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Latis II Underwater Remotely Operated Vehicle Technical Report

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stability. Since the ROV is bottom heavy, the<br />

primary thrusters for forward, backward,<br />

turning, and strafing motion were mounted on<br />

the underside, allowing <strong>Latis</strong> <strong>II</strong> to maneuver<br />

easier since the thrusters’ force is applied close<br />

to the center of mass. The skids also protect the<br />

thrusters from being damaged and provide a<br />

solid stand for the ROV to sit on the pool floor.<br />

The ROV was tested in a tow tank and<br />

coefficient of<br />

13<br />

Figure 14: Main Frame Parts<br />

ARMS<br />

Many different arm design ideas were<br />

considered during this part of the design<br />

process. The team eventually decided on using<br />

Hitec 7775MG digital hobby servos for the<br />

majority of the arm linkages, and Hitec 805BB<br />

analog high toque servos for the heaviest joint-<br />

the shoulder rotation. Most joints utilized a<br />

chain and sprocket power transmission design<br />

not only for its simplicity and effectiveness, but<br />

also for the ability to use sprocket ratios to<br />

increase the power at any given connection.<br />

The range of motion for each link was decided<br />

and the corresponding sprocket ratio calculated<br />

to reach that desired range from the 180deg<br />

range of the servos. Since the range was always<br />

less than 180deg the torque available at the link<br />

would always increase proportional to the<br />

range decrease. The servos were sized for their<br />

power, size, and weight. To waterproof the<br />

servos they were dipped in Plastic Dip. A<br />

LATIS <strong>II</strong><br />

TECHNICAL REPORT<br />

greased O-ring was installed between the servo<br />

case and the servo sprocket to protect the<br />

opening where the spline enters the case.<br />

Figure 15: Servo Waterproof Testing<br />

Lightweight plastics were utilized wherever<br />

possible for easier manufacturability and their<br />

high strength-to-weight ratios. HMWPE was<br />

used for the larger pieces of the arm and the<br />

connecting pins; a quarter inch thick PVC plate<br />

was used for the main structure of the links,<br />

and Teflon (PTFE) was used for bushings<br />

between the connecting pins and links as a soft<br />

slippery interface to reduce friction. All<br />

connections were made using press fit sizing to<br />

reduce the need for heavy metal fasteners. The<br />

grippers were designed using a rotation-tolinear<br />

linkage system and the grippers<br />

themselves were dipped in Plastic Dip to add<br />

extra grip.<br />

Figure 16: <strong>Latis</strong> <strong>II</strong> Arms

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