Free flight force estimation of a 23.5 g flapping wing MAV using an on-board IMU

Abstract

Abstract-Despite an intensive research on flapping flight and flapping wing MAVs in recent years, there are still no accurate models of flapping flight dynamics. This is partly due to lack of free flight data, in particular during manoeuvres. In this work, we present, for the first time, a comparison of free flight forces estimated using solely an on-board IMU with wind tunnel measurements. The IMU based estimation brings higher sampling rates and even lower variation among individual wingbeats, compared to what has been achieved with an external motion tracking system in the past. A good match was found in comparison to wind tunnel measurements; the slight differences observed are attributed to clamping effects. Further insight was gained from the on-board rpm sensor, which showed motor speed variation of ± 15% due to load variation over a wingbeat cycle. The IMU based force estimation represents an attractive solution for future studies of flapping wing MAVs as, unlike wind tunnel measurements, it allows force estimation at high temporal resolutions also during manoeuvres.

Onboard/Offboard Sensor Fusion for High-Fidelity Flapping-Wing Robot Flight Data

“…This may be due to the effect of the IMU mount, and, for the velocities, different sensitivities of the accelerometer along different axes may also have an effect. Nonetheless, comparing forces estimated from the IMU alone to wind tunnel data [35] showed an overall adequate agreement, with minor discrepancies. While no true values are available for validation, and there are known to be some differences between wind tunnel and free-flight forces [13], this observation nonetheless suggests that at sub-flap cycle level, the IMU information can be considered sufficiently reliable.…”

“…Table 2 provides an overview of the measurements obtained, and Table 3 presents the main specifications of the IMU. Further details on the hardware and flight test setup can be found in [35]. Table 2: Overview of relevant data obtained from each data acquisition system.…”

“…the forces relevant for longitudinal maneuvers) computed from EKF data, OptiTrack data and wind tunnel data, for four different flight conditions. The wind tunnel measurements [35] were conducted in conditions similar to the conditions observed in flight (in terms of angle of attack, forward velocity and flapping frequency), however it must be considered that small differences in the test conditions are inevitable, given the experimental setting. The data are shown for two different filter cutoff frequencies, chosen just above three times and five times the flapping frequency, respectively.…”

In-flight data acquisition and flight testing for system identification of flapping-wing MAVs

“…1b) [21]. Although this solution increases the power consumption of the system (around 75 mW per marker), the active markers greatly improve the tracking reliability and, most importantly, can be used for time synchronization.…”

“…In our tests, on-board logging with sampling rates of up to 1024 Hz was achieved with a 2.8 g Lisa/S autopilot board, running Paparazzi UAV system, and a microSD card [21]. Lightweight WiFi modules, such as the 0.5 g ESP8266 ESP-09 with UART communication, may be used with the same autopilot for high speed telemetry.…”