The launcher had two main solenoid valves, one to let in the water and one to pressurise with air.
The operator could use the little VB app to set the water fill level (timer based) from inside the classroom. Usually one student would volunteer as the 'fat controller' for the day.
The launching mechanism utilised a bundle of cable ties with the heads all facing inwards in order to grasp the ledge of the bottle opening (when the collar is in the up position). To release, the pneumatic cylinder would pull the collar downwards allowing the cable ties to deflect and release the bottle.
The electrical interface was a Jaycar kit which allowed control of 8 relays via the parallel printer port. A mutlti-core cable was run out to the solenoid box.
The launcher shown here is the second revision of the project. Initially I attempted to build the whole thing on a wooden base and the release mecanism had the cylinder moving horizontally with a fork style release mechanism. This didnt work well as the fork would pull the bottles to one side upon release. Also, the solenoids were exposed to the water.
Below is an old video of the launcher in action.
(I think all the launches shown were from the same 2 hour class)