55 research outputs found
Nonlinear MPC for Quadrotor Fault-Tolerant Control
The mechanical simplicity, hover capabilities, and high agility of quadrotors
lead to a fast adaption in the industry for inspection, exploration, and urban
aerial mobility. On the other hand, the unstable and underactuated dynamics of
quadrotors render them highly susceptible to system faults, especially rotor
failures. In this work, we propose a fault-tolerant controller using nonlinear
model predictive control (NMPC) to stabilize and control a quadrotor subjected
to the complete failure of a single rotor. Differently from existing works,
which either rely on linear assumptions or resort to cascaded structures
neglecting input constraints in the outer-loop, our method leverages full
nonlinear dynamics of the damaged quadrotor and considers the thrust constraint
of each rotor. Hence, this method could effectively perform upset recovery from
extreme initial conditions. Extensive simulations and real-world experiments
are conducted for validation, which demonstrates that the proposed NMPC method
can effectively recover the damaged quadrotor even if the failure occurs during
aggressive maneuvers, such as flipping and tracking agile trajectories.Comment: 9 pages, 13 figure
Performance, Precision, and Payloads: Adaptive Nonlinear MPC for Quadrotors
Agile quadrotor flight in challenging environments has the potential to revolutionize shipping, transportation, and search and rescue applications. Nonlinear model predictive control (NMPC) has recently shown promising results for agile quadrotor control, but relies on highly accurate models for maximum performance. Hence, model uncertainties in the form of unmodeled complex aerodynamic effects, varying payloads and parameter mismatch will degrade overall system performance. In this letter, we propose L1 -NMPC, a novel hybrid adaptive NMPC to learn model uncertainties online and immediately compensate for them, drastically improving performance over the non-adaptive baseline with minimal computational overhead. Our proposed architecture generalizes to many different environments from which we evaluate wind, unknown payloads, and highly agile flight conditions. The proposed method demonstrates immense flexibility and robustness, with more than 90% tracking error reduction over non-adaptive NMPC under large unknown disturbances and without any gain tuning. In addition, the same controller with identical gains can accurately fly highly agile racing trajectories exhibiting top speeds of 70 km/h, offering tracking performance improvements of around 50% relative to the non-adaptive NMPC baseline
NeuroBEM: Hybrid Aerodynamic Quadrotor Model
Quadrotors are extremely agile, so much in fact, that classic
first-principle-models come to their limits. Aerodynamic effects, while
insignificant at low speeds, become the dominant model defect during high
speeds or agile maneuvers. Accurate modeling is needed to design robust
high-performance control systems and enable flying close to the platform's
physical limits. We propose a hybrid approach fusing first principles and
learning to model quadrotors and their aerodynamic effects with unprecedented
accuracy. First principles fail to capture such aerodynamic effects, rendering
traditional approaches inaccurate when used for simulation or controller
tuning. Data-driven approaches try to capture aerodynamic effects with blackbox
modeling, such as neural networks; however, they struggle to robustly
generalize to arbitrary flight conditions. Our hybrid approach unifies and
outperforms both first-principles blade-element theory and learned residual
dynamics. It is evaluated in one of the world's largest motion-capture systems,
using autonomous-quadrotor-flight data at speeds up to 65km/h. The resulting
model captures the aerodynamic thrust, torques, and parasitic effects with
astonishing accuracy, outperforming existing models with 50% reduced prediction
errors, and shows strong generalization capabilities beyond the training set.Comment: 9 pages + 1 pages reference
Upset Recovery Control for Quadrotors Subjected to a Complete Rotor Failure from Large Initial Disturbances
This study has developed a fault-tolerant controller that is able to recover
a quadrotor from arbitrary initial orientations and angular velocities, despite
the complete failure of a rotor. This cascaded control method includes a
position/altitude controller, an almost-global convergence attitude controller,
and a control allocation method based on quadratic programming. As a major
novelty, a constraint of undesirable angular velocity is derived and fused into
the control allocator, which significantly improves the recovery performance.
For validation, we have conducted a set of Monte-Carlo simulation to test the
reliability of the proposed method of recovering the quadrotor from arbitrary
initial attitude/rate conditions. In addition, real-life flight tests have been
performed. The results demonstrate that the post-failure quadrotor can recover
after being casually tossed into the air.Comment: 7 pages, 9 figures, accepted by International Conference of Robotics
and Automation (ICRA) 202
Perception-Aware Perching on Powerlines With Multirotors
Multirotor aerial robots are becoming widely used for the inspection of powerlines. To enable continuous, robust inspection without human intervention, the robots must be able to perch on the powerlines to recharge their batteries. Highly versatile perching capabilities are necessary to adapt to the variety of configurations and constraints that are present in real powerline systems. This letter presents a novel perching trajectory generation framework that computes perception-aware, collision-free, and dynamically-feasible maneuvers to guide the robot to the desired final state. Trajectory generation is achieved via solving a Nonlinear Programming problem using the Primal-Dual Interior Point method. The problem considers the full dynamic model of the robot down to its single rotor thrusts and minimizes the final pose and velocity errors while avoiding collisions and maximizing the visibility of the powerline during the maneuver. The generated maneuvers consider both the perching and the posterior recovery trajectories. The framework adopts costs and constraints defined by efficient mathematical representations of powerlines, enabling online onboard execution in resource-constrained hardware. The method is validated on-board an agile quadrotor conducting powerline inspection and various perching maneuvers with final pitch values of up to 180 ∘ . The developed code is available online at: https://github.com/grvcPerception/pa_powerline_perchin
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