Should I be able to complete a loop of jointed components?

[lemelman]

I've spent a considerable amount of time trying to assemble a structure consisting of 4 equal length round rods and 4 identical right-angled connectors. Each connector containing two sockets at right-angles to each other, each having the same depth and the exact diameter of the rods. In the real world, such a structure would be self levelling when assembled. Three rods could be assembled with 2 connectors, the fourth, with a connector at each end, could then be attached to complete the structure.

In Fusion I can perform the same assembly with revolute joints, until the very last joint, to which Fusion issues the message that the computation has failed. I'm surprised that Fusion cannot create this structure "automatically" with the available joints. Are my expectations too high? It seems to be a rather severe restriction.

[chrisplyler]

TrippyLighting wrote:

The reason this does work for @chrisplyler and not for you that the parts have a more advantageous pre-orientation before joining them.

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That is not the reason. I am able to assemble them easily regardless of the starting orientations. The reason is that he just isn't joining the bits into the right positions.

[jeff_strater · Accepted solution]

Thanks for debugging that one, @chrisplyler.  I found I was able to delete all the joints and apply new ones fine, but I never did find what was wrong with the original set of joints.

I found that there is an opacity setting at the Body level of the cnctr component:

I have no idea how this opacity setting got applied, however

[TrippyLighting]

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@chrisplyler wrote:

@TrippyLighting wrote:

The reason this does work for @chrisplyler and not for you that the parts have a more advantageous pre-orientation before joining them.

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That is not the reason. I am able to assemble them easily regardless of the starting orientations. The reason is that he just isn't joining the bits into the right positions.

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You are correct. I did not actually debug this design to get revolute joints to work, because they are the wrong type of joint to se for such an application. This whole exercise with revolute joints is really more of academic value rather than practical.

The use of explicit joint origins as show in my screencast would totally avoid the issue of picking the wrong geometry for a joint.

[chrisplyler]

Not that it makes any difference, but I don't understand why he's starting out with the eight components in a jumbled mess anyway.

One sketch. With a parameter for the square dimension.

A rod and an ell modeled in place.

A circular pattern for each.

All already positioned correctly.

A single Rigid Group to bind them together.

[lemelman]

Thank you chrisplyler, it now works just fine. In mitigation, I had a very hard time fixing rev6 because the transparency made it very confusing to determine the joint origin. After fixing that it still didn't work, and then I noticed that rev3 was also wrong. Fixing that fixed it. Thank you again, I feel far more confident. Now to find the cause and cure of the transparency.

[lichtzeichenanlage]

I'm just hoping that you're respecting the underlying message: This way of assemblies will slow down things fast.

[lemelman]

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@jeff_strater wrote:

I found that there is an opacity setting at the Body level of the cnctr component:

Thanks for finding that Jeff, I'd checked the opacity setting for each component but didn't think of checking the bodies. So easy when somebody points it out.

[lemelman]

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@chrisplyler wrote:

Not that it makes any difference, but I don't understand why he's starting out with the eight components in a jumbled mess anyway.

This thread was started as a consequence of my original thread titled "Help with a wonky assembly", in which I requested help with untwisting a curved pipe that had assembled the wrong way round. I had spent a lot of time creating all the different types of connector needed to model a special wheelchair and decided, rather than starting again from scratch, to actually start with building the rectangular seat section, which I thought would be self aligning. It didn't work, so I decided to create a new "test" framework with the rods oriented arbitrarily to see if Fusion would self level it. That didn't work either but, because I knew it would work in the physical world, I got to wondering if my expectations of Fusion were wrong. It didn't occur to me that I had made a couple of stupid mistakes. As a consequence of this thread I've learnt three very important lessons:
1. Fusion can do the self levelling.
2. Use revolute joints only when they are really needed
3. Be pernickety about defining joints - it's very easy to select the wrong origins.

Thanks to everyone who helped get me out of a nasty jam.
   

[lemelman]

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@TrippyLighting wrote:

I've attached the model resulting from the screencast below that shows how to do this properly.

You can of course experiment with these revolute until until the cows come home but revolute joints are not the proper way to join this.

You might notice that I ground as early as possible. In the screencast I don't ground until after the first compost has been modeled, but in the attached model I've grounded the component before geometry was modeled in it and that is perfectly valid also.

Then I restructured you assembly or rather the order. I assemble each component after it has been inserted. I don't always do it that way myself in my own work, but then I don't run into these problems.

For assembling structures with repetitive components I also show how explicit joint origins can substantially speed up the assembly workflow.

Also notice if you Asse,ble this with rigid joints, you need one less joint than when you use revolute joints.

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Thanks for that Peter.  I didn't know you could pre-define joint origins; that's a definite time saver.

This type of modelling is very different to my previous 2D+3Daddons system, but the new concepts are beginning to seep through.

If only there was a proper user-manual - it's very difficult to glean the essential material from the various snippets scattered around the "Learning" section.

I very much appreciate the help and advice that this forum provides.