Welcome to 3DCADForums

Join our CAD community forums where over 25,000 users interact to solve day to day problems and share ideas. We encourage you to visit, invite you to participate and look forward to your input and opinions. Acrobat 3D, AutoCAD, Catia, Inventor, IronCAD, Creo, Pro/ENGINEER, Solid Edge, SolidWorks, and others.

Register Log in

DMU deflecting components - Forumlas

Mark One

New member
Hi, I'm new to the forum :)

I need to animate the following three components for a presentation in a few weeks time. The stick-like plunger components moves inside the stationary brown cylinder and displaces oil inside the green component which causes the green component to expand as shown.

Basically - The silver plunger and the green component have different stroke lengths.

The green component is basically made from a single revolve command. I've used an "Equivelent Dimension" to allow me to change the pitch of the ribbed section of the green component.

What I want to do is have a measure between the silver plunger and the brown cylinder > Divide that by 15 > and set that to the Equivelent dimension on the green component.

This youtube video shows how you can set the distance between 2 planes as the length of a helix - causing a deflecting spring.

If I find the Equivelent Dimension in the tree and click "edit Formula", CATIA won't allow me any references to measures/anything - "....cannot be used in this context"

Is there a way around this? Anything I can do?

Any help much appreciated


Super Moderator
Mark, nice images!

I think I might have an easy solution for you, based on the "cannot be used in this context" message.

First, try to open the original assembly that was used when you first modeled the parts.

If the original assembly can't be used, then open the parts in the current assembly. With the assembly active, right-click on the green component, click on Components + Define Contextual Link menu item. And then click OK in the popup panel.

After you do either the first or second option, you should be able to edit the formula.

Mark One

New member
Thanks for the quick reply!

Ok, so I opened the full assembly including all components.
Double clicked the product in the tree - "product1"
Right clicked the green part > Components>Define Contextual Links
and I get the error:

"Change context can't be applied on this object"


Super Moderator
I think you can do it with a parameter, instead of the equivalent dimension.

A parameter can be related to the measure, and have a formula to divide by 15. And the resulting parameter can be used as the length constraint in the sketch.

Mark One

New member
thankyou so much. I'll have a go with parameters, but I'm not familiar with them.

If you've got anymore info specifically on parameters let me know.
Thanks again,