How subtle can it get?
Flying drones have become common objects in our daily lives, serving a multitude of purposes. Many of these purposes involve outdoor scenarios where the user combines drone control with another activity. Traditional interaction methods rely on physical or virtual joysticks that occupy both hands, thus restricting drone usability. In this paper, we investigate one-handed human-to-drone-interaction by leveraging three modalities: force, touch, and IMU. After prototyping three different combinations of these modalities on a smartphone, we evaluate them against the current commercial standard through two user experiments. These experiments help us to find the combination of modalities that strikes a compromise between user performance, perceived task load, wrist rotation, and interaction area size. Accordingly, we select a method that achieves faster task completion times than the two-handed commercial baseline by 16.54% with the merits of subtle user behaviours inside a small-size ring-form device and implements this method within the ring-form device. The last experiment involving 12 participants shows that thanks to its small size and weight, the ring device displays better performance than the same method implemented on a mobile phone. Furthermore, users unanimously found the device useful for controlling a drone in mobile scenarios (AVG = 3.92/5), easy to use (AVG = 3.58/5) and easy to learn (AVG = 3.58/5). Our findings give significant design clues in search of subtle and effective interaction through finger augmentation devices with drone control. The users with our prototypical system and a multi-modal on-finger device can control a drone with subtle wrist rotation (pitch gestures: 43.24° amplitude and roll gestures: 46.35° amplitude) and unnoticeable thumb presses within a miniature-sized area of (1.08 * 0.61 cm2).