The brass rod 1/4in is a means to an end, I could only find 1 supplier in the world of straight out servo couplers and that was in the USA and that was 1/4in hence imperial measurement. straight out servo meant I could use the servo to control the speed of door opening and close doors before returning the boat, as 2 doors open in the water cause extra drag, and extra steering, +tube could slip onto the m3 bolts at the front already there. the problem with this design is a 1/4 hole in the hull that has the tube going through and it need to spin half a turn, how can it be sealed ?, Hence why i said any ideas on electro magnets .I've tried posting piccys but I`m getting you must post 10 before you can, just type in Angling technics microcat and you will see many, Also I have changed to Lipo already but as I've stated if you see any piccys its so rear heavy and batterys seat in the middle.