Choosing our Sensors

While designing the second version of RoboGoby we needed to decide what sensors were necessary to have incorporated into the basic design. If you have been following our blog you'll remember when we posted this in October 2013. That post had ideas for sensor we had gotten from different research institutions. After spending the past year and a half working on the sub, we created an updated list of sensors we want to have incorporated on the most basic version of RoboGoby. We decide that these environmental sensors are key to a well functioning submersible and are necessary if we want to have a well working product.

The updated list of sensors we chose is below. There is also a short description with each saying why it is important for our design. While choosing the new sensors we also made sure that they all interface with an I2C bus. This allows us to communicate with multiple different sensors while only using a minimal amount of wiring and only a single micro-controller. 

• MS5803-14BA Pressure Sensor

Breakout board w/ MS5803

We chose to use this sensor because it is waterproof and it can withstand up to 14 Bars of pressure, which is around 200 psi or 450 feet underwater. It allows us to determine the depth of the submersible.

• Pololu Current Sensors
• 12 bit ADC (for I2C)

We chose to use current sensors on this version of RoboGoby because we wanted the ability to have current control over the thrusters. As are unable to accurately measure the speed of the ROV in all directions, we will be using current to limit the thrust on each of the motors. This will make it easier to implement autonomous capabilities in the submersible. We are using the ADC in order to use multiple analog current sensors without having to use more analog pins. 

• Humidity and Temperature Sensor

This version of RoboGoby has a watertight compartment. Although this design is useful in many ways, we need to make sure that the compartment gets neither wet or too hot.

• LIDAR Lite

We chose to use a LIDAR instead of a ultrasonic sensor for ranging underwater. This sensor is very easy to integrate in an underwater environment and has an extremely large range. We will have to calibrate this for the reflectivity of water, but this sensor works for bathymetry, meaning it should also work for our purpose. Its had two advantages over a sonar sensor. The first is that it doesn't have a minimum range (a very small one), which is important if we end up having to navigate without a camera or with limited vision. Second, it is easier to waterproof as we don't have to find a substance which provides waterproofing without having any sound dampening properties. 

• 9 DoF IMU

This sensor is very similar to the Razor 9DOF IMU we used last year. The only difference between the two sensors is that this one doesn't have a micro-controller built in. Similar to last year, we will be using this sensor to get a better understanding of the submersible's position in the water. This will not only be useful for human drivers, but also useful in implementing autonomous station-keeping and driving.