I used a Coffee Can for the displacer on my Meyers Stirling fan. Having little experience with Stirling engines, I would have thought it would run faster on the wood stove. On a previous post someone mentioned cans with rounded bottoms. My Coffee Can does have the original crimped sealing lip on the bottom, and a thin aluminum plate on the top with a sharp edge. How critical is the sharp edge on the bottom and top? And now can I tell if it is running at "proper" speed?