A Discrete-time Adaptive Sliding Mode Controller for a Multicopter with a Suspended Payload

Authors

John Helzer, University of Nebraska-LincolnFollow

First Advisor

Justin Bradley

Committee Members

Chungwook Sim, Carl A. Nelson

Date of this Version

7-2025

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfilment of requirements for the degree of Master of Science

Major: Mechanical Engineering and Applied Mechanics

Under the supervision of Professor Justin Bradley

Lincoln, Nebraska, July 2025

Comments

Copyright 2025, John Helzer. Used by permission

Abstract

This thesis presents a Discrete-time Adaptive Sliding Mode Controller (DASMC) for control of a multicopter with a suspended payload. DASMC is designed to stabilize the multicopter at a desired position while minimizing the load oscillations induced by a significant hanging payload. The proposed DASMC minimizes the need for system-specific parameters like tunable gains and improves robustness to both external disturbances and model uncertainties compared with existing controllers. The controller is designed for direct digital implementation on a variety of multicopter platforms with considerations like discrete-time design, adaptive gain shrinking, and saturation handling. When deployed on a real multicopter in an outdoor field environment, our DASMC demonstrates tracking accuracy of less than \qty{20}{\cm} despite high wind speeds of up to \qty[per-mode=symbol]{6}{\meter\per\second} and up to 50\% uncertainty in model parameters.

The DASMC is specifically applied to the problem of multicopter-based bridge inspection. An end effector with a robotic hammer mechanism suspended below a multicopter physically impacts connection members (bolts or rivets) on a steel truss bridge and determines if the connection members are loose based on vibrational response. Because the DASMC precisely stabilizes the end effector and prevents payload oscillations, the robotic hammer mechanism can accurately contact the target connection member. This novel bridge inspection method eliminates the need for manual inspection of steel bridges and increases the safety and efficiency of steel bridge monitoring.

Advisor: Justin Bradley