Passive stability enhancement with sails of a hovering flapping twin-wing robot

Abstract

Hovering flapping wing flight is intrinsically unstable in most cases and requires active flight stabilization mechanisms. This paper explores the passive stability enhancement with the addition of top and bottom sails, and the capability to predict the stability from a very simple model decoupling the roll and pitch axes. The various parameters involved in the dynamical model are evaluated from experiments. One of the findings is that the damping coefficient of a bottom sail (located in the flow induced by the flapping wings) is significantly larger than that of a top sail. Flight experiments have been conducted on a flapping wing robot of the size of a hummingbird with sails of various sizes and the observations regarding the flight stability correlate quite well with the predictions of the dynamical model. Twelve out of 13 flight experiments are in agreement with stability predictions.

COLIBRI: A hovering flapping twin-wing robot

“…The damping constant K is easily evaluated by a pendulum experiment. 17 Here, we include the rotary damping:…”

“…Figure 17 shows the sensitivity to z d when it varies from À5 mm to þ5 mm. Although z d has a determinant influence on the open-loop behavior of the system, 17 its influence on the closed-loop poles seems more moderate, provided it remains in reasonable limits; the system experiences a divergent instability if z d 5 À 9 mm. The influence of the time constant T of the actuator is analyzed in Figure 18; one sees that the location of the oscillatory poles is strongly dependent on the time constant T of the wing twist actuators.…”

Experimental Studies of Tail Shapes for Hummingbird-Like Flapping Wing Micro Air Vehicles

“…But, importantly, via experimental study on such tail, we found that the lift and pitch moment was proportional to the tail position, which promoted us to study further on different tails. Also, such kind of the tail was successfully applied to the passive stability of flying [35].…”

Dynamic performances of a bird-like flapping wing robot under randomly uncertain disturbances

“…For example, periodic motion parameters should be used, the spring stiffness should be increased if anti-disturbance performances of the robot are weak, some measures should be taken to reduce the shaking of the mass center and the disturbance amplitude. As far as I know, these suggestions have rarely studied [44][45][46]. Though the above conclusions have been obtained, the following aspects should be further studied in the future: (1) A complex dynamic model should be established to approach the real robot under randomly uncertain disturbances, and a method should be proposed to solve the contradiction between the model complexity and the calculation feasibility; (2) Some quantitative conclusions, e.g., the influence mechanism curves of the disturbances on the robot performances, should be further studied; (3) Some other experiments under randomly uncertain disturbances, e.g., wind tunnel experiments, vibration and friction experiments, should be carried out in the future.…”