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S. Wang
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Delfly Flex
A flapping wing micro air vehicle with a bio-inspired unibody composed of compliant joints
Flying insects’ thorax houses the flight muscles that provide efficient, multi-axis wing actuation. Such bio-inspiration is essential for developing future flapping wing micro air vehicles (FWMAVs) that combine advanced maneuverability with design simplicity, low weight, and high power efficiency. In this work, we propose a novel unibody with distributed compliant joints inspired by the multiple degrees of actuation freedom of an insect thorax—in particular, wing stroke plane modulation for active pitch and yaw—yielding a compact multifunctional structural component for the 24.6 g FWMAV: Delfly Flex. All of these functions are achieved within a single 3.73 g 3D-printed integrated airframe. To design this unibody, we provide an analytical framework that guides compliant joint geometry using differential flexure beam analysis, along with an optimal joint orientation analysis for seamless integration into the unibody. To ensure sufficient structural endurance, we investigate various resin materials and printing configurations, resulting in a robust resin-printed unibody that incorporates two compliant joints and wing-root stabilizers. This single structure replaces the conventional multi-component FWMAV body composed of rigid-hinge-based dihedral pitch & yaw mechanisms attached to a rod-like fuselage. We characterize the flight capabilities of Delfly Flex through tethered experiments measuring force and moment generation. The results show thrust generation and yaw moment arms equivalent to its predecessor, while the pitch moment arm is approximately 50% smaller due to the concentrated mass distribution inherent to the unibody design. Free-flight experiments further validate the concept, demonstrating controlled pitch and yaw maneuvers enabled by compliant beams as thin as 0.4 mm. Combined with simplified assembly and more than 10% mass reduction, this unibody concept opens pathways toward future designs with increased deformability and expanded control authority. Overall, this study highlights the synergy between aero-mechanical design and additive manufacturing, achieving enhanced body intelligence through insect-thorax-inspired FWMAV structures.
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Flying insects’ thorax houses the flight muscles that provide efficient, multi-axis wing actuation. Such bio-inspiration is essential for developing future flapping wing micro air vehicles (FWMAVs) that combine advanced maneuverability with design simplicity, low weight, and high power efficiency. In this work, we propose a novel unibody with distributed compliant joints inspired by the multiple degrees of actuation freedom of an insect thorax—in particular, wing stroke plane modulation for active pitch and yaw—yielding a compact multifunctional structural component for the 24.6 g FWMAV: Delfly Flex. All of these functions are achieved within a single 3.73 g 3D-printed integrated airframe. To design this unibody, we provide an analytical framework that guides compliant joint geometry using differential flexure beam analysis, along with an optimal joint orientation analysis for seamless integration into the unibody. To ensure sufficient structural endurance, we investigate various resin materials and printing configurations, resulting in a robust resin-printed unibody that incorporates two compliant joints and wing-root stabilizers. This single structure replaces the conventional multi-component FWMAV body composed of rigid-hinge-based dihedral pitch & yaw mechanisms attached to a rod-like fuselage. We characterize the flight capabilities of Delfly Flex through tethered experiments measuring force and moment generation. The results show thrust generation and yaw moment arms equivalent to its predecessor, while the pitch moment arm is approximately 50% smaller due to the concentrated mass distribution inherent to the unibody design. Free-flight experiments further validate the concept, demonstrating controlled pitch and yaw maneuvers enabled by compliant beams as thin as 0.4 mm. Combined with simplified assembly and more than 10% mass reduction, this unibody concept opens pathways toward future designs with increased deformability and expanded control authority. Overall, this study highlights the synergy between aero-mechanical design and additive manufacturing, achieving enhanced body intelligence through insect-thorax-inspired FWMAV structures.
Aerial flyers in nature utilize strain sensing to monitor forces in real time, crucial for navigating through wind disturbances and obstacles during flight. While micro air vehicles (MAVs) typically utilize vision and airflow sensing [1], [2], the potential of strain sensing remains relatively unexplored, despite the abundance of available solutions crafted via advanced microfabrication techniques. After surveying available techniques in the literature, we introduce a streamlined fabrication process for rapid prototyping of strain gauges that requires a minimal set of low-cost tools, suitable for roboticists with limited microfabrication experience or resources. To showcase the effectiveness of our method, two kinds of strain gauges (with ginkgo-leaf-inspired patterns and conventional meander patterns) are integrated on a pair of flapping wings to monitor the wing deformation during flapping cycles. We aim to inspire researchers in aerial robotics to incorporate this lightweight and affordable strain-sensing technology to enhance flight navigation and control, opening new avenues for lightweight autonomy and intelligence.
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Aerial flyers in nature utilize strain sensing to monitor forces in real time, crucial for navigating through wind disturbances and obstacles during flight. While micro air vehicles (MAVs) typically utilize vision and airflow sensing [1], [2], the potential of strain sensing remains relatively unexplored, despite the abundance of available solutions crafted via advanced microfabrication techniques. After surveying available techniques in the literature, we introduce a streamlined fabrication process for rapid prototyping of strain gauges that requires a minimal set of low-cost tools, suitable for roboticists with limited microfabrication experience or resources. To showcase the effectiveness of our method, two kinds of strain gauges (with ginkgo-leaf-inspired patterns and conventional meander patterns) are integrated on a pair of flapping wings to monitor the wing deformation during flapping cycles. We aim to inspire researchers in aerial robotics to incorporate this lightweight and affordable strain-sensing technology to enhance flight navigation and control, opening new avenues for lightweight autonomy and intelligence.
Journal article
(2022)
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S. Wang, D.A. Olejnik, C. de Wagter, B.W. van Oudheusden, G.C.H.E. de Croon, S. Hamaza
Flyers in nature equip different airflow sensing mechanisms to navigate through wind disturbances with remarkable flight stability. Embracing bio-inspiration, airflow sensing with conventional sensors has long been utilized in flight control for larger micro air vehicles (MAVs). Bio-inspired flapping wing MAVs (FWMAVs) have extremely limited power and payload, therefore implementing onboard airflow sensing has remained a challenge in spite of various attempts at miniaturized airflow sensor designs. This work characterizes the measurement performance of a lightweight off-the-shelf thermistor-based airflow sensor through comparison with a hot-wire probe. Wind tunnel tethered flight tests on a 31.3-gram FWMAV Delfly Nimble examine the onboard sensing performance at low flow speeds (up to 2 m/s), under the influence of flapping motion. This performance characterization further motivates a miniaturized re-design of the airflow sensor with over 40% size and weight reduction. The redesigned airflow sensor helps to realize the first flapping wing MAV free flight with onboard airspeed measurements, providing remarkable flight stability under wind speeds in the range of approximately 0.5 to 1.2 m/s. This embodied sensing configuration pushes the weight and power limit of miniaturized electronics for FWMAVs, providing an easy-to-integrate solution with good performance, and paving the way for more complex control of FWMAVs in dynamic conditions.
...
Flyers in nature equip different airflow sensing mechanisms to navigate through wind disturbances with remarkable flight stability. Embracing bio-inspiration, airflow sensing with conventional sensors has long been utilized in flight control for larger micro air vehicles (MAVs). Bio-inspired flapping wing MAVs (FWMAVs) have extremely limited power and payload, therefore implementing onboard airflow sensing has remained a challenge in spite of various attempts at miniaturized airflow sensor designs. This work characterizes the measurement performance of a lightweight off-the-shelf thermistor-based airflow sensor through comparison with a hot-wire probe. Wind tunnel tethered flight tests on a 31.3-gram FWMAV Delfly Nimble examine the onboard sensing performance at low flow speeds (up to 2 m/s), under the influence of flapping motion. This performance characterization further motivates a miniaturized re-design of the airflow sensor with over 40% size and weight reduction. The redesigned airflow sensor helps to realize the first flapping wing MAV free flight with onboard airspeed measurements, providing remarkable flight stability under wind speeds in the range of approximately 0.5 to 1.2 m/s. This embodied sensing configuration pushes the weight and power limit of miniaturized electronics for FWMAVs, providing an easy-to-integrate solution with good performance, and paving the way for more complex control of FWMAVs in dynamic conditions.
Conference paper
(2022)
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D.A. Olejnik, S. Wang, J.J.G. Dupeyroux, S. Stroobants, M. Karasek, C. de Wagter, G.C.H.E. de Croon
This paper discusses a low-cost, open-source and open-hardware design and performance evaluation of a low-speed, multi-fan wind system dedicated to micro air vehicle (MAV) testing. In addition, a set of experiments with a flapping wing MAV and rotorcraft is presented, demonstrating the capabilities of the system and the properties of these different types of drones in response to various types of wind. We performed two sets of experiments where a MAV is flying into the wake of the fan system, gathering data about states, battery voltage and current. Firstly, we focus on steady wind conditions with wind speeds ranging from 0.5 m S-1 to 3.4 m S-1. During the second set of experiments, we introduce wind gusts, by periodically modulating the wind speed from 1.3 m S−1 to 3.4 m S−1 with wind gust oscillations of 0.5 Hz, 0.25 Hz and 0.125 Hz. The “Flapper” flapping wing MAV requires much larger pitch angles to counter wind than the “CrazyFlie” quadrotor. This is due to the Flapper's larger wing surface. In forward flight, its wings do provide extra lift, considerably reducing the power consumption. In contrast, the CrazyFlie's power consumption stays more constant for different wind speeds. The experiments with the varying wind show a quicker gust response by the CrazyFlie compared with the Flapper drone, but both their responses could be further improved. We expect that the proposed wind gust system will provide a useful tool to the community to achieve such improvements.
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This paper discusses a low-cost, open-source and open-hardware design and performance evaluation of a low-speed, multi-fan wind system dedicated to micro air vehicle (MAV) testing. In addition, a set of experiments with a flapping wing MAV and rotorcraft is presented, demonstrating the capabilities of the system and the properties of these different types of drones in response to various types of wind. We performed two sets of experiments where a MAV is flying into the wake of the fan system, gathering data about states, battery voltage and current. Firstly, we focus on steady wind conditions with wind speeds ranging from 0.5 m S-1 to 3.4 m S-1. During the second set of experiments, we introduce wind gusts, by periodically modulating the wind speed from 1.3 m S−1 to 3.4 m S−1 with wind gust oscillations of 0.5 Hz, 0.25 Hz and 0.125 Hz. The “Flapper” flapping wing MAV requires much larger pitch angles to counter wind than the “CrazyFlie” quadrotor. This is due to the Flapper's larger wing surface. In forward flight, its wings do provide extra lift, considerably reducing the power consumption. In contrast, the CrazyFlie's power consumption stays more constant for different wind speeds. The experiments with the varying wind show a quicker gust response by the CrazyFlie compared with the Flapper drone, but both their responses could be further improved. We expect that the proposed wind gust system will provide a useful tool to the community to achieve such improvements.
Flapping wing micro aerial vehicles (FWMAVs) are known for their flight agility and maneuverability. These bio-inspired and lightweight flying robots still present limitations in their ability to fly in direct wind and gusts, as their stability is severely compromised in contrast with their biological counterparts. To this end, this work aims at making in-gust flight of flapping wing drones possible using an embodied airflow sensing approach combined with an adaptive control framework at the velocity and position control loops. At first, an extensive experimental campaign is conducted on a real FWMAV to generate a reliable and accurate model of the in-gust flight dynamics, which informs the design of the adaptive position and velocity controllers. With an extended experimental validation, this embodied airflow-sensing approach integrated with the adaptive controller reduces the root-mean-square errors along the wind direction by 25.15% when the drone is subject to frontal wind gusts of alternating speeds up to 2.4 m/s, compared to the case with a standard cascaded PID controller. The proposed sensing and control framework improve flight performance reliably and serve as the basis of future progress in the field of in-gust flight of lightweight FWMAVs.
...
Flapping wing micro aerial vehicles (FWMAVs) are known for their flight agility and maneuverability. These bio-inspired and lightweight flying robots still present limitations in their ability to fly in direct wind and gusts, as their stability is severely compromised in contrast with their biological counterparts. To this end, this work aims at making in-gust flight of flapping wing drones possible using an embodied airflow sensing approach combined with an adaptive control framework at the velocity and position control loops. At first, an extensive experimental campaign is conducted on a real FWMAV to generate a reliable and accurate model of the in-gust flight dynamics, which informs the design of the adaptive position and velocity controllers. With an extended experimental validation, this embodied airflow-sensing approach integrated with the adaptive controller reduces the root-mean-square errors along the wind direction by 25.15% when the drone is subject to frontal wind gusts of alternating speeds up to 2.4 m/s, compared to the case with a standard cascaded PID controller. The proposed sensing and control framework improve flight performance reliably and serve as the basis of future progress in the field of in-gust flight of lightweight FWMAVs.