topic Re: Joints not obeying History timeline and other weirdness in Fusion Support Forum

Joints not obeying History timeline and other weirdness

peter_meilstrup — Thu, 06 Sep 2018 06:18:08 GMT

i have been trying to refactor a complex model by moving some sub-assemblies into linked documents. Along the way I have to debug some Joints and re-attach references. This model has now started to act very strangely around Joints and I am stuck.

I did a Build all which revealed a bunch of new joint conflicts, and one weirdness: when I roll back the History marker to the first conflicted joint, all the other joints remain on the Browser and display. The first conflicted joint, which moves the front wheel into place, is marked as conflicted but no other joints reference the same objects at that point in the timeline. If I try deleting the Joint from the timeline, it remains. I can even roll the History marker back to the beginning of the model and all of the top level joints still remain!

I am also getting a warning about "this model contains Removed components that are out of date". I don't think there are any Removed components in the model and don't know how to find them.

Another problem I am getting is later on in the timeline, if I dry to Drive any joints, Fusion crashes.

I am not sure how to proceed at this point.

I have shared the model to https://a360.co/2M16xqi

Re: Joints not obeying History timeline and other weirdness

paul.clauss — Thu, 06 Sep 2018 23:26:30 GMT

Hi @peter_meilstrup

Thanks for posting. I had a look at your file this afternoon and have some thoughts.

To be very frank, I am not sure how the model got into this state. I found that I was able to step through the timeline and recreate the joints showing errors (every one I believe), but every single joint needed to be fixed as it would show the "position calculation failed..." messaging.

This issue often does relate to removed components, reordering of the timeline, or cut/pastes of bodies between different components. I've discussed some of this in the forum thread linked here. There are a few Body>Component features in your timeline, which could be triggering some of these errors. With that said, it is hard to tell how this design got into its current state.

To avoid issues like this, it is important to remember R.U.L.E. #1 - when in doubt, create a component and make sure it is activated.

I've passed the file along to some members of the development team to see if they can provide any thoughts on this, but was unable to get your file into a workable state without slowly going through and deleting and recreating every joint showing an error. I've also inquired with them about why the joints are showing the browser when the timeline is rolled back to before them, as I'm unsure of how this occurred at this time. This suggests some sort of file corruption occurred at some point.

The errors and potential corruption may stem from the design process used for this assembly. It looks like you started by inserting some relatively minor components (crankset, handlebar) and then created some other components (stem, seatpost) at the beginning. You then created some sketches at the top level of the design and used them to create joint origins (presumably to position these minor components). This is kind of an odd workflow - if the bicycle frame was inserted into the design initially, the minor components could be joined to solid geometry directly when inserted (move point to point on insertion and then as-built joint). This would make it easier to visualize the assembly and prevent the types of errors that eventually stack up and cause behavior like this - the model would be much more robust. You could even draw parts like the stem and seatpost in place in the new file, as you could reference the frame geometry.

I think that the best course of action for you will be to save copies of all the components native to your assembly design (save copy as), and delete all the joints within subcomponents. This will allow you to keep the work you've already done, but start fresh in an assembly file. It would also let you insert the components in a more logical order - you wouldn't start assembling a bicycle in real life by putting the stem in a stand. Think about creating the Fusion model the same way - inserting the frame initially sets you up to have an "anchor" when the other parts are inserted or created.

To learn more about how to approach assembly designs in Fusion 360, I would recommend watching the videos linked below. These videos were incredibly helpful for me in understanding how to build strong assemblies.

I apologize that I don't have an easier fix - I think spending the time to create a new assembly will help ensure you have a nice robust model following the tips discussed here. If you are looking for a quick band-aid, you could always remove design history and redo the joints, but this will not allow you to use the parameters in the design. I'll let you know if the development team has further thoughts on this file.

Also of note - I was able to use this file to recreate a crash that the development team is looking into that appears to be related to some errors in geometry being allowed through but causing problems downstream. This is another reason I would recommend starting fresh.

Please let me know if you have any questions.

Re: Joints not obeying History timeline and other weirdness

peter_meilstrup — Fri, 07 Sep 2018 08:22:52 GMT

Thanks for taking a look. I'm not sure that I follow you on inserting the frame first. The intent of this model is to design a custom fit frame and fork, starting with the rider's measurements, laid out in the contact points sketch. The design location of the wheels, saddle, bars and cranks, and the parts to be used, are the constraints that the frame has to be constructed around. So my thinking is the rear wheel and crankset should be located in the design before I can work out which positioning for the the chainstays (also off-the shelf parts from specialty tubing manufacturers) avoids interference. Similarly, the seat should be in a known position, but turning that into a positioning for the seat tube angle depends on the intended seat post and saddle. That's the motivation for the outside-in, frame-last way the model is structured anyway.

I was able to do some more work from an earlier version of the file but I may eventually have to pull out all the separate components, since there does seem to be something weird.

Re: Joints not obeying History timeline and other weirdness

paul.clauss — Fri, 07 Sep 2018 15:35:53 GMT

Hi @peter_meilstrup

Thanks for posting - I can see why you are using this approach. Regardless, I think that positioning components as soon as they are added to the assembly would result in a stronger file.

I would also recommend creating a component for the joint origins and layout sketches rather than creating this geometry at the top level - this follows RULE #1.

I hope this helps! I'll keep you posted if development if development comments on the strange behaviors in this file.