It something that i saw someone use on Youtube and i really hope they dont mind me publishing this.
The idea is EFFECT! which i suppose is the idea of most if not all elements.

The ball rolls onto the platform causing it to swing down while remaining perfectly level.
At its lowest possible point the ball is kicked from underneath pushing it off the platform at which point is springs back up.

Here it is to the best of my ability!

Step 1: Frame

The frame comes in two sections. The box and the loading ramp
The box is a simple shape but it is important to note the red axle that crosses the box section at the far end.
Onto the box section will go all other components.

Step 2: Platform

Once you have these two parts, connect the grey rods to the yellow connectors noting that the hinges hang below the rails.

Step 3: Pivot A

This is the primary counterweight.
The yellow axle covered in spacers connects to the lower end of the frame.
The blue rods join to the blue and of the platform at the orange connectors.
You may substitute other materials for the tyres

Step 4: Pivot B

This is the other pivot point for the platform.
The yellow rod covered in connectors joins to the frame at the higher end.
The blue rods join to the yellow end of the platform at the orange connectors.
Its complicated because its important.

Step 5: Assembly

The frame comes together at the available connectors
The platform joins together (yellows to grays)
The pivots are first attached to the frame.
-Pivot A to the shorter end of the frame
- Pivot B to the higher end of the frame whilst remaining level with the first
The platform then joins to the pivots (blues to oranges)

I may have left out the onramp which goes on the pointy end of the frame

Step 6: Tinkering

The pictures for this step show the sequence of events of the component.
1     ball rolls onto platform
2 3 ball reaches end causing the platform to swing downwards
4     Pivot arm swings up and kicks the ball
5     Ball is ejected
6     Platform swings back into position

If it doesnt work the first time:
-Adjust the weight at the end of Pivot B.
          -More if it doesnt spring up.
          -Less if it doesnt swing down.
-Add guides so balls dont fall off