Simultaneous contact and aerodynamic force estimation (s-CAFE) for aerial robots

Abstract

In this article, we consider the problem of multirotor flying robots physically interacting with the environment under influence of wind. The results are the first algorithms for simultaneous online estimation of contact and aerodynamic wrenches acting on the robot based on real-world data, without the need for dedicated sensors. For this purpose, we investigated two model-based techniques for discriminating between aerodynamic and interaction forces. The first technique is based on aerodynamic and contact torque models, and uses the external force to estimate wind speed. Contacts are then detected based on the residual between estimated external torque and expected (modeled) aerodynamic torque. Upon detecting contact, wind speed is assumed to change very slowly. From the estimated interaction wrench, we are also able to determine the contact location. This is embedded into a particle filter framework to further improve contact location estimation. The second algorithm uses the propeller aerodynamic power and angular speed as measured by the speed controllers to obtain an estimate of the airspeed. An aerodynamics model is then used to determine the aerodynamic wrench. Both methods rely on accurate aerodynamics models. Therefore, we evaluate data-driven and physics-based models as well as offline system identification for flying robots. For obtaining ground-truth data, we performed autonomous flights in a 3D wind tunnel. Using this data, aerodynamic model selection, parameter identification, and discrimination between aerodynamic and contact forces could be performed. Finally, the developed methods could serve as useful estimators for interaction control schemes with simultaneous compensation of wind disturbances.

ARDEA—An MAV with skills for future planetary missions

“…The classical cascade of position and attitude controller enables to manually fly the MAV in attitude control mode. We explicitly consider changes in the atmosphere and compensate for and distinguish between external contact and wind forces (Tomić, Lutz, Schmid, Mathers, & Haddadin, 2018).…”

“…Parameter identification procedure according to Tomić et al (2018). The procedure is done in three steps to minimize coupling effects in the high‐dimensional parameter space…”

“…We find that the ‐identified parameters match closely to the least squares parameters, which confirms the correctness of the identified dynamics model. Identification of the aerodynamic model was done through wind tunnel experiments, this is beyond the scope of this paper but described in more detail in Tomić et al (2018).…”

“…Therefore, the estimator will also capture modeling errors, aerodynamic drag, as well as the change of propeller thrust and torque with airspeed. For a complete and more detailed description of this framework the reader is referred to Tomić et al (2018).…”

A Novel Robust Hexarotor Capable of Static Hovering in Presence of Propeller Failure

“…U NMANNED Aerial Vehicles (UAV)s are now widely used in research and industry thanks to their versatility and large field of applications, such as aerial physical interaction [1], [2] and human-robot collaboration [3], [4]. Among the variety of UAV designs discussed in the literature [5], it seems that in the above applications, quadrotors, hexarotors, and octorotors are the most commonly used; this is most commonly due to their flight efficiency as compared to more compex UAVs, in addition to the ease and low cost of their production.…”