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System block diagrams. (a) Outer loop PID control for position. (b) Inner loop PIV control combined with ANDO. (c) Simulation of quadcopter dynamics IGE.
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This paper focuses on modeling and nonlinear control of in-ground-effect (IGE) on multi-rotor aerial vehicles such as quadrotor helicopters (quadcopters). As the vehicle flies and hovers near obstacles such as the ground, walls, and other features, the IGE which is a function of the distance between the rotor and the obstacle induces a thrust that...
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Citations
... Previous researches only mentioned the infinite model between the motor current and the altitude in the GE region, which shows no current is flowing when the altitude is zero. This paper proposes a new finite motor current model which can show a non-zero current in the GE region based on [8]- [10], which discusses the finite thrust model in the GE region. The model is identified experimentally. ...
... In that situation, the finite in-GE thrust model is proposed in [8]- [10] by He et al. as ...
... From (7), (8), and (11), ...
To overcome the short flight duration of drones, research on in-flight inductive power transfer has been recognized as an essential solution. Thus, it is important to accurately estimate and control the attitude of the drones which operate close to the charging surface. To this end, this paper proposes an attitude estimation method based solely on the motor current for precision flight control in the ground effect region. The model for the estimation is derived based on the motor equation when it rotates at a constant rotational speed. The proposed method is verified on the simulations and experiments. It allows simultaneous estimation of altitude and pitch angle with the accuracy of 0.30 m and 0.04 rad, respectively. The minimum transmission efficiency of the in-flight power transfer system based on the proposed estimation is calculated as 95.3 %, which is sufficient for the efficient system. Index Terms-attitude estimation, ground effect, in-flight in-ductive power transfer
... To compensate for the in-ground effect, an adaptive nonlinear disturbance observer was designed in He et al. (2017) to enhance closedloop PID control. The observer and controller were implemented in a simulation framework. ...
... The ability of IESO to observe and compensate the GE was verified only in simulations. Similar to the previous work, He et al. [67] proposed to enhance the inner (attitude) loop with a nonlinear disturbance observer (NDO), while the outer (position) loop was commanded by a PID controller. The nominal controller of the inner loop consisted of a commonly used proportionalintegral-velocity controller. ...
This article aims at collecting and discussing the results reached by the research community regarding the study of the ground effect on small rotorcraft unmanned aerial vehicles, especially from the modeling and control point of view. Rotorcraft performance is affected by the presence of the ground or any other boundary that alters the flow into the rotors. Specifically, the ground effect can induce perturbations in the flight stability, when operating near the ground. For a rotorcraft, an accident is likely to happen when the vehicle leaves or enters the ground effect region, which may cause crashes and property damages. Today, the use of unmanned aerial vehicles has grown widespread, which raises safety concerns when they are flying at very low altitudes and near the ground. Consequently, studying the influence of the ground over rotorcrafts is of paramount importance for general safety. Also, these investigations can be used to design systems of guidance, navigation, and control. In this review, we break down the most relevant works to date. We discuss aspects related to modeling, control, and application of the ground effect for small-scale multirotors, as well as other aerodynamic proximity effects, such as the ceiling and wall effects. We conclude by mentioning potential avenues of research when studying the ground effect from the point of view of the robotics and artificial intelligence fields.
... Herein, a new quasi-steady IGE model [47,48] is developed that predicts finite maximum IGE thrust ratio based on BET. The model's coefficients are empirically determined through a series of experiments. ...
... A. Quasi-Steady Exponential Model for Single-Rotor IGE A quasi-steady IGE model is developed that relates the IGE thrust ratio K G to the rotor height, blade pitch, and solidity, while maintaining constant rotor angular velocity. From prior work [47], the basic quasi-steady exponential IGE model is ...
... The first coefficient C a denotes the maximum increment of the IGE thrust ratio when z 0. The second coefficient C b determines the strength of the ground effect as a function of the rotor height. Both coefficients were noted to be functions of blade geometry [47]. The model was verified experimentally for off-the-shelf propellers, and the results showed a more accurate prediction (0.6% root-mean-square error) of IGE thrust throughout the ground effect region, z ∈ 0; 2, compared to other quasi-steady models [48]. ...
This Paper presents a new quasi-steady in-ground effect (IGE) model for small multirotor aerial vehicles such as quadcopter unmanned aerial vehicles. The model offers three major advances to the state of the art: 1) predicting the IGE thrust ratio without singularity, 2) relating the strength of the ground effect to the blade geometry (pitch angle, solidity, and radius), and 3) capturing the effect of multirotor configurations. Two IGE coefficients, based on blade element theory, are introduced and then analyzed using the method of images. Additionally, the thrust-loss phenomenon on multirotor IGE is observed and modeled empirically. Experiments are conducted to validate each component of the model, and the results suggest that the model can be used to predict the onset of the IGE for vehicle motion control and planning in the regime where IGE dominates.
... Among all types of obstacles, operating near ground plane is inevitable especially during vehicle takeoff and landing. In this paper, advancement in the understanding of the ground effect is achieved by leveraging a previously-developed quasi-steady empirical GE model based on blade element theory (BET) [12,13]. Thus, the contribution of this work is a new quasi-steady in-ground effect (IGE) model for rotorcraft unmanned aerial vehicles that predict the aerodynamic behavior when the vehicle's rotor approaches ground plane. ...
... Focusing on the first drawback, a new quasi-steady IGE model was proposed that predicts finite maximum IGE thrust and ratio based on BET [12,13]. The model's coefficients were empirically determined through a series of experiments. ...
... The quasi-steady IGE model describes the IGE thrust ratio with respect to rotor height, blade pitch, and solidity at constant rotor angular velocity. The basic quasi-steady exponential IGE model proposed in [12] can be expressed as, ...
This paper introduces a new quasi-steady in-ground effect model for rotorcraft unmanned aerial vehicles to predict the aerodynamic behavior when the vehicle’s rotors approach ground plane. The model assumes that the compression of the outflow due to the presence of ground plane induces a change in the induced velocity that can drastically affect the thrust and power output. The new empirical model describes the change in thrust as a function of the distance to an obstacle for a rotor in hover condition. Using blade element theory and the method of image, the model parameters are described in terms of the rotor pitch angle and solidity. Experiments with off-the-shelf, fixed-pitch propellers and 3D-printed variable pitch propellers are carried out to validate the model. Experimental results suggest good agreement with 9.5% root-mean-square error (RMSE) and 97% p-value of statistic significance.
... (1) and still measurable when Z/R = 4, compared to the result from Cheeseman's model which states that the ground effect is significant up to Z/R = 1.5. The author in [15] presented another model to capture a wider range of the height ...
... In [31], a nonlinear adaptive backstepping controller was used to control the altitude of a small-scale helicopter during takeoff and landing while a horizontal wind gust is present. In [15], the authors designed an adaptive nonlinear disturbance observer (ANDO) to enhance the PID controller. The settling time with ANDO implemented was largely reduced in the simulation, however the experimental validation is lacking. ...
... In MRAC, we consider an unknown matched system uncertainty, F (x) added to the original linearized system (Eqn. (15)), which can be written as a linear combination of N provided locally Lipschitz-continuous basis functions, Φ (x), with unknown constant coefficients, Θ in Eqn. (16).ẋ ...
Mitigating ground effect becomes a big challenge for autonomous aerial vehicles when they are flying in close proximity to the ground. This paper aims to develop a precise model of ground effect on mini quadcopters, provide an advanced control algorithm to counter the model uncertainty and, as a result, improves the command tracking performance when the vehicle is in the ground effect region. The mathematical model of ground effect has been established through a series of experiments and validated by a flight test. The experiments show that the total thrust generated by rotors increases linearly as the vehicle gets closer to the ground, which is different from the commonly-used ground effect model for a single rotor vehicle. In addition, the model switches from a piecewise linear to a quadratic function when the rotor to rotor distance is increased. A control architecture that utilizes the model reference adaptive controller (MRAC) has also been designed, where MRAC is added to the altitude loop. The performance of the proposed control algorithm has been evaluated through a set of flight tests on a mini quadcopter platform and compared with a traditional proportional–integral–derivative (PID) controller. The results demonstrate that MRAC dramatically improves the tracking performance of altitude command and can reduce the rise time by \(80\%\) under the ground effect.
View Video Presentation: https://doi.org/10.2514/6.2022-1015.vid The ground effect impacts rotorcraft performance in cases such as takeoff, landing, and hovering in proximity of a rigid surface. This paper investigates the performance of a quadrotor tracking a continuous trajectory during vertical takeoff and landing. The baseline controller is a cascaded P-PI controller which is then augmented with a disturbance observer. The addition of a disturbance observer improves rejection of the ground effect compared to the baseline controller. A Simcenter 3D and Simulink co-simulation environment is used to obtain simulation results. The proposed controller correlates well in simulation and experiment. The proposed controller shows better performance in landing compared to the baseline controller in both simulation and experimental results.
Effective autonomous indoor flight requires an ability to sense and navigate ground, ceiling, and walls. While this can be accomplished in many ways including vision, one bio-inspired approach that is not well studied uses the detection of pressure changes when flying close to surfaces. As an example, an increase in pressure can be detected when a quadrotor flies close to the ground, a phenomenon known as ‘ground effect’. This work evaluates the viability of differential pressure measurements as a means of sensing ground, ceilings, and walls for small quadrotors. Extending existing models for thrust in ground effect, a model is derived to predict pressure changes due to ground effect in hover and tilt. The pressure response with ground effect is characterized across a range of distances, thrust levels, sensor locations, and quadrotor tilts using a Crazyflie 2.0 quadrotor and a small MEMS differential pressure sensor. Characterization experiments are also used to evaluate pressure measurements at varying distances from ceilings and walls, as well as the pressure behavior due to step changes in ground height. Manually controlled free flight tests are used to validate ground sensing in both nominal and visually challenging environments, as well as wall sensing in free flight.
