Air-cushion vehicle with sensor-driven adaptive skirt for enhanced stability over irregular terrain

Abstract

An air-cushion vehicle, such as a hoverboard, provides enhanced stability over irregular terrain using an adaptive skirt system. The vehicle includes a platform (Figure 1, 1), lift fans (e.g., ducted

Description

DESCRIPTION This invention relates generally to ground effect vehicles or air-cushion vehicles, and more specifically to a personal hoverboard-style vehicle utilizing an actively controlled, adaptive skirt system responsive to sensor input to maintain stability and traverse uneven surfaces. BACKGROUND OF THE INVENTION Personal transportation devices that provide a sensation of hovering have long been envisioned. Various approaches exist, each with limitations. Wheeled devices marketed as "hoverboards" do not truly hover. Magnetic levitation systems require specialized tracks or surfaces. Air-cushion vehicles (ACVs), which support themselves on a cushion of pressurized air contained by a skirt, offer true hovering capability over various surfaces. Conventional ACVs often employ passive flexible skirts (e.g., bag skirts, finger skirts) to contain the air cushion. While effective on relatively smooth surfaces or water, these passive skirts can struggle with stability and efficiency when encountering common ground irregularities such as cracks, bumps, uneven pavement, or small obstacles. The skirt may catch on obstacles, leading to instability, loss of cushion pressure, or damage. Attempts to mitigate this often involve complex passive skirt designs or simply operating at higher hover heights, which reduces efficiency. Prior art includes various skirt designs and control mechanisms for ACVs. For example, US Patent 3,318,405 describes flexible skirt deflecting means. Canadian Patent CA2187678C describes a hoverboard with a semi-rigid skirt. European Patent EP1353732B1 describes an air board with an inflatable skirt. However, these typically rely on passive skirt properties or simpler control schemes that may not provide rapid, localized adaptation to terrain variations. There remains a need for a personal air-cushion vehicle, particularly in a hoverboard form factor, that can maintain stable hover and efficiently traverse common irregular ground surfaces by actively and rapidly adapting its air cushion containment mechanism in response to real-time terrain sensing. SUMMARY OF THE INVENTION The present invention provides an air-cushion vehicle, preferably in the form of a rider-propelled hoverboard, featuring an adaptive skirt system controlled by a sensor suite and a high-speed microcontroller. The core novelty lies in the combination of localized terrain sensing (using differential pressure sensors across the skirt wall or distance sensors), rapid data processing with advanced filtering and PID control algorithms, and fast-acting actuators (digital servos) controlling multiple valves integrated into the flexible skirt. In one embodiment, the vehicle comprises a platform, one or more lift fans (preferably ducted fans) generating an air cushion beneath the platform, and a flexible skirt attached to the platform's periphery to contain the air cushion. Integrated within the skirt are multiple controllable valves, each actuated by a fast digital servo. A sensor suite, including multiple differential pressure sensors positioned to measure pressure differences across the skirt wall at various locations and potentially an Inertial Measurement Unit (IMU), provides real-time data to a microcontroller. The microcontroller executes control software that processes the sensor data using digital filters. It employs PID control loops, using the filtered sensor data (representing skirt deformation or ground proximity changes) as input, to calculate necessary adjustments for the skirt valves. The microcontroller then commands the fast digital servos to rapidly open or close the corresponding valves, locally venting or retaining air within specific sections of the skirt. This active, localized airflow management allows the skirt to dynamically conform to uneven terrain, maintaining cushion pressure and vehicle stability while minimizing drag and energy loss compared to passive skirts or simpler control methods. The system aims to react to surface irregularities within a fraction of a second, enabling smoother and more stable travel over common obstacles like pavement cracks and bumps. The use of ducted fans enhances lift efficiency and safety compared to open propellers. Propulsion is provided by the rider, simplifying the system compared to self-propelled designs. INTRODUCTION TO THE DRAWINGS Figure 1 is a perspective view illustration showing the primary components of an embodiment of the adaptive skirt hoverboard. Figure 2 is a top-down view illustration of the embodiment shown in Figure 1. Figure 3 is a detailed cross-section view illustrating the adaptive skirt mechanism of the embodiment shown in Figure 1. Figure 4 is a detailed top-down view illustration of the rotating foot strap mount assembly. Figure 5 is a cross-section view illustration of the rotating foot strap mount assembly shown in Figure 4. DETAILED DESCRIPTION OF THE INVENTION Referring now to the figures, Figure 1 illustrates a perspective view of an embodiment of the adaptive skirt hoverboard. Figure 2 shows a top-down view of the same embodiment. The vehicle comprises a main platform or deck (1), preferably constructed from a lightweight yet rigid material such as a carbon fiber / plywood composite, dimensioned approximately 32 inches by 12 inches. The platform (1) is designed to support a rider's weight (e.g., up to 250 lbs) and includes cutouts for mounting lift system components. A rotating foot strap assembly is mounted on the top surface of the platform (1) at approximately the three-quarter position along its length. This assembly comprises a low-profile circular mount (14), embedded substantially flush with the platform (1) surface, and a foot loop or strap (13) attached to the mount (14). The mount (14) is configured to allow the foot loop (13) to rotate freely through 360 degrees relative to the platform (1), accommodating various rider stances and aiding stability. Details of the rotating mount (14) are further illustrated in Figure 4 and Figure 5. The lift system comprises multiple (e.g., four) electric ducted fan (EDF) units (2), mounted within the cutouts on the underside of the platform (1). Each EDF unit (2) includes a high-efficiency brushless DC motor coupled to a multi-blade impeller, housed within a duct. The ducts improve static thrust efficiency and provide a degree of safety by shielding the rotating impellers. The motors are driven by individual Electronic Speed Controllers (ESCs) (3), such as 40A BLHeli_32 compatible units, which receive control signals from the main control system (5). Power is supplied by a high-discharge Lithium Polymer (LiPo) battery system (4), for example, two 6S (22.2V nominal) 5000mAh packs connected in parallel to provide lOOOOmAh total capacity. Power distribution is managed via appropriate wiring and connectors (12), including one or more Battery Eliminator Circuits (BECs) or voltage regulators (11) to provide stable lower voltages (e.g., 5V / 6V, 3.3V) required by the control system (5), sensors (6, 7), and servos (8). A flexible skirt (9), constructed from a durable, lightweight, and relatively airtight material like ripstop nylon, is attached to the perimeter of the underside of the platform (1). The skirt (9) extends downwards (e.g., 2-3 inches) to contain the air cushion generated by the EDF units (2). Integrated into the skirt (9) are multiple (e.g., ten) valve mechanisms, the principle of which is illustrated in the cross-section view of Figure 3. Each valve mechanism comprises a lightweight flap (10) actuated by a fast-acting digital servo motor (8), such as a KST DS215MG or similar coreless digital micro servo with a response speed preferably less than 0.1 seconds per 60 degrees. The servos (8) are controlled by the main control system (5) to rapidly open or close the valve flaps (10), thereby venting or retaining air within localized sections of the skirt (9). A sensor suite provides real-time data about the vehicle's state and its interaction with the terrain. As shown in Figure 3, this includes multiple (e.g., six) differential pressure sensors (7), such as the Sensirion SDP3x series, mounted strategically across the skirt wall. These sensors (7) measure the pressure difference between the inside and outside of the skirt at various points, providing an indication of skirt deformation or proximity to the ground. An Inertial Measurement Unit (IMU) (6), such as a Bosch BNO055, is mounted centrally on the platform (1) (location implied in Figure 1) to provide data on the vehicle's pitch and roll orientation. The control system is centered around a powerful 32-bit microcontroller (MCU) (5), such as a Teensy 4.0 (location implied in Figure 1). The MCU (5) executes the control software responsible for managing the entire system. It receives input data from the IMU (6) and differential pressure sensors (7) via an I2C communication bus (potentially utilizing an I2C multiplexer if sensor addresses conflict). The control software implements advanced digital filtering algorithms (e.g., Kalman filters, complementary filters) to process the raw sensor data, reducing noise and providing reliable estimates of the vehicle's orientation and the pressure state within different zones of the skirt. Based on these filtered estimates, the software executes multiple PID control loops. Each PID loop corresponds to a defined stability zone (e.g., front-left, rear-right) and uses the filtered pressure difference (Process Variable, PV) for that zone compared against a target pressure difference (Setpoint, SP) representing stable hover. The PID controller calculates an output signal representing the required adjustment to the valve(s) in that zone. The MCU (5) translates the PID outputs into precise PWM command signals sent to the digital servos (8), causing them to rapidly adjust the valve flaps (10), as depicted in Figure 3. This closed-loop control system actively manages airflow within skirt sections, allowing the skirt to conform to ground irregularities (e.g., bumps up to 1-2 inches) while maintaining overall cushion pressure and vehicle stability. The target reaction time for the system (sensor reading to valve actuation) is preferably under 200 milliseconds. The MCU (5) also sends command signals (PWM or DShot) to the ESCs (3) to maintain the required thrust from the EDF units (2) for hovering (e.g., 2-4 inches hover height). The software includes safety routines for ESC arming, battery voltage monitoring (triggering a failsafe on low voltage), and potentially failsafes based on excessive tilt angles or sensor failures. Propulsion of the vehicle is intended to be provided by the rider pushing off the ground, similar to a skateboard, simplifying the control system by focusing solely on lift and stability.

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