Dynamic Simulation - Understanding Spatial Joint

[high.lea]

Hello

I am trying to learn Dynamic simulation and have gone through the Dynamics Simulation Basics tutorial; showing a toy catapult.

In Task2 you add a Spatial Joint between the ball and the cup and then a 3D Contact between the same two parts.

The ball is free to roll around in the cup, then to be flung out when the catapult fires.

I cannot find the purpose of the Spatial Joint in any references. Why is it there when I would expect the 3D contact to be sufficient?

Any explanation would be appreciated.

[johnsonshiue]

Hi!

Spatial Joint is a joint allowing two components to freely move by themselves. Indeed, in theory it may not be needed if 3D Contact already exists. It is possible that the joint was created first to allow the components to move and then it is easier to do 3D Contact joint in this case. There seems to be a redundancy here.

Below is a brief description of Spatial Joint.

https://knowledge.autodesk.com/support/inventor-products/learn-explore/caas/CloudHelp/cloudhelp/2018...

Many thanks!

[JDMather]

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@johnsonshiue wrote:

.... There seems to be a redundancy here...

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@high.lea  Can you provide link to the tutorial?

@johnsonshiue

I don't think there is a redundancy.  3D Joint by itself does not add DOF to the Projectile.

But if the tutorial says to add the Spatial between the Projectile and the ArmBucket rather than between the Projectile and the GroundPlane - then I would suggest changing the tutorial.  It would work that way, but I always prefer to make the Spatial in reference to a grounded part.

[high.lea]

Thanks, this goes a way to explaining things. I also saw a You Tube Video:

Part 5 - Dynamic Simulation & Finite Element Analysis (FEA) - Autodesk Inventor 2011

that described the need to add a spatial constraint to allow the projectile to move. i.e. to get it out of the 'Grounded' section.

Would like to see this made clearer in the tutorials and help

[JDMather]

Basically,

the Dynamic Simulation Environment work the opposite way that the Assembly Environment works.

In the assembly environment you are adding constraints that remove Degrees of Freedom.

In the DS environment you are adding Joints that add Degrees of Freedom.

The end result is the same Degrees of Freedom for the mechanism, but approaching the problem from a different way.

The Spatial add all 6 DOF for an unconstrained object in space.

[johnsonshiue · Accepted solution]

Hi JD,

Many thanks for the suggestion! I will work with the team to understand it better and see what we can do.

Thanks again!