We are experiencing some stability issues flying our Y6, it tends to yaw a little to the left.
We made the frame ourselves and we are using 750kV motor with 14" x 4.7 props.
We used the APM2 as micro computer and we followed the motor arrangement from arducopter http://code.google.com/p/arducopter/wiki/APM2_Motor_order
As you can see from the pictures, the motors at the top of the left and right arms turn in the clockwise direction while the motor at the back turns anti-clockwise.
We read about some suggestion to place all 3 prop that are turning the same direction together on the same level. More importantly, the motors that turn anti-clockwise is alot hotter than the ones that are turning clockwise. Why is this so?