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non-circular rotation tutorial

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Simon Smithnon-circular rotation tutorial
by on Mar 17, 2016 at 5:57:57 pm

Hi all,
been trying and failing to find a tutorial for moving a non-circular 'circle' spline along a path and keep it flat on the surface as it rotates - am actually trying to roll a condensed letter o along a path, that might make it clearer what I'm on about.
If I get that working, that will then hopefully drive an up-down y-axis movement of an object sitting on top of it as it's driven along the path.

Have been getting into xpresso recently so think I'll be able to muddle through the second bit but am unable to get my head round the first bit with the non-circular circle at all.

If this make any sense, would be very grateful if anyone can point me in the right direction.

thanks!


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Adam TrachtenbergRe: non-circular rotation tutorial
by on Mar 17, 2016 at 7:27:26 pm

One way to do this would be to use a deformer on the spline/object, with the deformer being a sibling. Then animate the rotation of the spline/object and animate the whole shebang along a spline. You can look up the formula for end rotation value and get the length of your spline using Xpresso's spline node.


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Simon SmithRe: non-circular rotation tutorial
by on Mar 17, 2016 at 8:22:18 pm

Thanks for getting back Adam.

Sorry, tired so not quite getting what you mean.

Have attached a simple file as a sketch of what I'm on about as I probably didn't describe it very well (faked it with a spline and of course the cube floats and is not moving in y correctly).

Can brute force it in this manual fashion but was hoping to do it in a more elegant way (the xpresso in the file is pretty 'beginners' as you'll see).

if you get a minute to check it out, I'd be grateful.
First time uploading so dunno if the link'll work...

cheers

9893_noncircularproblem.c4d.zip


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Adam TrachtenbergRe: non-circular rotation tutorial
by on Mar 17, 2016 at 10:06:06 pm

So yeah, I didn't quite get what you were saying. I had a thought that could work to solve this problem but it requires the Studio Bundle (Constraint Tag) so hopefully you have that.

Basically what I'm doing is constraining the Cube's position to the letter object, and also clamping it's distance from the letter's surface. That solves the issue of the cube's placement.

However! You can also use this to generate a spline that will keep the letter from penetrating the floor. To do that you use a Mograph Tracer to trace the cube's path. So you'd move the letter along a straight path and trace the cube's position. At the last frame of the animation make the Tracer editable. Set the new spline's intermediate points to uniform and then use that spline as your Align-to-spline path. You'll just have to position it in Y so that the letter sits on the floor.

Example of the Constraint: 9894_noncircularproblemconstraints.c4d.zip


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Simon SmithRe: non-circular rotation tutorial
by on Mar 18, 2016 at 9:57:08 am

Thanks for that, Adam, that's impressive / a great help.

I'm still getting a tiny amount of penetration / rising above but guessing that might be to do with my example font 'o' not being exactly even in terms of radius so will keep that in mind when I do this proper.

Thanks for that constraint heads up, I've had pretty mixed success with constraints but this is a great example to refer to.

You've saved me a bunch of time, thanks again.

cheers,
Simon


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Adam TrachtenbergRe: non-circular rotation tutorial
by on Mar 18, 2016 at 3:23:50 pm

Glad I could help. After doing that file it occurred to be that you might also be able to use the Xpresso bounding box node for the cube position, but I'm not exactly sure how it works. I could get it to sort of work but not 100%.


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