## Random and constrained circular motion

For a small project in the near future I could need some objects to move fairly random, but constrained to a specific area. After a quick look on the web I thought of something I read before but could not find anymore. It involves movement aided by two circles and is (IMHO) really easy to grasp. Here’s a quick explanation.

Imagine (if you can’t, there a picture below doing it for you) one circle in the middle. OK, now imagine another circle centered on the edge of the first. This second circle moves over the circumference of the first, thus describing a circular motion. Now place something on the edge of the second circle and have it move over it’s circumference. Depending on the size of the circles and the rotation speeds the object on the outer circle describes a lot of different motions looking a bit like a spirograph.

The two circles and the moving object (blue)

In the above image, the red circle is the first one. The green one moves over the circumference of the red one. The blue dot moves over the circumference of the green circle. It cannot get outside of the blue circle.

This however is a very regular motion. Not what I had in mind or promised you with the title of this post. There’s no long explanation to it, so I’ll get to it right away: To make the motion random, just have the direction of both the rotations alter at random intervals. Not to often or the final object moves in a jittery fashion (and may not even leave it’s position), not to few or the object moves to predictable. In the example below you can alter the frequency of the direction change as well as the speed of rotation (with thanks to http://www.minimalcomps.com/).

Right-click on the flash file to view the source files.

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