Ok so that at least 1 drawback of going 18S. Thank you for pointing it. So please don’t do this at home.
In my favor, with my setup with ESC + battery in the Pelican, battery voltage is never exposed externally. I never open the pelican at the beach. The BMS on/off is Bluetooth controlled. And even if there is a leak, I do not see how both battery terminals would be exposed through a single leak at 2 different external spots so that you could simultaneously touch both. But we never know.
I’ll practice handling the case with 1 hand only so that I’m never exposed to a voltage diff through my heart.
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Thanks for answering my questions. 
Interesting cooling approach. Keep us posted on how that works out over time.
The front fin makes sense to me from a Wingfoil perspective - especially during the learning phase in helping keep the board going straight until up on foil.
I’m not so sure I would want that “feature” while
Efoiling. My concern is with nose touching the water when you are up to speed. If the water is flat and you are going straight and have a touchdown it wouldn’t affect much. However If you are in big close interval chop and are on an angle to the wave having the nose “grab” rather than be “slippery” might get interesting😀
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Beginning at 50V it starts getting really dangerous. It is less dangerous when you are in saltwater.
Great work and congrats on finishing the build!
Would you be able to share your motor detection parameters? I also use a 65121 and would be curious how our motor parameters compare.
very cool. I plan to build a foil system for my fishing kayak using same motor. this will help a lot. Would be driving it with 48V golf cart battery.
I think I found the relevant parameters from the autocalibration from my VESC Tool phone app:
# Flipsky Inrunner Brushless DC 65121 Motor 130KV 3700W
Motor Resistance 36.1 mOhm
Motor Inductance 19.56 uH
Motor Flux Linkage 14.1 mWb
Current KP 0.0196
Current KI 36.10
Observer Gain 5.03
Tell me if I missed some other parameters.
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Hey,
Thanks for the detailed recipe.
I need it as assist only ( like foil frive) Do you think it is ok or maybe too strong?
Also do you think that soldering the batteries will hold? Cause i dont have equipment for spot welding.
It’s half the torque of its big brother 65161. So it’s not super strong and might work well for a foil assist setup. You can always add software limit if you need.
The real question is: isn’t this motor too heavy for a light foil assist system? Most people use outrunners for their foil assist.
Also do you think that soldering the batteries will hold?
I would not recommend soldering directly on the cells. On the positive side it can work fine, as the positive cap is thermally decoupled from the cell and quite easy to solver. But on the negative side, a lot of heat will be transferred within the cell. (damaging it, or worse…)
Just buy a spot welder, it’s super fun to use and once you have one, you’ll see plenty of opportunities to make your own battery pack for various projects 
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yannpom nice set up! I think I’m going to try and use the 65121 motor as well to save some weight. How much do you and your setup weigh? I’m trying to figure out if I should get the L or XL X-Over wing.
Here is my setup weight in details:
- Pelicase (battery + ESC + wire): 7.1kg
- Mast (75cm mast + motor + prop + cables + ratchet strap): 5.3kg
- Board (Lance FSP 105L): 7.5kg
- Wing + stab + fuselage: 2.9kg
22.8kg in total
9.4kg for the “electric add-on” (removing the mast’s weight: 7.1+5.3-2.0)
My weight is 71kg but I’ve had friend taking off weighting up to ~90 kg.
XL is great for beginning, slow and stable, but I’ve never tried my setup with a smaller wing area. 
Hi @yannpom ,
Nice build! 
Can you share STL of 3D print plate for cable exit from the mast to the back of the board?
Here it is: eFoil top plate for Gong Alu mast V2 by yannpom - Thingiverse
I put the STL + Fusion 360 file in case you want to modify it.
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Do you think you could finish this Gong V2 plate so it looks like the full model ?
Cross ref with @JvdZ prior work, Gong V2 plate only with holes (STEP format, Jul 2023) :
The model I uploaded on Thingiverse is top plate that goes above the aluminium top plate you are showing. It’s not a top plate to replace the aluminium one.
The goal is to pass the cables inside the mast. Then drill a hole in the original aluminium top plate. Then with the 3D printed plate I provided you can bend the cables backwards to make them exit at the rear.
So there is no point in “making it look the original aluminium” one because it was not my purpose
Thanks Yann, I understood this and I will use your plate for this purpose. However, for a current project, I just needed a complete dummy one (PLA) and I don’t master Fusion 360 …
Curious on why didnt you run the motor cables into the box since they are pretty long? Do you also mind sharing the propeller you used? I have the same motor, still using stock propeller
The prop is listed in the components: it’s a 3 blade Mantafoils Volt Propeller 150mm.
The cables are actually not long enough to reach the box. But here are some pros of using 3 bullets connectors:
- easier transportation as I can separate the mast/motor from the box
- only 1 cable going into the box => only 1 sealed nut
- I could upgrade with a second mast with higher mounted motor and reuse the same box
I wanted to see what happens with those connectors exposed to salted water, and I’m surprised it does not do much. The gold is still shinny after 6 months of weekly use.
How secure is this type of binding? Have you fallen off the board? How hard did you fall? Did the board stick its nose into the water? Did the binding work well?
It came loose 3 times already. But everytime it was when I was letting a friend try the board. So I guess falls were harder. I think the worst is a nose dives on your all four: it’s your body that will violently kick the box.
The box is also attached with its handle to the board, so even if it falls I won’t loose it.
Also note that the belt is going through the top mast plate, so it cannot espace neither in the front nor in the back.
After a hard fall I always check the belt. And after 10 minutes in the water I add a safety click to retighten it.
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Thanks for the detailed answer. I plan to attach my battery the same way.
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