Advice on my 'Coaster' project

Here's a quick clip of the little 'roller coaster' I'm working on. Hope this is the right place to ask.

I could use some advice about a couple things; I'd like to use a bigger servo on the lifter, and I'd like to connect it to the lifter using levers and bellcranks, pushrods etc. to give it more 'Rube Goldberg-ness', I'm still researching this on some Radio Control forums, but anything anybody can add to the mix is appreciated.
I'd also like some opinions on a device/circuit to trigger the servo when a ball lands in the lifter. Photodiode? Hall effect sensor? I'm open to all suggestions.
Eventually this coaster will be mounted on a base with room for expansion and used to prototype new 'complications' (spiral tracks, loop-the-loops, trapezes etc) for other coasters. Thanks all!

It looks as if you are using metal balls, so perhaps you could arrange a 5V wire that was shorted to the chassis via the ball?