When building my latest and so far biggest K'nex ball machine, I've used a few elements which weren't on Instructables yet. I didn't describe all elements used in this machine, just the ones which weren't featured here yet.
It's also a nice chance to show some pictures of my 332 cm(130 Inch, 10,9 feet) tall machine itself! It's the biggest I've ever seen, and also the biggest on Instructables. As you can see I had to take out one of the ceiling plates to fit it in.
In K'nex terms, it's 21,5 red rod blocks tall.
Step 1: The Grabbing Dropping Arm
This arm grabs a ball at the end of a 45 degree down sloped path. It then releases it, and makes the ball fall into a basket below.
By sliding the counterweight up and down, you can tune the speed with which the arm moves.