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Joints and Inconsistent Contact Sets

Message 1 of 9
253 Views, 8 Replies

Joints and Inconsistent Contact Sets

We have, as a company, been running into the limitations of 360 quite a lot recently and I suspect that this is another one of them.


I am trying to examine the behaviour of a hydraulic ram and a rotating cog. The ram contains a piston that is able to slide back and forth and is fixed at the base by a pin, about which it is able to rotate. The cog has 16 teeth that the piston engages with. The full assembly has 4 rams that actuate in pairs with opposite rams actuating together, one pair pushes whilst the other retracts and the shape of the cog means that it acts like a ratchet.


Not shown in the media attached is a spring which pulls the ram towards the cog to ensure that it engages with the teeth.


My problem is that the contact set that I have created between the piston head and the cog only appears to work intermittently. As well as this, I have set a rest position for the rotation pin that the ram rotates on, which it sometimes returns to and sometimes does not return to when released.


It would be really helpful if I could animate / model the interaction of these parts as we are testing out some new cog geometries to try and solve an issue we are having with some of these pieces of equipment.


As I mentioned at the start, I know this might just be beyond what fusion can cope with, but if anyone has any advice on how to make it work or suggestions as to alternative modelling methods than the ones I am attempting, I would be very grateful.


(Can't figure out how to capture my screen for a video happy to do so if someone explains how to)


Message 2 of 9

Multiple hydraulic pistons



I would use Autodesk Inventor Professional - Dynamic Simulation Environment for this mechanism. 

Message 3 of 9

Please attach your model.  Open it is Fusion 360, select the File menu, then Export and save to your hard drive.  Attach the file to a reply post.

"If you find my answer solved your question, please select the Accept Solution icon"

John Hackney

Beyond the Drafting Board

Message 4 of 9

Thanks, but I'm looking for methods within 360.


If they don't exist, then so be it, but this isn't worth the time required to set up in a new program.

Message 5 of 9

What format would you like to view it in?
Message 6 of 9

It should be exported either as a F3D or F3Z file, I will use either.

"If you find my answer solved your question, please select the Accept Solution icon"

John Hackney

Beyond the Drafting Board

Message 7 of 9

Please see the attached file

Message 8 of 9

You have a few things working against the success of animating this model.  One, Contact Sets in Fusion 360 leave a lot to be desired. Two, you will need to build in a backstop of some type.  In the attached video you will see my simple backstop which adds an additional backstop.  Also you will have to come up with an animation sequence of the cylinder motion.  If contact sets worked well, this would not be an issue but the dragging of the cylinder across the gear really plays havoc with the contact set.  The little bit of manual operation I did in the video will fail after a little while, which I cannot explain.  If I had to get this animation to work, I would try and create a separate assembly will all active components in the same assembly, not external, make very simple single component joints and contact sets and then maybe you could be a working model.


By the way, your model is very nicely organized, a little to deep in its external referencing for my taste but that is me.  Good luck.


"If you find my answer solved your question, please select the Accept Solution icon"

John Hackney

Beyond the Drafting Board

Message 9 of 9

Thanks, I appreciate your time it sounds as though it is probably more effort than it's worth then.


We are probably going to try quite a few different iterations and I think I'll just have the parts cut from wood and test them physically. We already have the rams and the frame in the workshop and that method guarantees that no fusion bugs creep in to the testing.


We have to be sticklers for assembly hierarchy, some of our assemblies are getting quite big and it's easy to loose track of parts, especially if they are used across multiple projects. As I said above we have certainly started to reach the limit of fusion, we initially went for it so that we could model parts like these but our scope has expanded a little, the first image below has roughly 40,000 individual parts extending through up to 10 assembly levels and occupies roughly 40GB of RAM when open. The second one shows where this frame sits.


If I were to choose CAD software again knowing what we were going to end up using it for, I would have probably chosen something different, but the shear volume of models I would have to work out how to integrate make changing too much work.


Screenshot 2023-05-24 130206.png

Screenshot 2023-05-24 130340.png



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