How Do Flippers On A Lego Pinball Machine Work?

I am building a lego pinball machine and i have got the pullback right and the coin slot working but for the flippers they keep getting stuck! I use rubber bands but they dont always work and i have tried springs but they are way to strong. Any Sugestions? Oh by the way im only 12 so i would like to only use legos not tecnolegy (Im a very bad speller!!!)