infinite tube

I need a design for a tube that its outer envelope will be in constant move to one direction. imagine an escalator like in the shopping malls, that always moves in one direction - just in a tube and not a surface. i would like to have an idea how to make it work, it should be a tube that you hold in your hand, with a rubbery envelope. in conclusion: this tube has to have the feeling that its outer envelope is in constant movement. that if i put it on a table, the tube will move forward. i need the mechanism idea. size of the tube should be one that i can hold in my hand. i need a clear representation of the idea and the mechanism. in pictures, text, 3d models and whatever you think will help get the idea. thanks a lot you all! admit that this is an interesting task lol :) further jobs may be in the futur with much more money.