Droidekas, also known as destroyer droids (destroyers for short), or as rollies in clone trooper slang, were a type of battle droid used by the Trade Federation during the Invasion of Naboo and, later, by the Confederacy of Independent Systems during the Clone Wars.  
They could transform their shape by curling into a ball and moving up to 75 kilometers per hour across a surface, or stand on three legs and utilize a shield generator while firing at a target.