4-channel XRB helicopters

From UfoWiki

The term "XRB" stands for Cross or Counter Rotation Blades, an abbreviation referring to the coaxial rotor design mainly used in the RC industry. 4 Channel remote controlled helicopters mainly follow the XRB concept, since helicopters with a tail rotor often need further channels for triggering control options coaxial helis just don't have. The four Channels are used to control throttle, yaw, pitch and roll functions.