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Old 28-12-2005, 05:08 PM   #1
Steve555
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Default Attach To Motion Path: random speed fluctuations?

I created a curve on the surface of a NURBS sphere, then attached a locator to it using Animate->Motion Paths->Attach To Motion Path. When I play the animation, it correctly follows the path from the beginning to end of the duration over 200 frames that I set, but it speeds-up and slows-down during the journey, apparently randomly. It does it on playblast and batch render too, so it's not a performance issue.

It seems to happen by different amounts each time I try a new curve.
Is there anything that could cause this to happen, and is there a workaround?

Thanks
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Old 28-12-2005, 05:57 PM   #2
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Check that Parametric Length is unchecked in Attach to motion path options.

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Old 28-12-2005, 06:54 PM   #3
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Thanks, but that's not the problem here.
After trying various curves, it seems something to do with the curve crossing isoparms and amount of curvature. It's easy to recreate with a quick doodle on a basic nurbs sphere. Weird.
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Old 28-12-2005, 07:11 PM   #4
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... and it's worse when the curve goes near either of the poles.
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Old 28-12-2005, 08:37 PM   #5
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this is because of the spacing between the CVs of your curves. u can try and see this by ineractively moving a CV while the animation is stiooped at mid point
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Old 30-12-2005, 02:52 PM   #6
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Thanks for the suggestion, but that's not it. In the screenshot there are 13 equally spaced CVs along a motion path, for an animation 100 frames long.
Anything attached to this path covers a distance across the first 10 CVs in the first 30 frames, and then slows right down and takes 70 frames to travel the last 3 points.
It's definitely some kind of bug related to being close to the poles.
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Old 30-12-2005, 03:52 PM   #7
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no its not.

its the spacing and position and tengency to the next CV.

its really just like the graph editor.

adjust the tengency to adjust the speed.
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Old 30-12-2005, 04:41 PM   #8
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On the new screenshot you can see the identical curve placed in two different locations on the sphere. The copy on the side of the sphere does not exhibit the strange behaviour of the original one, i.e. its motion path speed is consistent across the whole length.
The *only* thing different about these two motion paths is their position on the sphere. Spacing, position and tangency are the same. It seems unreasonable that they should behave completely differently.

From Maya online help: "When you first assign an object to a motion path, by default, the object travels along the path at a constant speed."
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Old 30-12-2005, 07:46 PM   #9
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well, in this case thats your problem.

the curve is on a surface.

so the speed is relative to the UV of the nurbs sphere not the curve itself.
if u want to motion path on a curve that is projected on a surface, i suggest u duplicate the curve once its projected the uniformly rebuild the curve.

otherwise the speed will always fluctuate as the object travels along the curve, which is sitting on a surface;
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Old 30-12-2005, 08:01 PM   #10
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Thanks, duplicating it as a standalone curve fixed it, even without rebuilding it.
Shame the manual doesn't mention this glaring caveat.
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