Submarine Build


#1

I wanted to make a propulsion system that can be attached and detached from my kitefoil board. The goal was to have everything just screw-on and no drilling, cutting etc. This is what I came up with:

The hull was made from aluminum in a workshop by my grandfather. I gave him some drawings and material. Here the CAD picture (the pipe is transparent):


The components were afterward welded and painted.
The motor is APS 6384N 100KV 4000W PowerGlider:


I was reading the thread in direct drive outrunners and was amazed by PowerGliders idea to epoxy the stator and rotor and have it submerged under water. First I tried a smaller motor just for testing this concept and it worked fine. The losses are noticeable but not dramatic. I bought the motor and added stainless bearings since the motor will be under water. I used very similar epoxy that is used for making epoxy tables.
http://www.samson-kamnik.si/en/vista---transparent-uv-stable-molding-resin

For the ESC I used AeroStar Advance 150A 12S.


I mounted it inside the motor mount and it had metal to metal contact with thermal paste for great cooling. The first ESC died for no reason one time I plugged in the battery… I didn’t have any problems with the second one and it worked great every time.

For the battery, I used 18650 Sony VTC6 cells and connected them in 12S4P. I got 48V and 12000mAh, so that means 576Wh. I know that many of you will say they don’t support enough current and you are right, they shouldn’t, but…
I welded them in a hexagonal shape, so they fit inside the pipe. I added two layers of shrink tube for structural integrity. Turns out it completely prevents cooling, so I cut some holes in the shrink tube (and it still overheats).

I designed the propeller with a help of a professional who is by the way in charge of the production of JetSurfs. He asked me about the motor specs and gave me the diameter and pitch.
Diameter=130mm
Pitch=180mm
Did I mention the part about JetSurfs? He gave me numbers for ‘‘sport’’ version without me knowing.
So I 3D printed it, filled the spinner with epoxy and reinforced it with carbon fiber. I made a small mistake when I was drawing holes for mounting to the motor. The holes are to close together and of course don’t fit… My grandfather made a chrome adapter, so now is just not so good looking but still functional. (Red propeller is just for looking and has no practical use)

One more thing. For control, I used quanum pistol, but it turns out 2,4GHz doesn’t work underwater. I added an antenna extension and I ran it from the hull through the mast and to the tip of the surfboard. At the beginning I had it only in the mast, but it didn’t work great.
Also, I took the remote apart and added some rubber bands on the trigger because at the beginning it didn’t give me the proper control. I suggest it to everyone with this remote.

So the tests… First thing I immediately realized that a small board presents quite an issue. You have to start lying down and then get on your knees. Getting on your feet is a major challenge. Then I noticed that sport propeller and lack of control in my remote gave me no control over the throttle. So it was pretty much full throttle all the time. One time I took my phone with me and measured the top speed of 40km/h. I also bought EagleTree sensors for current and voltage. At full throttle, the current was 110A (27,5A per cell) and the voltage had a massive drop from 50V to 40V. When I was going fast the current dropped to 80A. Pretty much all the tests were lasting for about 5mins before something overheated (usually battery to ESC or ESC to motor connections). Battery got to about 20% so maybe a minute or two more…
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Here I have some random photos:






Lessons to take:
-Bigger board
-Bigger battery and better cooling
-Motor with less KV
-Bigger cables between the battery, ESC and motor
-Prop with smaller pitch and bigger diameter
-Heavier trigger on remote


#2

This is fantastic build @drswitch. Thank you very much for sharing this info. Why do you think you need bigger motor diameter, did you feel that the torque of powerglider motor wasn’t enough? Can you please share the prop design?

What do you think about this motor below:


This 8072 motor has 70kv and twice of torque (13nm) comparing the 6384 motor.


#3

The motor size is fine, I ment bigger cables. The prop design is a little problematic. I have so many versions I don’t remember which one I used… I can share some photos. Also I will check my CAD files and let you know.


#4

Great build, congrats!

ok, than we should define a motor based on the winding scheme of the 6384PG 100Kv in combination with a 63100 motor to bring down the Kv to below 80Kv. It would have 30% higher ohmic resistance and almost the same current capability as the 6384 you use now. The weight increase by 10% is neglible. Some openings at the end bell and a drilling scheme like the 6384 would be good. Also it shall be available as DIY version without stator glued to hub so we can epoxy it easily.
More whishes?


#5

Awesome build! Congratulations!


#6

I just saw you are from Slovenia also?
Maybe we could hook up sometime and ride together.
I will probably finish my e-foil this month.


#7

What is the limitation of the 6384PG we are trying to address? It seems to be all @drswitch can handle. And, I just ordered 3 :face_with_monocle: The speed issue can be addressed by a lower pitch prop.


#8

It seems to accept 90A phase current maybe 100A when cooled by water. 15 minutes. But you need to have a close look up at the duct, the hub and the prop. This is for Vesc motor current setting in FOC mode.


#9

And why don’t we put more batteries in the large foil? Battery cooling looks to be the next issue to address. And if he is not going wide open all of the time then maybe the cooling issue isn’t as great.


#10

I edited the video and here it is!


#11

You got really nice riding skills! Congratulations! Its looking like that the 6374 100kv motor Is more than sufficient to ride at fast speeds.


#12

Wow! I did not expect that this small motor can push you around like that! Looks like you are riding in Bled?
Please keep us updated.


#13

Cool! Its really awesome that the board is so sleak without the electronics. Good work!


#14

This solution is nice and clean. Good work!


#15

very impressive but dude you are gonna lose a toe - please put a guard on that thing