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Object Flips While Aligned to Spline / Tangential

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Dovlet Ov
Object Flips While Aligned to Spline / Tangential
on Oct 13, 2018 at 2:42:47 am

I have a wheel animation which is to follow a spline (road). The wheel consists of several components (tire, brake, rim and logo ) which I combined under a Null (group). I then applied a C4D Tag "Align to Spline". I applied rotation to the null and created start and end points. However as it moves along the path the wheel flips front and back side like crazy. It happens when I apply "Tangential" so that the wheel would turn along the road turns and curves. I have no idea why it's happening. Any suggestions? It's R16. Thank you.


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Brian Jones
Re: Object Flips While Aligned to Spline / Tangential
on Oct 13, 2018 at 4:19:29 am

can you post the scene file?


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Dovlet Ov
Re: Object Flips While Aligned to Spline / Tangential
on Oct 13, 2018 at 11:47:56 am

Not sure how to do it... the file is over 50 mb. And the wheel stopped spinning as well.


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Brian Jones
Re: Object Flips While Aligned to Spline / Tangential
on Oct 13, 2018 at 3:08:35 pm

I wouldn't try and send 50 megs (though I think the limit is 100), I would copy the wheel and the spline it's going to follow and paste them into a new project, save and send that. Sending is easy, there are two ways but the easier one is just to drag the file into the message window.

12798_wheelrotationalongspline.c4d.zip

Here's an old file which does what you are talking about, I think, it uses some xpresso to roll the wheel as the align to spline moves it along.


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Dovlet Ov
Re: Object Flips While Aligned to Spline / Tangential
on Oct 13, 2018 at 10:54:49 pm

I uploaded it but I can't find it. Tried to upload a "striped" version, with only the wheel and the road. I guess here's the link
12801_wheel3.c4d.zip


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Dovlet Ov
Re: Object Flips While Aligned to Spline / Tangential
on Oct 13, 2018 at 11:00:57 pm

Thank you Brian. I tried uploading the project, it's being moderated. Meanwhile I noticed the whee group (null)l flips 180 degrees along the B axis every 21 or 24 frame. And it stops spinning too. I was supposed to deliver the project a week ago...


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Brian Jones
Re: Object Flips While Aligned to Spline / Tangential
on Oct 14, 2018 at 2:27:26 am

there's a whole bunch of animation that shouldn't be there - keyframes on the splines for the spline type and the angle that are not doing any good, keyframes on all the parts of the tire that are not doing any good - The parts of the tire don't all have their axis at the center of rotation which can't be good.
If you remove all the animation except the Align to Spline expression's Position parameter the tire now follows the spline like it should. Inside the null I would make the wheel parts children of the tire itself (except for the brake which shouldn't spin - well the brake rotor should spin but the brake calipers should not, but your calipers are part of the rotor so you're stuck if you don't separate them, then whatever the tire does the parts follow.
After that you can spin the tire in P.

12802_wheel3a.c4d.zip


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Dovlet Ov
Re: Object Flips While Aligned to Spline / Tangential
on Oct 14, 2018 at 3:32:01 am

Thank you so much Brian! It's late now< but I will have a closer look tomorrow


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Dovlet Ov
Re: Object Flips While Aligned to Spline / Tangential
on Oct 14, 2018 at 2:36:27 pm

Hi, Brian. I can't thank you enough for helping me! It works just perfect. One final question: can you suggest a trick to make the wheel slow down shortly before it stops completely, not half way like it does now? Are there settings in the Align to Spline or I have to play with the wheel animation?


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Brian Jones
Re: Object Flips While Aligned to Spline / Tangential
on Oct 14, 2018 at 8:22:02 pm

if you right-click on the word 'Position' in the align to spline tag and choose Animation/Show F-Curve it will bring up the Timeline in F-Curve mode - the line you see is the motion of the Position parameter (which controls the wheel's movement). If the line was perfectly straight (while increasing upwards) it would mean the speed is constant. The curve by default does an 'ease-in/ease-out' it starts in slowly moves at a fairly constant speed then stops slowly, this makes for more natural looking motion (usually). You can change the rate of change by moving the handles of the curve (use the Move Tool). Nearly flat means slow speed change, nearly vertical is the most speed possible.
By default both points are selected and if you move one it will 'mirror-move' the other, if you want to adjust only one end of the curve make sure only that point is selected.
I'm guessing you want the wheel to move in and brake quickly, that would mean shortening the handle but leaving it still the same direction. If you wanted an instant stop that would mean align the handle with the spline so there is no slow down. Play around with it (particularly with a shorter timeline so it's quicker practice).


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Dovlet Ov
Re: Object Flips While Aligned to Spline / Tangential
on Oct 17, 2018 at 12:18:06 pm

Thank you so much, it's all so helpful!


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