Unmanned Systems Technology 014 | Quantum Tron | Radio links and telemetry | Unmanned Aerial Vehicles | Protonex fuel cell | Ancillary systems | AUVSI 2017 Show report

6 Mission-critical info for UST professionals Platform one June/July 2017 | Unmanned Systems Technology Researchers at the University of Waterloo in Canada are using an unmanned ground vehicle to develop a mobile damping system to suppress unwanted vibrations in lightweight, flexible bridges (writes Nick Flaherty). Damping systems are often permanent fixtures built into the bridge, but the team from the Civil Engineering Structures Lab is designing a system that is adaptable, autonomous and better suited for rapid, temporary deployment. These lightweight aluminium structures could be a temporary bridge used in a disaster relief situation, which are often more sensitive to external forces and so need additional damping. The team’s mobile control system is based around a Husky UGV developed by Clearpath Robotics. An electromechanical mass damper mounted on top of the vehicle is used to generate inertial control forces which are magnified by the body dynamics of the Husky. As the Husky moves onto a bridge it can respond to changes in the structural response by autonomously positioning itself at the appropriate location and applying the desired control force. “The Husky is a rugged vehicle suitable for outdoor applications and with sufficient payload capacity for both the damper and associated computational equipment,” said researcher Kevin Goorts. “The low profile and large lug thread tyres are well suited to providing the necessary static friction to prevent sliding and transfer control forces.” The Husky is also equipped with a laptop running the Robot Operating System, and Kinect 3D vision sensors on the front and back of the vehicle. Using wheel encoder data and measurements from the sensors, the system uses a simultaneous localisation and mapping algorithm to autonomously navigate back and forth along the span of the bridge. One of the immediate challenges the team faced was getting the robot to recognise its location on a bridge with a repetitive structural design, as everything looks the same to the vision system. To overcome this, the team placed augmented reality tags along the bridge to help the Husky navigate. The system has been tested with a real-time hybrid simulation that couples the physical control system to a numerical model of the structure. The tests were carried out on a full-scale aluminium pedestrian bridge with panels that measure the forces being applied by the system. Results from the simulations show the system can provide up to a 70% reduction in sideways movement. The current prototype is suitable for bridges weighing up to 1000 kg but it is designed to be scalable to accommodate larger structures, either with a larger vehicle or with multiple vehicles that work cooperatively. The team is now exploring the idea of making the system vehicle- agnostic, which could allow any UGV to be turned into an autonomous bridge stabilising machine. Ground vehicles Picking up bad vibrations The Husky UGV moves along a bridge to act as a stabiliser