Light-weight, autonomous ornithopters form a promise to observe places that are too small or too dangerous for humans to enter. In this article, we discuss the DelFly project, in which we follow a top-down approach to ever smaller and more autonomous ornithopters. Top-down signifies that the project always focuses on complete flying systems equipped with camera. We give arguments for the approach by explaining which findings on the DelFly I and DelFly II recently led to the development of the DelFly Micro: a 3.07-gram ornithopter carrying a camera and transmitter onboard. These findings concern the design, aerodynamics, and vision-based control of the DelFly. In addition, we identify main obstacles on the road to fly-sized ornithopters. INTRODUCTIONOne of the goals of research on Micro Air Vehicles (MAVs) is to arrive at fly-sized MAVs that can fly autonomously in complex environments. Such MAVs form a promise for observation tasks in places that are too small or too dangerous for humans to enter. Their small size would allow the MAVs to enter and navigate in narrow spaces, while autonomous flight would allow the MAV to operate at a large distance from its user.The requirements for the MAV described above are legion. For one, it needs to be as light as possible for endurance, while having enough onboard sensors and processing that allow it to navigate autonomously. Moreover, it needs to be able to hover, allowing it to get a "good look" at the object of observation. At the same time, it needs to fly at higher speeds to travel larger distances.It may come as no surprise that in their quest for a fly-sized MAV, researchers draw inspiration from natural systems. For example, flying insects comply with the requirements mentioned above and can thus provide inspiration for solving the engineering problems encountered in the creation of a fly-sized MAV. One of the key properties of systems inspired by flying insects is that they use flapping wing propulsion (they are ornithopters) 1,2,3,4,5,6,7,8,9 . Especially at smaller sizes, this propulsion method produces more lift than fixed wing configurations 10,11,12,13 .Essentially, there are two main approaches to creating small autonomous ornithopters: bottom-up and top-down. In the bottom-up approach, one starts by creating all the tiny parts that are deemed important to a fly-sized ornithopter 2,14,15 . The most remarkable example of this approach is the work of the Harvard Microrobotics Laboratory. They succeeded in creating a 60 mg robotic insect, which can produce sufficient lift to take off vertically. To achieve this, they made use of Smart Composite Microstructures (SCM) 2 . The robotic insect was still fixed to taut guide wires that restricted the robot to vertical motion and provided both energy and control. In future work, the group plans to allow all degrees of freedom and to incorporate onboard energy supply, sensors, and processing.In the top-down approach, one starts with a fully functioning (relatively large-scale) ornithopter. By studying this ornit...

One of the major challenges in robotics is to develop a fly-like robot that can autonomously fly around in unknown environments. In this paper, we discuss the current state of the DelFly project, in which we follow a top-down approach to ever smaller and more autonomous ornithopters. The presented findings concerning the design, aerodynamics and autonomy of the DelFly illustrate some of the properties of the top-down approach, which allows the identification and resolution of issues that also play a role at smaller scales. A parametric variation of the wing stiffener layout produced a 5% more power-efficient wing. An experimental aerodynamic investigation revealed that this could be associated with an improved stiffness of the wing, while further providing evidence of the vortex development during the flap cycle. The presented experiments resulted in an improvement in the generated lift, allowing the inclusion of a yaw rate gyro, pressure sensor and microcontroller onboard the DelFly. The autonomy of the DelFly is expanded by achieving (1) an improved turning logic to obtain better vision-based obstacle avoidance performance in environments with varying texture and (2) successful onboard height control based on the pressure sensor.

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To participate in the Outback Medical Express UAV Challenge 2016, a vehicle was designed and tested that can autonomously hover precisely, takeoff and land vertically, fly fast forward efficiently, and use computer vision to locate a person and a suitable landing location. The vehicle is a novel hybrid tail-sitter combining a delta-shaped biplane fixed-wing and a conventional helicopter rotor. The rotor and wing are mounted perpendicularly to each other,and the entire vehicle pitches down to transition from hover to fast forward flight where the rotor serves as propulsion.To deliver sufficient thrust in hover while still being efficient in fast forward flight, a custom rotor system was designed. The theoretical design was validated with energy measurements, wind tunnel tests, and application in real-world missions. A rotor-head and corresponding control algorithm were developed to allow transitioning flight with the nonconventional rotor dynamics that are caused by the fuselage rotor interaction. Dedicated electronics were designed that meet vehicle needs and comply with regulations to allow safe flight beyond visual line of sight.Vision-based search and guidance algorithms running on a stereo-vision fish-eye camera were developed and tested to locate a person in cluttered terrain never seen before. Flight tests and a competition participation illustrate the applicability of the DelftaCopter concept. K E Y W O R D Saerial robotics, control, emergency response, perception, sensors