This year (2016) I am participating in the Christchurch Brick Show and for the Great Ball Contraption I have created two contraptions.
This is a ski lift, it is based on MOC-3763. I added a ball pump based on nico71’s ball pump. The ball pump ensures one ball about every second is sent to the ski lift so that its pickup is not overloaded.
This is a wholly my own creation. The motion is switched by a power functions switch which is changed when the sliding section is at the top or bottom. The switch is in the middle.
The ball lift plan has been published on rebrickable. See MOC-5245