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Discussion

Discussion of “A Review of Propulsion, Power, and Control Architectures for Insect-Scale Flapping Wing Vehicles” by E. F. Helbling and R. J. Wood (Helbling, E. F., and Wood, R. J., 2018, ASME Appl. Mech. Rev., 70(1), p. 010801) OPEN ACCESS

[+] Author and Article Information
Satyandra K. Gupta

Fellow ASME
Smith International Professor
Aerospace and Mechanical Engineering Department,
Viterbi School of Engineering,
University of Southern California,
Los Angeles, CA 90089

Manuscript received December 7, 2017; final manuscript received December 11, 2017; published online January 18, 2018. Editor: Harry Dankowicz.

Appl. Mech. Rev 70(1), 015501 (Jan 18, 2018) (2 pages) Paper No: AMR-17-1091; doi: 10.1115/1.4038796 History: Received December 07, 2017; Revised December 11, 2017

Flying insects exhibit truly remarkable capabilities. There has been significant interest in developing small-scale flying robots by taking inspiration from flying insects. The paper by Helbling and Wood reports remarkable progress made by the research community in realizing insect-scale flapping wing vehicles and identifies research challenges and opportunities. This discussion builds upon their paper and examines the potential of insect-scale flapping wing flight from an application point of view. It summarizes requirements and mention implications of these requirements on propulsion, power, and control architecture.

Flying insects exhibit truly remarkable agility in flight and are able to fly in challenging conditions [13]. They are capable of interacting with the environment during search for food, feeding, migration, and reproduction. The nature has produced many different species of insects with significant differences in morphology and sizes. Insects provide good models of robust design and offer engineers interested in bio-inspiration of a diverse set of design options to meet really challenging engineering requirements.

There has been significant interest in developing small-scale flying robots by taking inspiration from flying insects. Researchers have been studying flapping wing flight of insects and developing aerodynamic models to explain how insects fly for many years. There has been interest in understanding how small insect sense the environment around them [4] and perform collision avoidance and navigate effectively over large distances. This line of work has been invaluable for roboticists interested in designing small-scale flying robots. Recent advances in microsystems area are providing components technologies (e.g., actuators, sensors) and manufacturing methods for realizing miniature robots. This field has seen a significant growth in recent years.

The paper by Helbling and Wood reports remarkable progress made by the research community in realizing insect-scale flapping wing vehicles. They describe all notable small-scale flapping wing platforms that have been reported in the literature. They point out challenges in propulsion, energy storage, and control architectures that arise at small size scales. They discuss how design of sensors and control electronics impacts the power consumption and overall flight duration. They also highlight differences between large-scale flapping wing platforms inspired by avian flight and small-scale flapping flight inspired by insects. They describe in detail advances needed in actuation, flight control, and control electronics to realize RoboBee platform. Advances in individual components technologies will be useful to the miniature robotics community in general. They identify several direction of future research that will be needed to approach the capabilities of insects found in the nature. They discuss challenges and opportunities from sensing and control perspective to realize autonomous flight. They also discuss challenges associated with the onboard power source to meet the demand of flapping wing flight. They discuss limitations of the current battery technologies and potential of solar cells for harvesting energy in insect-scale flapping wing vehicles.

The purpose of this discussion is to examine the potential of insect-scale flapping wing flight from an application point of view. I will try to extract and summarize requirements from the work reported by Helbling and Wood and mention implications of these requirements on propulsion, power, and control architecture. I will also summarize major technology breakthroughs that will be needed to advance the field further and use insect-scale flying robots in practice.

Obviously, controllable flight and obstacle avoidance are two fundamental requirements of a useful inset-scale flying platform. Ultimately, in most useful applications, the small flying robot will need capabilities that will go beyond these two basic requirements. The need for these additional capabilities will impose new requirements on propulsion, power, and control. Here is a nonexhaustive representative list of requirements that will be needed for inspect-inspired robots to be useful in applications:

  • Ability to fly in challenging weather conditions: Conducting useful mission will require the robot to fly in high winds and rainy conditions. These conditions significantly affect the flight performance. The robot will need sensors to detect the flight conditions and use a controller to modify the flight behavior to fly safely. This will also impact the design of wings to handle a wide range of aerodynamic loading conditions.

  • Ability to fly for sufficiently long periods of times to do useful tasks: Insects feed frequently to meet the energy needs. The robot will be unable to fly for long periods of times solely based on the onboard stored energy available at the beginning of the mission. It will need to harvest energy from the environment. Solar cells are obvious candidates. However, solar energy is not always available. So, other methods for energy harvesting will need to be examined and integrated in the robot. This will affect the platform weight and need new maneuvers that enable the robot to harvest energy efficiently.

  • Ability to physically interact with the environment: Many useful missions will require the robot to wait for an interesting event to happen and then get into the flight mode based on the event trigger. Therefore, the robot will need perching, landing, and take-off capabilities. The robot may also need to manipulate objects in the environment. This will require the robot to act as a mobile manipulator. This in turn will require the robot to include limbs and appropriate end-effectors. Manipulation at small size scales is quite different from manipulation at large-size scales. Therefore, new advances and capabilities will be needed. Safely performing aerial manipulation will require the robot to have new sensors and controllers.

  • Ability to perform sensing for task execution: A task may require the robot to land on an object in a particular manner. This will require the robot to have sensors that go well beyond sensors needed for doing collision avoidance and navigation. The presence of new sensors will significantly change the power requirements. New control architecture will be needed to make sure that sensors are only powered when they are actually needed.

  • Ability to communication with other members of the groups to enable execution of collaborative tasks: Small robots are likely to be more useful when a group of them can collaborate to carry out a challenging task. Collaboration among members of groups will require an ability to communicate among members of the group. Insects use a wide variety of methods to communicate. Robots will need to incorporate components to send and receive messages in a robust manner. This will impact the power requirement and sensors. Certain types of communication signals can be received by sensors needed for navigation and obstacle avoidance. The concept of multifunctional sensors will be useful in this context to minimize the impact on the platform weight.

Ultimately, realizing insect-scale flapping wing vehicle that meet the functional requirements outlined in Sec. 2 cannot be realized by traditional components technologies. Helbling and Wood highlighted several areas where significant technological advances were made to realize the platforms reported in their paper. Capabilities of current robotic platform are nowhere close to capabilities observed in insects. Major technologies breakthrough will be needed in the following areas to create platforms with significantly enhanced capabilities:

  • Multifunctional materials: Biological creatures are made from multifunctional materials that are able to perform more than one function and hence significantly reduce the weight. This in turn has significant impact on power requirement and flight endurance. We will need to develop engineered multifunctional materials to realize capabilities observed in nature.

  • Manufacturing methods: Realizing insect-scale flapping wing platforms requires geometrically complex structures with multiscale features. As designer look to newer materials to be used in designs, significant advances will be needed in manufacturing methods. Recent advances in additive manufacturing area are enabling fabrication of geometrically complex structures. However, material choices are very limited. Moreover, current methods cannot produce multiscale hierarchical structures.

  • Sensing modalities: Many new sensing modalities will be needed for insect-scale robots to perform useful tasks in real-world applications. These sensors modalities will need to emerge from multifunctional properties of the underlying material.

  • Information processing: Insects are able to perform “sophisticated reasoning” to perform complex navigation and manipulation tasks using very limited number of neurons. New neuromorphic computing architectures will be needed to match capabilities observed in nature.

  • Actuators: We will need energy efficient actuators that are integrated in structures through multifunctional materials.

  • Energy harvesting and storage: Current energy storage density based on battery technologies is very low compared to energy storage capacity of biomass. Significant advances will be needed in energy harvesting and storage areas for realizing platforms with meaningful flight durations.

  • Design tools: Designing complex flying platforms manually with traditional CAD tools is not possible. We will need new design tools that can synthesize new robots based on requirements. These tools will need to be integrated fluid–structure interaction simulation tools to evaluated designs alternatives generated by the computer.

As reported by Helbling and Wood, remarkable progress was made by the research community in realizing insect-scale flapping wing vehicles. However, currently robotic insects are nowhere close to their biological counterparts. Major technologies breakthrough will be needed in several technological areas to create insect-inspired robotic platforms that can be used in real-world applications.

Helbling, E. F. , and Wood, R. J. , 2018, “ A Review of Propulsion, Power, and Control Architectures for Insect-Scale Flapping Wing Vehicles,” ASME Appl. Mech. Rev., 70(1), p. 010801.
Sane, S. P. , 2003, “ The Aerodynamics of Insect Flight,” J. Exp. Biol., 206(23), pp. 4191–4208. [CrossRef] [PubMed]
Berman, G. J. , and Wang, Z. J. , 2007, “ Energy-Minimizing Kinematics in Hovering Insect Flight,” J. Fluid Mech., 582, pp. 153–168. [CrossRef]
Land, M. F. , 1997, “ Visual Acuity in Insects,” Annu. Rev. Entomol., 42(1), pp. 147–177. [CrossRef] [PubMed]
Copyright © 2018 by ASME
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References

Helbling, E. F. , and Wood, R. J. , 2018, “ A Review of Propulsion, Power, and Control Architectures for Insect-Scale Flapping Wing Vehicles,” ASME Appl. Mech. Rev., 70(1), p. 010801.
Sane, S. P. , 2003, “ The Aerodynamics of Insect Flight,” J. Exp. Biol., 206(23), pp. 4191–4208. [CrossRef] [PubMed]
Berman, G. J. , and Wang, Z. J. , 2007, “ Energy-Minimizing Kinematics in Hovering Insect Flight,” J. Fluid Mech., 582, pp. 153–168. [CrossRef]
Land, M. F. , 1997, “ Visual Acuity in Insects,” Annu. Rev. Entomol., 42(1), pp. 147–177. [CrossRef] [PubMed]

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