text: My daughter is also in 8th grade and you can appreciate the number of hours we dads struggle with these projects.....I am currently building (helping to build) a miniature, erupting volcano.....You know kids like flash....they love the show.  I sat here for a while and thought how about a real timer, like an old style egg timer. you know, the ones with the big knob that you wind up?  A 6 volt battery and a filament or model rocket igniter.(you can get these at the hobby store or make your own out of wire.....My daughter and I built a series of light bulbs for a 7th grade science project ) If you run a wire from the battery and glue it on the timer at an appropriate location...then glue(attach) the other wire to the knowb so that when the timer is wound up the wire moves toward the other and completes the circuit in the appropriate amount of time.  Connect a piece if thin wire as a "gate" to hold the ball and when the timer runs out the battery energizes the wire causing it to melt...the ball rolls down the ramp.  Have fun.....