This is an amusement machine which is made almost entirely from K’Nex. The non-K’Nex components are the balls (which are made of bouncy rubber), the signs and the column labels.
There are two slots; one is for children’s use and is low down, and the other (near the top of the machine) is for adults’ use. When a ball is inserted in the lower slot, a chain hoist raises it to the level of the higher slot - it's powered by a 12-volt K'Nex motor.
Each inserted ball runs down a channel near the top of the machine and bounces down an array of pins. It then lands in one of 14 columns.
Each column can hold up to seven balls. A full column is indicated by a pink flag (in the picture below, columns 4, 9 and 10 are full). When an eighth ball enters a column, the seven balls are released into a winnings tray. The winning ball ends up in a box at the base of the machine.
If one of the three columns at the far left or far right of the machine is filled, all three coulmns get emptied into the tray.
There are some ‘blockers’ between some of the pins so that the balls end up fairly evenly distributed through columns 4 to 11. The three columns at each end are visited less frequently.
The part of the development which was most time-consuming was the design of the ball unit (there are 14 of these - it's the part which holds up to seven balls and then releases them when an eighth ball enters it). It was important that no ball was left in the column after a win, and that the bottom of the column was always closed afterwards. There would have been a lot of time wasted if, after the assembly of the machine, a flaw was found.
The balls are made of some kind of bouncy rubber (K'Nex balls are far too light for the mechanism to work). A box of 400 new balls was bought from an eBay seller. There were four different types of ball, about the same number of each. A quarter of them were slightly larger but about 20% lighter than the ones which were used, and they didn't work very well. Another quarter felt slightly tacky, and the increased friction meant that they didn't work well either. The last quarter had a surface which was more like fabric than rubber, and they tended to slide down the pins instead of bouncing on them. Anyone want to buy nearly 300 bouncy balls?
A video of one of the ball units in action can be seen here: