Bryan, I see a lot of plan forming here. You have a choice of weight types, appearance appeal, size issues, and so forth to decide on, but the real question here is what to do about negatives. A bit of an inventor myself, I think the ideas of electromagnets, motors and all that are good in themselves, but would substantially add to the cost of the units. I'm thinking of a way to use a weight stack (what tha hey, we're talkin' machines, right?) that would use a preselected amount of weight, add weight at the top (when you lift it there) and release the weight at the bottom. This would be done mechanically, using catches of some sort, with plates waiting at the top to be released from a top stack, suspended above the working stack. Then, at the bottom of the stroke, the bottom plate would be released to allow you to be able to press the stack back up for the next plate. You would preload the top stack with your 'loaders' before each set, and the 'dumpers' released would be at the bottom after the set. The initial problem with this system would be that the stack would be getting higher each rep. So, the next step in this rough draft would be to figure out how to ...waitaminnit, I've allready figured most of it all out, heheh. That should be enough info to get some grey matter warmed up here...and I probably just gave away another good invention. Thing is...when I know what you want to build, I can design the mechanism into it to make the negs happen. You just can't do it with freeweights. And I don't need motors, airbags, or hydrogen pumps.