Here are three fast reasons to like these receivers: high-speed operation with digital servos and standard-size connectors on the end of the case. Here are two more. The R6106HF is a short-range Rx for indoors, park flyers and helis up to 450-size. The mid-range R6106HFC can handle up to a 50 span aircraft or 500-size heli, and includes an extended coaxial antenna perfect for carbon-fiber fuselages.