SmartBird

Bird flight deciphered

Aerodynamic lightweight design with active torsion

SmartBird is an ultralight but powerful flight model with excellentaerodynamic qualities and extreme agility. With SmartBird, Festohas succeeded in deciphering the flight of birds. This bionic tech-nology-bearer, which is inspired by the herring gull, can start, flyand land autonomously – with no additional drive mechanism. Itswings not only beat up and down, but also twist at specific angles.This is made possible by an active articulated torsional drive, whichin conjunction with a complex control system makes for unprece -dented efficiency in flight operation. Festo has thus succeeded forthe 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 significantideas and insights that Festo can transfer to the development and optimisation of hybrid drive technology. The minimal use ofmaterials and the extremely lightweight construction pave the wayfor efficiency in resource and energy consumption. The knowledgeacquired in aerodynamics and flow behaviour yields new approaches and solutions for automation.

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The fascination of bird flight

One of the oldest dreams of mankind is to fly like a bird – to movefreely through the air in all dimensions and to take a “bird’s-eyeview” 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, withwhich 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 regu-late their motion through the air continuously and fully autono-mously in order merely to survive. For this purpose they use theirsense organs.

Scientific precursors

As long ago as 1490, Leonardo da Vinci built rudimentary flappingwing models in order to come closer to achieving bird flight. In18, Otto Lilienthal published the book “Birdflight as the Basis of Aviation: A Contribution Toward a System of Aviation”. In thechapter “The Bird as a Model” Otto Lilienthal describes in detailthe flight of the seagull. More recent times have seen the develop-ment 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 mecha-nism, complete with pilot. In August 2010, a flying machine propel-led by its pilot’s muscle power alone covered a distance of about150 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 andrising in the air by means of its flapping wings alone, without theaid of other devices to provide lift. SmartBird flies, glides and sailsthrough the air.

The experience gained with the Bionic Learning projects AirRay andAirPenguin was incorporated into the creation of SmartBird. Theobjective of the project was to construct a bionic bird modelled onthe herring gull. The fascination of building an artificial bird thatcould 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 adriving force for the company for more than fifty years.

The unusual feature of SmartBird is the active torsion of its wingswithout the use of additional lift devices. The objective of theSmartBird project was to achieve an overall structure that is effi-cient in terms of resource and energy consumption, with minimaloverall weight, in conjunction with functional integration of propul-sion and lift in the wings and a flight control unit in the torso andtail regions. Further requirements were excellent aerodynamics,high power density for propulsion and lift, and maximum agility forthe flying craft. Under scientific supervision, an intelligent cyber -netic overall design was realised in discrete individual stages.

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Precisely twisted: Active torsion during the upward wing strokeActive articulated torsional drive

Flapping-wing flight comprises two principal movements. First, thewings beat up and down, whereby a lever mechanism causes thedegree 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 directedupwards during the upward stroke, so that the wing adopts a posi-tive angle of attack. If the rotation were solely due to the wing’selasticity, passive torsion would result. If on the other hand the se-quencing of the torsion and its magnitude are controlled by an ac-tuator, 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 anaxle bearing located on the torso, a trapezoidal joint as is used inenlarged form on industrial excavators, and a hand wing spar. Thetrapezoidal joint has an amplitude ratio of 1:3. The arm wing gener -ates lift, and the hand wing beyond the trapezoidal joint providespropulsion. Both the spars of the inner and the outer wing are

torsionally resistant. The active torsion is achieved by a servomotorat the end of the outer wing which twists the wing against the sparvia the outmost rib of the wing.

Partially linear kinematics for optimal thrust

When SmartBird lifts its wings, the servo motor for active torsiontwists 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 beatperiod. The angle of torsion remains constant between these phases. Thanks to this sequence of movements, the airflow alongthe 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 andthe control and regulation electronics are housed in SmartBird’storso. By means of a two-stage helical transmission, the exteriorrotor motor causes the wings to beat up and down with a reductionratio of 1:45. This motor is fitted with three Hall sensors that pre -

Lift and propulsion in the one movement: Upward ...

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cisely register the wing’s position. Both the flapping and bendingforces are conveyed from the transmission to the hand wing via aflexible link. The crank mechanism has no dead centre and thusruns evenly with minimal peak loads, thus ensuring smooth flight. The opposing movement of the head and torso sections in any spa-tial direction is synchronised by means of two electric motors andcables. The torso thus bends aerodynamically, with simultaneousweight displacement; this makes SmartBird highly agile and mano-euvrable.

The tail section: an aid for lift and control

The tail of SmartBird also produces lift; it functions as both a pitchelevator and a yaw rudder. When the bird flies in a straight line, theV-position of its two flapping wings stabilises it in a similar way toa conventional vertical stabiliser of an aircraft. To initiate a turn tothe left or right, the tail is tilted: when it is rotated about the longi-tudinal axis, a yaw moment about the vertical axis is produced.

... and downward wing strokes

Measurement, control and regulation

The on-board electronics allow precise and thus efficient control of wing torsion as a function of wing position. For this purpose, apowerful microcontroller calculates the optimal setting of two servo motors, which adjust the torsion of each wing. The flappingmovement and the torsion are synchronised by three Hall sensors,which determine the absolute position of the motor for the flappingmovement. Since the active joint torsion drive requires precisecoordination between the flapping and twisting movements, it issubjected to continuous all-round monitoring.

Intelligent monitoring

The wing’s position and torsion are monitored by two-way radiocommunication with ZigBee Protocol, by means of which operatingdata are conveyed such as battery charge, power consumption andinput by the pilot. In addition, the torsion control parameters canbe adjusted and thus optimised in real time during flight. Togetherwith the electronic control system, this intelligent monitoring en -ables the mechanism to adapt to new situations within a fraction ofa second. This facilitates the simple, efficient and weight-optimisedmechanical design of the bird model for optimised efficiency of theoverall biomechatronic system in flight operation.

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Theoretical basis

A high degree of aerodynamic efficiency can theoretically only beachieved by active torsion, with a small quantity of power requiredto be supplied by an actuator. With active torsion, the power of theflapping wings is converted very efficiently into thrust. The aero -dynamic efficiency factor is the ratio of thrust attained to theflapping and rotary power expended.

Scientific investigation of circular flight

Investigations and measurements of SmartBird were carried outover the course of its development on the basis of the work ofFrench physiologist Etienne-Jules Marey (1830 –1904), who ana -lysed the flight of birds that were made to fly in a circular path. Todetermine 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 efficien-cy 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 effi-ciency factors. Since the aerodynamic efficiency factor can be cal-culated but not directly measured, it is determined from measure-ments of overall and electromechanical efficiency. To determine theelectromechanical efficiency factor, the absorption dynamometercontinuously measures torque and angular velocity to calculate theavailable power expended during flight. For this purpose, the wingstroke 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. Anangle sensor measures the rotation of the shaft. The torque and angular velocity together yield the mechanical power. The electro-mechanical 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 wingsand have a power requirement of only 25 watts. SmartBird has atotal weight of around 400 grams and a wingspan of 2 metres. It isthus an excellent example of functional integration and resource-efficient extreme lightweight design, and demonstrates the optimaluse of airflow phenomena.

The control of the time behaviour of wing bending and wing torsiontakes place within the tact of a few milliseconds and results in opti-mum airflow around the wings. The SmartBird flight model has norotating parts on its exterior and therefore cannot cause injury.

Real-time monitoring of wing position and torsion

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A paradigm shift thanks to bionics

With SmartBird, Festo in its Bionic Learning Network is once againsuccessfully transferring a natural principle to a field of techno l -ogy. SmartBird provides a stimulus for turning to nature in thes

earch for new solutions in automation. An all-encompassing mechatronic design

SmartBird is an all-encompassing mechatronic and cyberneticd esign that combines numerous individual solutions into a fasci -nating whole. SmartBird could only be realised through the inte-gration of intelligent mechanics, electrical drive technology, find -ings from fluid dynamics, intelligent open and closed-loop controlengineering, condition monitoring and the constant scientific valid -ation and transfer of scientific findings into practice.

Festo already today puts its expertise in the field of fluid dynamicsto use in the development of the latest generations of cylindersand valves. By analysing SmartBird’s flow characteristics, Festohas acquired additional knowledge for the optimisation of its prod -uct solutions and has learned to design even more efficiently. This

Flow behaviour in the design and simulation of new productsefficiency in design allows the development of compactly

dimensioned products that require less installation space and areflow-optimised, and thus more energy-efficient.

Energy-efficient and resource-friendly

With its optimised contours and its lightweight carbon fibre design,SmartBird is an excellent example of energy-efficient motion and of the resource-friendly use of materials. The functional integrationof two types of drive into a hybrid solution likewise increases resource efficiency.

Functional integration for hybrid technology

This function integration provides information for the developmentand optimisation of hybrid drive technologies. With the hybrid axis,Festo is already combining the advantages of pneumatics with those of electric linear axes to achieve rapid, high-precision linearactuator technology.

Possible fields of application

The applications of coupled drives for linear and rotary movementrange from generators that derive energy from water – so-calledstroke wing generators – to new actuators in process automation. Inspired by the paradigm shift brought about by bionics, Festo hasalready in the past developed products that have met with accep-tance in industry; the focus here is on energy-efficiency and conser-vation of resources.

Safe operation through condition monitoring

Data on SmartBird’s wing position and torsion are constantly registered during flight. The torsion control parameters can be adjusted in real time during flight and thus optimised. This ensuresstable flight of the bird for safe operation.

Condition monitoring: Process-safety ensured by permanent diagnosis

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Technical data

Torso length: 1.07 m

Wingspan: 2.00 m

Weight: 0.450 kgStructure: lightweight carbon fibre structureLining: extruded polyurethane foamBattery:

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 sections2x 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 kByte flash, 8 kByte RAM

Radio transmission:868 MHz/2.4 GHz two-way radio trans-mission based on ZigBee ProtocolMotor: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

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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 JebensJNTech GbR, Gärtringen

Dimensioning and scientific supervision:

Dr. Wolfgang Send, Felix Scharstein, ANIPROP GbR, GöttingenPhotos:

Thomas Baumann, Esslingen, GermanyAxel Waldecker, Murr, Germany

Taxidermically prepared herring gull:

Stuttgart State Museum of Natural History Taxidermist: Jan Panniger

Festo AG & Co. KGRuiter Strasse 8273734 EsslingenGermanyPhone +49 711347-0Telefax+49 711347-21 55cc@de.festo.com

www.festo.com/bionic 1102/4 ne 06745