Advanced Assembly Motion

[adnewhouse]

I'm a bit of a newbie, but before I jump into a new project I want to know if it is even possible. The object I'm trying to model is called a Hoberman sphere. It looks like this:

 

(High-Rez: http://store.metmuseum.org/content/ebiz/themetstore/invt/80017595/80017595_1_l.jpg)

I know that I can probably model it but I want to know if motion would work. Is it even possible to model somthing like this in inventor?

System specs:

AMD FX-6100 proccesor

8Gb Ram

Nvidia GTX-550Ti Graphics Card 

[JDMather · Accepted solution]

I modeled a Hobermans's Sphere in Inventor back in 2002.

It is not an easy project.

If you are a student I recommend you pick something easier.

[LT.Rusty]

So that's what those are called.  I picked one of those up from one of the vendors in the exhibit hall at AU2012, had no idea what it was, other than a somewhat entertaining toy.  🙂

Like JD said, that's probably a little more complex than you want to tackle as a n00b.  I recommend finding blueprints for something online, something that's relatively well documented, and that there are plenty of photo references available for, and building that to start with.

[JDMather]

I attended a conference years ago where Hoberman was the presenter.

The real difficulty with this thing in Inventor is that the fastening dimensions have to be absolutely exact (for assembly constraints) and the large number of components with degrees of freedom (which slows Inventor down).

In the real assembly there are clearances that allow less restrictive motion, but in a CAD program everything must be exact mathematically to work.  I suspect I spent more than 80 hrs on this thing trying to figure out the motion geometry (rather than trial and error) even though there are only something like 6 different parts.

The process gave me real appreciation for the genius of Hoberman.

[LT.Rusty]

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@Anonymous wrote:

I attended a conference years ago where Hoberman was the presentor.

The real difficulty with this thing in Inventor is that the fastening dimensions have to be absolutely exact (for assembly constraints) and the large number of components with degrees of freedom (which slows Inventor down).

In the real assembly there are clearances that allow less restrictive motion, but in a CAD program everything must be exact mathematically to work.  I suspect I spent more than 80 hrs on this thing trying to figure out the motion geometry (rather than trial and error) even though there are only something like 6 different parts.

The process gave me real appreciation for the genius of Hoberman.

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You know, that's actually one of the things that I would REALLY love to see in a future release ... tolerances for assembly constraints.  I've got plenty of parts where, because someone made an error of .0001, I simply can't assemble things, and I have to just jury-rig the constraints, or manually align something so it looks sort-of-right and then ground it.

[alewer]

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@LT.Rusty wrote:

You know, that's actually one of the things that I would REALLY love to see in a future release ... tolerances for assembly constraints.  I've got plenty of parts where, because someone made an error of .0001, I simply can't assemble things, and I have to just jury-rig the constraints, or manually align something so it looks sort-of-right and then ground it.

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This is already in the product. Search for constraint limits. However, using constarint limits to give assemblies some "slop" generally strikes me as a bad idea. I think that it is far better to fix bad geometry in a part or subassembly than making more bad geometry in an assembly.

This isn't to knock constraint limits. They are a great tool for assemblies like pneumatic or hydraulic cylinders: You can use constraint limits to allow the rod to travel within the cylinder's stroke.

[LT.Rusty]

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@alewer wrote:

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@LT.Rusty wrote:

You know, that's actually one of the things that I would REALLY love to see in a future release ... tolerances for assembly constraints.  I've got plenty of parts where, because someone made an error of .0001, I simply can't assemble things, and I have to just jury-rig the constraints, or manually align something so it looks sort-of-right and then ground it.

---

This is already in the product. Search for constraint limits. However, using constarint limits to give assemblies some "slop" generally strikes me as a bad idea. I think that it is far better to fix bad geometry in a part or subassembly than making more bad geometry in an assembly.

This isn't to knock constraint limits. They are a great tool for assemblies like pneumatic or hydraulic cylinders: You can use constraint limits to allow the rod to travel within the cylinder's stroke.

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huh.

I use limits all the time for moving parts, but never thought about using them that way before.  Good idea, actually.

[JDMather]

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@alewer wrote:

This is already in the product. Search for constraint limits. However, using constarint limits to give assemblies some "slop" generally strikes me as a bad idea. I think that it is far better to fix bad geometry in a part or subassembly than making more bad geometry in an assembly.

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I doubt this would work for the topic of this thread (a Hoberman's Sphere).  And giving assemblies some "slop" is not a bad idea - it is real world.  We cannot manufacture perfect parts - there is a tolerance associated with every feature, size and position.  The closer we attempt to manufacture to "perfect" the more expensive the part (perhaps more expensive than the customer is willing to pay).  It is difficult to test these realistic tolerances in Inventor. 

Just to be clear - I am not advocating sloppy design practices.  Bad geometry should be fixed.  But this is a different topic.

[adnewhouse]

Thanks for the responses. I think that I'm still going to give it a try, but I suspect that I will fail.

[JDMather]

I'll try to see if I can dig up my old model, but  I think I lost that one in a HDD crash (back-up frequently).

[roboconnell2004]

I wouldn't go into this attempt expecting to fail, or you will... if you are expecting to accomplish your goal and then fail along the way the journey was worth taking. HOWEVER attempting something with the preconceived notion that you will fail is not only a waist of your time and effort, but furthermore is not going to offer the ability to learn from the exercise. You will constantly be fighting the urge to give up instead of marching on, and that is a slippery slope.

JUST A THOUGHT!