Fig. 6. Design of the self-propelled robotic pectoral fin with bilaminar fin rays. (A) Carriage that holds the robotic fin mounted above the flow tank on air bearings that allow horizontal translation in the X-direction with little friction. The pectoral fin can be seen submerged in the flow tank below the array of black actuating motors. (B) Base plate that holds the fin and compliant base support, and guides the nylon tendons to the fin rays. (C) Design of the base plate and the bilaminar fin rays that mimic the curvature control of fin rays in fin ray-finned fishes (Alben et al., 2007; Lauder, 2006). Note the two separate heads for each half of the fin ray, which receive separate nylon tendons. (D–G) Motion of the robotic pectoral fin from the rest position to show expansion, curling and cupping of the fin. Black lines have been drawn on the two leading edges of the fin to more clearly show the motion in F and G. Cupping, bending and expansion of the bluegill sunfish fin, as shown in Figs 2 and 3, are well replicated by the robotic model. Pectoral fin rest length=12.8 cm at the longest ray; fin width at base and tip is 5.5 cm and 8.0 cm, respectively. The base plate is 5.5 cmx8.5 cm. The fin rays vary from 9.0 cm to 12.5 cm long and the rays are 0.1 cm thick and 0.4 cm wide.