Figure 5.

Control block-diagram. The fly's dynamics is described by the fly block and the haltere sensors (S) measure its roll velocity . The signal is fed into a time-delay block that represents a neuromuscular response time. The delayed signal is then split into two branches: the proportional term with the K_P coefficient and the integral term with the K_i coefficient. The sum of both terms gives the actuation signal ΔΦ, also described in equation (3.1). The actuation signal is converted by the wings (W) into the counter-torque exerted by the fly. The counter-torque is opposite to the external perturbation torque τ_ext, thereby forming a negative feedback loop that eventually corrects for the external perturbation.