Morgan T. Pope

Dynamic surface grasping with directional adhesion

Dynamic surface grasping is applicable to landing of micro air vehicles (MAVs) and to grappling objects in space. In both applications, the grasper must absorb the kinetic energy of a moving object and provide secure attachment to a surface using, for example, gecko-inspired directional adhesives. Functional principles of dynamic surface grasping are presented, and two prototype grasper designs are discussed. Computer simulation and physical testing confirms the expected relationships concerning (i) the alignment of the grasper at initial contact, (ii) the absorption of energy during collision and rebound, and (iii) the force limits of synthetic directional adhesives.

Modeling the dynamics of perching with opposed-grip mechanisms.

Perching allows Micro Aerial Vehicles (MAVs) avoid the power costs and electrical and acoustic noise of sustained flight, for long-term surveillance and reconnaissance applications. This paper presents a dynamic model that clarifies the requirements for repeatable perching on walls and ceilings using an opposed-grip mechanism and dry adhesive technology. The model predicts success for perching over a range of initial conditions. The model also predicts the conditions under which other directional attachment technologies, such as microspines, will succeed. Experiments conducted using a launching mechanism for a range of different landing conditions confirm the predictions of the model and provide insight into future design improvements that are possible by modifying a few key damping and stiffness parameters.

Aggressive Flight With Quadrotors for Perching on Inclined Surfaces

Micro aerial vehicles face limited flight times, which adversely impacts their efficacy for scenarios such as first response and disaster recovery, where it might be useful to deploy persistent radio relays and quadrotors for monitoring or sampling. Thus, it is important to enable micro aerial vehicles to land and perch on different surfaces to save energy by cutting power to motors. We are motivated to use a downwards-facing gripper for perching, as opposed to a side-mounted gripper, since it could also be used to carry payloads. In this paper, we predict and verify the performance of a custom gripper designed for perching on smooth surfaces. We also present control and planning algorithms, enabling an underactuated quadrotor with a downwardsfacing gripper to perch on inclined surfaces while satisfying constraints on actuation and sensing. Experimental results demonstrate the proposed techniques through successful perching on a glass surface at various inclinations, including vertical.

Planning and Control of Aggressive Maneuvers for Perching on Inclined and Vertical Surfaces

It is important to enable micro aerial vehicles to land and perch on different surfaces to save energy by cutting power to motors and to perform tasks such as persistent surveillance. In many cases, the best available surfaces may be vertical windows, walls, or inclined roof tops. In this paper, we present approaches and algorithms for aggressive maneuvering to enable perching of underactuated quadrotors on surfaces that are not horizontal. We show the design of a custom foot/gripper for perching on smooth surfaces. Then, we present control and planning algorithms for maneuvering to land on specified surfaces while satisfying constraints on actuation and sensing. Experimental results that include successful perching on vertical, glass surfaces validate the proposed techniques.Copyright

Efficient jumpgliding: Theory and design considerations

A dynamic model of a jump glider is presented and correlated with the results obtained with a prototype glider. The glider uses a carbon fiber spring and a main wing that pivots approximately parallel to the airflow during ascent and latches into place for a gliding descent. The robot demonstrates longer traveled distance than an equivalent drag-free ballistic mass. A detailed numerical and a simplified algebraic model are also introduced, which are useful for exploring design tradeoffs and performance. These models suggest ways to improve the traveled distance and indicate that with modest variations in the wing angle of attack during ascent, one can choose from a variety of launch angles to accommodate variations in ground friction without greatly compromising range.

A Multimodal Robot for Perching and Climbing on Vertical Outdoor Surfaces

Perching can extend the useful mission life of a micro air vehicle. Once perched, climbing allows it to reposition precisely, with low power draw and without regard for weather conditions. We present the Stanford Climbing and Aerial Maneuvering Platform, which is to our knowledge the first robot capable of flying, perching with passive technology on outdoor surfaces, climbing, and taking off again. We present the mechanical design and the new perching, climbing, and takeoff strategies that allow us to perform these tasks on surfaces such as concrete and stucco, without the aid of a motion capture system or off-board computation. We further discuss two new capabilities uniquely available to a hybrid aerial–scansorial robot: the ability to recover gracefully from climbing failures and the ability to increase usable foothold density through the application of aerodynamic forces. We also measure real power consumption for climbing, flying, and monitoring and discuss how future platforms could be improved for longer mission life.

Perching failure detection and recovery with onboard sensing

Perching on a vertical surface carries the risk of severe damage to the vehicle if the maneuver fails, especially if failure goes undetected. We present a detection method using an onboard 3-axis accelerometer to discriminate between perching success and failure. An analytical model was developed to calculate acceleration differences for success and failure and set decision times. Two distinct decision times were shown to be effective, corresponding to properly engaging the gripper and overloading the grippers capabilities. According to a machine learning feature selection algorithm, the maximum Z axis acceleration of the quadrotor and the presence of near-zero readings are the most relevant features within these two time frames. Using these features, the detection algorithm discriminated between success and failure with a 91% accuracy at 40 ms, and 94% at 80 ms. Real-time detection and failure recovery experiments with a 20 g quadrotor verify the detection method. An improved approach that combines various decision times correctly identified success/failure for all 20 trials with an average total falling distance of 0.8m during recovery. We discuss the feasibility of extending our method to other quadrotor platforms.

Thrust-Assisted Perching and Climbing for a Bioinspired UAV

We present a multi-modal robot that flies, perches and climbs on outdoor surfaces such as concrete or stucco walls. Although the combination of flying and climbing mechanisms in a single platform extracts a weight penalty, it also provides synergies. In particular, a small amount of aerodynamic thrust can substantially improve the reliability of perching and climbing, allowing the platform to maneuver on otherwise risky surfaces. The approach is inspired by thrust-assisted perching and climbing observed in various animals including flightless birds.

One Motor, Two Degrees of Freedom Through Dynamic Response Switching

To minimize weight and cost, it is sometimes desirable to power multiple functions with a single actuator. In this letter, we present a new mechanism for powering two degrees of freedom with a single motor. We introduce a method, termed dynamic response switching (DRS), in which the actuator can drive either of two outputs, forward or backward. Switching is accomplished by briefly dropping the speed below a threshold at a particular orientation. Hence, a wide range of speeds above the threshold is available for both degrees of freedom. We demonstrate the performance available with this device in a proof-of-concept prototype.