piece in a couple of hours and have since spent the better part of half a day trying to get everything to mate properly. Every time I move the model around a mate breaks, it actually needs another 3 connecting rods added to it to restrict movement but it took long enough to get it to this point. 

I attached a copy of the model files. What am I doing wrong? Why is it so difficult to make assemblies?

 

[WHolzwarth · Accepted solution]

Try it with 3 new assys. All other parts are unchanged. Copy your fileset to a new folder, and then in this folder overwrite the old IAMs with the new ones.

IMO it's better using a single Insert constraint instead of an Axis Mate - Plane Mate combination. It's a remarkable decrease of total number of constraints.

[jtylerbc]

Additionally, you seem to be using Flexible subassemblies (rod end) that contain a grounded part (rod end receptacle).  I don't know if it is related to the specific issues you have been having, but this often causes instability and should be avoided. 

Instead of grounding it, constrain the "rod end receptacle" part to the origin planes of the "rod end" assembly.  This will cause your rod end subassemblies to behave much more reliably.

[johnsonshiue]

Hi! This particular constraint system is a bit unstable. There are too many DOFs left. Certainly, we have issues in constraint solving and flexible sub. But, leaving way too may DOFs does not help. I have added a few logical angular limit constraints. It seems to work better now. Could you take a look at the attached file?

Many thanks!

[WHolzwarth]

Hmm, Johnson.

Did you have a look at my files?

[johnsonshiue]

Hi Walter,

That was a great solution! Indeed, it is much more stable than the mates and angles.

Many thanks!

[Anonymous]

Wow! It actually works now! I will definitely be using the hole mate a bit more, I'm not sure how I missed that one and yes the "Winkel" is key. Thanks for looking into that, much appreciated.

[Anonymous]

Thanks for looking into the assembly. The base plate is still suppose to move in all directions so constraining it to the central axis won't work.  The assembly actually has 9 dof and I want to model the motion so I think I need to keep all of them.

Cheers. Mitch

[Anonymous]

Okay thanks, will do.

Cheers.