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Need less friction/bounce

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Gardner RaymondNeed less friction/bounce
by on Sep 29, 2011 at 5:57:15 pm

I'm working on an animation where there is a sphere dropping down through the ceiling on rails, and coming to a rest at a spot where I've placed a bumper. The rail system is three cylinders offset into a triangle shape, so the sphere can roll along the trough it creates (see a screen grab here: You can see that the beginning of the rail is nearly vertical (80 degrees) and curves to be parallel with the floor.
What I want to happen is the ball to roll down the rails, as if it were a polished steel ball bearing on polished steel rails. However, what happens is more like a slow-falling, bouncing sphere that comes to a stop very soon after the rails curve to parallel. Sometimes, it would bounce out of the trough on it's way down, which is why I added the top set of rails - ideally, I'd like to only have the bottom set. But, it just bounces back and forth on its slow way down.

As for the dynamics tags, the rails are set as Collider objects with 0% bounce and 0% friction. The Sphere has a Rigid tag, and both bounce and friction are set at 0 as well - it just doesn't seem to make a difference. Here is a screen grab of the Sphere Tag:
as well as the Rail Tag:

Any thoughts would be greatly appreciated. Thanks


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Brian JonesRe: Need less friction/bounce
by on Sep 29, 2011 at 11:05:21 pm

Slow falling could be a scale thing, If you are working in too big a scale you'd have to increase gravity to get a fall rate that looks right.

With the sphere on Automatic it should be mathematically smooth but your rails will benefit from having the right interpolation - I don't know which would be best for your setup without seeing the scene file or if it would make a difference in this case - and by not too many or too few polys. If the rails are sweep nurbs try making them editable.

Margins may help.

There has too be enough room for the sphere to fit in the rails with a bit of space, the left and right rails can't both touch the sphere at the same time and if you use margins remember to add that space.

you can also try adjusting some of the Dynamics settings particularly the Expert part, if your fall rate is too low because your scale is too large the scale setting there might help (or not)

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Adam TrachtenbergRe: Need less friction/bounce
by on Sep 29, 2011 at 11:25:17 pm

One thing that should help is increasing the linear damping properties in the force tab. Aside from that, just playing around with a test scene here, the key seems to be adjusting the bank angle of the rails (using rotation parameter of sweep nurbs in my case).

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Gardner RaymondRe: Need less friction/bounce
by on Oct 3, 2011 at 8:14:50 pm

Thanks guys. A combo of a few things helped - adding more height segments to my rails (created using three cylinders and a bend deformer, not sweep nurbs), making the transition angle less steep (solved the bouncing out problem), adding more polys to my sphere, and lowering the margin on the rails to 0.

Now though, when i drop my sphere into the rails to begin its journey, it rolls down the incline half way, and then stops as if it's hit an invisible wall. Any thoughts?

Thanks again


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