I used some of Greg Watson's ideas to build the following. A ramp with a track on it to control a roll of magnets (with wheels on it that run on the track) that is "forced" to roll up the ramp by magnets that are along the sides of the ramp (but not connected to it.)  When the roll of magnets goes past the center point on the ramp (where I have a pivot point) the weight of the roll of magnets causes the ramp to tip down on the new side. The magnets roll downhill and hit a stop at the end of the ramp. By the time they get to the bottom, the ramp on this side has tipped all the way down and is aligned with the magnets that are along the sides of the ramp on this side, which force the roll of magnets back up the ramp and past the pivot point again, tipping the ramp back into its original position. I have gotten the ramp to tip back and forth many times. Sometimes the wheels on the roll of magnets bind up as this is not a "high tech" build,  but I am convinced that by getting the exact right angle on the ramp I can get this to run indefinitely. Oh, I had to put tracks above the wheels on the roll of magnets right at the top of the pivot point, because when the magnets fly up the ramp they will go off into space if not forced to go down the other side. There are lots of different angles that can be adjusted, but I think the idea has tremendous potential.

I actually used model train track for my track and wheels from a model train for my roll of magnets. The ramp is made of plexiglass and the mounts on the side of the track are just wooden with magnets glued on them. All you need is enough "magnetic repulsion" to push the magnet up the ramp past the pivot point, so magnets do NOT have to line the entire length of the ramp.