The Idea of the injection needles didn't work out, they were slower than we expected.
So we came up with a simple, new, but solid idea. This ballast-tank has 2 waterpumps. The one pumps water through the hose in the tank (right) the other sucks it out (left). We also made a hole on the top of the tank so that air can flow in the tank when the water flows out.
This causes the submarine to submerge (water pumped in) or surface (water pumped out).
