AA Rationale

Introduction: ROV Frame and Propulsion

The ROV team must design and construct an ROV system that is capable of being submerged and remotely performing tasks like picking up underwater rings using a mechanical arm and placing them into crates in separately designated locations. Each team member is given a certain task and area of research and development. The rationale below is focused towards the area of frame and propulsion for the ROV. Summer work involving research and development and two months of joint team meetings have contributed to four separate designs for the ROV frame and propulsion systems. 

Alternate Solution 1

Introduction

Alternate solution one resembles a rectangular prism using PVC piping as the frame. The top front section is missing to reduce drag; it is also non-essential for structural support since PVC is used. The piping is jointed together using 90 degree and three way joints. A cross section is located in the middle of the frame. Two motors for horizontal propulsion and one for vertical propulsion are placed on the cross section. The top of the frame holds ballast for positive buoyancy.

Pros

Solution one is stable and relatively easy to maneuver due to the cube like shape. The geometric shape makes solution one easy to construct and design. Solution 1’s hydrodynamics through the water is also stabile due to the shape and location of vertical and horizontal propulsion. PVC construction also makes design one relatively cheap to build.

Cons

Solution is simple yet effective but does not specialize for any type of mission. The shape and location of propulsion is typical of most ROV’s and is not special for any one mission. The only adaptation for a mechanical arm is the absence of the top forward cross section. The prism like shape also makes the ROV look boring and gives the wrong mood for the mission.

Conclusion

All in all, solution one is a good, simple and sturdy design. Yet, it is too generic of a ROV for the specific mission and use of a mechanical arm. The prism like design also gives the incorrect mood of exploration and adventure. But the construction of PVC makes constructing and purchasing materials very easy.

Alternate Solution 2

Introduction

Alternate solution two is constructed of plastic pieces from common physics demo kits. The plastic pieces themselves are perforated with small holes through the entire length of the rods. The frame is in the shape of a cube with two support struts at the rear of the frame to provide stabile mounting for the propulsion systems. Empty film canisters serve as positive buoyancy ballast atop the frame.

Pros

The cube shape allows for easy handling and maneuverability through the water. The use of plastic physics kit pieces makes purchasing materials cheap or easy to look for. The plastic physics kit pieces also make the frame easy to build and manipulate wherever needed.

Cons

One drawback of design two is the cube shape. The cube shape prevents room for a mechanical arm to maneuver within the frame and allows for less room to mount equipment. The method to assemble the pieces also reduces the amount of weight it can carry since the plastic rods cannot stick together with too much stress.

Conclusion

In conclusion, design two provides a small cube like frame made of plastic physics kit rods. It allows for easy assembly and purchase but it means that it is weaker and has structural issues. The cube shape gives some more structural integrity but it also hinders the movement of a mechanical arm and room to mount potential equipment.

Alternate Solution 3

Introduction

Alternate solution three is slightly different from the other solutions. Design three also uses PVC piping and pool noodles for flotation, but the shape is what sets it apart. The bottom of the frame is a flat rectangular plane. The frame possesses wing like projections, which are flared out from the bottom of the frame at a forty-five degree angle. At the top of the “wings” are the foam ballast to provide some positive buoyancy to the craft. The horizontal propulsion motors are located at the rear of the “wings”; the vertical propulsion motors are located toward the left and right sides of the bottom of the frame.

Pros

The PVC construction of the frame makes purchasing materials cheap and construction simple. The wide and positively buoyant top of the craft make the entire frame very stabile. Since the base of the craft is heavier and narrower than the top of the craft, the frame remains steady during maneuvering due to basic physics. The wide top and narrow base also gives much more room for the mechanical arm to maneuver and to mount electrical equipment on the frame. Horizontal propulsion is located mostly toward the rear of the craft to account for the weight of the mechanical arm and the vertical propulsion is located in the middle of the craft. The locations for propulsion make handling smoother.

Cons

The wide top and narrow base of the frame may make maneuvering and steering stabile and smooth but speed is slower. The wider the frame the more drag is in the water. Although the horizontal propulsion compensates for the weight of the mechanical arm, it also means that left and right turning is not very accurate since steering is not located directly in the middle of the frame.

Conclusion

Overall, design three is the most stabile of all four alternative solutions. The splayed “wings” allow for greater control and stability of the craft during maneuvers and allows for more to mount the mechanical arm as well as electrical equipment. The PVC construction makes purchasing parts cheap and assembling them easy. But, the wide top frame makes turning slow and cumbersome. Horizontal steering located towards the rear also makes turning a bit of a hassle.

Alternate Solution 4

Introduction

Design four is also constructed of PVC piping for the frame. The entire frame is essentially a flat plane. The top of the frame uses empty bottles, which can be filled or emptied of water to control buoyancy on the craft. The bottom of the craft has small PVC pipes, which can be filled with weight to further help balance the weigh of the craft. The middle of the frame is empty and filled with either plastic or metal netting to allow equipment to be mounted in the middle of the rectangular frame.

Pros

The frame is very cheap and easy to manufacture. Parts are easily accessible and equipment can be easily mounted to the frame.

Cons

Since the frame has no vertical structures the frame is somewhat unstable. Balancing the craft is hard and the movement of the mechanical arm may cause the frame to list during maneuvers.

Conclusion

To conclude, the design is essentially too simple for the tasks the ROV must be able to perform. The flat plane design is too unstable and risky to use. But the PVC piping with weights is a great way to help bring the frame to neutral buoyancy.

Overall Conclusion
After using a rationale chart to determine the highest scoring designs, design three had the highest point score. Design three of all four designs was the most stabile because the ballast system was spread farther than the base of the ROV frame. Because the ballast is removed farther from the actual frame and there is no overhead support struts or structures, the ROV frame allows for more storage capability in terms of electronics and mechanical equipment such as a mechanical arm. However, the wide ballast structure also makes turning slightly more difficult. Lastly, an additional PVC pipe running down the center of the frame needs to be added due to mounting concerns for the mechanical arm.