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Objects orbiting around a central object

255 Views 1 Reply Latest reply: Jan 12, 2013 3:29 PM by fox_m RSS
Brie-Eating Surrender Monkey Level 2 Level 2 (260 points)
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Jan 12, 2013 8:31 AM

I have 15 or so objects which need to revolve around a car. One is a comet — I'll get to that in a moment.


I've tried the "Orbit" behavior, and it works okay. But it seems to orbit the objects around in a circle around the center of the car. This means the objects crash into the hood and trunk of the car (over or under it, of course). What I'm more looking for is an oval rotation.


I've tried using a motion path — or many identical motion paths— (one for each object) but always end up with unintended problems with the animation. First, once I build the path and duplicate it to the other objects, it pastes them way off to the side and I have to move them back to the same spot. But the biggest problem is that, once I get all the motion paths on top of each other, the objects all start at the same control point so they're all on top of each other as they move. I need to place them where I WANT along the motion path as they move, and I just can't seem to figure out how, and I haven't been able to find this at Is there a way to place ALL the objects on the SAME motion path and stagger them along the route? And how would I make it so the last object moved through the last and then first control points instead of stopping at the end?


Lastly, the comet — I want the comet to always point to the central object (or the center of the center object is okay). I know how to snap to the motion path, but that's, of course not the same thing. I've asked this in my local FCPUG listserve, but haven't received any responses.

Help would be greatly appreciated.

iMac, Mac OS X (10.7.5)
  • fox_m Level 4 Level 4 (3,340 points)

    Your best bet is probably still going to be the Orbit behavior, with some modifications...


    If you need a "3D-like" orientation, add a camera and set the project to 3D.


    For each object:


    Apply an Orbit behavior. Turn off the [Include] Y axis and turn on the [Include] Z axis. Adjust the Strength parameter to determine the speed of the orbiting object. (When you play this now, you should notice the size of the object changes in Z-space and that it will go behind the object it's orbiting around.)


    Select the object and type Command - Shift - G to create a group containing that object. You can use the Transform Rotation X parameter of the Group to offset the "plane" of the orbit and use the Transform Rotation X parameter of the object with the opposite value to reorient the object vertically for the camera.


    The orbits will now appear to be elliptical.


    For the comet object, add a Basic Motion > Point At behavior and supply the car graphic. You might have to adjust the anchor point to give some extra distance from the comet's head to the car graphic, but properly set up, the tail should rotate through "space" and appear to point at the car object.  If your comet is built of a circle and tail shapes in combination, then group those two objects and add the Orbit and Point At behaviors to that group. You will need to select that group and create another group to nest the comet graphic group as outlined above to adjust the "plane" and vertical alignment of the comet.


    Screen Shot 2013-01-12 at 5.17.39 PM.png

    (Perspective view in the canvas -- a "car" object, a blue dot and a "comet" [grouped circle and "tail"] ... note the relationship of the "Anchor Point" which lies on the orbit behavior path and was adjusted to make the comet graphic appear to align with the orbit's center point)




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