A Flexible Tether Management Model for Heterogeneous Marsupial Robot Systems
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Abstract
Heterogeneous marsupial robotic systems are systems comprised of two or more robots that collaborate and leverage the strengths of each other to complete missions. These systems consist of one dispensing agent that provides resources to one or more passenger agents. To exchange these resources, whether in the form of power or data, there must be a physical connection between the dispensing agent and each passenger agent, known as a tether. Tethers enable passenger agents to use large power supplies housed on the dispensing agent, which would otherwise be impractical or impossible to house on the passenger agents themselves. Additionally, tethers can provide bidirectional data communication between the dispensing agent and the passenger agent such that the sensing and computation capabilities of each component can be used in one system. Marsupial robot systems consisting of unmanned surface vehicles (USV) and unmanned aerial vehicles (UAV) are effective systems to dispatch in marine environments. These systems use the sensing capabilities of the UAV to explore more of an environment and the power capabilities of the USV to lengthen UAV flight times. The tether connected from the USV to the UAV changes length as the UAV changes positions. Maintaining a proper tether length is crucial to system efficacy. If the tether is too long, it is prone to catching on obstacles in the environment. If it is too short, it may limit the mobility of the UAV. Researchers have explored ways to maintain proper tether length, but also, the potential benefits of prioritizing slackness or tautness in the tension of the tether and the potential benefits that arise from either design choice. This paper proposes a tether management system that prioritizes consistency, reliability, and flexibility by meticulously maintaining a proper tether length while allowing for control over tether slackness and spool reactivity. It seeks to implement aspects of both the slacked and taut models. This system was implemented within a heterogeneous marsupial robot system, with its dispensing agent represented as a ground station and its passenger agent represented by the Duckiebot DB21J UGV. The hardware decisions and modifications for the spool, ground station, and DB21J are discussed in this paper, as well as the overall ROS workspace structure designed to maximize efficiency and data transfer. After implementation, the tether management system was then tested by running a series of trials with varying spool control and tether model parameter values, specifically slackness and control gain. In each of these trials, the DB21J drove in a square path in the environment, and the response of the spool was recorded in each trial. The data was used to determine the consistency of the system and its response to varying parameters. The conclusion drawn from observing the behavior of the tether management system is that the system is designed for consistency and flexibility in spool control and tether length. During trials, slackness and control gain were manually set. In the future, these values are meant to be modified based on environmental factors.
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robotics, marsupial robot systems, tether management