Engineering goals and challenges
The main engineering goal for SCINI this year is to be shoot quality video at depth up to 300 meters. This might sound simple, but actually it involves several complex engineering challenges.
At 300m below the surface of the ocean, the pressure is very high. Over a surface of 100cm3 (about the size of a CD), the force, or weight of the water pushing on that surface is over 3 tons, the equivalent of 3 medium size cars! This means SCINI must be able to withstand these high pressures. Here are a few examples of solutions we can use to deal with this problem.
The main electronics housing has thick walls and can go as deep as 2000m.
The side thrusters are filled with oil to compensate for the outside pressure, they can go to full ocean depth.
The camera housing has thinner walls and a clear plastic dome. It would probably get crushed if it we took it deeper that 300m.
The main difference between SCINI and other ROVs is its size. It must fit through an 8 inch hole in the ice so the diameter of SCINI must not exceed 6 inches. While designing SCINI we always had to make everything as small as possible so it would fit inside the 6 inch diameter.
SCINI is long and thin unlike most ROVs, so it can fit through an 8 inch hole in the ice.
So we can easily maneuver SCINI, it must be neutrally buoyant, meaning is does not sink nor float. It must also sit level in the water. We use foam and lead weights to adjust SCINI’s buoyancy and trim. A problem with foam is that it will get crushed by the high pressure, so we must use special foam which can handle high pressures.
Seawater is highly corrosive and will damage equipment very rapidly. To prevent corrosion, we try to use materials which do not corrode, such as plastics. Titanium is very resistant to corrosion but unfortunately, it is very expensive. Aluminum parts are all anodized so they do not corrode as fast. After each deployment of SCINI, we rinse it in fresh water and dry it.
Most remote control vehicles such as model planes, cars or boats are controlled by radio. So why don’t we do this for SCINI? It would be much easier if we could. Radio waves can not travel very far through water, so we are forced to use a tether to transmit data and controls to and from the vehicle. The tether is also used to transmit power to SCINI. The longer the tether, the more difficult it becomes to transmit data and power through it, because of increased electrical resistance and noise.
When we fly SCINI under the ice, we need to know where it is and what position it is in (tilt, roll and yaw). To get some good video footage, SCINI must be steady and easy to pilot.
SCINI is equipped with a pressure sensor which tells the pilot how deep SCINI is. It also has an IMU (Inertial Measurement Unit) which measures acceleration and rotation.
Sound travels very far, and very fast in water and we use this physical property to determine SCINI’s position. A “pinger” mounted on top of SCINI emits a ping (short, high frequency sound wave) at regular intervals. Three baseline stations, attached to cables under the ice listen to this ping. Given the speed of sound in water, and the time of arrival of the sound at these three stations, the position of SCINI can be calculated very accurately. This system was developed by Marco Flagg and his company, Desert Star.
With the appropriate software, the information from the IMU and the acoustic positioning system can be used to determine SCINI’s motion, and even to correct it automatically.
The main electronics housing and the camera housing. Everything fits very tightly inside the housings.
We tested SCINI in a 10n deep seawater tank at the Monterey Bay Aquarium research Institute.
Scott and Bob are assembling SCINI on the bench in the lab.
Francois spent many hours in the machine shop building parts for SCINI. The more complex parts were built by a professional machinist.
Scott working on the control software in Moss Landing.