a robot that fly like a bird!
Aerodynamic lightweight design with active torsion
SmartBird is an ultralight but powerful flight model with excellent
aerodynamic qualities and extreme agility. With SmartBird, Festo
has succeeded in deciphering the flight of birds. This bionic technology-
bearer, which is inspired by the herring gull, can start, fly
and land autonomously – with no additional drive mechanism. Its
wings not only beat up and down, but also twist at specific angles.
This is made possible by an active articulated torsional drive, which
in conjunction with a complex control system makes for unprece -
dented efficiency in flight operation. Festo has thus succeeded for
the first time in realising an energy-efficient technical adaptation
of the natural model.
Know-how for automation
The functional integration of coupled drive units yields significant
ideas and insights that Festo can transfer to the development
and optimisation of hybrid drive technology. The minimal use of
materials and the extremely lightweight construction pave the way
for efficiency in resource and energy consumption. The knowledge
acquired in aerodynamics and flow behaviour yields new
approaches and solutions for automation.
The fascination of bird flight
One of the oldest dreams of mankind is to fly like a bird – to move
freely through the air in all dimensions and to take a “bird’s-eye
view” of the world from a distance.
No less fascinating is bird flight in itself. Birds achieve lift and
remain airborne using only the muscle power of their wings, with
which they generate the necessary thrust to overcome the air
resistance and set their bodies in motion – without any rotating
“components”. Nature has ingeniously achieved the functional
integration of lift and propulsion. Birds measure, control and regulate
their motion through the air continuously and fully autonomously
in order merely to survive. For this purpose they use their
sense organs.
Scientific precursors
As long ago as 1490, Leonardo da Vinci built rudimentary flapping
wing models in order to come closer to achieving bird flight. In
1889, Otto Lilienthal published the book “Birdflight as the Basis
of Aviation: A Contribution Toward a System of Aviation”. In the
chapter “The Bird as a Model” Otto Lilienthal describes in detail
the flight of the seagull. More recent times have seen the development
of ornithopter projects such as that of Professor Dr. James
DeLaurier and his research team at the University of Toronto.
In 2006 this group succeeded for the first time in taking off from
a runway with a flying device powered by a flapping-wing mechanism,
complete with pilot. In August 2010, a flying machine propelled
by its pilot’s muscle power alone covered a distance of about
150 meters after being towed to flying altitude.
Bird flight deciphered
In 2011, the engineers of Festo’s Bionic Learning Network devel -
oped a flight model that is capable of taking off autonomously and
rising in the air by means of its flapping wings alone, without the
aid of other devices to provide lift. SmartBird flies, glides and sails
through the air.
The experience gained with the Bionic Learning projects AirRay and
AirPenguin was incorporated into the creation of SmartBird. The
objective of the project was to construct a bionic bird modelled on
the herring gull. The fascination of building an artificial bird that
could take off, fly and land by means of flapping wings alone
provided the inspiration for SmartBird’s engineers. Moving air in
a specific manner is a core competence of Festo that has been a
driving force for the company for more than fifty years.
The unusual feature of SmartBird is the active torsion of its wings
without the use of additional lift devices. The objective of the
SmartBird project was to achieve an overall structure that is efficient
in terms of resource and energy consumption, with minimal
overall weight, in conjunction with functional integration of propulsion
and lift in the wings and a flight control unit in the torso and
tail regions. Further requirements were excellent aerodynamics,
high power density for propulsion and lift, and maximum agility for
the flying craft. Under scientific supervision, an intelligent cyber -
netic overall design was realised in discrete individual stages.
Active articulated torsional drive
Flapping-wing flight comprises two principal movements. First, the
wings beat up and down, whereby a lever mechanism causes the
degree of deflection to increase from the torso to the wing tip. Sec -
ond, the wing twists in such a way that its leading edge is directed
upwards during the upward stroke, so that the wing adopts a positive
angle of attack. If the rotation were solely due to the wing’s
elasticity, passive torsion would result. If on the other hand the sequencing
of the torsion and its magnitude are controlled by an actuator,
the wing’s torsion is not passive, but active.
The wing: Lift and propulsion in birds
SmartBird’s wings each consist of a two-part arm wing spar with an
axle bearing located on the torso, a trapezoidal joint as is used in
enlarged form on industrial excavators, and a hand wing spar. The
trapezoidal joint has an amplitude ratio of 1:3. The arm wing gener -
ates lift, and the hand wing beyond the trapezoidal joint provides
propulsion. Both the spars of the inner and the outer wing are
torsionally resistant. The active torsion is achieved by a servomotor
at the end of the outer wing which twists the wing against the spar
via the outmost rib of the wing.
Partially linear kinematics for optimal thrust
When SmartBird lifts its wings, the servo motor for active torsion
twists the tips of the hand wings to a positive angle of attack,
which is then changed to a negative angle a fraction of a wing beat
period. The angle of torsion remains constant between these
phases. Thanks to this sequence of movements, the airflow along
the wing profile can be optimally used to generate thrust.
The torso: a secure housing for the technology
The battery, engine and transmission, the crank mechanism and
the control and regulation electronics are housed in SmartBird’s
torso. By means of a two-stage helical transmission, the exterior
rotor motor causes the wings to beat up and down with a reduction
ratio of 1:45. This motor is fitted with three Hall sensors that pre
Lift and propulsion in the one movement: Upward ...
Intelligent monitoring
The wing’s position and torsion are monitored by two-way radio
communication with ZigBee Protocol, by means of which operating
data are conveyed such as battery charge, power consumption and
input by the pilot. In addition, the torsion control parameters can
be adjusted and thus optimised in real time during flight. Together
with the electronic control system, this intelligent monitoring en -
ables the mechanism to adapt to new situations within a fraction of
a second. This facilitates the simple, efficient and weight-optimised
mechanical design of the bird model for optimised efficiency of the
overall biomechatronic system in flight operation.
cisely register the wing’s position. Both the flapping and bending
forces are conveyed from the transmission to the hand wing via a
flexible link. The crank mechanism has no dead centre and thus
runs evenly with minimal peak loads, thus ensuring smooth flight.
The opposing movement of the head and torso sections in any spatial
direction is synchronised by means of two electric motors and
cables. The torso thus bends aerodynamically, with simultaneous
weight displacement; this makes SmartBird highly agile and manoeuvrable.
The tail section: an aid for lift and control
The tail of SmartBird also produces lift; it functions as both a pitch
elevator and a yaw rudder. When the bird flies in a straight line, the
V-position of its two flapping wings stabilises it in a similar way to
a conventional vertical stabiliser of an aircraft. To initiate a turn to
the left or right, the tail is tilted: when it is rotated about the longitudinal
axis, a yaw moment about the vertical axis is produced.
Theoretical basis
A high degree of aerodynamic efficiency can theoretically only be
achieved by active torsion, with a small quantity of power required
to be supplied by an actuator. With active torsion, the power of the
flapping wings is converted very efficiently into thrust. The aero -
dynamic efficiency factor is the ratio of thrust attained to the
flapping and rotary power expended.
Scientific investigation of circular flight
Investigations and measurements of SmartBird were carried out
over the course of its development on the basis of the work of
French physiologist Etienne-Jules Marey (1830 – 1904), who ana -
lysed the flight of birds that were made to fly in a circular path. To
determine the electro-mechanical efficiency, a new apparatus was
developed which acts as a dynamometrical brake.
SmartBird’s efficiency factors
SmartBird and its predecessors have an electromechanical efficiency
factor of around 45%. Measurements of circular flight have dem -
onstrated an aerodynamic efficiency factor as high as 80%.
The overall efficiency factor is the product of the two partial efficiency
factors. Since the aerodynamic efficiency factor can be calculated
but not directly measured, it is determined from measurements
of overall and electromechanical efficiency. To determine the
electromechanical efficiency factor, the absorption dynamometer
continuously measures torque and angular velocity to calculate the
available power expended during flight. For this purpose, the wing
stroke movement is transferred to a shaft that is impeded by a
brake shoe; the lever arm of the brake is held by a force sensor. An
angle sensor measures the rotation of the shaft. The torque and
angular velocity together yield the mechanical power. The electromechanical
efficiency factor is calculated as the ratio of this quan -
tity to the electrical power supplied.
Optimal use of airflow
Propulsion and lift are achieved solely by the flapping of the wings
and have a power requirement of only 25 watts. SmartBird has a
total weight of around 400 grams and a wingspan of 2 metres. It is
thus an excellent example of functional integration and resourceefficient
extreme lightweight design, and demonstrates the optimal
use of airflow phenomena.
The control of the time behaviour of wing bending and wing torsion
takes place within the tact of a few milliseconds and results in optimum
airflow around the wings. The SmartBird flight model has no
rotating parts on its exterior and therefore cannot cause injury
efficiency in design allows the development of compactly
dimensioned products that require less installation space and are
flow-optimised, and thus more energy-efficient.
Possible fields of application
The applications of coupled drives for linear and rotary movement
range from generators that derive energy from water – so-called
stroke wing generators – to new actuators in process automation.
Inspired by the paradigm shift brought about by bionics, Festo has
already in the past developed products that have met with acceptance
in industry; the focus here is on energy-efficiency and conservation
of resources.
Technical data
Torso length: 1.07 m
Wingspan: 2.00 m
Weight: 0.450 kg
Structure: lightweight carbon fibre structure
Lining: extruded polyurethane foam
Battery: lithium polymer accumulator, 2 cells,
7.4 V, 450 mA
Servo drive: 2x digital servo unit with 3.5 kg actuating
force for control of head and tail sections
2x digital servo units for wing torsion,
with 45 degree travel in 0.03 s
Electrical power
requirement: 23 W
Microcontroller: MCU LM3S811
32-bit microcontroller@50 MHz
64 kByte flash, 8 kByte RAM
Radio transmission: 868 MHz/2.4 GHz two-way radio transmission
based on ZigBee Protocol
Motor: Compact 135, brushless
Sensors: Motor positioning 3x TLE4906 Hall sensors
Accelerometer: LIS302DLH
Power management: 2x LiPo accumulator cells with ACS715
voltage and current monitoring
LED activation: TPIC 2810D
Project partners
Project initiator:
Dr. Wilfried Stoll, Managing Partner,
Festo Holding GmbH
Project manager:
Dipl.-Ing. (FH) Markus Fischer, Corporate Design,
Festo AG & Co. KG
Design and production:
Rainer Mugrauer, Günter Mugrauer, Andreas Schadhauser,
Effekt-Technik GmbH Schlaitdorf
Electronics and integration:
Dipl.-Ing. Agalya Jebens, Dipl.-Ing. Kristof Jebens
JNTec GbR, Gärtringen
Dimensioning and scientific supervision:
Dr. Wolfgang Send, Felix Scharstein, ANIPROP GbR, Göttingen
Photos:
Thomas Baumann, Esslingen, Germany
Axel Waldecker, Murr, Germany
Taxidermically prepared herring gull:
Stuttgart State Museum of Natural History
Taxidermist: Jan Panniger
Project initiator:
Dr. Wilfried Stoll, Managing Partner,
Festo Holding GmbH
Project manager:
Dipl.-Ing. (FH) Markus Fischer, Corporate Design,
Festo AG & Co. KG
Design and production:
Rainer Mugrauer, Günter Mugrauer, Andreas Schadhauser,
Effekt-Technik GmbH Schlaitdorf
Electronics and integration:
Dipl.-Ing. Agalya Jebens, Dipl.-Ing. Kristof Jebens
JNTec GbR, Gärtringen
Dimensioning and scientific supervision:
Dr. Wolfgang Send, Felix Scharstein, ANIPROP GbR, Göttingen
Photos:
Thomas Baumann, Esslingen, Germany
Axel Waldecker, Murr, Germany
Taxidermically prepared herring gull:
Stuttgart State Museum of Natural History
Taxidermist: Jan Panniger
Project initiator:
Dr. Wilfried Stoll, Managing Partner,
Festo Holding GmbH
Project manager:
Dipl.-Ing. (FH) Markus Fischer, Corporate Design,
Festo AG & Co. KG
Design and production:
Rainer Mugrauer, Günter Mugrauer, Andreas Schadhauser,
Effekt-Technik GmbH Schlaitdorf
Electronics and integration:
Dipl.-Ing. Agalya Jebens, Dipl.-Ing. Kristof Jebens
JNTec GbR, Gärtringen
Dimensioning and scientific supervision:
Dr. Wolfgang Send, Felix Scharstein, ANIPROP GbR, Göttingen
Photos:
Thomas Baumann, Esslingen, Germany
Axel Waldecker, Murr, Germany
Taxidermically prepared herring gull:
Stuttgart State Museum of Natural History
Taxidermist: Jan Panniger
Project partners
Project initiator:
Dr. Wilfried Stoll, Managing Partner,
Festo Holding GmbH
Project manager:
Dipl.-Ing. (FH) Markus Fischer, Corporate Design,
Festo AG & Co. KG
Design and production:
Rainer Mugrauer, Günter Mugrauer, Andreas Schadhauser,
Effekt-Technik GmbH Schlaitdorf
Electronics and integration:
Dipl.-Ing. Agalya Jebens, Dipl.-Ing. Kristof Jebens
JNTec GbR, Gärtringen
Dimensioning and scientific supervision:
Dr. Wolfgang Send, Felix Scharstein, ANIPROP GbR, Göttingen
Photos:
Thomas Baumann, Esslingen, Germany
Axel Waldecker, Murr, Germany
Taxidermically prepared herring gull:
Stuttgart State Museum of Natural History
Taxidermist: Jan Panniger
Festo AG & Co. KG
Ruiter Strasse 82
73734 Esslingen
Germany
Phone +49 711 347-0
Telefax +49 711 347-21 55
cc@de.festo.com
www.festo.com/bionicFesto AG & Co. KG
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