# Drone Rider: Foot Vibration Stimuli to Enhance Immersion and Flight Sensation in VR
## 1 Introduction  
One of the most captivating experiences offered by virtual reality (VR) technology is the sense of flight. Flight simulators for airplanes and helicopters have long been a prominent example of this [1; 2; 3; 4; 5; 6]. Beyond these, VR applications have expanded to include experiences such as gliding and bungee jumping [7; 8; 9; 10; 11; 12]. Building on this tradition, we have developed Drone Rider, a VR flight system described in detail in Section 2, which allows users to experience the freedom of flying through the sky on a drone [13; 14]. In this system, the user rides atop a drone, soaring over natural landscapes with birds and navigating through stunning architectural structures. The operator controls the drone by tilting their body back and forth and left to right, causing passive tilting on a suspended platform. This tilting motion enhances the reported sense of flight and immersion [13]. Most VR drone simulators are designed for training the maneuvering techniques of remote-controlled drones [15; 16; 17; 18; 19]. In contrast, Drone Rider provides the experience of free flight while standing on a drone. In this study, we focused on footplate vibrations that simulate the characteristic oscillations produced by drones. Through our earlier study [13], we noticed that the vibratory pattern applied to the operator's soles influence the sense of immersion and flight. Hence, in this study, we investigate effective vibratory patterns. Thus far, few studies have examined the effects of vibratory stimulation to the soles on the sense of flight in VR environments. One notable study by [PERSON] et al. [8] investigated the effects of sole vibration on the sense of immersion and hovering in a VR application where users experience flight using jet engines attached to the feet. They identified an effective frequency of the sinusoidal vibration at 80 Hz. However, as described in Section 3,pure vibratory stimuli tend to produce a lesser sense of immersion and flight compared to those based on vibratory machines, such as engines. Our study advances this area by introducing realistic vibratory stimuli that simulate the operational vibrations of rotary mechanical systems, rather than relying solely on sinusoidal patterns. By examining vibrations derived from naturalistic sources, such as motorcycles and laundry machines, we demonstrate their potential to significantly enhance the sense of flight and immersion in VR flight simulators. These findings not only fill a gap in the existing literature but also offer practical guidance for VR designers seeking to improve haptic feedback systems in flight experiences, minimizing sensory adaptation while maximizing user engagement and realism. Several studies have investigated the effects of foot stimulation on the sense of self-locomotion in VR applications unrelated to flight experiences [20; 21; 22; 23; 24; 25; 26]. [PERSON] et al. [21] reported that vibratory stimuli applied to the feet enhanced the sensation of being in a moving elevator within a VR environment. They found that both white noise and 50 Hz vibrations were effective in evoking a sense of illusory upward motion. [PERSON] et al. [22] demonstrated that foot vibrations in a seated posture amplified the sense of self-locomotion induced by section. Similar effects have been observed with seat vibrations, which improve the sense of visually induced [23] or auditory-induced [24] self-motion. Especially, [PERSON] et al. [24] applied vibration mimicking an engine to foster the sense of moving on a cart. In our experiment, the forward section caused by the optical flow from VR goggles may be enhanced by the vibratory stimuli applied to the feet. Additionally, foot vibrations have been shown to increase the perception of self-locomotion during virtual walkthrough experiences [25; 26]. While these studies are relevant, our research does not directly address walking experiences. Further, vibratory stimuli to soles are typically used for presenting virtual ground materials [27; 28; 29; 30; 31].