R-series/Legends

"Hmmm... An R-Series. No, no, not for a long time..."

- Gha Nachkt to Anakin Skywalker on having an R2 unit in stock

The R-series was an astromech droid line created by Industrial Automaton.

The R-series was an incredible developmental project, setting several standards and paradigms that other astromech droids would later adhere to, such as fitting into a starfighter socket and having immense aftermarket upgrade and modification abilities. They were very common throughout the galaxy and by far the most famous and popular astromech droid series.

Variations
The original R1 unit was designed from the body shell of the earlier Mark II reactor drone and was generally seen as an improvement of the P2-series astromech droids in its early years. The R1 was much less bulky than the P2, although still large, and able to hold 500 starship configurations. It was the first of the series to hold hyperspace navigational capabilities.

The R2 unit then far surpassed the R1, proving to be smaller, able to fit into a standard starfighter, and with more capabilites than its previous model. It was extremely popular to pilots, and was often used by the Galactic Republic. It could hold 700 configurations, featured full-spectrum, electromagnetic, heat, motion, and life-form sensors. The R2 unit was built for all environments, and came with an array of tools, which depending on the cases, could be electric zappers, fuel squirting compartiments, pincers, lights, holoprojectors and computer arms able to access any computer. R2-D2 is the most notable one of its class.

The R3 unit was based on the R2's basic design, and was only distinguished visually by its clear dome. Unlike the R2, this unit was built for military and government uses, and could hold an immense amount of data.

The R4 unit was designed for antigrav vehicles, and was more suitable to the public than its predecessor. Several of the R2's advantages were removed to lower the price, and make it more available.

The R5 unit followed the R4 in many ways, including its inexpensive build. It was prone to malfunction and an unpleasant personality, so production ended soon after.

The R6 unit was released after the Battle of Endor by Industrial Automaton to cover the huge failure of the R5 unit. Its programming was similar to that of the R2 unit, although it was built using the shell similar to that of the R5. However, the R6 boasted a higher amount of storage than the R2, and was equipped with extra tools.

The R7 model was designed specially for the E-wing escort starfighter, and did not show the same performance with other ships. Its systems were even more advanced than that of the R6 and R2 models.

The R8 model was designed similarly to the R7, but with a satellite dish instead of a sensor "eye". It was built to accommodate a larger array of starfighters, instead of focusing on a particular ship, such as the E-wing.

The R9 model was similar to that of the R2, but with enhanced systems.