Final Design

The Autonomous Underwater Explorer (AUE) is:

• relatively low-cost

• miniaturized

• sensor-equipped 

The AUE is designed to:

• unveil sub-mesoscale features in ocean circulation

• track plumes of chemicals

• mimic larval behavior

These tasks allow researchers to gain a better understanding of the role that behavior can play in dispersal and settlement in our oceans. In order to effectively record information, 100 meters below the ocean surface an efficient and reliable ballast system is required of any subsurface float. The Jaffe Laboratory at Scripps Institute of Oceanography designed a two-stage mechanical linear actuator to control the volume and consequently depth of the AUE.

The design challenge was to:

• decrease the undesirable noise heard by the hydrophone from the motors by a factor of two

• increase the overall consistency of the mechanical drive system

The flaws inherent in the original system were:

• compromised data recorded by the hydrophone

• mechanically unreliable for multiple float deployments

In order for the AUE to perform properly, the design challenges needed to be addressed while eliminating the flaws the original system possessed.

Knowing the original motors were too loud for the ultimate solution, three design proposals were chosen based on CAD modeling and force requirements at depth.

Other areas of concentration included:

• vibrational dampening of structural connections

• energy budget analysis

• efficient drive-train systems from the motors to the piston.

Using data recorded from a constructed test platform the team was able to benchmark and quantify the noise heard by the hydrophone and the cycle time of the various systems (see Figure 1). Through analytical analysis using MATLAB, design improvements were quantified for various components, enabling certain problematic components to be identified and discarded. The noise is measured in relative amplitude, which is on a linear scale rather than a dB scale.

Figure 1: Noise comparison of original design vs. finalized design

These investigations resulted in:

• replacing the existing lead screw with a ball screw

• replacing the worm gear with two inline spur gears

• replacing the two original motors with a single higher quality motor

• incorporating vibrational dampening mounts

The inclusion of these components required the removal of a single battery from the six C cell battery pack originally included in the AUE; a compromise approved by the sponsor.

In conclusion, the team presented a finalized design solution using a flat geared motor and inline spur gears (See Figure 2). It is recommended that the existing lead screw be replaced with the more efficient ball screw and incorporating grommets to isolate the hydrophone from any direct metal to metal connections. It is the team’s understanding that we have provided a design solution sufficiently adhering to the demands set forth by our sponsor.

Looking forward, the AUE system will need to be tested in water to verify that the seal integrity of the system has not been compromised, and possibly cycled to replicate multiple deployments. 

Figure 2: From left to right: Frame of the prototype with flat geared motor, bottom view of prototype displaying spur gears, CAD of prototype with housing