To compete in the MATES Rov competition the Rov requires an arm capable of completing all the tasks that will be released on November first. I must design the Rov arm to be able to complete any tasks that could possibly be chosen. This requires a powerful universal arm which has no major limitations and is not prone to breaking. It is important to keep the arm simple, while still being complex enough that it is able to work in all the tasks. A major problem I noticed during the competition of previous years was failure of very important components that stopped the team from having any chance of winning. I must be sure that the design has no major flaws that would cause a failure such as this
My first alternate solution is a simple design run off a hydraulic arm. As the arm is retracted due to a negative pressure in the line the arm closes. This makes it very easy to close the arm. The negative pressure in the arm can cause a problem as it is limited by how much pressure can be applied. As the pressure becomes lower, and more force is applied to the arm, outside water may be pulled into the line through small leaks. This will cause the pressure to slowly change and may eventually lead to the arm being useless, as there will be too much liquid in the hydraulic line to close all the way. It is very useful in that it has a large opening which can be used to grab items. It also has a compact design and can be mounted very securely so there is little risk of it separating from the Rov. The design of the arm also makes it hard for the pads to close directly against each other and at an angle instead.
The second alternative solution uses an electric motor as power. Due to the gearing system the motor will be capable of exerting large amounts of force; however it can not sustain this force for extended periods of time. Running the motor for anything longer than short fifteen second intervals runs the risk of burning out the motor, which will leave the Rov useless. This arm will not be good for carrying items to the surface as it may take up to a minute to reach the surface and remove the item. It is useful for moving heavy items short distances, such as picking up a rope off the bottom of the pool and moving it to the side. This design will be very stable as it has one stationary and one mobile arm. The stationary arm will be mounted in multiple locations so that there is little chance that it will separate from the Rov. This design is also good because it can open to a very large degree.
The third alternate solution also uses hydraulics but relies on a positive pressure to close rather than a negative pressure like design one. This design is very useful for grabbing small items as it has a small pointed tip, but may be restricted in how wide it can be opened. This can be adjusted by how far away the pivot points on each arm are mounted. The positive pressure of the hydraulic line lowers the chance of water leaking into the line as only a slightly negative pressure will be used to open the arms. A larger amount of pressure can then be applied to the object, up to 40 psi according to the competition rules. The positive pressure can create a problem in that if the pressure is too high the line may break, rendering the system useless. This can be solved by installing a pressure gauge in the line, and researching the maximum pressure the tubing used can hold, which for normal aquarium silicon tubing is 30 psi. Due to the length of this design its mounting may become inadequate if a large load is used. It is possible that the entire arm could break from the mounting and fall off the Rov, rendering it useless.
Alternate Solution 4 also uses a hydraulic arm as power, but can easily be adapted to use a servo or electric motor. This design is based off that of a slide ruler and is good in that it has a large surface area which it can use to grab an item. The physics of the actual arm allow the arm to close tightly and lock into place. A problem with this design is that it has a very small opening space between the claws, which makes it difficult to grab large items. This design will be very stable due to its stationary arm and multiple mounting locations. Its narrow profile is also useful for reaching into small areas.
As discussed each idea has its pros and cons but only one can be selected for the competition. I have decided on design three as it is capable of performing the widest variety of tasks. Many of the issues associated with the design can be easily remedied, unlike the others. I believe that in the competition I will need to pick up both large and small items, and I believe design three is capable of both. The use of a positive pressure in the hydraulic line allows me to vary the pressure I exert on the payload and the design of the arms allows for a secure fit on any item.
Figure 5: Rear view
