I need to build a stair unit that will be 4' Tall, 4' Wide, and 8' Long. Thats the easy part. It needs to move, and it needs to be enclosed on all sides. I need to make sure that it won't move when my actors are on it. I am thinking of some kind of weight sensitive mechanism that will allow it to raise up when nobody is on it, but will 'lock' down on the stage floor when someone is sitting/standing on it. Has anyone ever built anything like this?