Rules
Robot Combat Rules
There is no single governing body for Robot Combat which means each event can use whatever rules they like but the different rule sets have a lot of overlap. The first thing you should do before building your robot is to figure out which event you are building for and determine which rule set they use. Before you get too far into your robot make sure to know if the event you are building for have any exceptions for changes to the standard rules.
Sparc.tools has the most commonly used rules for Robot Construction and Match Procedures.
The Fighting Robot Association is centered in the UK and most events in Europe use their rules. The RFA rules are very similar to the Sparc.tools rules but there are a few differences so if you plan on competing in events across the two rule sets be sure that your robot will qualify.
The Norwalk Havoc Robot League has their own set of rules and have some differences in weight allowances for multi-bots.