Slinkys

[[olly]]

hey,

Is there an easy way to animate a slinky? I have looked at the contest entrys for the helical cable and they are somewhat difficult for me to understand, being a total houdini novice. The slinky doesn't have to move just like a real one, but something similar would be nice.

Cheers for any help

Olly

[old school]

Here is a 10 minute hack at a slinky using the path tool to create a curve, build a tube by sweeping NURBs circles then creeping a line to build the slinky.

It needs some more work but should give you one approach to do it.

I should have used 3 times as many bones.

The bones have to be made stretchy to fit the endpoints of the curve. See Rabbit Spine.

Have to add a mid point controller to move the stretchiness about to get that nice pulsing effect as a slinky moves around. Probably CHOPs dynamics driven with keyframe overrides.

You could control the endpoints with keyframes, particles, expressions, whatever.

Slinkys are very difficult because you have to manage coil intersection with extreme bends. To do that, I captured and deformed a tube with bones using proximity capture. I then used a Carve SOP to cut it up in to a few column curves. I then smoothed the curves to remove the kinks then skinned the result. It is the kinks in the curve that cause the slinky band intersections and that is what the Smooth SOP is for. Increase the iterations to get more smoothing at the trade-off of interactive speed.

I quickly crept a single line to the tube using rotate in Z and scale in Y until the line spiralled nicely along the tube.

I believe none of the helical demos dealt with the problem of coil interference as the chord spiral diameter was far too small compared to it's length. An entirely different problem.

-jeff

slinky.hip.zip