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Heading hold and tail lock are the same thing. The most popular gyro by far is the Futaba GY 401. it is a fantastic gyro that works very well even with standard servos even in reverse flight. HPM is mechanical mixing of single servos for each function. SWM is electronic mixing of 3 servos more or less directly conected to the swashplate. the rest of the world calls it mechanical or normal mixing and CCPM or eCCPM (marketing
) usually the CCPM ends up a littel lighter, but i can not confirm that is the case for the Sceadu. i am curently building a sceadu with mechanical mixing. I'm using Hitech 625 MG, but you can use standards to start with.