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Forces and springs to animate part of tube

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The idea is a thick rubber band with both ends tightly clamped so that when a ball strikes the rubber band, the body of the rubber band fluctuates the most at the center and less as it gets closer to the clamped edges.

 

Here's the technical run down, I need to make a tube with 5 ringlets made up of vertices(I don't remember what they're called in A:M) be struck by another rigid body that causes the center ring(#3) to spring/bounce at say 100%, the rings directly above and below(#'s 2 & 4) to spring/bounce at 50%, and finally the top and bottom rings (#'s 1 & 5) not to move at all with a spring/bounce of 0%.

 

How do I go about this?

 

[Apologies in advance for lack of proper technical terminology]

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That's a tough one.

 

You have two different simulations going on; springs and physics. Either Newton Physics (better) or rigid body physics. The "rubber band" tube could be done with cloth. Unfortunately cloth and newton physics don't interact well. It's either one or the other... the chicken and the egg... the horse before the cart. ;). You can simulate cloth or physics first but not at the same time so the ball wouldn't be able to "bounce off" of the rubber band. The ball could hit the rubber band and cause it to move or stretch though. You could have a dynamic constraint to behave like a spring. The trick is how to have it "springy" from the center to the ends AND also be "flexible" to some degree. Usually springs are "stiff" and vibrate like a "stick".

 

This is a tricky one. Not saying this isn't possible. Someone else may post with the perfect solution. I just can't think of one easily without playing around with it.

 

-vern

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bending the tube doesn't really need a simulation. put a bone in the center and weight the middle ring to it 100%, weight the next two rings 60% to center bone/40% to the model bone and the outer rings are 100% to the model bone.

 

right click on a group in teh model window to "Edit CP weights". CP weights are covered in the Help.

 

 

animate the center bone to react appropriately to whatever is hitting it.

 

(very quick example)

rubbertubebonesA.mov

 

 

rubbertube.zip

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Ha!

 

I am rendering another version that uses a "proxy" physics object (static) path constrained to the rubber band at the point of contact with the ball.

 

The steps are:

 

1. Simulate ball newton physics.

2. Simulate cloth rubber band

3. Add proxy physics object with a path constraint to spline in rubber band.

4. Adjust ease so the proxy physics object lines up with the ball at the point of contact.

5. Remove the ball physics motion keys from step 1.

6. Resimulate newton physics

7. Set the proxy physics object to inactive or just delete it.

 

Now the ball will "appear" to bounce off of the rubber band and continue to act like a newton physics object.

 

-vern

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Thanks for this question!

 

It lead to my rag doll physics concept. Constraining that newton object to the spline inspired the idea. If a constraint can make it look like the ball is hitting the rubber band then the reverse would work. Constrain a character to a newton object.

 

I don't think I would have even tried that if it wasn't for this topic.

 

-vern

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