Vision control improves tethered drone payload positioning in flight
Vision-Based Control of a Tether-Suspended Aerial Radiation Sensing Payload
Robotics
Summary
Radiation detectors work best when close to the ground, but flying drones low can cause problems by stirring up dirt and dust. The authors propose a solution where the detector is hung from a drone using a tether, letting the drone fly higher while keeping the detector close to the surface. They developed a camera-based system to track and control the hanging detector’s position despite swinging, helping the payload follow a planned path better. Tests showed this method reduced the error in keeping the payload on course by 20% during flight in windy conditions.
What this means in practice
- •For environmental monitoring teams: Use vision-guided tether control to keep radiation sensors close to the ground without disturbing contaminated sites during aerial surveys.
- •For search and rescue operators: Maintain precise control of tethered sensors to detect hazardous materials near surfaces while keeping drones safely elevated.
Authors
Ian Snider, Brian J. Quiter, Emil Rofors, Mark W. Mueller
Abstract
Aerial radiation surveys achieve higher sensitivity when the radiation detector is held close to the ground. Detector sensitivity falls off roughly with the inverse square of the distance to the source, so a detector flown high is slower to reach a given minimum detectable activity. Flying the vehicle low puts the propellers near the ground, where downwash can disturb the surveyed area and resuspend contaminated particulates. Tether suspension decouples the detector from the vehicle altitude, but leaves the payload unactuated and only indirectly controllable. We therefore present a vision-based control approach for an aerial sensing payload suspended on a tether beneath a heavy-lift drone. Because a survey plan is decided as radiation detections arrive, we design a pilot aid for commanding the survey trajectory manually with a handheld transmitter. The controller regulates the payload, rather than the vehicle, onto that trajectory. The system uses onboard sensors with a downward-facing camera fixed to the drone body tracking a ring marker on the payload. A four-state Kalman filter estimates the tether swing angles and rates from payload bearing measurements, and a linear quadratic regulator with integral action takes the payload position as the regulated output. In outdoor flight tests under wind, the payload-aware controller reduced payload tracking error during transit by 20% when compared against a vehicle-referenced baseline, with the cost of higher peak error on arrival at a waypoint.