topic Re: Joints for 6DOF Platform will not calculate in Fusion Support Forum

Joints for 6DOF Platform will not calculate

cbredel7UJ2X — Fri, 04 Aug 2023 13:35:46 GMT

I'm working on a preliminary design for a 6 degree of freedom motion platform. It uses 6 linear actuators for motion that have ball joints at the ends. I'm attaching to the platforms using cylindrical joints, though once I have the design more refined, they will just be revolute. I can manipulate the the cylinder's joint to line up everything, so I know it fits.

I've done a similar project where I have 3 cylinders moving an item and while I got the joints to attach, it wouldn't let me manipulate the object through space correctly.

Is this outside the abilities of Fusion, is there a better way for me to do this, or am I just being stupid?

Re: Joints for 6DOF Platform will not calculate

TrippyLighting — Fri, 04 Aug 2023 16:20:18 GMT

Before you progress to the admittedly finicky ball joints, my recommendation would be to start with a solid design foundation.

That means that all of your sketches should be fully defined, meaning fully dimensioned and fully constrained.

I've done this once on a simpler design to see if Fusion 360 can solve this (design is attached).

After opening it, you can drag the top around and it works for a while, but it is also very easy to get the joints to misbehave.

Re: Joints for 6DOF Platform will not calculate

jhackney1972 — Fri, 04 Aug 2023 17:03:48 GMT

This is what the Joints folder looks like when your file is first opened. The assembly joints on the OP model will be a real challenge.

Re: Joints for 6DOF Platform will not calculate

TrippyLighting — Sun, 06 Aug 2023 16:49:06 GMT

@jhackney1972 thanks for pointing that out.

Attached is the version I should have attached.

But even that one, after some playing around with it in the viewport will exhibit that strange behavior.\

All the ball joints features in the timeline will get sick!

I've not tried digging into why ...\

https://youtu.be/MK9mg8tlKd4

Re: Joints for 6DOF Platform will not calculate

cbredel7UJ2X — Mon, 07 Aug 2023 13:35:19 GMT

Thanks for the responses guys. I've been playing with it and I have found an interesting method to make this work.

I have the ball joints preset in the cylinders

Move the top frame to a point the joint calculation is simpler (e.g. right above the lower joint) and make a cylindrical joint. Do not set joint limits.
Set loose Joint limits through the Edit Motion Limits (I used 1.5" for the slider), do not use the option through Edit Joint.
Repeat for all joints.
Re-edit the slider limit so the max and min are the same
Now go back and switch for cylindrical to revolute joints.

It's quite time consuming but it does work. I'm thinking Fusion must have a limit on the number a joints it will manipulate when calculating joints