I was thinking the same thing.. Custom plugs that attach to the shelf. You could increase speed considerably, which would shorten the time away from lights and create water flow.
the problem being that the racks will have to be free hanging to rotate without turning over, so faster speed might get them flying off level as they swing around (centripetal force?)
Man. Go to sleep n wake up to all kinds of ideas.
So ya, I originally though about a Ferris wheel idea but couldn't see it working as you loose the height of the tank. Since you can only go as wide as the tank say on 29 u only use 12"x12". That's what lead me to using chain and track.
The rack itself I figured would be a double bottom. So basically a shallow box with the shelf inside. The bottom would heavy enough to keep frags from tipping it, while the water does not push directly on the frags. I actually really like the Lego idea but I think attaching would be hard to do. Since the rack is 27" long any hard push in the center to connect you run the risk of it bowing and pulling the ends from the track.
The pool vacuum is a neat idea but do they make small ones? I think it would take too much space in the tank.
Jay do you think the KNex motor would have enough torque to it?
I am pretty much set on a DC Motor tho, allows me to run on a small wall converter or batteries at a swap.
I've done a lot with RC Cars on the past. I'm kinda thinking a brushless motor as I can adjust speed based on voltage and what works best for coral.
Traxxas makes a waterproof one. I'm pretty much on the idea of canopy mounted but it would still be nice to not worry about splashing water.