The decidedly decent dropper

This is a major simplification of the dazzlingly didactic dropper, which you should read about first if you have not already done so. The two dropper variants illustrate the extremes of mechanical complexity that we expect to see in this exercise. As external link: this movie shows, there is no mechanism to return the ball between runs and the light sensor has to be repositioned manually. The decidedly decent dropper took us around one hour to build and another 30 minutes to write the software. While we do admittedly have a lot of Lego and Python experience, a model of this complexity should be perfectly achievable by a team of three novices in a few hours, leaving plenty of time to do some science with the completed apparatus (i.e. measure gravitational acceleration and observe drag effects). In fact, since the fall is over a greater distance, and the light sensor positioning more repeatable, you should be able to do better science with this than with the dazzlingly didactic dropper. The downside is that you will learn very little about structures and mechanisms, and you certainly won't win any prizes for an outstanding Lego system!

Some annotated photographs 
general viewThe dropper comprises a release mechanism (top), light sensor (lower) and microphone (bottom). The light sensor spots the ball passing by and the microphone detects the moment of impact.
NXT brick positioningA Lego NXT cable will not reach from the tabletop to the floor, so the NXT brick needs to be positioned part way down the column.
release mechanismA close-up photograph of the release mechanism.
light sensor and shadeThe light sensor (left) can be mounted at any height by moving the black axle to another hole. The shade (right) makes the system less sensitive to ambient light variations.
microphone and friction footBeneath the microphone is a friction foot to anchor the column firmly on the floor.

The decidedly decent dropper was designed and built by Graham Treece in May 2010.