Rigid Group, Rigid Joint or As-Built (rigid) Joint ? which to use and when NOT?

[petrara]

I have a model with a lot of parts making one rigid element which will then have to move in relation with others. My struggle here is to choose which is the best method for locking together all the parts which form one single "block".

I've been reading that As-Built joint and Rigid Group may not perform as expected in combination with other joint types and when doing motion studies... don't know what to believe about that, if they don't perform as they should, then is either a bug, or a feature that should be re-evaluated.

So, from three ways to rigidly assembly elements together: rigid group, rigid joint and as-built rigid joint, which would you recommend and why? And most importantly, when you DO NOT recommend a certain type of joint (and why?)?

Not long ago, @jeff_strater made a very clear video about differences between copying and mirroring (see it here: https://forums.autodesk.com/t5/fusion-360-support/what-is-the-difference-between-mirror-and-copy-in-...)
Maybe he would be kind enough to bring some light about joint types in the same manner. Many thanks to anyone could provide some helpful answers about this matter.

[jeff_strater · Accepted solution]

thanks, @petrara .  This is a very good question.  I thought about a video, but there is just not that much to show in Fusion itself.  So, I'll just write a post that hopefully answers your question.

The short answer is:  these are all fairly equivalent methods of connecting components together rigidly.  There are a few differences, though, that are worth pointing out:

• Like all joints, the difference between Joint and As-Built Joint is important and worth understanding.  Joints can do two things:  They position components relative to each other, and they define relative motion between two joints.  The Joint command does both things at once - defines how the components should be placed relative to each other and (optionally) define the motion between the two.  Since here we are talking about Rigid Joint, there really is no motion component to the Joint (other, than, I suppose you could argue that Rigid defines motion as "whatever motion the other component has, I'll go along with").  So, the difference between Rigid Joint and Rigid As-Built Joint is simply that As-Built says "I'm OK with the components where they are, there is not need to reposition them for this joint",
  • As an aside here - the idea of an As-Built relationship between components is unique to Fusion.  The fact that you can design a component in place and be able to create a relationship to other components based on that position is, IMO, pretty powerful.  Joints are taking a beating by one user on this other thread:  joints-after-18-months-i-still-hate-joints, but I think that being able to do this kind of position-based modeling outweighs some of the (valid) concerns.
• Rigid As-Built vs. Rigid Group.  Not to bore you all with history, but, originally there was no Rigid Group in Fusion.  As we implemented the Rigid As-Built command, we realized that, because there was no motion, there was no need to prompt for geometry in this command.  Only joints that define motion needed that extra information.  So, it kinda dawned on us:  Why limit Rigid As-Built to just two components?  That's how Rigid Group came to be.  A Rigid As-Built joint is just a Rigid Group with two members.

regarding which to use when:  If you can build your design in-place, definitely use Rigid Group.  There is definitely an efficiency benefit to a single Rigid Group vs lots and lots of Rigid As-Built joints, simply because Fusion has to go through that long list of Rigid Joints at solve time.  The only time I would use a regular Rigid Joint is when you have to:  Because you are creating multiple instances (so only the first instance can be built in place), or if you are reusing components from another design (external components).

Hope that helps to shed some light on the topic.

Jeff

[petrara]

@jeff_strater  so, i don't know how to say it differently, but you should ask for a raise. 

Your explanations were always comprehensive and clear.

To summarize, My understanding is the following: as-built (rigid) and rigid group are in essence the same command, except that rigid group is more efficient in computing.

Also، I assume all (rigid) joint types would behave the same during simulations, copy, import, etc? No surprises?

Thank you once again to make light in my head.

[I_B_Jones]

Jeff, in your very good and helpful answer you say at the end "The only time I would use a regular Rigid Joint is when you have to: Because you are creating multiple instances (so only the first instance can be built in place), or if ..."

Please will you clarify what you mean here? (and perhaps update the original post) E.g. are you saying in "Because you are creating multiple instances" that RJs should be used rather than RGs if you might later create copies of those rigid set components? And why? Does it matter which operation you're "copying" them via?

Many thanks...

[jeff_strater]

sorry for the delay.  Sorry I was not clearer.  Hopefully the attached screencast will help clarify what I meant.  The short answer is:  When you just have one instance of a component, you can build it in place, and an as-built joint or rigid group works fine in that case.  However, when you go to create a second instance, it is difficult to get it positioned correctly, so you can't easily use as-built.  This is when I would use a regular rigid joint

[jason_wee1369]

How do you find the rigid group in which a component is tied to, with joints i can right click -> select referencing joints, but rigid group i have to find it under joint of the parent component which can be hard if i have so many other joints.