A team of young engineers from Southampton University is working with Igus to improve the gearbox of its underwater sub.
The Southampton University Human Powered Submarine Society (SUHPS) was founded in 2014 to compete in the International Submarine Races (ISR), created to encourage young people to fill the shortfall in marine engineers. Each team designs and builds a unique flooded submarine from scratch to compete in the races every year. The pilot (a single scuba diver) pedals and steers the sub around an obstacle course in a timed race. SUHPS competed in its first year at the 2015 ISR in Washington DC with the University Of Southampton Ship (UoSS) Orca. The team returned two years later with the UoSS Kaiju.
The team consists of around 20 undergraduate students studying a range of disciplines including Mechanical Engineering, Mathematics, Oceanography and many more. Five sub-teams each specialise in one area of design/manufacture: Hull & Life Support, Transmission, Propulsion, Control and Diving.
As the ISR event is held once every two years, to fill the year gap, SUHPS entered the European International Submarine Races (eISR) with UoSS Nauti Buoy, which took place earlier this year in Gosport. During the qualification sessions, a few teething problems were discovered. The initial gear ratio (4:1) selected was too high, making it difficult for the pilot to pedal. There was also unwanted sliding of the gears, which was caused by the supporting frame bending under the high loads caused by the pilot’s pedalling. This meant that the loading path through the gears was suboptimal, reducing the efficiency of the overall system.
“The contra-rotating gearbox developed over the past year was successful as a proof of concept of the design,” said Caroline Layzell, who co-leads with Transmission Team alongside Gareth Caine.
“This academic year, we are using vastly different gear ratios and dimensions and more precise manufacturing methods such as water jet cutting for the mounting plates. We have reduced the initial gear ratio to 2:1, which will make the pedals easier to push for the pilot, and redesigned an entirely new frame to house the gears.”
Within the transmission system, Igus xiros bearings are used to ensure smooth rotation of the propeller and crankshafts where they pass through the outer walls of the gearbox. “The beauty of the xiros bearings from Igus is that they are plastic, and a plastic bearing does not corrode underwater,” explained Caroline. “This is really useful for extending the life of the systems we make.”
There are also tight restrictions on the lubricants and oils that can be used on the submarine during the race to remove the risk of contaminating the water in the competition tank. “The fact that the xiros bearings are lubrication-free makes them even more applicable for our submarine application and is what sets them apart from other bearings on the market,” said Caroline.
As for the other parts of the submarine – the new submarine shell is designed by Hull Team Leader, Euan French. Over the last few months, he has been running CFD calculations on potential hull designs to ensure that the new shape optimises the trade-off between drag and space for the pilot. It is currently undergoing fibreglass lay-up and, once ready, work on installing the control surfaces and the transmission system will commence.