You are almost certainly picturing a four-rotor design ... If the extra motor on a quadrotor is cheaper than a servo and linkage, then you’ll make quadrotors. And finally, there is a reliability ...

The motors are mounted on a beam running perpendicular to the direction of travel. Each of them is mounted on a bearing which can be rotated by a servo motor. They rotate independently of each ...

ECM’s new servo motor delivers 18.8Nm of torque from just 0.57kg-achieving an exceptional torque-to-weight ratio in an ultra-compact footprint.