Toward Sub-Gram Helicopters: Designing a Miniaturized Flybar for Passive Stability

• Published in: 2023 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) pp. 2701 - 2708
• Main Authors: Johnson, Kyle, Arroyos, Vicente, Villanueva, Raul, Schulz, Adriana, Fuller, Sawyer, Iyer, Vikram
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.10.2023
• Subjects: Damping; Laminates; Low voltage; Reliability engineering; Rotors; Tail; Three-dimensional displays
• ISSN: 2153-0866
• DOI: 10.1109/IROS55552.2023.10342256

Sub-gram flying robots have transformative potential in applications from search and rescue to precision agriculture to environmental monitoring. However, a key gap in achieving autonomous flight for these applications is the low lift to weight ratio of flapping wing and quadrotor designs around 1 g or less. To close this gap, we propose a helictoper-style design that minimizes size and weight by leveraging the high lift, reliability, and low-voltage of sub-gram motors. We take an important step to enable this goal by designing a light-weight, micfrofabricated flybar mechanism to passively stabilize such a robot. Our 48 mg flybar is folded from a flat carbon fiber laminate into a 3D mechanism that couples tilting of the flybar to a change in the angle of attack of the rotors. Our design uses flexure joints instead of ball-in-socket joints common in larger flybars. To expedite the design exploration and optimization of a microfabricated flat-folded flybar, we develop a novel user-in-the-loop bi-level optimization workflow that combines Bayesian optimization design tools and expert feedback. We develop four template designs and use this method to achieve a peak damping ratio of 0.528, an 18.9x improvement from our initial design. Compared to a flybar-less rotor with a near 0 damping ratio, our flybar-rotor mechanism maintains a stable roll and pitch with relative deviations < 1°. Our results show that, if combined with a counter-torque mechanism such as a tail rotor, our miniaturized flybar could mechanically provide attitude stability for a sub-gram helicopter.