Slow build from Italy + Avoid my mistakes!

I want to open a discussion about my not straightforward journey, maybe someone in a similar situation can find this useful also i didn’t find a discussion like that in the forum, Enjoy!

My build is a work in progress, if I’m doing something wrong or if you want to know more about something let me know, i’m more than happy to provide more details (or help), I would also advise new builders like me that even if you have some knowledge, some things may not go as planned (will see later why ahahaha).
After some time i finally decided to build my efoil board. Since I am a student my main goal is to keep it as low-cost as possible. I would start by saying that I have some EE background so for me some choices were simpler and more cost-effective than others.


  • Board: Used Tribord surf ~30€
  • Foil: Aztron Rocket 1450 ~250€
  • Motor: Aliexpress sensorless 6384 ~65€
  • Inverter: Cheap FOCer 2 ~50€ (1 board)
  • Battery: (not yet sure) 12S5P INR21700-M50LT (~1kW/h) ~200€ (only cells)
  • Controller/Remote: Custom PCB that manages throttle input + some extra features
  • Misc: Wiring, Connector, Sealant, Resin… ~200€

Now, let’s discuss more about my gained knowledge, thoughts, and future modifications to my build.

Foil/Board: Since I’m pretty lightweight (~60kg) almost any foil and board combination will work (I guess?). I read around that too much surface area is not very good for lightweight riders like me however until now I have zero experience in the water.

Inverter: Pretty simple, it is a Vesc 6 based inverter until now in my test I had no problem, judging by the power components choice I think that with minimal heatsink will drive the 4kw peak motor without problems.

Motor: Ahh that went bad… Let’s start by saying that in the beginning, I was undecided whether to choose the 6384 or the “waterproof” 7070 by Flipsky. The 7070 motors should be in theory already waterproof however even without a prop it costs more than double the 6384 (~150€), by searching on the forum I found a guy’s post showing signs of rust in his motor, also props choice seems not existent. The 6384 on the other end was cheap, pretty well tested, good prop selection, the only downside was the waterproofing part.
If the waterproof part was still a problem in the 7070 motor why spend more than double for a motor that still needs waterproofing? So, I bought this 6384 sensorless motor from Aliexpress, around 65€ shipped, works pretty well when arrived, the problem began in the waterproofing part. Not as simple as I imagined… After I fully disassembled I saw PowerGlider post however, since I had neither a vacuum pump nor a fridge compressor I decided to use a simple paintbrush to coat the stator. I masked the critical part, mixed the epoxy, and covered the stator and the outer rotor with a thick layer. After the epoxy is cured the problem starts, when free to move the phase wire moves in a way so the backplate can be fully inserted, when fixed in place by the epoxy however they become rigid making insertion impossible. At this point, I tried to gently break the epoxy that held in place the phase cable without success. The stator is now immersed in a solvent to dissolve the epoxy (polyurethane resin), this can damage the lacquer in the phase wire. At this point, the main solutions are: to buy a new 6384 motor and find another way to epoxy it without special equipment or rewind the stator that i currently have with the same winding configuration. Until now I think that I will try to rewind it, maybe in a star configuration (should archive less speed but higher torque) however if I find a way to epoxy it in a cleaner way that does not involve complex machinery (vacuum pump, lathe, cnc ecc) or fully disassembly of the motor I prefer to start with a new ones.

Battery: Sizing an accumulator, especially in larger projects, is always the critical part of the project. Incorrect sizing could cause powertrain malfunctions and in the worst case could put people’s safety at risk. Personally, it is not the first time that I have designed an accumulator so I am already aware of the basic rules. On the internet (even in the forum), I find a lot of designs made of high discharge rate cells. Some of them are made up of 10 or 12 parallel cells capable of delivering 35 amps, which causes the battery to weigh like 7kg and cost around 700 to 1000€ which is a lot for a 1.5kW/h accumulator, also, does a 4oooW peak motor really need 240A continuously? I think not ahahaha.
I was keeping an eye out for these INR21700-M50LT cells. I read in some forums that this exact model caused some fire around the world, however, i think that was mainly caused by bad design. In the future, I will maybe order some of these cells to perform further analysis to see if they are safe for this application or not. In the meantime, i will not suggest anyone build this design.

I have 3 7070 waterproof motor, litlle rust on one rotor (but still working well after corrsion X application), but if you remove the rotor and use corrosion X after each session , it’s ok, finally not such a bad choice, I don’t regret it, plenty of power.

If you buy the 7070 at the right moment on Ali, you can buy one for 112 €, good deal

Uh, thanks for the suggestion, i will keep an eye on that too. In the meantime just for the sake of the experiment, i was thinking to try rewind my motor with ultra-thin FEP/PFA wire, if it works should in theory remove the need for coating.

Why would it remove the need for coating?

Well maybe I explained myself wrong, the iron part of the stator and the outer magnets should in every case be coated in order to prevent rust, however, speaking only for the windings, if we compare polyurethane with FEP for example, we can see that FEP have higher dielectric strength and also lower dielectric constant, this will overall result in lower leakage current and less interwindings parasitic capacitance, also generally fluoropolymer like FEP have better mechanical specs, normal PU coated wire can be easily scratched even by very small rock, so in the long term this may result in isolation loss. It’s worth saying that these are small details which however can make the difference and especially if the price difference is not exaggerated in my opinion it’s worth a try.

Small afterthought: for a three-phase motor which, as in this case, works at low voltage, perhaps the parasitic capacitance between the phase windings is negligible I’m not an expert on electric motors, if anyone knows more I’m very curious to hear their opinion on it

parasitic capacitance? insulation types won’t make any difference in these motors and the potting of the winding is mostly to fixate the wires from getting damaged by turbulent water inside the motor bell. I’ve had two outrunners that was potted die from minor shorts due to erosion - winding needs to be potted/fixated with winding varnish or a thin layer of epoxy.

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I didn’t know that, I thought it was just an isolation issue, thanks