Selection Rejection Report

The final step in the design process is selecting a final solution. In the following paragraphs I will outline the positives and the negatives of each design. By the end of this report I will have chosen the design that best fits the tasks the arm must perform.

The first solution that I have proposed is the arm design that clamps horizontally only. This design is a very simple one that would be easy to build. The motor would be attached at the back of the arm (seen below). The motor would turn a grooved screw which would then turn two gears that would move the clamps of the arm at variable speeds and would allow them to be stopped at any distance of separation. This simple design allows for minimal power usage, which is a key to the project. This design also has the added bonus of being easily fixed if broken, not just by the designer, but by the whole team due to its simple design and use of simple machines to create the desired motion. This design however does have some drawbacks. With the strictly horizontal opening and closing motion the arm is limited to grasping objects that are less wide than tall. With this limitation the arm would only be able to grab very small objects, considering it would not be able to reach around the larger and therefore wider objects.

The second solution( seen right) that I have proposed is the arm that clamps both horizontally and vertically. This design is the most complex of all the designs that I have proposed, for the arm possibilities. This design would be the most complex to build, but still within the realm of possibility for this project. The design features a dual action claw that clamps both horizontally and vertically. This action allows the claw to grab any objects that would be in a competition task, whether the objects be large of small. The design although it is not overly heavy, it is still a quite deal heavier than the other two designs because of its dual claw feature and all the accoutrements that would be required to allow for the movement of the arm. The design, since it is much more complex would require much more skill to actually build and operate. This design would also require more power than the other two designs, which takes away power from the propulsion of the ROV. The complexity of this design would also make it much harder for it be fixed on the fly, unlike the other two which have much simpler designs that require much less knowledge for others to fix, and or make last minute adjustments to before the competition.

The third and final solution(seen right) is the arm design that clamps vertically. This design is simple and easy to control. It uses no more power than the horizontally closing arm, is just as simple to build and fix as the horizontally closing arm. This design can grasp objects that larger than average because of its vertical clasping action allows it objects that are wider than they are tall. This design also uses very little power, which allows more power for the propulsion. This design although it is light, uses little power, and is able to grasp larger objects has one huge drawback; it cannot grasp the smaller and more intricate objects. This could cause a big problem, considering in past years there have been small and intricate tasks, such as the rope threading of last years competition which require an arm that can grab thinner and smaller objects, which this arm design cannot.

For my final solution (below) I have decided to go with the horizontally closing arm because of a couple reasons. It is light, uses less power, easy to control and fix, and most important of all it can perform the intricate task better than the other two designs could. In my opinion this design gives the ROV the best chance at completing any and all tasks at the MATES competition in April of 2008.

Research

Hercules

• One of the few ROVS designed specifically for scientific research
• Built for the IFE (Institute For Exploration)
• Max depth 4000 meters ( 2.5 miles)
• Pair of manipulator arms attached to front of it
• One of the arms is force-reflective meaning the operator feels the forces acting upon it
• Carries an array of cameras ( some HD) and acoustic devices
• Aluminum frame
• Hydraulic thrusters control movement
• syntactic foam allows the ROV to be just a little buoyant but it only requires a small thrust downwards to descend
• operated via fiber-optic cable
• can move in any direction

Robotic Arm

• Servo motors cannot exceed 180 degrees of motion
• Understanding in staics and dynamics need to help program arm
• Force calculations are for motor selection
• First draw a Free Body Diagram (FBD) ( seen right)
• Label all weights and force on it
• The more degrees of freedom the more complicated the calculations
• Make sure arm is reinforced and lightweight
• Keep heaviest components closest to arm base
• DOF are important

Newman, Jim. "Hercules (ROV) and Friends." Ocean Explorer. 24 Feb 2006. NOAA. 31 Aug 2007 http://www.oceanexplorer.noaa.gov/technology/subs/hercules/welcome.html.
"Robot Arm Tutorial." Society of Robots. 2007. 1 Sep 2007 http://www.societyofrobots.com/robot_arm_tutorial.shtml.

Alternatice solution 1

Alternative solution One
For my first alternative solution I chose to design an arm that has a basic horizontal closing action. This arm has is run by a simple motor and screw motion. The screw, which is colored purple in the isometric drawing is turned by the motor( color), which in turn causes the gears( brown) to be turned, which opens or closes the claw depending on if the motors turns the screw in reverse or not. The moving parts of the claw will be housed in either PVC or some other material than can be easily accessed if a problem needs to be resolved. The motor will be attached to the rear of the actual arm, and will sit inside the actual body of the ROV. This design will allow the ROV to grab objects ranging in size from very small to medium size objects, depending on the width of the objects.

Alternative Solution 2

Alternative solution Two
The second alternative solution has both a vertical and horizontal claw movement. This arm will once again be run by a single motor which turns a screw inside the body of the arm. The horizontal claw will be moved the same way as in solution, which is by a simple turning of a gear by the screw. The vertical claw will be moved by the screw, as well. As the screw is turned it will turn another gear, which is attached to the vertical arm causing it to open and close. This arm will be able to grasp any size object that is in the competition.

Alternative Solution 3

Alternative solution Three
The third and final alternative solution is the vertical closing arm. This arm is also turned by a screw as seen in the above illustration. The screw will be turned by a motor which will be attached at the back end of the arm. As the motor turns the screw, the screw will then turn a gear which will move the top vertical arm either up or down depending on the turn of the screw. This arm will be able to grasp medium to large objects, rather than small or intricate objects.

Brainstroming

One of the most crucial parts of an ROV is its arm. Without the arm the ROV cannot properly perform its operations. Having a working and easy to control arm is a key to winning the MATES competition. Seen at the bottom of this post is the sketches I have made and above them the corresponding information from each design in numerical order.

The first arm design is a simple claw design in which two gripping claws, each being placed on the opposite side of each other are used to grab hold of an object. The two components of the arm are attached to separate rods, which then connect to two different motors allowing each competent of the claw to be used individually allowing for more freedom. This design has both the strength to do some of the heavier jobs because of the two separate motors, and it can also perform the more delicate tasks because of the flexibility the dual motor system allows.

The second design is another simple one in which a claw is created using to components situated at the top and bottom of the arm. The vertical movement allows for the arm to grab wider objects, than the horizontal movements do. The systems works by a single grooved rod that is either extends or retreats opening or closing the claw then it is turned to lock it in place. The system would work well for any tasks that require the rov to grab a very wide object rather than a tall one. The only problem with is design is the strength of the grip is vastly weaker that some of the others.

The third design is a combination design of the first and second design. With both a horizontal and vertical movements the arm could grasp almost anything. The arm could handle any task that was assigned to do. the only issue with this design is its power consumption and how to control it

The forth design is the most complex design. This design uses multiple levels to create a more advanced arm which can change height and move forward out of the ROV to grab objects. This design however is very bulky, hard to program and control, heavy, and very power consuming.

The final design that I brainstormed was the two pronged arm which was designed to have a long reach to allow the ROV to waste less time getting to the object. Although the reach is good on this design it has a lot of stress on both prongs and little gripping strength.