Manohar Srikanth

DC Motor Damping: A Strategy to Increase Passive Stiffness of Haptic Devices

Physically dissipative damping can increase the range of passive stiffness that can be rendered by a haptic device. Unlike simulated damping it does not introduce noise into the haptic control system. A DC motor can generate such damping if its terminals are shorted. We employ a configuration of the H-bridge which can cause this damping to impart stability to our haptic device. This results in an increase in passive wall stiffness of about 33.3% at a sampling rate of 100Hz and 16.6% at 1kHz over the performance of an undamped DC motor. We have also attempted to implement the system on the hybrid haptic control system [1], it was seen that a perceivable change in the performance of this system was not observed by the use of DC motor damping.

A robust environment for simulation and testing of adaptive control for mini-UAVs

A simulation environment is developed to assist in the design, development, and validation of complex controllers with applications to mini-UAVs, such as the four-rotor DraganFly RC helicopter (quadrotor). The simulation system is modular and includes interfaces which allow for substitution of software subsystems with hardware components. This approach enables a smooth transition from the design and simulation phases to the implementation phase. The benefits of the proposed simulation environment are examined through the application of model reference adaptive control to a quadrotor UAV in the presence of actuator uncertainties and nonlinearities.

Computational rim illumination with aerial robots

Lighting plays a major role in photography. Professional photographers use elaborate installations to light their subjects and achieve sophisticated styles. However, lighting moving subjects performing dynamic tasks presents significant challenges and requires expensive manual intervention. A skilled additional assistant might be needed to reposition lights as the subject changes pose or moves, and the extra logistics significantly raises costs and time. We present a new approach to lighting dynamic subjects where an aerial robot equipped with a portable light source lights the subject to automatically achieve a desired lighting effect. We focus on rim lighting, a particularly challenging effect to achieve with dynamic subjects, and allow the photographer to specify a required rim width. Our algorithm processes the images from the photographers camera and provides necessary motion commands to the aerial robot to achieve the desired rim width in the resulting photographs. We demonstrate a control approach that localizes the aerial robot with reference to the subject and tracks the subject to achieve the necessary motion. Our proof-of-concept results demonstrate the utility of robots in computational lighting.

Covering hostile terrains with partial and complete visibilities: On minimum distance paths

We present a method for finding paths for multiple unmanned air vehicles (UAVs) such that the sum over their lengths is minimum as they cover a 3D terrain (represented as height fields). The paths are constrained to lie beneath an exposure surface to ensure stealth from enemy outposts. The exposure surface is also computed as a height field. The algorithm greedily clusters the terrain such that gain in visibility per distance would be higher for intra-cluster points than points across clusters. Paths generated on clusters formed by such a per distance visibility metric are reduced by more than 25% over other related decoupled methods. The method is extended to cover terrains with partial visibilities. The advantage of the coupled metric extends under constrained visibility also. We again show performance gain by comparing with an existing decoupled algorithm that solves a similar problem of minimum distance terrain coverage with constrained visibility. The paper reveals that decomposing the terrain based on visibility first and then distance is always better than the other way round to cover the terrain in shorter distances.

Visibility volumes for interactive path optimization

We describe a real-time system that supports design of optimal flight paths over terrains. These paths either maximize view coverage or minimize vehicle exposure to ground. A volume-rendered display of multi-viewpoint visibility and a haptic interface assists the user in selecting, assessing, and refining the computed flight path. We design a three-dimensional scalar field representing the visibility of a point above the terrain, describe an efficient algorithm to compute the visibility field, and develop visual and haptic schemes to interact with the visibility field. Given the origin and destination, the desired flight path is computed using an efficient simulation of an articulated rope under the influence of the visibility gradient. The simulation framework also accepts user input, via the haptic interface, thereby allowing manual refinement of the flight path.

Computational rim illumination of dynamic subjects using aerial robots

Lighting plays a major role in photography. Professional photographers use elaborate installations to light their subjects and achieve sophisticated styles. However, lighting moving subjects performing dynamic tasks presents significant challenges and requires expensive manual intervention. A skilled additional assistant might be needed to reposition lights as the subject changes pose or moves, and the extra logistics significantly raises costs and time. The associated latencies as the assistant lights the subject, and the communication required from the photographer to achieve optimum lighting could mean missing a critical shot.We present a new approach to lighting dynamic subjects where an aerial robot equipped with a portable light source lights the subject to automatically achieve a desired lighting effect. We focus on rim lighting, a particularly challenging effect to achieve with dynamic subjects, and allow the photographer to specify a required rim width. Our algorithm processes the images from the photographers camera and provides necessary motion commands to the aerial robot to achieve the desired rim width in the resulting photographs. With an indoor setup, we demonstrate a control approach that localizes the aerial robot with reference to the subject and tracks the subject to achieve the necessary motion. In addition to indoor experiments, we perform open-loop outdoor experiments in a realistic photo-shooting scenario to understand lighting ergonomics. Our proof-of-concept results demonstrate the utility of robots in computational lighting. Graphical abstractDisplay Omitted HighlightsWe demonstrate the first approach for studio quality lighting using aerial robots.Our lighting robot automatically positions itself to produce optimal rim lighting.Our robot adapts to changes in subject position, subject posture and camera position.We validate our approach with several indoor experiments.Using an open-loop outdoor setup, we discuss design issues and ergonomic issues of robotic lighting.

Dynamic Modeling and Control of A Flexible Four-Rotor UAV

This paper presents a novel design for mini rotor-craft Unmanned Aerial Vehicles (UAV) that are intended to be used in tight spaces. In this design, the UAV is allowed to flex when subject to external forces that occur during collisions. A four link mechanisms with revolute flexure joints is used as a support frame, which allows both flexibility and controllability. The paper presents the design of such a flexible UAV, denoted as ParaFlex, its modeling, and a closed-loop PI controller for stabilization at hover. Through simulation study, the robustness of the ParaFlex is demonstrated in the face of an impact. The goal of this work is to propose and evaluate a new design of four-rotor UAV that will make it robust to collisions which is common in cluttered and tight spaces. UAVs are well suited for applications such as surveillance, search and rescue, remote monitoring, target tracking, and aerial photography. The future road map for UAV calls for robust navigation in urban setting. Robust to external forces, indoor ingress, precision hover, perching are some of the key challenges put forth in the UAV vision 1 . Vertical takeoff and landing (VTOL) UAVs have the basic advantage of the ability to hover and land in tight spaces. Many applications demand UAVs to navigate in tight spaces such as ducts lines, collapsed buildings, and hazardous environments. UAVs are fragile (they easily become unstable) and hence they often need a safe trajectory to navigate successfully without collision. This limits the speed and performance of the mission. While they can be somewhat protected by adding shrouds or cages around the UAV, the problem still persists. Feedback control based solutions are possible but may prove to be either expensive or difficult to implement. This is because collision generally involves large magnitude impulsive force and the corrective actions have to be generated at high bandwidth. Even if the control loop runs at high bandwidth, slow actuators may limit the performance. The main contribution reported in this paper is the novel design that introduces flexibility (passive or active suspension) to the four-rotor UAV shown in figure 1. The basic reason for introducing flexibility is to absorb collision forces and allow the controller sufficient time to react. There can be many different ways to introduce flexibility. We present one particular design called ParaFlex that is very similar to Quadrotor but has skewable frame.