This is another one of those ideas I had for awhile hoping I could eventually use for myself but I don't think I'll ever get to a ball machine. K'nex is dieing hobby for me. Anyways the concept is pretty simple. As long as you don't have any other motorized moving parts and all you need is a lift, this should work. What if you just made a simple rubber band powered sling? You could have 2+ balls running on the track. One hits the bottom and then stays right over the launcher. Another ball will pass over a trigger device that shoots the launcher and the the ball flings upwards. Suppose it could work? The trigger device would be a little tricky but if you end up getting it to work, plenty more people could make ball machines if they don't have motors. Of course you'd be limited to the amount of bands you could place on the device but that's better than nothing.