# Development of Modular Bio-Inspired Autonomous Underwater Vehicle for Close Subsea Asset Inspection
## 7 Initial Testing and Lessons Learned
### Testing Propulsion  
This prototype is printed in ASA, with print parameters listed in Table 2 and KPAs listed in Table 1. The prototype underwent its first test outdoors in December 2020. The test went well and answered a number of questions. In this test, the prototype undertook some important tasks, but the test was not a very long test that examined all the RoboFish features. This test was the foundation of more task-oriented trials to come. The objectives of the test can be summarised as follows:  
Figure 16: RoboFish prototype with a Head, one Segment and Tail: 3D printed in ASA and using FDM.  
Figure 15: Locomotion Control Architecture: an example of RoboFish with three joints, where \(\theta_{1}\)\(\theta_{2}\) and \(\theta_{3}\) are the main parameters for locomotion control; the maximum angle of each parameter is \(\pm\)40 degrees.  
* Testing water-tightness
* Testing the functionality of magnetic-coupling joints
* Testing propulsion  
These initial trials were conducted in the University of York Campus West lake. The depths were around 1-2 m, with temperature of around 8 \({}^{\circ}\)C, 10 mph wind speed and poor water visibility. The prototype was put together and tested briefly on the shoreline (the lake's edge platform) just before it was let go into the water as shown in Figure 17. In one testing scenario, the RoboFish was dropped slowly into the water from the platform using two ropes. To test swimming on the surface, two side plastic buoys were included to maintain positive buoyancy and good balance with the right position by preventing RoboFish from going below surface or turning upside down. With it being directed toward the centre of the lake, the Go button was pressed and the RoboFish swam as expected. It was tethered to be brought back to the home point in the case of failure or untimely need for battery recharge. In another testing scenario, the RoboFish was released to operate underwater. This was the first outdoor trial for RoboFish. The shallow lake seems to be an ideal place to carry out more tests to examine the functionality of control, electronic and communication. As for computer vision, the location needs to be investigated further.  
Given that it was the first real outdoor trial, the performance of RoboFish was as good as was predicted. Initial testing of the propulsion mechanism revealed problems with electrical connections and power cable wiring associated with batteries. To overcome this, a new battery mounting plate was designed and is currently being 3D-printed to enclose all of the power network connections. The prototype is fitted out with cable  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Comment** \\ \hline Layer height & 0.254 mm & Standard \\ extrusion width & 0.5 mm & Standard \\ Wall thickness & 2.032 mm & To print more perimeters per layer \\ Solid infill & Enabled & To help preventing water ingress \\ Variable width fill & Enabled & To fill any small gaps \\ Room temperature & 25\({}^{\circ}\) & Enclosure \\ \hline \hline \end{tabular}
\end{table}
Table 2: List of the 3D Printer Parameters.  
Figure 17: RoboFish prototype swimming on the surface of a lake: two side plastic buoys were included to maintain positive buoyancy; a rope was attached to it to drag it to the home point in the case of failure or battery recharge.  
penetrators, ensuring watertight connections for the discrete cable that is used for both power distribution and control signal communications between modules. In future design, plug and bulkhead socket connectors would be a better option. Furthermore, if the modules are equipped with wireless chargers as an option, it will save time, especially during testing. Improvements in its buoyancy, thrust and swimming gait can be achieved via further hydrodynamic analysis. This could involve making the head undulate less and the tail oscillate more. Adding more segments will also improve the swimming gait.