timer controler

We've built a number of scares over the years, each one capable of being triggered remotely with a simple push-button control. However, this requires someone to actually sit there and trigger the scares every time someone walks by them... not overly practical, since we get quite a few visitors...

I want to make or buy some kind of a timed device to bang on the inside lid of a coffin to make it look like something inside is trying to get out. If the banging is too regular, the effect won't be very good. I need some way to put a timer to something like a 110v electric variable speed drill...

I bought a Constant fog f/x timer controller (model # 17463) a year or two ago and i though it would fit my fog machine i had but it did not. so i am selling it for $7.00 including shipping email me if interested.