# particle system move in an elliptical orbit.

I am trying to move a particle system in an elliptical orbit around a stationary central point using rigging like in this video  https://www.youtube.com/watch?v=4kEjyOMCNFA.   In essence I am trying to make a rudimentary atomic structure with three orbits around a nucleus.   Any thoughts?  Thanks.

• Moderator

I haven't watched the video you linked.

I assume the video covers a circular orbit by rigging the Emitter point to a center point.

For an elliptical orbit you need to add a couple of steps. First, make certain your emitter lines up with your pivot directly along an axis. So if the pivot point is 0, 0, 0, put the emitter at 0, 0,1000 (Z-axis. You can use a different axis if you prefer).

Now lets rotate the pivot point 1 complete rotation every 4 seconds by animating the Y-axis of the pivot. Your speed may vary, but I'm using 4 seconds because the numbers line up for easy explanation.

Ok, an ellipse has a major (long) and minor (short) axis. Lets make our major axis 2000 units in diameter and our minor axis 1000.

As set up on frame one we're currently doing a 2000 unit diameter circle. To make an ellipse, keyframe the Z-position property of the emitter point. At seconds 1, 3, 5, 7, 9, etc,  set the emitter Z-position to 500. At seconds 0, 2, 4, 6, 8, etc set emitter Z-position to 1000.

That's one ellipse down.

Duplicate/rename both points for ellipse 2--reparent duplicate emitter to duplicate pivot. Repeat for ellipse 3.

Now, adjust the ORIENTATION property of each ellipse to get it spinning in the direction you want. Adjusting the SCALE of a pivot point will increase or decrease the total size of its ellipse.

If you use a different rotation speed, the key is you need position keys for major/minor axes every 90 degrees of pivot.

For a more "parabolic" orbit, make the positions of the major axis asymmetrical. Maybe Z=300 at perigee and Z=1300 at apogee.

• Thank you, Triem. That was very helpful.