I agree, just do an experiment once a week and you should be good, also keep it simple experiments with alot of factors are a no bueno, like at regionals a few years back we got a mini catapult, rubber balls, rubber bands, tape, and a meter stick. The obvious choice was a catapult but we decided to do a drop and bounce experiment, (If the color of the ball changes the structure of the balls, then the balls should bounce different heights). It was a good decision, everyone else in our block used the catapult, people were running everywhere for balls that got thrown to hard, catapults were slipping, it was not good. We ended up getting third which i think is decent, so in short practice, and keep it simple.
hope this helps