13th Bristol International RPV Conference, Bristol England, 30 March - 1 April 1998 UPDATE ON FLAPPING WING MICRO AIR VEHICLE RESEARCHOngoing work to Develop a Flapping Wing, Crawling “Entomopter” Robert C. Michelson Principal Research Engineer,Georgia Tech Research Institute Adjunct Associate Professor , School of Aerospace Engineering, Georgia Institute of Technology Past President, Association for Unmanned V ehicle Systems, International Steven Reece Graduate Student, School of Mechanical Engineering, Georgia Institute of Te chnology ABSTRACT: An electromechanica l multimode (ying/crawling) insect is being developed by Robert Michelson and his design team at the Geo rgia T ech Research Institute. The project has receiv ed initial IRAD funding from the Georgia Institute of T echnology . The mechanical insect, known as an “Entomopter” is based around a new development called a Reciprocating Chemical Muscle (RCM) which is capable of generating autonomic wing beating from a chemical energy source. Through direct conversion, the RCM also provides small amounts of electricity for onboard systems and fur- ther provides differential lift enhancement on the wings to achieve roll and hence, steered ight. A testbed for the RCM technique has been constructed and demonstrated. Tri mmed stable short range ight in a micro version of the entomopter is expected during 1998. In contrast to the testbed, entirely different mechani sms will be used to implement the RCM in the ying vers ion. This paper details progress to date on the Entomopter development. AUTHOR BIOGRAPHICAL SKETCH Robert Michelson is the Technical Area Manager, Battleeld Robotics & Unmanned Systems at the Georgia Tech Research Institute. He is currently Director of the Department of Transportat ion’s T rafc Surveillance Drone project as well as Director and Principal Investigator for the top-rated IRAD program at the Institute for FY97 involving the development of a multimode mechanical insect-based micro air vehicle. He has worked on and directed a number of remote sensing projects relat ed to RF and radar applications. In ad- dition he has performed verication and validation analyses of man-in-the-loop virtual reality ight simulators for STRICOM. He directed a project to develop the avionics suite for an Air Force Robotic Air-to-Air Combat vehicle . He directed a project to specify dual-mode IR/MMW seeker parameters for a lethal unmanned aerial vehicle (UA V) system. He was responsible for generating remote ight control system specications for Soviet “HA VOC” and “HOKUM” gunship drone simulators for the U.S. Army, and directed a task to develop a rotary winged UAV digital stability augmentation system for MICOM. As adjunct Associate Professor to the School of Aerospace Engineering, he teaches classes in avionics for UAVs. He is also the creator and organizer of the annual International Aerial Robotics Competitions. Prior to joining the GTRI staff, he participated in design and endo-atmospheric ight testing of computer-controlled space-based radar ocean surveillance systems while empl oyed by the Naval Research Laboratory in Washington, DC. He is author/coauthor of more than 60 major technical publications. Steven Reece has been instrumental in implementing the milli-scaled reciprocating chemical muscle testbed, testing it, and compiling the performance data contained in this paper.
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UPDATE ON FLAPPING WING MICRO AIR VEHICLE RESEARCH
Ongoing work to Develop a Flapping Wing, Crawling “Entomopter”
Robert C. Michelson
Principal Research Engineer, Georgia Tech Research InstituteAdjunct Associate Professor, School of Aerospace Engineering, Georgia Institute of Technology
Past President, Association for Unmanned Vehicle Systems, International
Steven ReeceGraduate Student, School of Mechanical Engineering, Georgia Institute of Technology
ABSTRACT: An electromechanical multimode (ying/crawling) insect is being developed byRobert Michelson and his design team at the Georgia Tech Research Institute. The project has receivedinitial IRAD funding from the Georgia Institute of Technology. The mechanical insect, known as an“Entomopter” is based around a new development called a Reciprocating Chemical Muscle (RCM)which is capable of generating autonomic wing beating from a chemical energy source. Throughdirect conversion, the RCM also provides small amounts of electricity for onboard systems and fur-ther provides differential lift enhancement on the wings to achieve roll and hence, steered ight. Atestbed for the RCM technique has been constructed and demonstrated. Trimmed stable short rangeight in a micro version of the entomopter is expected during 1998. In contrast to the testbed, entirelydifferent mechanisms will be used to implement the RCM in the ying version. This paper detailsprogress to date on the Entomopter development.
AUTHOR BIOGRAPHICAL SKETCH
Robert Michelson is the Technical Area Manager, Battleeld Robotics & Unmanned Systems at the Georgia Tech
Research Institute. He is currently Director of the Department of Transportation’s Trafc Surveillance Drone project
as well as Director and Principal Investigator for the top-rated IRAD program at the Institute for FY97 involving the
development of a multimode mechanical insect-based micro air vehicle.
He has worked on and directed a number of remote sensing projects related to RF and radar applications. In ad-dition he has performed verication and validation analyses of man-in-the-loop virtual reality ight simulators for
STRICOM. He directed a project to develop the avionics suite for an Air Force Robotic Air-to-Air Combat vehicle.
He directed a project to specify dual-mode IR/MMW seeker parameters for a lethal unmanned aerial vehicle (UAV)
system. He was responsible for generating remote ight control system specications for Soviet “HAVOC” and
“HOKUM” gunship drone simulators for the U.S. Army, and directed a task to develop a rotary winged UAV digital
stability augmentation system for MICOM.
As adjunct Associate Professor to the School of Aerospace Engineering, he teaches classes in avionics for UAVs. He
is also the creator and organizer of the annual International Aerial Robotics Competitions. Prior to joining the GTRI
staff, he participated in design and endo-atmospheric ight testing of computer-controlled space-based radar ocean
surveillance systems while employed by the Naval Research Laboratory in Washington, DC. He is author/coauthor
of more than 60 major technical publications.
Steven Reece has been instrumental in implementing the milli-scaled reciprocating chemical muscle testbed, testing
it, and compiling the performance data contained in this paper.
Not all ying animals implement all of these motions. Unlike
birds, most insects do not use the spanning technique. Insects
with low wing beat frequencies (17-25 Hz) generally have very
restricted lagging capabilities (Brodsky3, 1994). Insects such
as alderies and mayies, have xed stroke planes with respect
to their bodies, and the only way these insects can alter the
stroke plan with respect to gravity is to change their body angle
(Brodsky3, 1994). Thus, apping ight is possible with only
two degrees of freedom: apping and feathering.
Using only these two degrees of freedom, there are 3 important
variables with respect to wing kinematics: wing beat frequency,wing beat amplitude, and wing feathering as a function of wing
position. When coordinated, these motions can provide lift not
only on the down stroke, but also on the up stroke. The abil-
ity to generate lift on both strokes results from a change in the
angle of attack of the wing whose tip inscribes an ellipse when
considered relative to a body-referenced point. The ability to
generate lift on both the up- and down-stroke leads to the po-
tential for hovering ight in entomopters and ornithopters.
Wing beat amplitudes vary in nature from approxi-
mately 25° to 175°. In general, as wing beat frequency
increases, wing beat amplitude decreases. The feath-
ering of the wing as a function of wing position is
crucial to the ight dynamics. Each line represents
the wing section at some arbitrary position across
the span of the wing (Ward-Smith
5
,1984). Generallyinsects with a constant, vertical stroke plane must use
a large angle of attack on the descending part of their
wing trajectory.
Other techniques such as optimizing wing shape,
using elastic wing deformation, and employing the
Weis-Fogh clapping mechanism (Lighthill6, 1975)
can be used to enhance the wing kinematics, and thus
produce more efcient apping ight.
Entomopter X-Wing FlappingLike the alderies and mayies, the entomopter will
have a xed stroke plane for each of its four wings.
Coupled to the RCM, each wing pair will be part of
resonant mechanical structure that will provide a self-
regulating wing beat frequency. The amplitude of
the wing beat is a function of the stiffness and spring
constant of this structure. The third important vari-
able, feathering, is accomplished through the use of
“smart materials” that exhibit a different compliance
under varying loads.
This latter feature will be controlled by not only by
the wing rib structure, but also the interstitial wing
material itself. Stereolithography and Fused Depo-
sition Modeling techniques have allowed the design
team to create intricate wing structures directly from
computer models. Careful attention is being paid to
material selection. Resilience, stiffness in opposite
planes, chemical compatibility, and ease of bonding
are but a few of the points being considered in the
choice of wing materials. Figures 2 through 4 show
wings being grown in our stereolithography machines
as well as ABS wing stiffening structures with, and
without interstitial materials.
These wing structures are designed with hollow micropassages to allow intelligent venting of waste gasfrom the RCM over the wing surface for directionalcontrol of the entomopter. The circulation controlledairfoils of the entomopter allow differential modu-lation of the lift while maintaining a constant auto-nomic wing beat. This simplies the mechanics of the wing and is scalable to the micro level by usingvalves constructed with microelectromechanicalsystems (MEMS) techniques.
but crawling. When in flight, they will have to be able
to move slow enough to negotiate winding corridors,
stairwells, and narrow openings. Slow flight for un-
obtrusive reconnaissance missions is best done with
flapping-wing propulsors.
Near term propulsion for tiny multimode roboticvehicles will be fueled from chemical or fossil fuel
sources. Electrical storage density is insufficient to
support missions of reasonable endurance at this time.
A reciprocating chemical muscle (RCM) has been de-
veloped and tested at a macro- and milli-scale for use
in a mechanical insect called an “entomopter”. The
Entomopter uses a novel X-wing pair design that is
resonantly driven by the RCM.
Empirical tests on the milli-scaled RCM show that
it develops sufficient force and motion to drive the
wings of an entomopter at frequencies necessary for
flight. The characteristics of the RCM comport withthose of insects, though currently at a larger “milli
scale”. In particular, a muscle extension/contraction
range of 1.7 percent of the overall muscle length has
been demonstrated at a reciprocating frequency of 20
Hz and a force available of between 2.5 and 3 lbs over
the entire range of motion.
The design of the entomopter and its RCM have been
tailored with size reduction in mind, such that MEMS
implementations will be possible to further reduce size
and final production cost.
References1. Ellington, C., “The Aerodynamics of Flapping Animal
Flight,” American Zoology, vol. 24, 1984, pp. 95 - 105
2. Azuma, A., Springer - Verlag, The Biokinetics of Flyingand Swimming, Tokyo, 1992, pp. 77 - 154.
3. Brodsky, A., The Evolution of Insect Flight , Oxford;New York: Oxford University Press, 1994, pp 35 - 39.
4. Ellington, C., “The Aerodynamics of Insect-basedFlying Machines,” invited presentation at IROS-97,Intelligent Robots and Systems Conference, Grenoble,France, 1997 (from unpublished manuscript).
5. Ward-Smith, A., Biophysical Aerodynamics and the Natural Environment , John Wiley & Sons, New York,1984, pg. 93.
6. Lighthill, J., Mathematical Biouiddynamics, Society forIndustrial and Applied Mathematics, 1975, pp. 179 - 195.
7. Michelson, R., Helmick, D., Reece, S., Amarena, C.,“A Reciprocating Chemical Muscle (RCM) for MicroAir Vehicle “Entomopter” Flight,” 1997 Proceedingsof the Association for Unmanned Vehicle Systems,International, June 1997, pp. 429 - 435
8. Alexander, R.M., “Springs for Wings,” Science, Vol-ume 268, 7 April, 1995, pp. 50 - 51