Minimal Energy Quadcopter Descent

Abstract

In this research electric quadcopters have been proposed as an alternative and more sustainable solution for meteorological data collection. The descent stage in a quadcopter’s flight is identified as the
phase where energy optimisation can have a significant impact on the endurance. Hence, a minimal
energy descent strategy has been proposed and developed.
Through wind tunnel experiments, it has been shown that it is possible to regenerate electricity and
recharge the flight battery in a free-fall. It has also been shown that it is possible to control the drag
load on a propeller in a free-fall, while regenerating electricity. In these experiments, three distinct
operation zones (1. Low Control Authority, 2. No/Minimal Control Authority and 3. High Control
Authority) have been identified on the thrust vs motor throttle graph.
A tandem rotor dynamic rig is developed to replicate a quadcopter’s roll action. This rig was used in
a wind tunnel environment to study the controllability of the dynamic system in a descent, using the
minimal energy descent approach. In these experiments, ArduCopter, an open-source flight controller
software, has been utilised to stabilise the rig. It has been observed that ArduCopter’s attitude controller, effectively tracks the desired roll rate while operating within the No Control Authority region,
but with a noticeable offset. Despite the observed offset, the system maintains stability and achieves
a regenerative current of 0.4 amp when powered by a 6S LiPo battery, while descending at a rate of
20 m/s.
To analyse the performance of the proposed minimal energy descent strategy, a dynamics model of the
proposed quadcopter for this research, has been developed. The model was implemented in Matlab
and ArduPilot’s native Software In the Loop was used to simulate vertical flight missions. It has been
shown, a maximum flight altitude of 6, 060 meters is achievable for the weather monitoring quadcopter.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Tom S Richardson (Supervisor)