Here are some pictures of the mechanism that makes the Kitchen Sink Coffin rock.......

Wiper motor is from a Saturn. I run it on 5 volts which provides the perfect speed for this application. See my wiper motor page for more details

Coffin rocker mechanism spans the width of the coffin, making for a long pivot arm and therefore very little stress on the motor. The pivot arm pushes on the 1/2" bolt which goes through the bottom of the box (the bolt is loose in the hole). Because of the way the coffin is "balanced" (see drawing below), this causes the coffin to rock when the motor is turned on.