Start with an outline - possible one listed (badly) below

Soccer Robot Report

by Stanley Lio

Intro (thesis) Statement - (write statement about what it is and what is does, write statement about what you designed. Explain what this documents contains and how you plan to present it.

(optional executive report - summarize document into one or two paragraghs, ususally do this if paper is going up the chain of command, as execs generally don't like to read tech papers, they would ususualy like to have it bottom lined)

Make list of function(s)ality and describe each one

Make list of your designs and describe each one (theory, scematic,testing, and implimentation)

Conclusion(s)

Thats is Stanley, I only spent a few minutes on it, but this could serve as a general outline for you. I hope others will chime in on this too.

Andy