Research Papers

Spring-Assisted Motorized Transmission for Efficient Hover by Four Flapping Wings

[+] Author and Article Information
Yao-Wei Chin

School of Mechanical and
Aerospace Engineering,
Nanyang Technological University,
Singapore 639798
e-mail: ywchin@ntu.edu.sg

Ziyuan Ang, Yukai Luo

School of Mechanical and
Aerospace Engineering,
Nanyang Technological University,
Singapore 639798

Woei-Leong Chan

Temasek Laboratories,
National University of Singapore,
Singapore 117411
e-mail: tslcwl@nus.edu.sg

Javaan S. Chahl

School of Engineering,
University of South Australia,
Mawson Lakes 5095, SA, Australia
e-mail: Javaan.Chahl@unisa.edu.au

Gih-Keong Lau

School of Mechanical and
Aerospace Engineering,
Nanyang Technological University,
Singapore 639798
e-mail: mgklau@ntu.edu.sg

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received April 22, 2018; final manuscript received August 30, 2018; published online October 5, 2018. Assoc. Editor: David J. Cappelleri.

J. Mechanisms Robotics 10(6), 061014 (Oct 05, 2018) (12 pages) Paper No: JMR-18-1116; doi: 10.1115/1.4041430 History: Received April 22, 2018; Revised August 30, 2018

Elastic storage has been reported to help flying insects save inertial power when flapping their wings. This motivates recent research and development of elastic storage for flapping-wing micro air vehicles (fwMAVs) and their ground (tethered) flight tests. The previous designs of spring-loaded transmissions are relatively heavy or bulky; they have not yet been adopted by freely hovering prototypes of fwMAVs, especially those with four flapping wings. It is not clear if partial elastic storage can still help save power for flapping flight while not overloading the motorized transmission. Here, we developed ultralight and compact film hinges as elastic storage for four flapping wings. This spring-assisted transmission was motor driven such that the wing beat frequency was higher than the natural frequency of elastically hinged wings. Our experiments show that spring recoil helps accelerate wing closing thus generating more thrust. When powered by a 3.18 g brushless motor, this 13.4 g fwMAV prototype with spring-assisted transmission can take off by beating four flexible wings (of 240 mm span) with up to 21–22 g thrust generation at 22–23 Hz. Due to lower disk loading and high-speed reduction, indirect drive of the four elastically hinged wings can produce a thrust per unit of electrical power of up to 4.6 g/W. This electrical-power-specific thrust is comparable to that generated by direct drive of a propeller, which was recommended by the motor (AP-03 7000kv) manufacturer.

Copyright © 2018 by ASME
Topics: Wings , Hinges , Motors , Springs , Storage
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Fig. 1

Illustration of wing reciprocation about a pivotal film hinge: (a) isometric view, (b) hinge bending and rocker stroke, and (c) hinge bending in the presence of transverse flexibility

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Fig. 2

A prototype of spring-assisted motorized transmission for four flapping wings (X wings): (a) a complete assembly without a tail, (b) breakdown of component weights, (c)–(d) photographs of the wing transmission in angled and side views, (e)–(f) schematic drawings of the wing transmission in angled and side views, and (g)–(h) front views with the presence or absence of a brushless motor

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Fig. 3

Design and prototype of elastic film hinges for X-wings in the closed position (top row) and the open position (bottom row)

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Fig. 4

Design and construction of a light wing plane: (a)–(b) schematic drawing showing the assembly of wing film and spar, (c) photograph of two overlapped wing planes with carbon spar reinforcement, (d) design and dimension of the wing film, and (e) photographs of the components

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Fig. 5

Experimental setup for static thrust tests, measuring wing kinematics, thrust generation and power expenditure for (a) flapping X-wings using a single-axis load cell and (b) a spinning propeller (GWS 3020 prop) using a six-axis load cell

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Fig. 6

Static deformation and recoil of a polyimide film hinge that supports a wing pair: (a) static deformation under a deadweight, (b) a snapshot of recoil post the deadweight release, (c) the applied moments required to bend the film hinge, and (d) transient of recoil in terms of stroke angle

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Fig. 7

Wing kinematics of four wings on a 20 mm wide hinge pair: (a) snapshots showing the wing opening and closing at 13.Hz, (b)–(c) stroke angle and speed as measured from the midchord rib of one of the four wings, and (d)–(e) pitch angle and speed as measured from the mid-chord rib of one of the four wings

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Fig. 8

The effect of hinge stiffness on frequency-dependent wing kinematics: (a)–(b) amplitudes of stroke angle and speed at approximately 17 Hz, (c)–(d) amplitudes of pitch angle and speed at approximately 17 Hz, (e)–(f) frequency-dependent amplitudes of stroke and stroke speed, and (g)–(h) frequency-dependent amplitudes of pitch and pitch speed

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Fig. 9

Effect of elastic storage on lift generation and power expenditure by flapping X wings: (a)–(b) frequency dependence of mean lift generation, (c) transient of lift generation, (d)–(e) frequency dependence of mean electric power expenditure, and (f) transient of electric power expenditure

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Fig. 10

Power components incurred by a brushless motor for driving a transmission with 20 mm wide hinged wings: (a) frequency dependence and (b) transient powers incurred for beating wings at 17.0 Hz for two cycles

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Fig. 11

Take-off of an 13.4 g MAV prototype with flapping X wings (on 20 mm film hinges), along a guided wire. See supplemental Movie S1 which is available under the “Supplemental Data” tab for this paper on the ASME Digital Collection.

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Fig. 12

Benchmark of motorized propulsion systems for micro air vehicles: (a) flapping X wings on 20 mm elastic hinges versus propellers, e.g., Prop 3020 and Prop 7035, (c) electromechanical conversion efficiency of a brushless motor (AP-03 7000kv) for either indirect drive of flapping X wings or direct drive of propellers, (c) lift or thrust generation as a function of mean electrical power input, (d) frequency dependence of electric-power specific thrust generation, (e) lift or thrust generation as a function of mean shaft power, and (f) frequency dependence of shaft-power specific thrust generation



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