Multi Body Work Flow Forces Work Around?

[Anonymous]

Not a tech issue. A user experience issue rather, and here it is:

I want to make a plastic case for a small assembly like a remote control or speaker, for instance. I would start my assembly by placing the circuit board assembly or speaker guts, and then model parts around it.

I wish to use the multibody and plastics tools to facilitate this work flow. Everything goes fine until it's time to create the case components (top half, bottom half), and in the process Inventor prompts me to make a new assembly out of the multibody ipt, or insert the new components into the current (target) assembly.

OPTION 1:

When I place the new components into the current assembly they are not in the right place. They are off to the side. Now I have to constrain them around the very same parts they were modeled in place with or the original multibody part. This is reworking a portion of the TOP DOWN workflow. Model in place, make components, and then re-position.

OPTION 2:

Or I can create a new subassembly out of the parts. But this also requires a work around. I have to RMB>component,>replace, and put the new assembly in place of the multibody part, or I insert the new sub-assembly and position it with constraints, like option 1.

Not too intense, but seems like there should be a more graceful (efficient and on purpose way) of doing this as I create components, like "replace in current assembly" or "put in the actual correct place in current assembly".

Did I miss something?

[udayag]

Please check out Kent Keller's "iMaster" approach:

http://www.teknigroup.com/tutorials/Inventor/iMaster%20Skeletal%20Modeling.html

[Anonymous]

Thanks, but this is not what I had in mind.

All this solution says is to put all the data into the multibody part. You wind up pushing out the assembly components and having to manually place/position stuff anyway. Either that or use component>replace to swap out the copy of the shelf components, with the parts that created the copy. Confusing, manual manipulations are not what I am seeking.

I was hoping someone would tell me where the missing button is that maintains the multibody part in the assembly, and automatically places the made components precisely where you intended them to be when you made them from the multibody solid. I still feel like I've missed a key step and someone will tell me "just check the box....". It makes less sense to use this work flow if you have to reposition everything you make, despite the fact that the master copy is sitting precisely where it should be in the assembly. Why not automatically replace the master multibody part with it's own components, automatically?

[stevec781]

Not exacty sure I understand but I use multibody parts as the basis for all my models.  I make sure that they all are modelled with the same orientation about the 0,0,0 origin.  So  when I use make components they are placed in the assembly exacty as they are in the part in relation to 0,0,0.  If I was to add the multibody part to the assembly at 0,0,0 it would sit on top of the components.  However if I was to mate the multibody part somewhere else, then it would be in a different location as the created components would all still be grounded at 0,0,0.  So for me the key to using multibody workflow is to always work with the top level assembly origin in mind.

[udayag]

My understanding  of Kent's method is that, he uses an Inventor addin called KWIKInsertNFix (which he wrote) to position and constrain the parts. I think it's available for free trial.

This program automates the following: either position each part at the origin and ground them, or add 3 flush constraints between each of the three principal workplanes of a part (xy, yz, and zx) and the corresponding workplanes of the assembly.

[Anonymous]

I am not interested in any third party solutions. I want out of the box functionality. The multibody work flow is built in, therefore to make it practical to use on a day to day basis should be built in.

So I take it the answer is to continue manually replacing the multibody parts. Either I manually replace the copy of the shelf parts, or I manually replace the multibody solid. Now I wonder why someone didn't think this through all the way, it's been out for years now.

If multibody solids are for use in top down work flow, why do they seem so "bottom up"? Obviously my eyes work and I haven't missed anything.

Here's the pull quote for the multibody brochure: (attention Autodesk Marketing!)

"We combine the best top down work flows with the most tedious and manual bottom up work flows, it evens out eventually."

[Anonymous]

Here are three jpgs showing the problem.

First, I show the circuit board and multibody part in the assembly. The circuit board was the first component placed into the assembly, the case was modeled around it. So far so good.

Next, I show the create component dialog. It wants to put the new components into the existing assembly. Still on track.

Last, I show the resulting skewed placement of the components.

0,0,0 was thrown out the window by Inventor. How is the new component set compliant with the 0,0,0 of the multibody part it was made from? Z got flipped, and everthing else is off center.

This is the exact problem I am trying to find a solution for. Did I push a button wrong, or is this the intended outcome?

[udayag]

The problem is due to the multi-part body ("multibody case.ipt") not being placed at the origin. You need to make it grounded and set its origin to be (0,0,0). You can set the position in the occurrence tab of the iProperties dialog.

You should not try to replace the "multibody case" with the newly created parts, but simply set it as a reference part. Yoou could also make non-visible.

If your "multibody case" was designed associatively (using associtive copy body, adaptive cross-part sketches etc.) then the new parts should now position correctly.

[Anonymous]

"The problem is due to the multi-part body ("multibody case.ipt") not being placed at the origin. You need to make it grounded and set its origin to be (0,0,0). You can set the position in the occurrence tab of the iProperties dialog."

[actually no. The multibody case created it's own origin. The circuit board has it's own origin. The circuit board is sitting with it's origin at the same place as the assembly origin. I have no control over where the multibody part takes it's origin from, in this case it made it's own, see attachment. FYI there is no "occurance" tab in the iProperties of the multibody case part]

"You should not try to replace the "multibody case" with the newly created parts, but simply set it as a reference part. Yoou could also make non-visible."

[This is not the problem I am having. Optimally I would keep the multibody master in the assembly file, but if I have to manually place the components created from this master, I am doing what is called "a work around". To users, "work arounds" are not the correct way and are considered sub-optimal. I am looking for the non-work-around, more optimal solution, such as having the parts show up automatically in the correct place, incidentally, where they were created]

"If your "multibody case" was designed associatively (using associtive copy body, adaptive cross-part sketches etc.) then the new parts should now position correctly."

[Again, not according to the jpgs I've provided. It appears that the "insert components into target assembly" feature (during component creation) is taking the origin of the multibody solid (which was generated automatically) and using it to position the components around an entirely different origin, being that of the assembly.]

I think I have my answer. There is no way to use the program, as designed, out of the box, to create assembly components from multibody solids without the need to take time and diligence to manually RE-POSITION the newly created components.

The comment about creating the multibody parts around 0,0,0 assumes I can move the circuit board to the origin that my created component will have, prior to creating the new component. That's just silly. Imagine moving the roller coaster assembly so that 0,0,0 of the coaster assembly is precisely where the origin of the Create Component will be when you make the cover for the electric motor assembly. Wow.

My only quest was to find the right way here because this seems like extra work and requires manual diligence. If someone knows the correct way for this to happen without trying to out guess Inventor's Create Component dialog, or upload some third party work around, please let me know.

[udayag · Accepted solution]

My imprecise use of the term, component origin, may have caused confusion. And I understand your impatience with this issue.

Let me suggest a simple change to your workflow that should give you the correct behavior.

I assume that your workflow was as follows:

1. Place the circuit board assembly, 6K0595B.iam

2. Create a new empty part for "multibody case" during which you selected some planar surface in the circuit board assembly.

3. Finish "multibody case" by adding various features

4. Call "Make Components", etc.

These are the workflow changes I suggest:

In step 2, instead of picking a circuit board face, select the origin workplane "XY Plane" of the assembly.

Now, in step 3, you might have to use Copy Object command to copy the relevant circuit bord surface in to the "multibody case" part. You could then use the copied surface to define a sketch.

This workflow change would cause all the new parts created to have the same component origin as the assembly.

[Anonymous]

@ phil-mcam

First, I'm not sure I understand the purpose of placing multibody case.ipt into the assembly, but typically I would approach this situation like this:

1. Create multibody case.ipt 
2. Derive 6K0595B.ipt into this part.
3. Create Cover and Base solid bodies, by modeling around the derived body of 6K0595B.
4. Use Make Components to create Cover.ipt and Base.ipt in a new assembly (Multibody Assembly.iam)
5. Place 6K0595B.ipt in Multibody Assembly.iam
6. Use the Ground and Root Component command (found on the Productivity pull down) to place 6K0595B.ipt precise at the same coordinates it originated at.

There is no need to have multibody case.ipt in the assembly, but even if you do want to place it there for some reason you could use the Ground and Root Component command. I think you're workflow just needs a bit of adjustment then you'll find it all to work fine.

Second, I understand getting frustrated, but not the attitude you display at the person who was trying to help you.  I considered not replying at all, because I've learned that some people just have nasty attitudes and are better left to figure it out the hard way, but figured I'd take a chance. Most people on this forum are happy to help, but will also be happy to ignore your posts if they read you post as ungrateful, etc.

[Anonymous]

Not everyone designs like you BMiller.

Your steps:

1. Not going to happen. I am making parts in an existing assembly.

2. Why derive when I can work directly on the assembly I am creating components for? Extra work, extra diligence, no thanks.

3. No need for this, the assembly already exists in a state in which I wish to model around it.

4. I might need a new assembly, but in this case, I am already working in the assembly I wish to create parts in. No new sub assembly required or desired.

5. So I should place a component into an assembly where it already exists? This makes no sense to continually need to insert the same components or representatives thereof.

6. This is the extra step I am trying to avoid by simply having the components placed into the existing target assembly. 

I ask for a non-work-around and all I get are work-arounds which involve copies and replacing copies. I finally get what the other person was saying about using the origin of the assembly. That makes sense. I am about to test it out. In which case, it's a zero work around solution exactly as I was asking for. 

[Anonymous]

sorry I tried to help.

[Anonymous]

Dear Udaya,

Thank you for your clear and precise explanation. I just tried it and it worked perfectly. I am too used to creating components by selecting the other parts as the reference.

For a part like this it doesn't matter much where the origin is and choosing the assembly origin is just the same as any other choice, with the brilliant exception that the new parts go right where they belong. Benefits: no extra button pushing, no extra copies of the reference assembly, no extra part constraining/positioning. It's a win-win.

Thank you again for answering the question I actually asked, and thanks for your patience with my responses! 

Kind Regards,

Phil

[udayag]

Hi Phil,

I am glad that you were able to finally find a solution. As you noticed the idea of a coordinate system that is shared among parts and assemblies has many benefits. It's a simple answer to the chicken-and-egg problem where you need geometry in one part defined with respect to another part, in order to define the relative position of the two parts. So by simply saying that both parts have the same position, geometry becomes independent of position.

I also want to point out that you might want to look out for instabilities that may happen when "incontext relationships" are used heavily. These relationships are created through commands like copy object and crosspart sketch projection. As the other user pointed out derived approach is an alternative for establishing relationships between components. Derived approach tends to be more stable though not quite as natural as the incontext approach as you too noted. Just recognize that these are various tools at your disposal, and use them as the circumstances warrant.

Regarding your original observation, it seems that we should have done a better job of at least warning the user when he used Make Components with a part that did not share the coordinate system with its assembly. A better solution would have been to apply 3 flush constraints between corresponding principal planes of the multibody part and newly created component. This should have been done as part of the Make Component command.