Monday, November 26, 2007
Monday, November 19, 2007
Tuesday, November 13, 2007
Monday, October 29, 2007
Model
I have designed and built my model at a scale of 1:2. The main arms and top supporting block is made of plywood. The bottom base is made from a piece of PVC tubing, similar to the final design. The hydraulic arm is slighlty larger than the 1:2 scale but was the smallest available. This causes the slight kink of the tubing seen in the pictures. The tubing is standard aquarium airline tubing rated to a pressure of about 20 psi. The black grips shown are modeled using balsa wood but will be made of rubber in the final design. The model is also functional and is capable of holding large amounts of weight. The only noticable problem is picking up very thin items, as the model arm does not close completely.
Figure 1: Overall view
Figure 2: Arm fully closed
Figure 3: Arm half open
Figure 4: Arm fully open
Figure 5: Rear view
Figure 6: Overall view
Friday, October 12, 2007
Selection Rejection Report
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.
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.
Monday, October 1, 2007
Wednesday, September 19, 2007
Brainstorming: Platform Design
The stability and functionality of a Rov depends on the platform upon which it is built. A common idea is to build a frame out of PVC tubing which all components can be mounted too. Since water flows through the rov there is little resistance but very high speeds are impossible to obtain due to the friction causing body shape. A hydrodynamic body may be formed using sheeting or fiberglass. This will increase the overall speed of the Rov and make it more stable in the water, although it can also lessen the amount of room left to mount equipment. On Appendix II, which is shown below, I have sketched multiple designs which will be considered.
Design number one uses a long and skinny body to help increase the speed of the Rov. This design uses three motors to propel it through the water. The two forward motors swivel up and down to change the rov's depth in the water. The rear motor turns left and right to steer the Rov. This rov is very good at moving quickly since it may turn at full power. When operating at slow speeds the Rov may become difficult to handle and keep in one place. An arm can easily be mounted to the front of the platform although care must be taken to evenly balance the Rov.
In figure two a round design is considered. This rov will resemble a saucer and is capable of making precise movements at slow speeds. This Rov also employs three motors to work. Two are mounted on the left and right side which propel the Rov forward and turn it. A third is mounted vertically and is used to change the Rov’s depth. This design uses a closed body and is capable of moving quickly. Care must be taken when changing depth as the rotary movement of the vertical motor may cause the Rov to spin. If this becomes apparent it can be fixed by adjusting the trim on one of the motors to produce slight propulsion which will cancel out the movement from the vertical motor.
Figure three is designed as an all purpose Rov frame and makes use of less motors. Only two are used and they are mounted horizontally on the roof of the Rov. This makes sure that they will not be blocked by any of the other components. One problem that could arise is if the motors float above the water and are unable to propel the Rov. This is why a variable ballast tank is used instead of a third motor. The box in the middle will contain a variable ballast tank. When empty the Rov will have negative buoyancy and sink below the surface. When inflated the Rov will have positive buoyancy and float to the surface. If inflated fully the Rov will rise out of the water which can be helpful in retrieving items from the bottom of the test tank. Like all the designs an arm may be mounted although care must be taken to not throw off the balance of the Rov.
The fourth and final design is a larger Rov. It is meant to be very thin and should not weigh too much. Two motors are used on the left and right wings of the Rov. These can be operated independently to steer the rov left and right. A large paddle is built near the tail which can be adjusted to change the dive plane of the Rov. To change depth the Rov will also employ a variable ballast tank which will give it stability when operating in a stationary spot. This Rov will have less propulsive force due to the need to shut a motor off to turn, but will make up for it with its aerodynamic shape. The hull will be constructed of a fiberglass and a large hole will be left in the front to accommodate any type of robotic arm. This hole can also be used as a storage compartment if the tasks require one.While all these designs are possible and have been used to compete in the past the ultimate decision will come from the team and their decision on the attributes required of the Rov. It is important to keep in mind the electronic usage of motors and how this can be avoided by using pneumatic and hydraulic power. The size of the Rov must also be carefully decided as the larger and heavier it is the slower it will move due to the restricted amount of energy.
Design number one uses a long and skinny body to help increase the speed of the Rov. This design uses three motors to propel it through the water. The two forward motors swivel up and down to change the rov's depth in the water. The rear motor turns left and right to steer the Rov. This rov is very good at moving quickly since it may turn at full power. When operating at slow speeds the Rov may become difficult to handle and keep in one place. An arm can easily be mounted to the front of the platform although care must be taken to evenly balance the Rov.
In figure two a round design is considered. This rov will resemble a saucer and is capable of making precise movements at slow speeds. This Rov also employs three motors to work. Two are mounted on the left and right side which propel the Rov forward and turn it. A third is mounted vertically and is used to change the Rov’s depth. This design uses a closed body and is capable of moving quickly. Care must be taken when changing depth as the rotary movement of the vertical motor may cause the Rov to spin. If this becomes apparent it can be fixed by adjusting the trim on one of the motors to produce slight propulsion which will cancel out the movement from the vertical motor.
Figure three is designed as an all purpose Rov frame and makes use of less motors. Only two are used and they are mounted horizontally on the roof of the Rov. This makes sure that they will not be blocked by any of the other components. One problem that could arise is if the motors float above the water and are unable to propel the Rov. This is why a variable ballast tank is used instead of a third motor. The box in the middle will contain a variable ballast tank. When empty the Rov will have negative buoyancy and sink below the surface. When inflated the Rov will have positive buoyancy and float to the surface. If inflated fully the Rov will rise out of the water which can be helpful in retrieving items from the bottom of the test tank. Like all the designs an arm may be mounted although care must be taken to not throw off the balance of the Rov.
The fourth and final design is a larger Rov. It is meant to be very thin and should not weigh too much. Two motors are used on the left and right wings of the Rov. These can be operated independently to steer the rov left and right. A large paddle is built near the tail which can be adjusted to change the dive plane of the Rov. To change depth the Rov will also employ a variable ballast tank which will give it stability when operating in a stationary spot. This Rov will have less propulsive force due to the need to shut a motor off to turn, but will make up for it with its aerodynamic shape. The hull will be constructed of a fiberglass and a large hole will be left in the front to accommodate any type of robotic arm. This hole can also be used as a storage compartment if the tasks require one.While all these designs are possible and have been used to compete in the past the ultimate decision will come from the team and their decision on the attributes required of the Rov. It is important to keep in mind the electronic usage of motors and how this can be avoided by using pneumatic and hydraulic power. The size of the Rov must also be carefully decided as the larger and heavier it is the slower it will move due to the restricted amount of energy.
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