topic Re: Constrained and dependent motion joints in Fusion Design, Validate & Document Forum

Constrained and dependent motion joints

tperry5XEH6 — Sun, 29 Jun 2025 02:25:02 GMT

I am having trouble modeling the joints and driving them here. The outer box is stationary. The middle box moves about the rods, and the inner box about their rods. Additionally I want to constrain the motion if they hit each other if that is possible. This is just an example of part of something I am working on and having trouble with joints similar to these. Any help is appreciated. I've attached the f3d file.

Thanks,

Tim

Re: Constrained and dependent motion joints

TimelesslyTiredYouth — Sun, 29 Jun 2025 09:21:27 GMT

I could waffle in a feeble attempt to explain minimum and maximum turning points and making the joints, or I could give you the document where I learn everything:
Fusion Help | Joint Motion Limits | Autodesk

you may need to go back a few pages to see joints and how they work...

With your issue with constraining the motion

Fusion 360 has a tool called Contact Sets.

This lets you tell Fusion: “These two bodies should act like they’re solid — and stop if they hit.”

How to use it:

Go to the Assemble menu and choose Contact Set.
Select the two bodies you want to interact with (in your case, the middle and inner boxes).
In the browser, expand the Contacts folder and make sure “Enable Contact Sets” is turned on.

Once that’s done, when you move the joints, Fusion will prevent bodies from moving through each other — they’ll behave more like real physical parts.

I'll see if I can do this to your file if I get the time, otherwise I'm presuming someone else from the forum will do so

Tired regards

Ricky

Re: Constrained and dependent motion joints

jhackney1972 — Sun, 29 Jun 2025 15:18:58 GMT

Using a Contact Set will work ONLY between the outer and first inner box. It can be applied between the first inner box and the inside box but it will not function. This is because your cannot have a Contact Set between two components that have a motion joint between them. If you change the first revolve joint to a Rigid joint you can add a Contact Set to the first inner box and the inside box.

This problem will probably be best handled using Motion Links. Even then you will probably only be able to rotate one joint at a time and lock the other. Your model with "eyeballed" Motion Links is attached.

Re: Constrained and dependent motion joints

TheCADWhisperer — Sun, 29 Jun 2025 16:06:10 GMT

@tperry5XEH6

Common logical mistake made by beginners.

The Components are ALWAYS in contact because the pins and holes are the same size.

In the real world there must be clearance between the pins and holes for the mechanism to operate as expected.

Re: Constrained and dependent motion joints

TheCADWhisperer — Mon, 30 Jun 2025 19:58:50 GMT

@tperry5XEH6

If you want this to work without interference - the construction circles give the correct sizes (with .01 for clearance which you can edit as desired, if you are going to 3D print this keep in mind that 3D printing is not particularly precise).

After Revolving the Pin Rectangles for pin and hole you will have to Offset either pin or hole for logical clearance. Mirror the holes and pins.

Only one sketch needed to define the geometry.

I used the Polygon tool rather than Centerpoint Rectangle to keep down the clutter.

You need to add a step on the pins to keep the boxes centered.