You basically need to make a conveyor belt or tank-track arrangement - such that you have a load of identical pieces, all joined together in a loop (probably loosely bolted together, but you could also use string or something similarly inflexible).
Then some wheels or cogs being powered by motor bolts inserted into the loop to drive the whole thing like a fan-belt.
If you build such a thing, do make sure to test it thoroughly, for long periods, with lots of stress testing (jumping sackfolk on and off repeatedly), to make sure it will work consistently. Newbie creators often fail to test such mechanisms properly, then they break or slip during gameplay and make the level impossible to complete.
