I was talking with Gareth (of Trolley Rage) about this and he suggested something very similar. In terms of an controller for axes, I guess you would want it to be a on-off affair to get maximum oomph on the swing rather than have any finesse in the controls of it. I've been putting a wiring diagram together for a controller using relays but I found how to wire up reversing solenoids last night so I may need to revise it.