Quentin Lindsey

The GRASP Multiple Micro-UAV Testbed

In the last five years, advances in materials, electronics, sensors, and batteries have fueled a growth in the development of microunmanned aerial vehicles (MAVs) that are between 0.1 and 0.5 m in length and 0.1-0.5 kg in mass [1]. A few groups have built and analyzed MAVs in the 10-cm range [2], [3]. One of the smallest MAV is the Picoftyer with a 60-mmpropellor diameter and a mass of 3.3 g [4]. Platforms in the 50-cm range are more prevalent with several groups having built and flown systems of this size [5]-[7]. In fact, there are severalcommercially available radiocontrolled (PvC) helicopters and research-grade helicopters in this size range [8].

Design, modeling, estimation and control for aerial grasping and manipulation

This paper addresses mechanics, design, estimation and control for aerial grasping. We present the design of several light-weight, low-complexity grippers that allow quadrotors to grasp and perch on branches or beams and pick up and transport payloads. We then show how the robot can use rigid body dynamic models and sensing to verify a grasp, to estimate the the inertial parameters of the grasped object, and to adapt the controller and improve performance during flight. We present experimental results with different grippers and different payloads and show the robots ability to estimate the mass, the location of the center of mass and the moments of inertia to improve tracking performance.

Construction of Cubic Structures with Quadrotor Teams.

We propose and investigate a system in which teams of quadrotor helicopters assemble 2.5-D structures from simple structural nodes and members equipped with magnets. The structures, called Special Cubic Structures (SCS), are a class of 2.5-D truss-like structures free of overhangs and holes. Grippers attached to the bottom of each quadrotor enable them to pick up, transport, and assemble the structural elements. The design of the nodes and members imposes constraints on assembly which are incorporated into the design of the algorithms used for assembly. We show that any SCS can be built using only the feasible assembly modes for individual structural elements and present simulation and experimental results with a team of quadrotors performing automated assembly. The paper includes a theoretical analysis of the SCS construction algorithm, the rationale for the design of the structural nodes, members and quadrotor gripper, a description of the quadrotor control methods for part pickup, transport and assembly, and an empirical analysis of system performance.

Simultaneous Coverage and Tracking (SCAT) of Moving Targets with Robot Networks

We address the problem of simultaneously covering an environment and tracking intruders (SCAT). The problem is translated to the task of covering environments with time-varying density functions under the locational optimization framework. This allows for coupling the basic subtasks: task assignment, coverage, and tracking. A decentralized controller with guaranteed exponential convergence is devised. The SCAT algorithm is verified in simulations and on a team of robots.

Study of group food retrieval by ants as a model for multi-robot collective transport strategies

Group food retrieval in some ant species serves as a useful paradigm for multi-robot collective transport strategies that are decentralized, scalable, and do not require a priori information about the payload. We investigate this phenomenon in Aphaenogaster cockerelli in order to extract the ants’ roles during transport, the rules that govern their actions, and the individual forces that they apply to guide a food item to their nest. To measure these forces, we designed and fabricated elastic structures with calibrated stiffness properties, induced ants to retrieve the structures, and tracked the resulting deformations with a camera. We then developed a hybrid system model of the ant behaviors that were observed in the experiments. We conducted simulations of the behavioral model that incorporate a quasistatic model of planar manipulation with compliant attachment points. Our simulations qualitatively replicate individual ant activity as well as certain macroscopic features of the transport.

Distributed Construction of Truss Structures

We address the construction of truss structures with standardized parts and simple fasteners using multiple aerial robots. Robotic construction, unlike assembly in industrial settings, often occurs in unstructured environments where it may be difficult to manipulate objects to a high level of precision. This is particularly true with aerial assembly. There are challenges in positioning aerial robots and in deploying complicated manipulators or material handling devices in constrained environments characteristic of partially-built structures.We consider a scaled-down version of the problem with quadrotors, lightweight truss elements, and magnetic fasteners. Specifically, we present a provably-correct distributed construction algorithm that allows multiple robots to assemble structures according to a specified blue print with only local knowledge. In addition, we describe several heuristics for choosing the order in which parts are placed to improve performance measures like completion time. We illustrate the performance of the algorithm and the heuristics with simulations of our multi-quadrotor testbed.

Cooperative Quasi-Static Planar Manipulation With Multiple Robots

In this paper we address the modeling, control, and planning of planar manipulation tasks with multiple robots equipped with simple end-effectors. Each robot is able to influence the motion of an object either by exerting forces through the end-effector or by contact through a robot body. We develop a quasi-static model for the planar manipulation task that incorporates mathematical models of the object-ground contact, the object-robot contact and the compliant end-effector. This model allows us to predict object velocities for specified robot motions. We use this model to develop a simple motion planning algorithm for object manipulation that allows robots to select grasps, regrasp when necessary and manipulate an object along desired trajectories. Our experiments validate the mathematical models and demonstrate the feasibility of multirobot manipulation using the quasi-static model and the motion planning algorithm.Copyright