Flexible tether control in marsupial systems

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Project highlights

Wouldn’t it be great to have a base station transfer power, data and other information to other autonomous vehicles through a tethered connection? But how to deal with the challenges arising from controlling the length and tension of the tether?

Here is an overview of the authors’ results:

Isometric view of a CAD model of an automated spool designed for flexible tether control in Duckietown UGVs. — Figure 1. Spool CAD Design – Isometric View.

Front view of a CAD model of a spool mechanism for flexible tether control in Duckietown robots. — Figure 2. Spool CAD Design – Front View.

Physical implementation of the automated spool system for flexible tether control in Duckietown UGVs. — Figure 3. Physical Spool for Flexible Tether Control.

Modified Duckiebot DB21J with an attached tether for flexible tether control in robotic testing. — Figure 4. Modified Duckiebot DB21J for Tether Control Testing.

ROS graph illustrating data flow in a flexible tether control system for Duckietown UGVs. — Figure 5. ROS Graph for Tether Management System.

Three different cases of tether length in a flexible tether control system: too long, too short, and correctly adjusted. — Figure 6. Tether Length Cases – Too Long, Too Short, Just Right.

DB21J trial trajectory demonstrating the effect of flexible tether control on robot mobility. — Figure 7. DB21J Trial Trajectory with Tether Control.

Figure 8. Wheel Velocities vs. Time for Multiple Trials.

Robot distance from the spool and tether error measurements in a flexible tether control system. — Figure 9. Robot Distance & Tether Error vs. Time.

Measured tether length across different slackness values in a flexible tether control system. — Figure 10. Measured Tether Length vs. Slackness.

Tether error measurements for different control gain values in a flexible tether control system. — Figure 11. Tether Error vs. Control Gain.

Flexible tether control in Duckietown: objective and importance

Managing tethers effectively is an important challenge in autonomous robotic systems, especially in heterogeneous marsupial robot setups where multiple robots work together to achieve a task.

Tethers provide power and data connections between agents, but poor management can lead to tangling, restricted movement, or unnecessary strain.

This work implements a flexible tethering approach that balances slackness and tautness to improve system performance and reliability.

Using the Duckiebot DB21J as a test passenger agent, the study introduces a tether control system that adapts to different conditions, ensuring smoother operation and better resource sharing. By combining aspects of both taut and slacked tether models, this work contributes to making multi-robot systems more efficient and adaptable in various environments.

The method and challenges in implementing flexible tether control in Duckietown

The authors developed a custom-built spool mechanism designed to actively adjust tether length using real-time sensor feedback. The tether system comprises a custom-built spool mechanism, integrated with sensor feedback for real-time tether length adjustments.

To coordinate these adjustments, the system was implemented within a standard ROS-based framework, ensuring efficient data management.

To evaluate the system’s effectiveness, the authors tested different slackness and control gain parameters while the Duckiebot followed a predefined square path. By analyzing the spool’s reactivity and the consistency of the tether’s behavior, they assessed the system’s performance across varying conditions.

Several challenges emerged during testing, e.g., maintaining the right balance of tether slackness was critical, as excess slack risked entanglement, while insufficient slack could restrict mobility.

Hardware limitations affected the spool’s responsiveness, requiring careful tuning of control parameters. Additionally, environmental factors, such as potential obstacles, underscored the need for a more adaptive control mechanism in future iterations.

Flexible tether control: full report

Check out the full report here.

Flexible tether control in heterogeneous marsupial systems in Duckietown: Authors

Carson Duffy is a computer engineer who studied at the Texas A&M University, USA.

Dr. Jason O’Kane is a faculty research advisor at Texas A&M.

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