# Results

## 9.0 Results and Analysis

Figure 52: Completed Robot with Actuated Fins

### 9.1 Project Results

The initial monetary and time budget were quite optimistic. As the fabrication process progressed, issues arose that were never even considered. Many of the issues were difficult to predict or circumvent, leading to a frustrating reworking of the initial plans on several occasions. One important lesson to take from this project is that of adding a contingency to every budget in a project. While some contingency was allowed in the project timeline for the testing and analysis, it was not nearly enough to satisfy the scope of the project. Additionally, as expected, personal funds were used to offset costs of fabrication. This removed many of the funding limits this project had, but put financial burden on the group members. A total of $600 was raised on the team website to put towards the advancement of the project. This, in addition to the WPI MQP funds, provided the majority of the required funds. Much of the cost of the project was in research and design. This was most noticeable in the volume of silicone used for the multiple iterations of the fin fabrication process. In order to reflect the cost of the prototype, the additional costs were removed from the final project budget.  Material Units Used Cost per Unit Total Cost Dragonskin Silicone (1 gal) 2$135.00 $270.00 Electronics Box 1$15.00 $15.00 Acrylic Sheet 4$20.00 $80.00 Hatch 1$10.00 $10.00 Acrylic Cement (1 tube) 1$10.00 $10.00 Silicone Caulk (1 tube) 1$10.00 $10.00 4-way Quick Connector 8$5.00 $40.00 2-way Quick Connector 14$5.00 $70.00 Tee Quick Connector 3$5.00 $15.00 Check Valve 1$5.00 $5.00 Polyethylene Tubing (25ft) 1$5.00 $5.00 3-way Solenoid Valves 12$20.00 $240.00 Gear Pump 1$380.00 $380.00 MSP432P401R LaunchPad 1$20.00 $20.00 Pressure Sensor 1$60.00 $60.00 IMU 1$30.00 $30.00 Pump Motor Driver Circuit 1$30.00 $30.00 Valve Motor Driver Circuit 3$5.00 $15.00 Battery 1$150.00 $150.00 Expenses Total:$1,455.00

Figure 53: Prototype Material Budget

### 9.2 Fin Results

The fin was the most critical aspect of this project, and required the most attention when evaluating the success of the prototype. It required the most innovation and adaptation of previous works to achieve. During small scale prototyping, the fin saw multiple iterations with varying degrees of success. The small scale prototyping phase was a vital step in the design process, as little documentation existed on the relationship between channel length, width and depth in relation to the motion it created. Additionally, it allowed potential issues to be identified and amended, such as the need for degassing of the silicone. Results seen in the small scale tests allowed the comparison of a multitude of designs with minimal resources invested.

The cost of the silicone proved to be the primary limiting factor when considering advancing from medium to large scale fins. The manufacturing process would have been the same as the medium scale fins, so the major hurdle would have been scale. This became significant, as it drove the hull size calculation, and meant that the medium fin would have to be redesigned to incorporate 3 channels instead of the previously planned 2.

Figure 54: Fin Actuation

The set of complete fins that was created was mounted on the robot for a bench test. The fins were pressurized, then the valves started to sequence. The fins had trouble actuating upward because of their weight. To combat the issue, the robot was tilted onto the end of its hull so it would be actuating along a plane parallel to the ground. To increase the amount of actuation, all of the channels on one side were actuated at once, rather than sequenced. The fin was found to yield 60 degrees of actuation at the tip. Comparing this to our goal of 35 degrees of actuation, the fin performed greater than expected. This increase in actuation range suggests a greater value in this technology for future biomimetic robots.

Figure 55: Pressurized Fin with Degrees of Actuation

### 9.3 Plumbing System Results

The plumbing system required much more work than previously anticipated. The quick connectors caused significant leaking due to the tubing being pulled at harsh angles, and over used. Although the plumbing system fulfilled all its objectives, the issues with leaking took away from the ability to focus on more vital aspects of the project, and thus, would warrant a significant improvement. While flexible connectors were incredibly helpful when making modifications to the prototype, a solid plumbing system would be much more reliable.

### 9.4 Hull Results

While the fiberglass hull had room for significant improvement, the acrylic hull was largely successful for this prototype. It is worth noting the acrylic hull was a rectangular cube versus the smoothed body of the fiberglass hull.

The fiberglass hull ended up with many small holes as a result of the manufacturing process. Multiple attempts to seal the leaks were ultimately unsuccessful. This lead to the decision to prioritize the function of the hull over the hydrodynamic form, and switch to a simple acrylic box to house the components and support the fins.

The squared form of the new hull was not ideal from a hydrodynamic perspective, but was sufficient for the scope of this prototype. In the end, the acrylic hull was able to be successfully sealed, protecting the sensitive electronics from the outside environment.

### 9.5 ECE Results

Input from the sensors was communicated properly between the IMU and Pressure sensor. Signals from the MSP432 are controlling valve and pump drive as directed. Ultimately, the electrical systems were able to interface with both the mechanical systems and the code uploaded on the MSP432.

### 9.6 System Level Results

The integration of all the components was a challenging aspect of the project. In many cases, simply bonding surfaces together proved to be complicated processes requiring testing and multiple iterations. By scaling down the fin size, and thus the whole robot, the plumbing system was difficult to incorporate into the hull. Bonding the pressure sensor to the exterior of the hull while maintaining waterproof rating also provided a challenge. The most surprising difficulties of this project came from interfacing between components.

Figure 56: Completed Prototype Awaiting Testing

## 10.0 Conclusions and Future Work

### 10.1 Conclusion

There are many approaches that can be used to develop an efficient AUV. By using biomimetic design and soft robotic actuation, it is possible to create a quiet and efficient AUV. A baseline technology was developed that has excellent potential for further development and improvement. Initial testing suggests the current prototype can perform the range of motion needed for lifelike actuation.

### 10.2 Future Work

Further research may include optimizing the oscillatory aspect of the fin motion. This would require additional progress in the design of the silicone fins, channel configurations, and timing of the pressurization of the channel segments. Increased accuracy could also be achieved by employing professional manufacturing methods of the mold and fin positives.

The outer covering, or “skin”, of the robot should provide optimum flow characteristics, while being flexible enough to move with the articulation of the fins. Waterproofing also stands to be a significant challenge if there will be an interface between the internal electronic systems and the exterior of the robot.

The hull is a topic for significant future work. Utilizing a production methodology that would result in an accurately fitted, waterproof hull, that also incorporates the contours and shaping for improved hydrodynamics and anatomically accurate profile.

Additional sensors and control systems could also be implemented in the future for increased control and awareness in the environment. With a functional prototype tested in the water, the control could be developed specific to the movement of the robot. This would allow for fine tuned manipulation of the fins for accurate, biomimetic motions like flapping, gliding, turning and other methods of locomotion used by manta rays. Sensors for terrain mapping and avoidance, such as sonar or a camera with image processing, would also allow for intelligent maneuvering in an environment with obstacles.

Moving forward, the team will be presenting this project at the Harvard 2016 Soft Robotics Toolkit Competition. This competition allows for greater visibility of the project, and opportunities to advance research in this topic through the Soft Robotic Toolkit’s open source documentation.

Special Thanks

The Manta Ray Robot team would like to thank the following:

• Professor Jarvis for advising the project

• Joe St. Germain for allowing access to his lab, resources, and expertise

• Professor Ludwig for allowing use of his lab space

• Marleney of WPI Facilities for all her help and encouragement