3 servos movements are electrically controlled (mixed) by transmitter signals.
For pitch control, all 3 servo move。For aileron and elevator, 2 servos
are used. This system is recommended for pilots with more building and
set up skill who are looking for more advances flight styles either 3D
HPM is mechanical mixing using each servo for each control channel. This
system does not require electric mixing from transmitters and assembly
and setup could be easier, thus recommended for beginners.