Search

Payload manipulation with aerial robots has been an active research area for many years. Recent approaches have sought to plan, control, and execute maneuvers with large, yet deliberate, load swings for more agile, energy-optimal maneuvering. Unfortunately, the system's nonlinear dynamics make executing such trajectories a significant challenge and experimental demonstrations thus far have relied completely on a motion capture system and non-negligible simplifications like restriction of the system to a two-dimensional workspace or closing of the control loop on the quadrotor, instead of the payload. In this work, we observe the payload using a downward-facing camera and estimate its state relative to the quadrotor using an extended Kalman filter. We demonstrate closed-loop payload control in the full three-dimensional workspace, with the planning, estimation, and control pipeline implemented on an onboard processor. We show control of load swings up to 53o from the vertical axis. To the best of our knowledge, this represents the first realization of closed-loop control of agile slung-load maneuvers and the largest achieved payload angle.

In this work, we present Hold Or take Optimal Plan (HOOP), a centralized trajectory generation algorithm for labeled multi-robot systems operating in obstacle-free, two-dimensional, continuous workspaces. Given a team of N robots, each with nth-order dynamics, our algorithm finds trajectories that navigate vehicles from their start positions to non-interchangeable goal positions in a collision-free manner. The algorithm operates in two phases. In the motion planning step, a geometric algorithm finds a collision-free, piecewise-linear trajectory for each robot. In the trajectory generation step, each robot’s trajectory is refined into a higher-order piecewise polynomial with a quadratic program. The novelty of our method is in this problem decomposition. The motion plan, through abstracting away robots’ dynamics, can be found quickly. It is then subsequently leveraged to construct collision avoidance constraints for N decoupled quadratic programs instead of a single, coupled optimization problem, decreasing computation time. We prove that this method is safe, complete, and generates smooth trajectories that respect robots’ dynamics. We demonstrate the algorithm’s practicality through extensive quadrotor experiments.

In this paper, we present a learning approach to goal assignment and trajectory planning for unlabeled robots operating in 2D, obstacle-filled workspaces. More specifically, we tackle the unlabeled multi-robot motion planning problem with motion constraints as a multi-agent reinforcement learning problem with some sparse global reward. In contrast with previous works, which formulate an entirely new hand-crafted optimization cost or trajectory generation algorithm for a different robot dynamic model, our framework is a general approach that is applicable to arbitrary robot models. Further, by using the velocity obstacle, we devise a smooth projection that guarantees collision free trajectories for all robots with respect to their neighbors and obstacles. The efficacy of our algorithm is demonstrated through varied simulations. A video describing our method and results can be found here.

In this work, we solve the labeled multi-robot planning problem. Most proposed algorithms to date have modeled robots as kinematic or kinodynamic agents in planar environments, making them impractical for real-world systems. Here, we present experiments to validate a centralized multi-robot planning and trajectory generation method that explicitly accounts for robots with higher-order dynamics. First, we demonstrate successful execution of solution trajectories. Next, we verify the robustness of the robots’ trajectory tracking to unmodeled external disturbances, in particular, the aerodynamic interactions between co-planar neighbors. Finally, we apply our algorithm to navigating quadrotors away from the downwash of their neighbors to improve safety in three-dimensional workspaces.

In this work, we consider the labeled multi-robot planning problem. In this paradigm, a team of robots at fixed start positions must navigate to pre-specified and noninterchangable goal positions. While many algorithms have been proposed for finding optimal solutions to this problem, most methods assume that the robots are kinematic agents, whereas in reality, robots often have high-order dynamics that must be respected by their trajectories. Here, we propose a centralized method for generating trajectories for teams of robots with general nth-order dynamics navigating to labeled goals. Our algorithm is safe and complete and additionally allows for decoupled optimization of each robot's trajectory as a Quadratic Program with linear constraints. We present simulation results for teams of up to 20 robots.

We address the problem of high speed autonomous navigation of quadrotor micro aerial vehicles with limited onboard sensing and computation. In particular, we propose a dual range planning horizon method to safely and quickly navigate quadrotors to specified goal locations in previously unknown and unstructured environments. In each planning epoch, a short-range planner uses a local map to generate a new trajectory. At the same time, a safe stopping policy is found. This allows the robot to come to an emergency halt when necessary. Our algorithm guarantees collision avoidance and demonstrates important advances in real-time planning. First, our novel short range planning method allows us to generate and re-plan trajectories that are dynamically feasible, comply with state and input constraints, and avoid obstacles in real-time. Further, previous planning algorithms abstract away the obstacle detection problem by assuming the instantaneous availability of geometric information about the environment. In contrast, our method addresses the challenge of using the raw sensor data to form a map and navigate in real-time. Finally, in addition to simulation examples, we provide physical experiments that demonstrate the entire algorithmic pipeline from obstacle detection to trajectory execution.