Personally, I think it can be. The problem with any of these gravity wheels or magnetic motors is one of symmetry. Gain a little but then loose a little. In the end, there is no net gain. In order for something to demonstrate an excess of energy, it must be constructed in such a way that symmetry is not maintained, gain a little, loose a little less. I think it can be done. If multiple forces (IE gravity and magnetic attraction) are used and if a path can be plotted that requires less energy out than in. - At least thats my theory.

I don't believe anyone really knows conclusively what gravity is.  There are many theories, but they are still just theories.  I don't believe anyone can conclusively say whether it is a monopole or a dipole force.  The observable effect that all objects in earths gravity field are accelerated at the same rate - regardless of mass - is an important observation that bears pondering on ... is gravity is a dipole - a bit like a "river" of energy -  and anything flowing in that river gets accelerated up to the same speed and can't exceed it? ... if gravity was a monopole attraction, shouldn't the speed just keep on increasing the closer the masses get to each other?

A big factor in how we view gravity is whether we believe that space is an empty vacuum with mass dispersed throughout it - or is space comprised of a real but invisible material (lets call it aether), and mass is like bubbles or standing waves in this material?  The great electromagnetic scientists who gave us electric power all tended to believe in aether.  It makes good sense: electromagnetic waves have to "wave" something - otherwise they aren't "waves".  There are good reasons to believe that Einstein A/ wasn't the originator of his key concepts, and B/ set science back 100 years by pushing certain wrong concepts. 

Personally - I tend to view gravity as a flowing river of aether.  Aether has no mass - but mass is created out of aether.  Aether flows like a fluid - highly complex movements.  Study things such as the "Aspden Effect" or "Casimir Effect" to get some clues as to why I believe this should be considered as true science.  As for the Michelson Morley experiment which "proved" the aether doesn't exist - that is either deliberate fraud or very bad science.  All it proved is that there is little or no velocity difference between earths rotation and the aether they were looking for.  If you believe that the earth is completely embedded in the aether, and in fact each particle composed out of aether, then obviously the aether will be rotating at exactly the same speed as the earth too - no speed difference will be detected.  Bad assumptions leading to stupid conclusions (or deliberate fraud used to hide important truths).