Publications

@mastersthesis{uuid:f97ac167-38e5-4155-933c-efa2ee179712,

title = {Stereo Vision for Flapping Wing MAVs: Design of an Obstacle Avoidance system},

author = {S. Tijmons},

url = {http://resolver.tudelft.nl/uuid:f97ac167-38e5-4155-933c-efa2ee179712},

year  = {2012},

date = {2012-01-01},

school = {Delft University of Technology},

abstract = {In the field of Micro Air Vehicle (MAV) research the use of flapping wings attracts a lot of interest. The potential of flapping wings lies in their efficiency at small scales and their large flight envelope with a single configuration. They have the possibility of performing both energy efficient long distance flights as well as hovering flights. Most studies on Flapping Wing MAVs (FWMAVs) have focused on the design of the airframe and making them able to fly. Currently, the state-of-the-art permits investigation of the necessary autonomous flight capabilities of FWMAVs. Most previous studies have made important preliminary steps by using external cameras or an onboard camera with the FWMAV flying in a modified environment. However, since autonomy is most useful for flight in unknown areas, it will be necessary to use an onboard camera while flying in unmodified environments. Research in this direction has been performed on the DelFly. In particular, the well-known cue of optic flow was found to be rather unreliable for the determination of 3D distances, and it was complemented by a novel visual appearance cue. Since the combination of these cues may still not be sufficient for robust and long-term obstacle avoidance, this study focuses on a different well-known method to extract 3D information on the environment: stereo vision. The potential advantage of stereo vision over optic flow is that it can provide instantaneous distance estimates, implying a reduced dependence on the complex camera movements during flapping flight. The goal is to employ stereo vision in a computationally efficient way in order to achieve obstacle avoidance. The focus of this study is on using heading control for this task. Four main contributions are made: The first contribution comprises an extensive study on literature in the field of computational stereo vision. This research has been done for decades and a lot of methods were developed. These mainly focus on optimizing the quality of the results, while disregarding computational complexity. In this study the focus was on finding one or more time efficient methods that give sufficient quality to perform robust obstacle avoidance. It was concluded that Semi-Global Matching is a good candidate. The second contribution is that for the first time it has been investigated what the requirements are for a stereo vision system to do successful stereo vision-based obstacle avoidance on FWMAVs. In order to achieve accurate stereo vision results, both hardware and software aspects are found to be of importance. FWMAVs can carry only a small amount of payload and therefore there is a large restriction on sensor weight. The third contribution is the development of a systematical way to use the 3D information extracted by the stereo vision algorithm in order to find a guaranteed collision-free flight path. The focus was on dealing with the limited maneuverability of the MAV and the limited view angle of the camera. The fourth contribution is in giving an indication on the usefulness of stereo vision based on multiple experiments. These focus on determining the accuracy of the obstacle detection method as well as on validating the functionality of the obstacle avoidance strategy. The designed system proved to be successful for the task of obstacle avoidance with FWMAVs. The DelFly II successfully avoided the walls in an indoor office space of 7.3×8.2m for more than 72 seconds. This is a considerable improvement over previous monocular solutions. Since even reasonable obstacle detection could be performed for low-textured white walls, the experiments clearly show the potential of stereo vision for obstacle avoidance of FWMAVs. In combination with existing methods for speed and height control the proposed system has the potential of making fully autonomous (flapping wing) MAVs possible.},

note = {Mulder, J.A. (mentor); De Croon, G.C.H.E. (mentor); Van Kampen, E. (mentor); Remes, B.D.W. (mentor)},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{uuid:7d688e57-328c-4d76-990f-e619221feeb4,

title = {Flow visualization and force measurements on a flapping-wing MAV DelFly II in forward flight configuration},

author = {Jerke Eisma},

url = {http://resolver.tudelft.nl/uuid:7d688e57-328c-4d76-990f-e619221feeb4},

year  = {2012},

date = {2012-01-01},

school = {TU Delft Aerospace Engineering},

abstract = {Flapping wing flight has attracted increased interest among aerodynamics researchers recently in view of the recent expansion of design efforts in the field of Micro Aerial Vehicles (MAVs). MAVs are given specific attention because of their potential as mobile platforms capable of reconnaissance and gathering intelligence in hazardous and physically inaccessable areas. To achieve these missions, they should be manoevring with ease, staying aloft and propelling themselves efficiently. Conventional means of aerodynamic force generation are found lacking at this point and the apping-wing approach becomes an appealing or even necessary solution. In contrast to the conventional (fixed and rotary wing) force generation mechanisms, apping wing systems take benefit from the unsteady ow effects that are associated to the vortices separating from the wing leading and trailing edges, which create low pressure regions around the wings that lead to the generation of higher lift and thrust.},

note = {Scarano, Fulvio (mentor); van Oudheusden, Bas (mentor); Perçin, Mustafa (mentor); Remes, Bart (mentor); Delft University of Technology (degree granting institution)},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{uuid:f8848255-1831-482a-be21-2da3ca3e50bb,

title = {Vision-based automatic landing of a quadrotor UAV on a floating platform: A new approach using incremental backstepping},

author = {A. S. Mendes},

url = {http://resolver.tudelft.nl/uuid:f8848255-1831-482a-be21-2da3ca3e50bb},

year  = {2012},

date = {2012-01-01},

school = {Delft University of Technology},

abstract = {The development of systems that allow unmanned aerial vehicles, known as UAVs, to perform tasks autonomously is a current trend in aerospace research. The specific aim of this thesis is to study and achieve vision-based automatic landing of a quadrotor UAV on a floating platform, a known target that possesses oscillatory behavior. The research contributions to be taken from this study can be divided into two perspectives, as described below. From a theoretical point of view, a design solution is proposed which includes GPS navigation to enable the quadrotor to find the target, and vision-based control to approach and land upon it. From this design, several control-related issues must then be solved, mainly the development of a controller for the autoland mission. To accomplish this control task, an incremental backstepping control law is developed. Additionally, linear and standard backstepping controllers are designed for comparison. The derived control laws require knowledge of the states to close the feedback loops; therefore, state estimation algorithms are designed for complete state reconstruction. The approach selected is modular, thus separating position/velocity estimation from attitude determination. The former is performed using an extended Kalman filter, and the latter using a complementary filter. Furthermore, an augmented Kalman filter formulation is developed for estimation of the platform’s vertical motion. The combination of control and state estimation algorithms is tested in a simulated environment using a simulation tool developed in this study for Monte-Carlo analysis. This tool allows for evaluation of the design not only for the nominal case, but also for random combinations of external conditions. Results show that successful performance is obtained for the nonlinear controllers since the desired criteria is met and the risk of crashing is demonstrated to be residual. Additional tests show that incremental backstepping is, in general, more robust than standard backstepping in the case of model mismatch, even in the presence of state estimation errors. From a practical perspective, the findings are twofold. First, this thesis presents a procedure to experimentally determine the moments of inertia of the quadrotor by using a two-axis motion simulator and a six-component force/torque sensor. The inertia properties are also determined analytically using two modeling approaches: point mass analysis and assumption of simple geometric shapes. The results show that point mass analysis can lead to erroneous inertia estimation deviation of 20-30% from the real value), thus resulting in a significant model mismatch. The experimental and simple shapes assumption methods render similar results, which strongly indicates not only that the experimental method proposed is valid, but also that the assumption of simple geometric shapes can be used as a reliable and cost-effective method to determine moments of inertia of small UAVs. Second, in this thesis the system is tested in real time using an actual quadrotor. Flight tests are performed for hovering above a target with known characteristics, and to achieve this end, a vision system is developed to obtain relative position measurements from images captured by an on-board camera. A Kalman filter is implemented for real-time integration of vision with IMU data, and a linear controller with reference command filters is used. Tuning procedures are then carried out until satisfactory performance is achieved.},

note = {Chu, Q.P. (mentor); Van Kampen, E. (mentor); Mulder, J.A. (mentor); Remes, B.D.W. (mentor)},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{koopmans2012,

title = {Delfly Freeflight -- Autonomous Flight of the Delfly in the Wind Tunnel using Low-Cost Sensors},

author = {Andries J Koopmans},

year  = {2012},

date = {2012-01-01},

address = {Delft, NL},

school = {Delft University of Technology},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{uuid:4b95f124-7ea5-49ea-af65-dfb436d6bdc7,

title = {Bats in Gliding Flight: A comparative wind tunnel investigation of the aerodynamics of gliding bats and a bat inspired gliding wing model},

author = {M. Stuiver},

url = {http://resolver.tudelft.nl/uuid:4b95f124-7ea5-49ea-af65-dfb436d6bdc7},

year  = {2011},

date = {2011-01-01},

school = {Delft University of Technology},

abstract = {Due to the high cost of flight, there is a high evolutionary selection pressure for energy efficient flight patterns, such as using external natural forces for soaring or flying intermittently. Some bats at time soar, glide or flap glide. Bounding flight is not possible as their membranous wings will go slack, and soaring is not common amongst bats, as most bats are nocturnal and during night thermals are usually of insufficient strength. From an aerodynamic point of view, gliding flight is less complex than flapping flight, however in bats undulating flight patterns are less observed than in birds. So, why should bats glide? Flight performance studies on live bats have revealed a part of the complexity of hovering and steady flapping flight, but gliding flight in these animals is poorly studied. To get insight in how bats glide and in their gliding flight performance, gliding flight of bats is studied from two points of view; gliding flight of real bats and gliding of a flexible, bat inspired wing model, in a low speed, tiltable wind tunnel. The kinematics of both the bats and the model are filmed by two synchronised high speed cameras, and the flow field in a transverse plane behind the wings is visualized by means of a PIV system. Three medium sized bats Leptonycteris yerbabuenae, are trained to glide at a feeder in the test section of the wind tunnel at a know, fixed glide angle. This known glide angle enables to calculate the aerodynamic forces, which are fixed properties in steady gliding flight. A gliding wing model, based on a bat’s wing, with an adjustable leading edge flap, is designed, build, and tested at different angles of attack. The wing model is tested with both a smooth and a structured top surface to see what the effect of ’turbulators’ can be. Additionally the wing model is mounted onto a balance in order to measure the aerodynamic forces. By means of experiments with the wing model, wake structures of gliding flight can be connected to a single changing morphology parameter to explore the parameter space, and the wake structures can be compared to the wake structures of the gliding bats. The bats are observed to glide for some seconds in the test section, but only the parts of the glides at the feeder where the tip vortex strength and position were stable are analysed. From the PIV data, an average wake is constructed per glide sequence of the bats, and for each leading edge setting and speed combination of the model wing. From the average wake the flight forces and the resulting flight performance properties are derived. The wing model approaches the glide behaviour of the bats. Deploying the leading edge flap increases the span efficiency and the lift coefficient at low angles of attack. Also the structure on top of the wing is beneficial for flight performance at low angles of attack.},

note = {Bijl, H. (mentor); van Oudheusden, B.W. (mentor); Muijres, F.T. (mentor); Remes, B.D.W. (mentor)},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{uuid:291207fc-5ada-435c-be39-8e1436fd96c9,

title = {Fixed-Wing UAV Integrated Navigation with Low-Cost IMU/GPS},

author = {B. A. Hummelink},

url = {http://resolver.tudelft.nl/uuid:291207fc-5ada-435c-be39-8e1436fd96c9},

year  = {2011},

date = {2011-01-01},

school = {Delft University of Technology},

abstract = {Today, there is an increase in the use of Unmanned Aerial Vehicles (UAV's), for applications that can be considered dull, dirty or dangerous when compared to those applications of conventional aircraft or helicopters. To further increase the use of UAV's, their navigation filters must be robust and reliable. The trend in current autopilot development is defined by the ever decreasing size of vehicles leading to the creation of miniature Inertial Navigation Systems (INS) with low cost, low grade sensors. Small flying vehicles have fast dynamics requiring higher control rates and higher dynamic ranges with minimal available onboard computational capacities. Sensor and processing limitations have consequences for the achievable navigation performance. This in turn poses limits on the minimal vehicle stability, weather conditions and trajectory smoothness. The most important aspect and thesis goal is to guarantee the navigation filter solution robustness during all flight maneuvers. A navigation filter is an integration algorithm that provides a navigation solution on the vehicle's state vector from sensor data. This thesis focuses on one UAV platform in particular, namely small fixed-wing UAV's. One of the main challenges with designed navigation filters is that they can be theoretically stable but the outcome can sometimes not be used. In practice, the navigation filter outcome can give a diverging solution while theoretically stable. The goal of this thesis is to define the minimal requirements of sensors and other hardware for an INS such that the stabilization requirements posed by the vehicle dynamics and size can be satisfied. With the requirements stated, smaller and more dynamic fixed-wing UAV's can be stabilized based on the integrated navigation solution. The developed observability analysis tool is able to provide a quantitative analysis on the state observability that can be used to analyze different systems or sensor configurations. The observability matrix is composed of the system and observer dynamics. The system dynamics is based on the Inertial Measuring Unit (IMU) prediction of the system states, the observer equations correspond to the observer dynamics. A non-linear local observability analysis has been performed to calculate the observability matrix. The traditional Singular-Values Decomposition (SVD) algorithm provides the singular values of an observability matrix in a decreasing order and indicates the rank of the system. The rank of the observability matrix corresponds to the number of observable system states, the SVD can however not directly link the singular values to the system states. To overcome this problem a different matrix decomposition is used that is able to directly couple the singular values to the system states. This developed matrix decomposition algorithm is based on the QR factorization, called QRsvd. With this algorithm it is possible to quantitatively indicate the observability (degree) of each system state. An analysis into the physical properties of fixed-wing aircraft kinematics resulted in new insight into the movement of flying vehicles. Based on the derived kinematics together with the coupling of an IMU, GPS receiver and fixed-wing aircraft kinematics this resulted in new physical insight. This resulted in three angle correction (AC) equations that can be used as additional attitude/heading angle observers to the conventional IMU/GPS integration. With these three additional observers, the three orientation angles become instantaneously observable. Without the AC equations, a rotational rate constraint is always present to integrate the IMU with GPS. GPS receivers and IMU are separate, self-contained subsystems with different updating frequencies and processing times. Resulting clock differences are called time synchronization errors and result in filter estimation problems. A time synchronization requirement is derived, which is a function of changes in vehicle accelerations and filter innovation. The time synchronization requirement is proportional to the magnitude of the change in vehicle accelerations a and negatively proportional to the magnitude of the identification filter innovation. Vehicles with fast dynamics, like fixed-wing UAV's, can have larger changes in vehicle accelerations magnitude, resulting in a more stringent time synchronization requirement. Based on performed simulations and verification with flight test data, it can be concluded that the improved IMU/GPS filter with AC equations can provide a stable long-term navigation solution with accurate short-term performance, by using (Iterated) Extended Kalman filters. During the performed simulations the position states give the largest source of error, due to the large GPS position uncertainty. For the three orientation angles, the heading angle has a larger identification error compared to the pitch and roll angle. For the orientation angles, the influence of atmospheric wind on the identification performance is minimal except for the heading angle due to the presence of a side-slip angle beta. Coordinate transformations between the Earth, North-East-Down (NED) reference frame F_E and the body-fixed reference frame F_B can be performed using a rotational transformation matrix R_BE. The antisymmetric matrix R_BE holds special properties that can be utilized and fits in the category of Special Orthogonal Lie groups with a dimension of three, called SO(3). Based on SO(3) group properties, a non-linear complementary filter can be constructed that uses this matrix as a single state. The non-linear complementary filter on the SO(3) group, can be used as an alternative to conventional Kalman state identification filters. For (I)EKF the heading angle is the largest source of error of the attitude/heading angles, this is also the case for the SO(3) filter. Differences between the SO(3) filter and (I)EKF are due to two aspects. The SO(3) filter uses constant proportional and integrator gains, where Kalman gain matrices include process and observer uncertainties. The other source of differences can be found in the strong coupling between the individual attitude/heading angles for the non-linear SO(3) filter compared to (I)EKF.},

note = {Chu, Q.P. (mentor); Mulder, J.A. (mentor); De Croon, G.C.H.E. (mentor); De Wagter, C. (mentor)},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{uuid:610da696-9202-4f11-ba65-bea67d2edd0b,

title = {PIV and force measurements on the flapping-wing MAV DelFly II: An aerodynamic and aeroelastic investigation into vortex development},

author = {M. A. Groen},

url = {http://resolver.tudelft.nl/uuid:610da696-9202-4f11-ba65-bea67d2edd0b},

year  = {2010},

date = {2010-01-01},

school = {Delft University of Technology},

abstract = {Recent years have seen an increasing interest in Micro Air Vehicles (MAVs). MAVs are small (micro sized) aircraft and find their application in a multitude of commercial, industrial and military purposes. To perform their missions MAVs should be small sized, have good manoeuvrability, be well controllable and have a broad flight envelope. When flying in small confinements, the ability to fly at low airspeed and to have good manoeuvrability is critical. One type of MAVs, the flapping-wing MAV, particularly has attractive characteristics for flight in confined spaces. DelFly is a biplane flapping-wing MAV designed and built at Delft University of Technology. DelFly is able to hover and has an onboard camera for observation and vision-based control. For the DelFly project a top-down approach is followed, where from the study of a relative large model experience and theoretical insights can be gained, that can assist to create smaller, functional versions of the DelFly. The ultimate aim of the DelFly project is to improve the design to a very small full autonomous aircraft. For the current experimental investigation, force and flow field measurements were performed on a hovering DelFly II, since this model has a broad flight envelope and proven flight performance. The flow field is studied using particle image velocimetry. Due to the flexible wings there is a strong fluid structure interaction, therefore also the in-flight wing deformation is determined. The aerodynamic mechanism generating forces on the DelFly are related to those found in insect flight. Since leading edge vortices (LEVs) in insect flight are identified as the most important unsteady aerodynamic mechanism enhancing lift generation for insects, the development of these for the DelFly are very interesting. The vortex development is studied for various wings, at various flapping frequencies and at various spanwise positions. For the DelFly wing a conical LEV is developed, starting at out-board spanwise positions, approximately halfway during the translation. This LEV grows larger and is shed along the chord and at this time a new LEV starts to grow at the leading edge. This second LEV is dissipated at the end of the out-stroke during wing rotation, but at the end of the in-stroke this LEV moves above the wings and interacts with the counter-rotating LEV from the mirror wing. Inside the vortex tube a spanwise velocity component out-board is present. The shedding of the initial vortex and start of a second LEV is not completely consistent with LEV development for insect flight (which typically operate at a lower Reynolds number).},

note = {Bijl, H. (mentor); van Oudheusden, B.W. (mentor); Goosen, J.F.L. (mentor); Remes, B.D.W. (mentor)},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{Bruggeman2010,

title = {Improving flight performance of DelFly II in hover by improving wing design and driving mechanism},

author = {Bart Bruggeman},

year  = {2010},

date = {2010-01-01},

pages = {123},

school = {Delft University of Technology},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}

@mastersthesis{trips2010,

title = {Aerodynamic Design and Optimization of a Long-range Mini-UAV},

author = {D Trips},

year  = {2010},

date = {2010-01-01},

number = {December},

address = {Delft, NL},

school = {Delft University of Technology},

keywords = {},

pubstate = {published},

tppubtype = {mastersthesis}

}