We ran into a problem this year, as another member mistakenly stripped the wires and parts out of the device not knowing what it was. While we salvaged the switches back from them we still had to rewire the device all over again.
To address the issue of the balloons not popping and the darts rebounding we changed from popping water balloons to knocking down cups. To fix the device overheating a water pump was used to pump water in tubes around the outside of the coil and a computer fan was used to cool some parts the water didn't run over.
I worked less on the project than I would've liked and did not have the ability to present it at Imagine this year.
The water reservoir was too small so the water would heat up too quickly to be effective long term.
Darts were going through the cracks between cups.
The button that participants pressed short circuited.