User:Heights and Depths/sandbox

Team Heights and Depths' ROV

Project Scope “Students are required to build a large scale ROV which is able to support ancillary items such as cameras, robot arms and the like and is able to undertake specific tasks. The competition between schools will be based around diving down and recovering items on the flocr of a pool, along the way filming the activity. At this level the students will be required to extend their understanding of Maths and Science around underwater operation together with robotic control.

Design Designing the ROV began with getting a vague idea of where to position the electronics. This was done on paper, then quickly modelled on Autodesk Inventor as a basic box like model. We worked around the cargo space to help us create a frame which is large and compact enough for us to work with. Keeping in mind the size of the 3D printer, this created difficulties as we were working on the edge of the printer’s base, which could cause warping. After finding this out and receiving critiques, these problems were mostly solved in the next design. The next design had the side frames split in two, to fit the printing size of the 3D printer. We also added in support across the top of the ROV, which was suggested by the mentors at SAAB. The concept of this frame was to create something that can have easy modifications. This was mainly due to the very vague idea of how big the equipment would be, which in the end, resulted in guessing. You can see where my predictions went wrong in the final outcome, as parts are not very well fitted. The holes at the back were intended to help house the motor, but ended up somewhat useless as they are too small for the hose clamps, and the propeller guard is not very appealing. The space at the front also has problems as the parts are very crammed and attached so they are best positioned. When constructing the final frame design there was many things that we had wanted to implement off of the bat, but one of the SAAB Members, “Will” had recommended that we start with the basics, a box containing the virtual cargo and then begin to implement our changes as we go. The initial prototype of our ROV was shown below the Blocky Shape, From there we had decided to add in more of a curvature to make it more hydrodynamic, with the slightly larger image next to the 1x2 of images was our second to last iteration, which had more cross bracing than the previous design, but had some drawbacks, such as only just being the right size to print which did end up warping the print at times. Moving on to the final frame design we had fixed up many errors from the competition, covering up more than 30% of each side, more secure slots for the motors.

Motor Choice for propulsion

Standard Brushed Motor

Motors are an essential part of a submarine as they help power the propellers which help move the craft. A DC motor is any of a class of electrical machines that converts direct current electrical power into mechanical power. The most common types rely on the forces produced by magnetic fields. In a typical DC motor, there are permanent magnets on the outside and a spinning armature on the inside. The permanent magnets are stationary, so they are called the stator. The armature rotates, so it is called the rotor. The armature contains an electromagnet. When you run electricity into this electromagnet, it creates a magnetic field in the armature that attracts and repels the magnets in the stator. So the armature spins through 180 degrees. To keep it spinning, you have to change the poles of the electromagnet. The brushes handle this change in polarity. They make contact with two spinning electrodes attached to the armature and flip the magnetic polarity of the electromagnet as it spins.

This setup works and is simple and cheap to manufacture, but it has a few problems: •	The brushes eventually wear out. •	Because the brushes are making/breaking connections, you get sparking and electrical noise. •	The brushes limit the maximum speed of the motor. •	Having the electromagnet in the centre of the motor makes it harder to cool. (caused by friction) •	The use of brushes puts a limit on how many poles the armature can have. •	Chlorine needs to be washed out after use.

Average price: $2.00/each

Standard Brushless Motor

It became possible to "turn the motor inside out" and eliminate the brushes. In a brushless DC motor (BLDC), permanent magnets are placed on the rotor and then move the electromagnets to the stator. This means that the motor won’t wear out as quick as a brushed motor, making it more reliable. Disadvantages: •	Higher price than brushed motor. •	Chlorine needs to be cleaned out after use. Average price: $18.00/each Bilge Pumps

Bilge pumps move water by kinetic energy using a rotating, solid impeller, similar in design to a turbine. Water enters the pump, picks up speed as the impeller rotates, and is then forced out by its own momentum. A Bilge pump acts like a little wet-vacuum to suck out bilge water. Considering that, bilge pumps are pretty much water-proof motors, meaning that they don’t need to be cleaned. The only disadvantages of a bilge pump are its higher initial cost and it is also slightly heavier than the DC motors. Average price: $50.00

Analysis: Standard brushed DC motor’s best feature is its price. With only $2 per motor, it makes it an easily accessible motor that is usable underwater. However, considering that it uses brushes, it will eventually wear out which makes it less reliable. Standard brushless DC motors are a much better alternative to brushed motors. Since their brushless features make it so that it doesn’t wear off as quick, it makes it a lot more reliable underwater. Although slightly more expensive than the brushed motors, it is still fairly affordable and accessible. Bilge pumps are the best of the three motors when it comes to efficiency and reliability. It works as well as a DC motor and is fully waterproof. This makes it more reliable than the other motors.

Discussion: Order or preference: (lowest-highest) Brushed DC motors - Brushless DC motor - Bilge pumps The reason that the preference of motors is listed this way is because their price is inconvenient. Brushed motors are second in the list because they are cheap and easily accessible. The brushless motors are the second most preferred motor because of their convenient price and their reliability. Brushless motors don’t wear off easily, are reliable in water and are not too expensive, making them ideal for use. Despite their price and slightly heavier weight, bilge pumps are the most preferred for use because they are the most reliable underwater. Since there isn’t a big difference between each motor, it wouldn’t matter too much if the brushed DC motor was used. However, the bilge pump was chosen because it has the least issues.

Choice of Propeller for Propulsion

The propulsion of the ROV submarine helps the craft move forwards, backwards, up, down and it helps the craft turn in both horizontal directions. Propellers can rotate counter-clockwise as well as clockwise which helps the craft move in two different directions. Because of this, only 3 propellers are required: two of which can move the craft either rightwards, leftwards, forwards or backwards. When the two rear propellers turn simultaneously in a clockwise direction, the craft will thrust forwards however, when they both move anti-clockwise, the craft will move backwards. However, if the left propeller were to turn individually, it would turn the craft rightwards and when the right propeller was to turn individually, it would turn the craft leftwards. When the top propeller turns clockwise, the craft will thrust downwards but on the other hand, when it turns anti-clockwise, the craft will move upwards. With this in mind, one propeller was chosen to be placed at the back-left of the craft to turn it rightwards, another placed on the back-right of the craft to turn if leftwards and a final propeller placed at the top of the craft to move upwards and downwards. The larger the diameter, the more blade will push the water. The drawback is that the greater the diameter, the larger the frame has to be to separate the motors and also offer protection from obstacles. Also, the propeller guard would have to be larger which can cause some problems with the compactness of their placement. If the propellers are too close together, they may hit an adjacent blade. Pitch is defined as "the distance a propeller would move in one revolution if it were moving through a soft solid”. Therefore, the greater the pitch of the propeller, the larger the distance the craft will move in one revolution. The chosen propellers to be used the ROV were two right-gear propellers and one left gear-propeller. The diameter of the propeller is 4cm and the pitch of the propeller is 11.33/revolution. The pitch was calculated using this formula:

(2.36*diameter*height )/width=pitch (2.36*4*3 )/2.5=11.33

The pitch of this propeller (11.33) won’t move the craft very fast compared to other propellers but in order to have a higher pitch, the diameter of the propeller would have to be larger as well. Since the design of our submarine is small and the bilge pumps we are using are fairly large, we chose to have a propeller with a smaller diameter. Propellers with larger diameter with increase the weight of the propeller and there won’t be room to fit large enough guards. The size of the propeller is large enough to move the ROV. The need for a changing blade angle from the hub to the tips stems from the fact that angular speed varies also and is greatest at the tips. Combine this with any forward speed the propeller may have, the relative airflow is also different from the hub to the tips. To keep thrust equal along the blade, they have a build in twist. The design is such that the blade is thick at the hub with a large blade angle and thin at the tip with a low blade angle. This is also why this propeller was chosen. The propeller has two blades which are also enough to push the craft forwards. It also gives option for a larger variety of guard shapes (ovular of hemi-spherical).

Choice of Gripper

The gripper for the ROV needed to be able to effectively pick up and release items, whilst not hindering the ROV’s manoeuvrability or stability. Three possible gripper designs were considered for the ROV, which are outlined below: 1) A simple rod, no wiring or mechanisms, attached to the front of the ROV. 2) A small gripping claw attached to an arm that could be manoeuvred. 3) A large claw, only able to open and close, attached to front of the ROV. The first design has the benefit of being extremely simple to create, as it doesn’t entail any wiring, just a simple rod. It also doesn’t require an additional control, making the controls slightly easier to use. Furthermore, the design won’t significantly impact the stability or centre of gravity of the ROV. However, this design does have some significant drawbacks, including the fact that it has no way to secure items that it may pick up, meaning that the design isn’t completely reliable. The second design is very manoeuvrable and reliable. It is able to secure items using a claw and isn’t too large. The claw can also function as a rod when closed. However, there are several components required for this gripper to work, which are difficult to attach to the ROV, and the added weight could potentially shift the centre of gravity. Additionally, this gripper design is extremely manoeuvrable, which means that it has more controls and is therefore more challenging to operate. This design will also take a lot of time to construct. The third design isn’t overly manoeuvrable, but is still reliable. It is able to pick up fairly large items, and secure them using a claw. It can be constructed fairly easily and quickly, as the majority of the gripper’s components are contained inside a small box attached to the claw. As this gripper is only designed to be opened and closed, it’s fairly simple to control. However, this design is somewhat heavy because of the large claw which may affect the centre of gravity. The largeness of this design means that it may be somewhat difficult to attach securely to the ROV’s frame. The first design was selected for the ROV, because it was reliable and would be quick and easy it would be to assemble and program. It is relatively heavy, but the buoyancy can be altered to keep the centre of gravity in the middle of the ROV.

ROV Buoyancy

It was important to create the ROV so that it would it would be stable and easily controllable, meaning that buoyancy would be taken into consideration. The final decision was to make the ROV slightly positively buoyant, as it would be easily controllable and if the up/down thruster failed, it would eventually float back to the surface. Additionally, the tether was designed to be neutrally buoyant. The design and arrangement of the floats, involved attaching a pool noodle to each the four corners of the ROV, as this would create a fairly versatile design that would keep the centre of gravity in the middle of the ROV. The ROV was made to be slightly positively buoyant, as this would make it easily controllable, as it wouldn’t have a tendency to sink or float too readily, reducing the amount of resistance experienced while manoeuvring the submarine. The advantage of having the ROV positively buoyant is that in the event of an electrical failure, the ROV will resurface. The main drawback of this design is that some use of the down thruster will be needed to maintain the ROV’s position in the water. The tether was made to be neutrally buoyant, because it is important that the tether doesn’t drag the ROV down or lift it to the surface. Having the tether neutrally buoyant enables the maximum amount of control, as it provides no resistance, no matter which way the ROV is being steered. Achieving neutral buoyancy for the tether involves attaching floats, (such as pool noodles) to the tether to counteract its weight. The arrangement for the floats involves placing a pool noodle on each of the four corners, which is an effective design because it is fairly versatile, and helps the ROV maintain stability. The size of the pool noodles can be adjusted to counteract the weight of the ROV’s components, making it especially useful if the weight of each end is uneven. Because the floats are positioned at the four corners, if the positively buoyant force is even at both ends, the centre of gravity would stay in the middle of the ROV, therefore helping the ROV to remain stable in the water.

Electronics

Control Box Wiring

The control box is the control system with three switches that operate three motors and a tether connects the control box to the motors. All wires except those connected to the switches are soldered and covered with a layer of heat shrink A toggle switch is an electrical switch that are manually attached by a lever of the control box each have three screws. The toggle switches on this control box have six screws where wires are attached to by tightening those screws. Then an electrical current can be sent through those wires. One positively charged and one negatively charged wire are attached to the two middle screws of each switch. Those wires are connected to one end of the tether. The rest of the screws on one side, are occupied by positively charged wires and on the other side, by a negatively charged wires. Those positive wires are connected to each switch (from one switch to another) and same with the negative wires. In order for the motors to be powered by the switches, two batteries are required to connect to those switches (two 11.1VLithium batteries). Each battery has two outlets, one for a negative wire and one for a positive wire. A positively charged wire is connected from one of the switches to the positive outlet of one battery. A negatively charged wire is also connected from a switch to the negative outlet of the other battery. Each motor has a positively and negatively charged wire attached to it. Those wires are connected to the other end of the tether, making sure that the wires from that end of the tether match to those on the other end of the tether. One final (standard) wire connects from each motor to the remaining two outlets of the batteries.

Arduino and Claw Programming

Programming the claw was relatively easy as I had some (limited) knowledge of the structure of the code and how it had to be written. This whole process was made very simple due to the use of an Arduino Uno and the Arduino software. The claw was programmed to be operated with a potentiometer allowing for accurate use when collecting objects whilst completing the sea trial. I did run into the issue of the claw shaking when a large amount of pressure was placed on it. This was due to the microcontroller not being provided with a sufficient amount of power. This issue was solved by adding an electronic speed controller which varied the amount of power supplied at any given time. This ESC was then attached to a separate battery allowing a larger amount of power to be put through the claw. This allowed for the adequate amount of power in order to stop the claw from shaking.