Characterizing pitch and roll torque coupling in insect-sized flapping-wing robots using a microfabricated gimbal

TL;DR

This paper introduces a microfabricated gimbal sensor to accurately measure pitch and roll torque coupling in insect-sized flapping-wing robots, providing new insights into their aerodynamics and control independence.

Contribution

A novel microfabricated gimbal sensor capable of precise, simultaneous measurement of pitch and roll torques in tiny flapping-wing robots is presented.

Findings

Negligible cross-axis torque coupling observed.

High linear regression coefficients for torque measurements.

Thrust force varies by less than 6% from mean value.

Abstract

Sub-gram flapping-wing flying insect robots (FIRs) are challenging to model because of mechanical complexity in their wings, unsteady aerodynamic flow, and the difficulty of making precise measurements at a small scale. Coupling effects between roll and pitch torque actuation have not previously been measured because a two-axis sensor that is sensitive enough has not been realized. To address this shortcoming, we introduce a microfabricated gimbal design capable of precisely and simultaneously measuring roll and pitch torques as well as thrust. We then used it to measure the extent to which a pitch torque command affects roll torque and vice versa on a 180 mg piezo-actuated flapping-wing flying platform. Our results show a high coefficient of determination in the linear regression for both pitch (0.95) and roll (0.98) and low cross-correlation coefficients (-0.001 and -0.085, respectively) across the full range of simultaneous torque commands, indicating negligible cross-axis coupling. Similarly, thrust force deviates by a maximum of only 5.8% from the mean thrust value. These results validate the assumption that pitch and toll can be considered independently in control and will inform future models of how inputs affect the aerodynamics of resonant flapping-wing systems.