Hello Community 
I am new here and i am thinking about my own build for a while.
I am a mechanical engineering student in the first semester (after 5 years at a Higher Technical Institute for mechanical engineering) in Vienna. Maybe there are some people in or next to vienna for some real life tips?
I want to try a new build without buying a hydrofoil fin and mast. I think i can print the fins with my 3d printer and cover them with glass fiber. Maybe i will put a carbon fibre tube inside the fin to support it.
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What do you think about that? How many layers would be needed for enough strenght? Do you know good designs (with files (not .stl because i need to adjust the size for my 3D printer))? do you think its possible to cut the fin in parts and glue it together?
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Secondly I will use a aluminium profile ( Machifit 200-1000mm Black 2080 V-Slot Aluminum Profile Extrusion Frame for CNC Laser Engraving Machine, 3D Printers, Camera Sliders, Robotics, Furniture, Woodworking DIY and Much More Sale - Banggood USA-arrival notice-arrival notice ) as my mast. To get the right “mast” profile i would print a cover arround the cuboid profile. Do you think that will work? or do you think it would be better to buy an aluminium plate and adjust it with grinding and welding?
For the connection between fins and mast i would like to take a cuboid aluminium profile or this one ( Machifit 100-1000mm Black 2020 V-Slot Aluminum Profile Extrusion Frame for CNC Laser Engraving Machine, 3D Printers, Camera Sliders, Robotics, Furniture, Woodworking DIY and Much More Sale - Banggood USA ). I would also cover the profile to get a flat surface.
I want something strong enough for 20-30km/h. So i need a good motor and gear setup. What setup are you using? I tend to the SSS 56104 with a 5:1 gear and Seaking 130A-HV V3 ESC. My problem is i can’t find a good supplier for the gearbox. Where did you get your gearbox? Many people use the Reisenauer 5:1 Chief but the specs say it is just for 3000W, but the Motor have peaks much more than 3000W. Which parameters are important for the selection of the gearbox? How long last an overused gearbox with 18.000rpm instead of the allowed 5000/10.000rpm (20.000h lifetime by normal usage)
I also dont know how i will connect the motor and the gear. I have read many threads but I can’t find a detailed motor and gear (assembled) CAD-file, to find the best solution.
What do you think about this gear CP040 WITTENSTEIN alpha? It’s rpm is rated to 8000 rpm. do you think it will last for >100h?
For the power supply i would like to take one of these batteries (2 times for 12s):
what do you think about these batteries?
I hope somebody can help me.
thank you in advance
Alex