Looking for some insight: Mechanical hammer linkage

Hey all-
I've been looking over a design for an upcoming project, and I decided I'd come here for some inspiration on the best method of doing something.

Here's my issue: I have three pounds total, for the entire project. Exotic materials (like Titanium and Carbon Fiber) aren't really available to me, unless there's no alternative. I need to power a hammer coming down, with as much force as possible. This hammer will most likely be a 1/8th inch thick plate of some sort, with a spike/point at the end. The hammer can be as long as necessary, but I only have three pounds for the hammer assembly, and two drive motors, and some rudimentary armor.

Now the question I have for you all: How would you power it? I don't have weight for pneumatics, or for huge motors that need big speed controllers. The lighter the mechanism, the better. So what would you use?

I've been thinking of directly driving it to an old RC car motor I own, but that option has very little control for the hammer... And I'd prefer to be able to have a button that I'd hit which would send the hammer down, HARD.