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# 2 pivot points noob question

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 2 pivot points noob question on Aug 16, 2018 at 1:45:43 am

This is probably insanely easy.

I want to rotate an airplane taxiing on the ground first around it's left wheel then around it's right wheel. I can put the plane in a null centered on the left wheel and that under one centered on the right wheel. That works. Once.

Any ideas or link to a post. I couldn't find one.

Thanks so much.

Jeff Goin
Educational Material For Aviation
FootFlyer.com

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 Re: 2 pivot points noob questionon Aug 16, 2018 at 9:03:24 pm

I don't think it is easy if you have a normal hierarchy of parts. The reality is a forward force in the center of the airframe and the plane turns by braking an outboard wheel. If you used dynamics and forces you could simulate that but the set up and keeping everything connected and getting friction and mass correct so you could apply force at a wheel (Which I'm assuming and not involving the rudder) and get the airplane to rotate around that without wheel slippage (assuming a normal speed) would be a lot of work.
Getting a normal setup to work would be tough too ( as you talked about).
What sorts of shots are you using? Can you cheat and cut from one shot to another with two planes, one with the left wheel as the parent (or a null parent on the left wheel) and one for the right, even in a continuous shot you could have two planes and make them visible/invisible at the appropriate times.

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 Re: 2 pivot points noob questionon Aug 16, 2018 at 10:24:34 pm

I wonder if you can use the trick in character animation where the character would pick up and object and then give it to another character. Initially the object is controlled by itself, and then by the motion of the characters hand and then by the motion of the other character's hand.
In your case the plane would be the object and nulls along the path would "takeover" to rotate the plane and then send it on its way to the next null.
The trick is the Parent Constraint tag - heres a link to a tut.
https://www.youtube.com/watch?v=3NjLWf5wwrE

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 Re: 2 pivot points noob questionon Aug 17, 2018 at 12:22:31 am

I've not done even done that but will check out the vid.

Thanks!

Jeff Goin
Educational Material For Aviation
FootFlyer.com

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 Re: 2 pivot points noob questionon Aug 17, 2018 at 12:21:18 am

It's not for a shot but rather how you put a 44 foot wingspan plane (C414A) into a 50 foot hangar with a 40 foot door.

You're right that using forces like that would be above my paygrade/willingness. I want to use a turning radius described the nosewheel's turning limit.

LeftWheel.null
---RightWheel.null
------Plane.null
---------PlaneParts

I may try motion clips. what if I had one clip with rotation around LeftWheel.nul (top level of hierarchy) then the next clip around RightWheel.null. Of course after that second rotation, LeftWheel.null is in the wrong place. But I only need to do the motion twice. I'll see. Even that will take me some time because I've not used motion clips before. Or I may try something even simpler involving rotation around the airplane's center.

Thanks.

Jeff Goin
Educational Material For Aviation
FootFlyer.com

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 Re: 2 pivot points noob questionon Aug 17, 2018 at 12:31:32 am

If its not for a shot then just nest two planes in your null set up. Run the time marker up to where you have made your first two turns, and just before you make your third. Then make a new plane a child of the original plane, you can make plane 2 be exactly where the first is by zeroing out the coordinates of the 2nd plane. Then bring in nulls as children of the first plane and put them where plane 2's rotation points are, setting them as one null parented to the other (4th turn will be a child of the 3rd turn null). Then make the 2nd plane a child of the nulls. animate nulls 3 and 4 dragging the second plane around. Use a display tag on the planes and animate their visibility in the tag so that on the frame before the 3rd turn, the first plane turns off and plane 2 turns on.

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 Re: 2 pivot points noob questionon Aug 17, 2018 at 3:07:36 am

I like that the best. Appropriately simple for my need. Thanks.

Jeff Goin
Educational Material For Aviation
FootFlyer.com

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