64 research outputs found
Attitude Control of a Small Helicopter UAV using Incremental Nonlinear Dynamic Inversion
No full textThis paper presents an attitude controller for a small helicopter Unmanned Aerial Vehicle (UAV) based on Incremental Nonlinear Dynamic Inversion (INDI). INDI is a sensor-based control method which responds quickly to the commanded input, but also to disturbances. While previous implementations of INDI used a control effectiveness matrix describing effects on rotational accelerations, the implementation presented in this paper uses rotational rates. This is possible with small hingeless-rotor helicopters since the rotational rates are achieved almost immediately, but also the transient is taken into account. By doing so, the matrix contains only constants and the control structure is much simpler. The proposed controller is implemented on a small helicopter which weighs less than 50 grams. The performance of the controller is demonstrated with step responses on roll and heading angles. Also disturbance rejection capabilities are demonstrated. Finally, the controller is deliberately configured incorrectly with wrong control effectiveness and actuator model parameters. A theoretical derivation is provided to predict the effect of incorrect parameters. With experiments, it is demonstrated that the helicopter can be stabilized over a wide range of incorrect values. It is concluded that the demonstrated controller is a suitable choice for small autonomous helicopters.Aerospace EngineeringControl & Operation
Incremental Nonlinear Dynamic Inversion controller for a Variable Skew Quad Plane
No full textThis paper presents the design of an Incremental Nonlinear Dynamic Inversion (INDI) controller for the novel, patent pending (NL 2031701) platform Variable Skew Quad Plane (VSQP). Part of the identified challenges is the development of a model for the actuator effectiveness and lift especially as a function of skew, the newly added degree of freedom. The models and assumptions are verified through static and dynamic wind tunnel tests at the Open Jet Facility (OJF) of TU Delft. Transition tests have been successfully performed thanks to an automatic skew controller derived from the proposed models and aimed to maximize control authority.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Control & Simulatio
Design and joint control of a conjoined biplane and quadrotor
No full textUnmanned Aerial Vehicles (UAVs) have the potential to perform many different missions, some of which may require a large aircraft for endurance and a small aircraft for manoeuvrability in a building. This paper proposes a novel combination of a quadrotor and a hybrid biplane capable of joint hover, joint forward flight, and mid-air disassembly followed by separate flight. We investigate cooperative control strategies during joint flight that do not require any communication between the quadcopter and the biplane. This means that the two aircraft have their own independent control strategy based on their own sensors. Secondly, to avoid communication the biplane leads the flight and the goal for the quadrotor is to help in producing thrust and increasing stability. Three control strategies for the quadrotor are compared: a proportional angular rate damper, a proportional angular acceleration damper, and constant thrust without attitude control. Simulation and practical tests show that for intentional attitude changes of the biplane, the quadrotor rate- and angular acceleration damper strategies lead to a small performance degradation. However, the angular rate damper strategy for disturbance rejection has the lowest roll angle error and requires the smallest input command. The in-flight release is successfully tested in joint hover up to a forward pitch angle of -18 [deg].Control & Simulatio
Design and testing of a remotely controlled surfkite for the Laddermill
No full textThis paper presents the design and testing of a remotely controlled surfkite for the Laddermill. The Laddermill is a novel concept to generate electricity from high altitude winds. It generates electricity by pulling a rope from a generator, with lift generated by kites. Part of the rope that is connected to the kites is wound around the generator. The kites pull the rope from the generator, thus driving it. Subsequently the kites fly down in a configuration that generates significantly less lift than during the ascent. This way the tether is retrieved and the process is repeated. The Laddermill concept allows very large single unit powers. For an early demonstration of the Laddermill principle, a commercially availably Peter Lynn surfkite is used. This surfkite is radio controlled, by means of drag creating actuators on the wing tips. This paper presents the actuator design and results of testing of the surfkite. Preliminary results of generation of Laddermill energy are also presented.Aerospace Engineerin
Bats in Gliding Flight: A comparative wind tunnel investigation of the aerodynamics of gliding bats and a bat inspired gliding wing model
No full textDue 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.Aerospace Engineerin
Aerodynamic Design and Optimization of a Long Range Mini-UAV
No full textThis thesis focuses on the development of an aerodynamic optimization algorithm for long range mini-UAV’s. This algorithm is applied to the design of the TU Delft mini- UAV that participated in the EMAV2009 outdoor endurance mission. The analysis of the low Reynolds number (< 2.5 · 105) aerodynamics on the wing is performed using a quasi-3D method which combines a vortex lattice method with viscous airfoil data. The optimization part of the program is accomplished by a sequential quadratic programming algorithm. RANS-CFD calculations and wind tunnel experiments were performed to validate the newly developed quasi-3D method. The final design for the mini-UAV has lift over drag ratio of 11.8 and a high capacity battery (8Ah) which give it a total range of 166 kmAerospace EngineeringDepartment Of System Engineering and Aircraft DesignAerospace Engineerin
Vision-based automatic landing of a quadrotor UAV on a floating platform: A new approach using incremental backstepping
No full textThe 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.Dynamics and Control of Aerospace VehiclesControl and SimulationAerospace Engineerin
Stereo Vision for Flapping Wing MAVs: Design of an Obstacle Avoidance system
No full textIn 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.Control & OperationsAerospace Engineerin
Never Landing Drone
No full textIncreasing endurance is a major challenge for battery-powered aerial vehicles. A method is presented which makes use of an updraft around obstacles to decrease the power consumption of a fixed-wing, unmanned aerial vehicle. Simulatory results have shown the conditions that the flight controller can fly in.The effect of a change in wind velocity, wind direction and updraft has been analysed. The simulations showed that an increase in either updraft or absolute wind direction decrease the throttle consumption.A change in wind velocity results in a shift of the flight controller’s boundaries. The simulations achieved sustained flight at 0 per cent throttle. The practical, autonomous tests reduced the average throttle down to 4.5 per cent in front of the boat. The unfavourable wind conditions and inaccuracies explain this minorthrottle requirement during the final experiment.Aerospace Engineerin
Improving flight performance of DelFly II in hover by improving wing design and driving mechanism
No full textRecent years have seen an increasing interest in micro aerial vehicles (MAV). The same can be said about flapping flight. The Delft University of Technology started to develop a flapping wing MAV in 2005, ”DelFly”, which relies on a flapping biplane wing configura- tion for thrust and lift generation. DelFly has evolved significantly during the last years. At the time of writing there are already three version of DelFly; DelFly I, DelFly II and DelFly Micro. The test subject of this study is DelFly II because of its stable and broad flight envelope. The aim of this study is to improve flight performance of the DelFly II. Hereto, in this thesis report, a wing geometry study is performed in order to improve the aerodynamic performance of the wing and the driving mechanism is improved in order to increase the efficiency of energy transfer from the battery to the movement of the leading edges. The current study resulted in a increase of thrust-to-power ratio of 5% due to the wing design and 20% due to the new crank-shaft mechanismAerospace EngineeringDepartment of System Engineering and Aircraft DesignAerospace Engineerin
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