When designing the chassis, there were four main constraints;
The first was that the design could be manufactured without many long winded and expensive processes
Secondly I had to ensure that it would fill all requirement set by the client
Thirdly it should meet the requirements of the parts that my team will be designing i.e. mounts for electric component boxes, camera mounts and other components
Lastly it needed to be updated to any extra specifications will be supplied with when Babcock visited
With those restraints in mind, the final design is this:
The frame has all the mountings for the prop housings, servo housings, and serves as a platform to mount all the components.
The chassis has been designed to allow the ROV to rotate on the spot, this will facilitate maneuvering in tight spaces and has allowed the design to be a bit larger which will allow it to have more space for the electronic components.
The camera mount will be placed in the middle of the chassis and we are currently working on the design for this. The image bellow shows an example for the camera mount.
The camera would be mounted on this which will rotate to allow the users a better view of the object being inspected
This week we developed several propellers with various pitches for testing on started designing the gearing system to attach to the drive shaft.
After advancing further upon using pre-existing CAD designs, we realised that this was not the best option as they were not as easily adjusted as anticipated, so we designed our own.
We came across the a thrust equation , where F=Thrust, =density of fluid passing over the blades, A=propeller disc area, Ve=the velocity of fluid exiting the propeller and Vo=speed of fluid travelling towards the propeller. To calculate a simple we derived this equation to calculate the potential speed of the exiting water, Ve=(RPM*prop.pitch)/60, and the speed of fluid travelling towards the propeller is just assumed as Om/s just for simplicity.
The RPM has been estimated to need to be around 300 RPM so there’s enough torque and so the propellers aren’t giving out too much thrust, as the ROV needs to move steadily to allow surveying on hulls or inside of fuel tanks. The propellers are also going to be in a tube like casing, which should therefore reduce slip and direct the thrust to go 1 direction. I used the density figures as water-1000kg/m^3 and diesel-835kg/m^3
we calculated a range of pitches thrust, varying from 0.36 inches to 6.72 inches.
Thrust in water (N)
Thrust in diesel (N)
These calculations are obviously going to be different to the true value which is why testing is very necessary.
After these have been printed then we will attach it a motor and test it in a body of water with a pivoted arm attach to a newton meter.
From this we will be able to chose the ideal pitch for the ROV.
This week we focused on finding the best way to transmit data/communicate between the ROV and the team stationed on the dock. We also looked at what we think would be the most important sensors to use within our ROV.
We found a variety of ways in which we can communicate with the ROV however a few of the methods found would not be feasible to use. We narrowed it down to two methods we planned on testing:
We were going to select low frequency transmission however we found that all Radio Controlled Models in the UK are only permitted to function under a specific frequency. This is to prevent interference with other devices such as radio broadcasts. This limited us to using a buoy for communication.
The sensors we think are the most suitable for use on the ROV are:
A Magnetic Sensor – This will allow us to calculate the direction in which the ROV facing effectively acting as a compass.
Gyroscopic Sensor – This would help by determining the orientation of the ROV when it is underwater.
Proximity Sensor – Proximity sensors would allow us to detect when an object is within a certain range of the ROV.
Pressure Sensor – This will allow us detect the depth at which the ROV.
This week the main focus of our research was the movement of the ROV. We have decided to use DC Brushless Motors as they a water resistant so will work fine in the required environment. We have ordered a motor to test the gearing we will require as well as how well the propellers work. Its specs are below:
Rather then making our own propeller we have decided to download one off of GrabCAD. This will save us a lot of time compared to making one from scratch due to the number of calculations we would need to make as well as repeated testing to make sure the design functions. The CAD is shown below:
We are planning to 3D print 5 of these propellers each with a different pitch to find the best one to use on the ROV.
Finally we looked at what type of gearing we want to use. We concluded the best would be worm and wheel gearing as this will reduce the size of the gearing system. We are looking for an in water RPM of about 300-400, which will require a gearing ratio of 1:10-20. The RPM will be reduced in water, so testing it is highly necessary for these calculations.