To get this model working well, note the following:
- The counterweight needs to be at least 700g (1½lb). In this case, 100 2p coins were used. This is 2” away from the pivot.
- The projectile is a 3/8” ball and only weighs 3.5g or 1/8oz. This is held in a slingshot which is connected 10” away from the pivot.
- It is possible to project the ball by about 3m or 10’ with these weights.
- One string of the slingshot is permanently connected. The other detaches when the arm is just coming vertical, allowing the ball to be catapulted out.
- It is important that there is as little friction as possible. The string to pull the arm to the firing position is placed as close to the pivot as possible. This reduces friction when the cable drum unwinds.
It only worked two out of five times at the September 2009 meeting. The slingshot has been a constant problem and needed redesigning. The redesign is in the second photo.