AirCharge: Amplifying Ungrounded Impact Force by Accumulating Air Propulsion Momentum

Impact events, which generate directional forces with extremely short impulse durations and large force magnitudes, are prevalent in both virtual reality (VR) games and real-world experiences. However, despite recent advancement in ungrounded force feedback technologies, such as air jet propulsion and propellers, these technologies remain 5-100x weaker and 10-500x slower compared to real-world impact events. For instance, they can only achieve 4N with a minimal duration of 50-500ms compared to the 20-400N forces generated within 1-5ms for baseball, ping-pong, drumming, and tennis. To overcome these limitations, we present AirCharge, a novel haptic device that accumulates air propulsion momentum to generate instantaneous, directional impact forces. By mounting compressed air jets on rotating swingarms, AirCharge can amplify impact force magnitude by more than 10x while matching real-world impulse duration of 3ms. To support high-frequency impacts, we explored and evaluated a series of device designs, culminating in a novel reciprocating dual-swingarm design that leverages a reversing bevel gearbox to eliminate gyro effects and to achieve impact feedback of up to 10Hz. User experience evaluation (n = 16) showed that AirCharge significantly enhanced realism and is preferred by participants compared to air jets without the charging mechanism.