*2.3.2. Free swimming robot design*

234 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

**Figure 12.** Power consumption versus operating frequency.

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Power consumption (W)

**Figure 13.** Control circuit and battery (Chen et al, 2011).

*2.3.1. Control circuit* 

signal is generated on-board, greatly simplifying the control strategy.

four control signals on-board. In this paper, we present an IPMC-enabled robotic manta ray capable of free swimming. Since there is only one IPMC beam in the leading edge, a single

The on-board circuit, which was developed in our previous work (Chen et al, 2011), provided a square wave voltage signal to the IPMC actuator in the pectoral fin. Fig. 13(a) shows the schematic of the circuit. A 555-timer was used to generate a frequency adjustable square wave. The amplitude of the voltage signal, Vp, was controlled by an adjustable voltage regulator. An H-bridge driver was used to draw up to 2 A output peak current. A rechargeable 7.3 V Lithium Ion Polymer battery (400 mAh, AA Portable Power Corp) was selected as the power

10-1 <sup>100</sup> <sup>0</sup>

Frequency (Hz)

source for the robot. Fig. 13(b) shows the picture of PCB board and battery.

Fig. 14 shows the overall shape of the robot. Two acrylic frames with gold electrodes were made to clamp the artificial wings to the body support. Gold electrodes were used to minimize corrosion. Polymer foam was put into the middle of the frame to make the robot slightly positively buoyant. A simple hinged plastic box was used to house the circuit board and battery. Once closed, only two wires were exposed outside the box. PDMS was used to seal the box waterproof. The plastic box was then glued on the top of the robot. With the robot was put under the water, the cover of the box was above the water level thus water could not leak into the box. The fully assembled robot was 11 cm long, 21 cm wide, and 2.5 cm thick with a mass of 55 grams. The free-swimming robot with the control unit is shown in Fig. 15. The total cost of the robot is about \$200.

**Figure 14.** Robotic manta ray body.

**Figure 15.** Free swimming robotic manta ray body.
