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.

Brainstorming: Robotic Arm

The robotic arm is a crucial item in the Rov construction. Many of the tasks rely solely on its effective use. Having an easy to use multipurpose arm may be the key to winning the MATES competition. I have sketched out various designs as seen in Appendix I, which is at the end of this post.

The first design uses a hydraulic system. The arm is locked down in two pivot points indicated by the circle with a cross in the middle. It is then connected to a hydraulic arm that may either extend or retract. In this design creating a negative pressure and retracting the hydraulic arm closes the space between the two gripping arms. This design is simple and is useful for grabbing delicate items. It would best be used when an item must be retrieved and returned to the surface. The fact that it closes relying on a negative pressure means it is easy to keep the arm closed, however large amounts of force may not be applied as this could cause leaks that would let water into the closed system.

The second design relies on an electronic motor. This design has one stationary arm, which is shown on the left side of the drawing, and one arm connected to a geared motor. The gear allows a greater torque to be applied to the arm. This design requires greater monitoring from the control station. If care is not used the motor may easily become overworked and burn out, rendering the arm useless. This arm is best suited situations where large amounts of force are needed for short amounts of time, such as grabbing and pulling an item.

The third design also relies on a hydraulic arm, which is useful as it does not require excess energy. The arms are locked into pivot points in the middle of the arms as shown by the circles with a cross in them. This design, unlike the first one, requires a positive pressure from the control station to close the arm. This makes it easier to apply more force, although care must be taken not to create a tear or leak within the line. This is useful for grabbing items with large amounts of force and holding them for an extended period as the hydraulic line may simply be locked at the required pressure. This differs from the second design in that although they both can produce greater force, there is no risk of burning out the motor from extended use. A pressure gauge would be very useful in this design as it will make it easier to produce the required force and lower the risk of exceeding the maximum pressure of the system.

The fourth design is similar to the second in that one arm remains completely stationary. The second arm is attached by mobile rods that allow it to extend and retract. This design is shown running off a hydraulic system although it could easily be adapted to use a motor or servo. This design is also locked down in multiple locations to provide a secure base. This design is useful as it is less prone to breaking off from the main body. Its narrow profile is also useful for a situation where there is little room to maneuver the arm, such as reaching inside a hole. This same profile limits the design as it is unable to grasp large items.

While all these designs will prove effective if constructed properly, the true deciding factor will depend upon the tasks assigned. The construction of multiple arms may even be necessary to accommodate varying tasks. The use of hydraulics instead of electronics allows more energy to be focused on the motors, increasing their speed.

Brainstorming Outline

A. Propulsion
1. Outboard electric motor.
i. More prone to damage.
ii. Least bulky.
2. Enclosed electric motor.
i. Less likely to be damaged.
ii. Easiest to mount.
iii. Requires large space.
3. Water jet.
i. Requires extensive tubing inside ROV.
ii. Produces swift motion.
iii. Hard to fix due to enclosed nature.
4. Paddle system.
i. Can move heavy items easier due to larger surface area of paddle.
ii. Slower speed due to restricted energy use.
B. Robotic Arm
1. Hydraulically powered.
i. Requires lower pressure inside tubing.
ii. Possible to leak contaminants.
2. Pneumatically powered.
i. Requires higher pressure.
ii. Prone to leaks.
3. Servo powered.
i. Use of additional energy.
ii. Due to power restrictions will have less torque.
4. Electric motor powered.
i. Possible to have large amounts of torque due to gearing.
ii. Large energy consumption.
C. Frame material
1. PVC tubing.
i. Easy to acquire.
ii. Positive buoyancy.
2. Plastic sheeting.
i. Can make more hydrodynamic.
ii. Prone to breaking.
3. Metal Tubing.
i. Negative buoyancy.
ii. Costly.
iii. Strong.
4. Metal sheeting.
i. Easy to acquire.
ii. Prone to rust.
iii. Negative buoyancy.
5. Composite plastic tubing.
i. Costly.
ii. Strong
iii. Positive buoyancy.
6. Fiberglass.
i. Longer construction time.
ii. Strong.
iii. Can make more hydrodynamic.
7. Wood.
i. Easy to acquire.
ii. Prone to water damage.
iii. Various styles.
D. Buoyancy control
1. Compressed air buoyancy tank.
i. Limited amount of depth changes.
ii. Reliable.
iii. Accurate.
2. Inflatable balloon.
i. Requires input of air from control station.
ii. Greater chance of leaks.
3. None, use of propulsion means to change depth.
i. Least accurate.
ii. Requires least amount of additional components.
E. Steering control
1. Two independently controlled motors.
i. Must be placed far apart to be effective
ii. Hard to make small adjustments.
iii. Cannot steer while drifting.
iv. Requires least amount of additional components.
2. Rudder behind motor.
i. Additional servos required.
ii. Very accurate.
iii. Does not require propulsion force to steer.
3. Moveable motor housing
i. Faster movement through water.
ii. Cannot steer while drifting.
F. Speed control
1. Multiple motors.
i. Requires more wiring and motors
ii. Greater chance of component failure.
2. Variable current switch.
i. Bulky.
ii. Large degrees of adjustment.
3. Electronic Speed control.
i. Most expensive.
ii. Finest control over movements.
G. Control Box
1. Minimalist control box.
i. Use of smallest size control box and as few wires as possible.
ii. Easy to store and move.
2. All in one control box
i. Larger design with all needed controls in one place.
ii. More controls may be added due to less size restrictions.
3. Computer controlled
i. Requires computer programming
ii. Most accurate
H. Waterproofing
1. Electronic waterproofing liquid.
i. Easy to use.
ii. Incorrect use results in loss of component.
iii. May need to be explained at safety check.
2. Tape.
i. Easy to use.
ii. Hard to make repairs.
3. Fiberglass.
i. Harder to use.
ii. Very effective
iii. Permanent and repairs may not be made.
I. Underwater Cameras.
1. Must be waterproof.
i. Enclosed in shell.
ii. Clear image necessary.
2. Mounting location
i. Birds eye view from rear.
ii. Close-up by Robotic Arm.
iii. Top Front unobstructed view.