Flexible Sub Assemblies - a Tip

ZW3D 2020 introduces Flexible Sub Assembly.

So if an assembly has some Degrees of Freedom (DOF) is can move. e.g. a shock absorber is models so the shaft can slide and rotate.
When the shock absorber is inserted into an assembly - by default it is rigid.
To make is Flexible within the parent assembly, RMB on the assembly in the Assembly Manager and choose Make Flexible

So here is the important part:
If the sub-assembly was created in any version prior to V2020 you may find the result is unpredictable

To fix this you need to recreate a new version of the Sub-Assembly within V2020.
Before you do that, rename the old Sub-Assembly_OLD
Create the new Assembly in the same original file as the existing(old) Sub-Assembly and use the original name(no _OLD). Remember to save occasionally.
Once completed - return to the parent Assembly and use the Change Component Option to swap the OLD for the new replacement.
You will have to Redefine the constraints to locate the Sub-Assembly.
Now you can Make Flexible the fresh Sub-Assembly and it should behave correctly.

Cheers - Paul

I am building a model with sliding subassemblies mounted on pivotting subassemblies and am in the design strategy stage. I want to use subassemblies to help in trouble-shooting constraint conflicts as there will be very long constraint chains. There will be constraint conflicts partly because computers use a binary approximation of small numbers and the small errors add up over a long constraint chain. Does anybody know how many levels of subassembly can remain flexible or is it just one level. If I incorporate a foreign subassembly into my top level assembly, can the foreign subassembly be made flexible?

Hi Jim,
not sure what you mean by foreign! Made in France perhaps?
Any imported geometry/assembly looses its a constraints.
So you rebuild the constraints within ZW and it should be fine.
The Shape format is irrelevant.
Cheers - Paul

I should have said external part. Assuming that I do not bring any external parts into the top assembly, this is the scenario for a tilt tray truck. The tilt frame pivots on the truck chassis using hydraulic rams. The slide frame slides within the tilt frame to extend the tray down to the ground. It is easy enough to keep the tilt frame pivot flexible to the chassis and to keep the slide frame flexible to the tilt frame but, will the slide subassembly still be flexible when the tilt frame subassembly is being tilted and will the hydraulic cylinder subassemblies be free to slide axially and pivot about their upper and lower mounts. I do not want to do all this in one assembly without using subassemblies because of the number of constraints. In other CAD packages I have used there is a limit of 2 levels of subassembly which can remain flexible, top assembly, subassembly, sub-subassembly.

Hi Jim,
I understand Inventor did flexible subs but I did not know about sub/sub.
I have not tried that level.
Sub assemblies are OK but it can get a bit tricky keep it all together if there is to much ‘losseness’ in the constraint system. One has to try and see what works.
Curious to hear how you get on.

Paul, so far so good. I am finding that tangent constraints are unstable in this design with few parts but lots of subassemblies and constraints. I have had to build a workaround for one tangent. It may be that my laptop is running out of memory. I have a hydraulic cylinder with each end constrained to a different flexible subassembly which only works if inserted as two separate parts and even then can only be constrained in two directions, either both mount holes concentric to their lugs or one mount hole concentric to one lug and the rod and cylinder concentric. It is overconstrained with all three constraints in the assembly but OK as a standalone part. Interestingly I can have the mounts constrained and the rod and cylinder parallel but not concentric in the top assembly. This allows me to push the alignment close enough to make a usable drawing. On the troubleshooting wish list is a method of documenting the chain of constraints in a way that lets you work across subassemblies. Part of my enthusiasm for subassemblies is that the workshop organisation can follow the model. Each workstation can build one subassembly using its own cutting list and BOM with final assembly at another workstation, a bit like building a car.

Hi Jim,
thanks for the update.
Just a little thing but it catches me out often is the Lock rotation element of concentric constraints.
It has its used but I like to see that if could be switched from RMB with out having to redefine the constraint.
I am presuming you have figured that out.
Re management. of constraints.

USE - RMB pick from list when a part is highlighted?

Pick the Assembly in the tree and RMB Constraint Redefine?

Cheers - Paul