Adorable as the cats are, they do like to spread their kitty-litter everywhere. In fact I think they have a completion to see who can get it the furthest! Just sweeping up after them is the obvious answer, but why do the obvious; build a robot instead!
Kitty-Litter Bot, first prototype
The first prototype is shown below.
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The robot moves from left to right. At the front is a saxophone cleaner which is driven by the RCX type motor. This flicks the kitty-litter into the catch-area behind. The video below should make the operation clear. This is only a quick 'proof-of-concept' system; I'll add more details when I get around to the mark 2.