In the esk8 world, the capability of those 4.20 to sustain a 50A output is entirely dependent on ability to dissipate heat. Typically, when in an enclosure, 25-35A over 10s and heat starts to creep in big time. If you can manage some efficient cooling to keep the ESC under 65C, then it will run well. If it gets too hot, it’ll self destruct pretty quickly.
I’ve never had one self destruct, When my ones get hot the board is just speed limited until it’s cool enough to run at full power again.
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Jezza, thanks for confirming the thermal throttling on the 4.20.
Using a higher voltage battery (10s) and low kV motor would reduce the current, giving the VESC an easier time. The 6374 is produced in a 60kV winding by APS. We’re after slow speeds with a foil assist, so a low kV motor could be preferable?
I’d like to see how optimized the prop can be for this purpose, because battery life will be at a premium. With a low speed target for this purpose, and being able to mount the motor higher up the mast, would a higher aspect propellor work more efficiently?
This old thread suggested that a 10" RC prop was efficient at low speeds, but all the efoilers seem to be after high speed. Home Made Flume - #55 by Winging_it
Perhaps a folding RC prop would work, eg. TBS 10″ Folding Prop Set - KiwiQuads
On a related note of efficiency, the propellor hub on the f.d.a. doesn’t look ideal, with a massive step from the motor body into the propellor - it must cause plenty of turbulence over the inner half of the prop blades.
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You’re right, should have mentioned, “unless controlled by software”. Once in thermal throttling, it takes a fair bit of time to cool down. While on a skateboard, it’s ok to limp back home, it’s not really something that’s doable on a foil, below some level of power, you’re just staying bogged down. But, maybe there’s more potential for active cooling in a water environment, to keep that ESC fresh under a continuous 50A load…
My point is that your parts should be a bit overspec’ed so that you don’t always run on the edge of failure.
Is there an inexpensive, small esc that will have more headroom?
Running 10s, I would think 10-30A will be the working range, if you’re not trying to continuously foil (eg. efoil).
It could well be enough power in which case, the 4.12 or 4.20 would be adequate, but I was under the impression that there was more power required than on land. Being on the heavy side, I was definitely planning to use something beefier in my aquatic contraptions.
I got a couple of those : https://tomiboiesk8.com/esc-based-on-vesc-6/
I think they are somewhat related to the MakerX ESC.
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Awesome project guys! I’m looking at doing the same thing. Has anyone had success with a 6374 / 6384 running in water and paired fairly well with a prop? Keen as to see what other people have done.
Has anyone built a lightweight battery using 18650 cells for this project yet?? I’m thinking of a 24cell 6S4P pack. Keen to see what others are doing.
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!
IMG_20210609_182213_750|690x388
You need Prop with 170 - 200mm diameter an 6-8zoll pitch
By 6s lipo an 30-35A
ESC 150A flycolor
Greetings Frank
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Regarding the ESC 150A flycolor( I hav 3 of those:)) , did You add a capacitor pack to them or do you run them “as is” water cooled?
Without water cooling
Startpower 80 A
Foiling 32A
OK, and no added capacitor pack? 32amp on 6S is pretty amazing! You are one of the few running a 2 blade prop i guess.
Without capacitor pack… I used short wires.
2 blade Prop have a better ETA, higher rpm and smaller current.
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Thanks Frank! I see the motor is 120kV in one of those shots… can you share where you got the motor from? And man those stats are impressive. That would be 800W foiling… Any chance you can elaborate on the prop you are using to get that efficiency (or is it a secret 
). Custom prop I assume.
Outrunner is from Ebay
High Aspekt wing
Caprinha Mast (15mm)
Light board
2x 6s Lipos 12Ah for good 35min ride time
17kg complete
And a small driver (65kg)
The Prop ist 190mm, and 7,5zoll Pitch, designed from enzymfax here in this forum.
Is not a secret 
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Awesome. I’m a similar weight so a similar setup should work well.
Couldn’t find the prop guy on the forum ( any chance you can add a link?).
How many hours do you think you’ve done on the build so far and is there anything you’d do differently?
First water testing today for my DIY foil assist motor. It’s taken around two months of sourcing parts and building everything. A big help from a few forum folk. Hopefully this is robust enough, time will tell.
The motor has enough power to get me up onto foil on a sup in flat water.
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Well done. That looks super professional.
Now how can I get my hands on your build list :)…
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Yes please a parts list! Would really love to see that connection from the phase wires into the control box. That would really help clean up my builds.
I’ve used a rubber sheathed wire for the motor.
Aristoflex 0.6/1kV. 2C + Earth in 2.5mm2.
This cable used in commercial electrical submersible pumps
Used a nylon cable gland through the box into the ESC.
All up it’s cost $1400 AUD (excluding 3D parts) The box I went for is the explorer 1908. This seem the right size to fit a 6S4P battery, ESC and cable connection into with a bit of wiggle room.
Still in early water testing stage so need more confidence it works without breaking before listing a BOM.
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