Circular motion - now there's the possibility for an interesting experiment, which unfortunately I'll have to leave for someone else to try even though I've got the necessary bits... but not the time.
First of all, a thought experiment - what would happen if my sat dish beam experiment was mounted on a rotating platform and the modules trigger timeout was reduced down to momentary instead of the 2 sec default?
So then in theory, when the dish is rotated, only objects moving towards or away from the sensor should cause doppler shifted reflections to trigger it, and the direction of such moving triggers could be mapped to the surroundings.
Ok, now to turn that into a practical experiment... using just a radar sensor and a rotating emergency flashing beacon (or cheap kids toy equivalent). Fit the radar sensor in place of the light bulb (using a 3-contact slip-ring if necessary), thereby causing the light reflector to now act as a radar reflector, so now you can start mapping the location of nearby moving objects in its 360 degree 'field of view'!
If you're struggling to think of a useful application for that, think robotic vehicle (or any vehicle for that matter).