In order to control the movement of the ROV, we have to attach an electronic speed controller (ESC) to each of the motors. An ESC allows you to alter the speed of the motor it is attached to based upon an analogue input which for the ROV would be an analog stick controller. This week we tested this by trying to control our motor using an ESC and an Arduino board. We substituted the analog stick with a potentiometer to just alter the speed rather than both speed and direction.
The video below shows our test of controlling a motor using an ESC:
As shown when the potentiometer was turned the motor starts to rotate slowly increasing its speed as it turns.
To further test the motor we need to measure the torque of the motor both by hand using calculations and then underwater with a propeller attached. This will give us the force produced by each motor underwater.
After a planetary gearing system was designed, including the outer casing and a protruding drive shaft, it was analysed in Solidworks.
This system has a ratio of 10:1. Due to the small size of the teeth and the quality of the 3D printer being used, it was highlighted that the individual gear teeth would more than likely result in being merged into one.
As this is only for testing, to prove feasibility, the team decided to study this design on Solidworks instead of physically printing it which would give us more information about forces that it suffers whilst working and can help us work out the wear
The meshing of the gears was then tested and approved in solidworks. To bypass the problems of gearing printing we decided to invest in a higher torque, lower RPM motor. This would also avoid the problem of debris getting in the system.
The main purpose of the ROV is to survey infrastructure underwater. In order to accomplish this we are using a camera mounted on the top however as a backup we will also be using a Ultrasonic PING Sensor to detect when the ROV comes to close to an object in front of it.
We wanted the PING Sensor to effectively act as a radar. In order to accomplish this we will mount the sensor on a servo and have it rotating constantly over a range of 180 degrees. A video of our test is shown below:
While the servo is rotating the sensor constantly takes readings to determine how close an object is to the ROV. If its too close it will give a more accurate reading as well as a warning to tell you this.
After further consideration of designing the planetary gearing system, it has been concluded that it may be susceptible to clogging from debris in the water environment.
To avoid this a new brushless motor with a slower RPM and higher torque has been selected.
It has a given Kv of 380. This can be used to calculate the theoretical torque of the motor using the formula T=Kt*I (eric, 2015), where T is torque, Kt is the torque constant and I is the applied current. Kt can be calculated by Kt=1/Kv. (eric, 2015)
If our current supply in around 9A then our theoretical torque will be, T=(1/380)*9=0.02368Nm.
Since our propellers are 50mm in diameter this torque should sufficient enough to allow the propellers to turn through the resistance of the water.
The Kv is also a good indicator of the RPM/volt applied tot he motor (in air). So out of the water we expect the motor to turn at 4560 RPM, as we are using a 12v supply.
These torque calculations seem to be too low however so a simple test will have to be done to confirm the torque.
eric, 29 july 2015. meaning of motor kv. [online]. Learning RC [accessed: 01/02/2017]. available from: http://learningrc.com/motor-kv/
After basic propellers, with varying pitches, had been designed they needed to be ran through Solidworks simulations to asses whether the designs would withstand the forces endured as it would rotate in the water.
50 Newtons was applied to each blade acting perpendicular to the face.
After these simulations were ran it identified the highest areas of stress and thus the most likely areas to fail. After adding some fillets to the corners the amount of error indicated was to a low enough level to expect no failure while being used.
After the propellers had been printed they needed the support structures removed by hand. Due to the small size of the parts there was a breakage of one of the blades.
During this week we have been working on the wiring and the coding for our pressure sensor. For our tests we used a force resistor sensor as prove of concept, and this can be extrapolated when we use an underwater sensor. This will also allow us to work out the pressure and from this calculate the depth. As you can see in the following video the sensor reading comes with a message to alert the users to stop going further down
The following flowchart shows how the code for the pressure sensor works. This will be how the underwater sensor will work so nothing will change here
The main purpose of the ROV is to survey infrastructure underwater. In order to accomplish this we are using a camera mounted on the top. In order to make the camera more functional we wanted it to have the ability to move allowing for a larger view while staying stationary.
We tested if this is feasible using 3-axis servo mounts. A video of our test is shown below:
As the video shows we programmed the servos to move based on the input on a controller.