Correct me if I am thinking of something different, but I remember having some of my Lego League kids build a similar robot.
Here is what it looks like:
The gears would turn, making the legs go down, then the legs would push backward (moving the bot forward) as the gears rotated back up again. It does sort of remind me of a locomotive, but different in that the legs do the pushing against the ground, not the gears.
I don't know which team did this, but it would be pretty cool to see on a FIRST robot. If the legs used a good traction material, I could see its potential advantages.