No, there is no fancy mechanism. One of the key features of these projects is that they are very simple to make. I dont know about the weight issue... I have a heavy belt/disc sander combo on one and its a bit awkward to flip, but not terribly so. On another I have a small router table and that one is fine. The major drawback to a heavy tool on top is actually flipping it under as opposed to flipping it up (kind of a controlled 'drop'). Keep in mind its not a dead lift--the pivot supports some of the weight during lift (less at the beginning of the lift till all the weight at the end of the lift).

So the short of it is that the lighter tools are a bit easier. You could make one to give it a try, and always mount a different tool if the planer is to heavy.
-Ted G