Challenge

Monitoring and observing life is an important aspect of getting an insight on the current state of animal life and if they are in danger of extinction. This can however be a difficult process to do if the life you are trying to monitor is in difficult to reach places, or even hazarded environments to humans like deep water bodies. The ocean is a very fast place with many species that may suffer the hardest from climate change. Therefore, it is important to monitor, inspect and preserve them as much as possible. From the tiniest sea creatures living on the bottom of the ocean to the school of flying fish. Currently, doing so is an expensive operation and require a lot of human labour and expensive equipment like ROVs (remove operate vehicle). A marine expert has to be present to analyse the data and draw conclusions. To do this in a continues matter would be a very cumbersome and expensive task. As new equipment for monitoring is being developed it may be difficult to adapt the already existing hardware to these new equipment.

Solution

I propose a low cost, highly modular ROV: Aruna, with specialized equipment that can be used for underwater monitoring and marine research. The ROV can have a wide range of sensor and equipment such as:

Any other equipment can be easily introduced later because of the modular nature of the ROV. The ROV was designed with modularity in mind, so it can be easily adjusted to the desired situation. The current design has 5DOF (degrees of freedom) using 6 propellers. Adding two extra propellers can be used to get full 6DOF. The model can also be substantially changed by converting it to a glider model, so it can be more effective on longer missions with greater distances where high mobility is not required. The high modular design of the ROV allows for all these adjustments and is at the heart of the implementation of the device.

Aside from the monitoring sensors described above a number of other sensors are to be used for navigation like gyroscope, pressure sensor, accelerometer, GNSS, compass and sonar. The goal is to allow the ROV to complete a mission with as little human interference as possible. Thus, the user can choice to deploy multiple ROVs at a site which all perform a set mission and communicate their findings back to the user. This could also happen periodicity so that a continuously monitoring function can be achieved. The user may also choice to manually control the ROV for precise missions, this is the current focus of the project.


Technique

Software

At the base of the project lies the Aruna C++ library. This library is build of multiple modules. The goal of these modules is to be written portable so that they may run on any platform. Beneath the modules are drivers-interfaces. These are abstract classes that divine the behaviour of the platform specific drivers. These are platform specific and need to be rewritten for every platform. Aruna currently has full support for ESP32 (using ESP-IDF 3.2.2), there is partially support for Linux. And lastly, planned support for the STM32 family.

Software Diagram
Architecture of Aruna


Module

Platform


ESP32

Unix*

STM32

Logging (log)

v

v

v***

Communication (comm)

v

v

x

Safety instrumented system (SIS)

v

v**

x

Control

v

x

x

Blinky

v

x

x

* Only tested on Linux x86

** Performer and Reporter untested

*** Untested

Current modules are:

Hardware

There are several CAD models developed for the ROV. All the components for the ROV life in (or on) an 80 mm PVC pipe. A certain set of design rules are applied to ensure that the hardware is as modular as the software. All the components must be able to “snap-on” the pipe, as to not require drilling, glueing or any other modification of the main PVC pipe. This ensures quick and easy swap out of new components and grantees hull integrity. All the components on the inside are held together by four M4 threads. All the components have their own bracket to hold them into place.

BLHeli holder
CAD design to hold the BLHeli controller in a 80mm tube with four M4 screws


For components on the outside there is a bracket with four M4 screw holes to hold the BLDC (brushless DC) motor or any other accessories. For more CAD object see the repository

Universal holder
used to hold the BLDC motors on the outside of the ROV

Implementation

The current implementation of Aruna is quite bare. It consists of a simple surface control software that allows for 4DOF movement by keyboard input and monitors SIS reports. Attached to the computer running the software is a serial to RS485 converter. The signal travels back and forth to the ROV where the signal is feed into the ESP32. The ESP32 controls the motors based on the command received from the surface. Four SimonK drivers for forward, backward, sideways and yaw. Two BLHeli controllers are used for upward and downward movement. Water level is reported using a rain-meter. All written in C++ as described in the “software” section.

Hardware Block diagram
Diagram of the hardware used in the ROV,
Inside
Breakdown of the inside of the ROV, complimentary of the diagram above.

Four motors are attached to the outside of the PVC pipe in a diamond shape (see figure) to allow for 3DOF using just four motors that can only spin in one direction. The upward and downward motors are driven by BLHeli controllers and thus support clockwise and counter-clockwise rotation. See table for more information.

Axis

Motor


1

2

3

4

5

6

X+

N

N

Y

Y

N

N

X-

Y

Y

N

N

N

N

Y+

N

Y

N

Y

N

N

Y-

Y

N

Y

N

N

N

Z+

N

N

N

N

Y

Y

Z-

N

N

N

N

Y (counter)

Y (counter)

Yaw+

N

Y

Y

N

N

N

Yaw-

Y

N

N

Y

N

N

Pitch

Not possible with current configuration.

Roll+

N

N

N

N

Y

Y (counter)

Roll-

N

N

N

N

Y (counter)

Y

motor layout
Layout of the motors. Blue arrow represents push direction of individual motor; red arrows for possible directions; motor number shown in green

Repositories

The Aruna project currently consist of five repositories.