Length of rope is constant, however the center point isn't. This is exactly what I gave as an example, a ball tied to a rope being spun around. It's an idea for poi, for a performer to use. One in each hand, spinning around.
What they want is LEDs embedded in them that will change color based on the speed in which those things are being spun. There are several static displays on the market already, push a button to turn them on and spin away, but there's no interaction. If you want to change the display you end up having to stop, push the button again, and go on. So I was asked if I can make something that will change colors based on the speed at which they're being spun around.