R3-Series Astromech Droids were a line of R-Series Astromech Droids. They had faster processing capabilities than R2 units due to their Intellex V processors. Most had transparent domes made of plastex. They were manufactured by Industrial Automaton.
The typical height was 0.96m to 1m (3ft 1.7in to 3ft 3.4in). R3s were equipped with a computer interface arm, a holoprojector, a scanner antenna and a retractable third leg.
One R3-Series Astromech Droid, R3-S6, was assigned to Anakin Skywalker during the Clone Wars to substitute R2-D2, who was currently captured by the Separatist. During a mission to rescue R2-D2 from a Separatist listening post known as Skytop Station, R3-S6 repeatedly sabotaged the mission. Unbeknownst to the Republic, R3-S6 was actually serving as a double-agent for the Separatists. During a duel on a catwalk outside of Skytop Station's hangar, R3-S6 was pushed off of the catwalk by R2-D2 and was smashed by falling debris.Canon Film Appearances:
-Star Wars: The Clone WarsCanon or Legends?: Canon

YOU ARE READING
The Guide to CIS Droids
Random(Credits to @-grievousharm for the cover) This book will tell you about all the droids of the Confederacy of Independent Systems (CIS), or more commonly known as the Separatists. Hope you enjoy and learn something. If you don't mind please vote.