Problems happening with ~15 joints

[kennymcmackHQFTN]

I have an assembly with about 15 joints and motion links.  One rotary motion starts the motion which drives others joints and links.    They all work on their own individually.  As an assembly, not so much.  The first 8 or so work well as an assembly.  But as I go down the timeline and add more, funny things happen like when I click a piece to start the motion, one part will just jump out of rotation like 10 degrees.  I've isolated that joint to make sure it works and it works fine.  I've remade it so many times.  Then as I turn on more joints to the time, the problem just gets worse and it never works as a complete assembly.  Is there a limit to the number of joints that Fusion can simultaneously compute? 

Thanks 

[aliobidi]

Hi , 

attach your file, with screenshot to mention the part that you meant 

[kennymcmackHQFTN]

Sorry, cant. Its sensitive data.
I was looking for people who have experience with having many joints in a
single assembly and they all moving at the same time.

[davebYYPCU]

I have made Assemblies with 20 joints, and with 2 distinct driving joints, the system works.  There are times that click drag upsets things temporarily, but just have to change the holding point and comes good.

Might help....

[g-andresen]

Hi,

I can only confirm the statement by @davebYYPCU .

Without analysis of the movement system a statement is not possible.

günther

[TrippyLighting]

There is no hard limit to the number of joints. However, there are situations where the joint solver simply locks up when there are too many local minima or maxima in a kinetic system to find a viable solution.

A good way to approach this is to set sensible joint limits.

Also, even with joint limits the chain of joints might be too long. Some folks want to "simulate" a chain where every link is modeled and every link  is connected to the next one with a revolute joint. That usually  stops working smoothly after a number of such chain links have been assembled.

Do NOT use contact sets! 

If you cannot share the design, then the Forum is only going to be able to help with very simple problems and you are limited to "official" Autodesk support.

[TheCADWhisperer]

Can you make up a dummy assembly that exhibits the same Joint behavior as your proprietary data?

[jeff_strater]

15 is not too many.  There is no theoretical limit to the number of joints, but the more that exist and interact, the more complex the solve gets.  Hopefully, you are not using Contact Sets.  Contact Sets can severely impact the functioning of an assembly, performance and otherwise.  Use Joint Limits instead. 

You could be seeing bugs, or there might be some slight alignment mismatch in your geometry and joint system.  Of course, it's impossible to speculate.  If you are a commercial customer, you can create a product support case to get help.

One point I would add is:  Component drag is not the only way to "test" your joint system.  In fact, it is not really even the best, since drag is trying to interpret a view-space motion into a component motion, which then kicks the joint solver into effect.  Some additional pseudo-constraints are added during component drag, in an attempt to make the system favor the component being dragged, which can also affect the solve.  Try Drive Joint or Animate Model as other ways of driving your assembly.  I can't guarantee that you will see different results, but I have seen that in the past.

[kennymcmackHQFTN]

Thanks alot yall. Yall have been very helpful and I appreciate the support. I will try those things out. 

[kennymcmackHQFTN · Accepted solution]

SOLVED!!!  I finally found what I had wrong.  One on my planar joints was fixed in rotation and that was preventing my entire assembly from working.  It's all working good now.  Thanks everyone!

Kenny