80100 direct cooling

Finally yesterday was first test in water…

It’s still in a testing phase…
so i’m using a board i made for surf foil, the electronic is in a case, and the wires are running outside the mast… and duct-taped to the board.

the idea was to see if i could get away without water-cooling of the ESC… the ESC held up well, but got to 70+ degree celsius… so ill add the water-cooling in next version.

i still need to perfect the balance of the whole thing… flight is very unstable and the nose is pointing way too high, may be because of my custom huge wing 3d printed already posted somewhere on this forum … next test will be with the original foil fish front wing.

motor is 80-100 80 kv with the following modifications:

  • completely open stainless bearing, soaked in CorrosionX
  • titanium shaft shorter than original, much shorter.
  • space between magnets epoxied to get the inside of the rotor smooth
  • stator with a few layer of epoxy on the windings (no vacuum)
  • shorter leads with liquid tape on them and layers of adhesive shrink tubing
  • plate added on the spoke side of rotor to fill the gaps (it reduces a lot the hydro-something losses)

ESC is a 400A Boat ESC 16S … that’s why i was hoping no cooling would be ok. passive cooling with an aluminum plate might be enough, but adding a small pump will be safer… and it’s a boat ESC so it will be easy to connect to the cooling.

The propeller is a Solas 0001-073-06P, modified with a dremel to attache it with 2 screws

batteries are 2x Turnigy MultiStar 6S 16000mAh 10C .
i played for an hour, but not continuous use… and plenty energy left… next test i hope to learn more about autonomy

the case also contains:

  • 200A Amp Manual Reset Inline Circuit Breaker (it tripped mid way to the test, may be because of heat… i don’t think i reached 200A.
  • HTRC 200A High Precision Battery Checker Watt Meter And Power Analyzer HT-0011. Bad choice… it doesn’t keep memory once powered off and is unreadable when riding …
  • antispark is done with anti spark XT90 connectors.
  • W1209 12V -50-110°C Digital Thermostat. for now, it just monitors temperature, but i might use the switch function as a safety in the future.

I still need to open the case to turn the system on/off.

The remote is custom made arduino based with 315mhz modules.
acceleration is kind of smooth, the program on the receiver is limiting the ramp up. The ramp down is straight from the trigger position, but that’s not ideal… When things starts to go wrong, and i release the trigger, the motor just stops and the wipeout is assured.
the good point is that it doesn’t loose connection when you go quickly under water (i have a led on the receiver showing that connection is established) and it stayed dry inside!

first picture is the battery in the first position i tried:
i though, same as my center of gravity when i ride the foil without motor… big mistake, the motor changes everything …

this is the second position, muuuuuch better. but not far enough to the front i think…
the pads are where i have my feet when surf foiling, not adapted at all when using the motor…
and yes, the wires are not completely covered by the “wire covers” … i wanted to test and couldn’t wait for more to be printed :slight_smile:

The next steps will be to:

  • add a cooling pump,
  • route the wires inside the mast and add cooling line,
  • play with the angle of the back wing to try to level the board in flight
  • play with the box position to find the right balance
  • improve the remote programing. May be have a dead man switch on one side, and use the trigger to bring the power up or down slowly… still some thinking to do there…
  • build a new board to get rid of the box once balance is right. It will be shorter (i’ll aim around 6ft) and wider to be more stable when standing up. the thickness will come from the volume needed (i’ll aim around 80 liter)

Very nice, i am impressed. You integrated it in pragmatic and good way, congratulations.
Be careful with the electric in water, do not open lid.
Man its awesome! Thank you! This is a very good basis for further development. E.g. the output end of the motor/prop can be further optimized, streamlined.



first version was fancy and over-engineered… ended up an underpowered failure…
so this one is overpowered and oversimplified… it works much better.

by luck, there’s no way to open the box in the water because if the way i modified it to attach the straps… there’s no way to put your fingers behind the latch… you need a screwdriver :slight_smile:


Cool! I like that board, maybe in a few run you’ll find it just of the right size.
Can you post a photo and some details of your remote? The box in front of the board helps a lot in keeping the transmission steady, if receiver antenna goes underwater one inch… things get more unreliably.

the remote is based on arduino, and the 315mhz module i use allows it go through a couple feet of water :slight_smile:
i described it a lot a the beginning of the “waterproof remote thread”

it’s all 3d printed with no moving seals. ON/off is with a magnet (held by painter tape for now. and the trigger works with magnets in from od a hall effect sensor.

it’s powered by a 9v battery to increase transmitter power

and on that picture you can see the hall effect sensor that slides in the part that hold the trigger

now that i opened it, it might have taken a bit of water inside… but still working great :slight_smile:


2ft of water it’s a lot, would save me to move the antenna in front of the board, 2.4GHz can’t make it thru 2inches… I will check those modules

that’s the ones i’m using:
Seeedstudio 315MHz RF Low Cost Transmitter/Receiver Pair

You can put up to 12v to the transmitter to boost the signal.

For the antennas it was a lot of trial and error… and walking in the street outside my home to test range looking at a bunch of wires, batteries and blinking lights… i’m surprised the neighbors didn’t call the cops :slight_smile: .But there’s some documentation online.
With some more professional test equipment / or with the help of a “radio guy” i’m sure you could go deeper.

First iteration i tried reaching 3+ feet to have the receiver with the motor (and everything else attached to the fuselage) so i tried to push it as much as i can with custom antennas on both sides. Now that my receiver is back on the board, i reverted back to the original antenna on receiver side (the modules came with a coiled piece of wire attached that is smaller than my custom one) and a a custom one on the remote side, because it was already there since previous attempt, you can see the coiled copper wire on the pictures above.


I just ordered 315Mhz modules, I want to give a shot to your remote solution, seen the great results!

nice job! Must feel good to get it working. That’s what I want to do with direct cooling…no gear box. Great to see this type working.
Did you use the prop unmodified?..so 7.25" dia? Sounds big but I don’t know. I think you’ve done the hardest part…now its just working out the details. Oh, why did you go to a Ti shaft? Not sure I see the advantage.

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The Ti shaft is for better corrosion resistance, and the one i found online was exactly 10cm long… exactly the length of the housing, the original one is 21.5cm. I had only 2 modification to do:

  • make a circlip grove. i just put it in a drill press and “machined” the grove with a dremel and a cutting disk.
  • adjust the diameter to get a sliding fit with the bearings. i used the drill press, fine sand paper and frequent measurement.

overall easier than cutting the original shaft i think :slight_smile:

and yes, the blade of the prop are unmodified. i just sanded the motor side to have it sit flat on the motor, and cut the other side to get a flat surface where to make the hole to install the screws attaching to the motor. i was planning on installing 4, but 2 seem to be doing the job.

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Hi Mat, awesome build! What specific case do you have? I like the idea of just strapping on the box to the board for my first build.

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I’ll have to check the exact reference, but it depends on the size/numbers of your batteries, and all the electronic you have to put inside.
If you’re in the US, i found it at Fry’s. They have a lot of choice, Pelican brand , but also cheaper ones. Mine is a cheap one.
I modified it to get a transparent window at the top (it’s lexan from Home depot) that is screwed in threaded aluminum bar that are inside. I added some silicon in between before screwing it.
I also added some screws inside aluminum tube at all 4 corners where the straps are attached. That allows the straps to be routed under the case letting me opening it without unstrapping everything.
Finally cables are going through : “Waterproof Cable Connectors - 3mm 4mm 5mm 6mm 6.5mm max” cheap and plastic, with load of silicon added during installation.

Update with pictures:
attachment for the straps

alu bar to screw the window

reference/dimensions of the case

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What 80-100 80kv motor is that?

C80100 Outrunner brushless motor 80KV 7000W

I ordered the sensorless version, but as he had the sensored one in stock, that’s what i got.
Removing the sensors is straightfoward.

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Thank you, and it looks in your picture like you just have your motor out in the open?

Exactly. With a few modification explained in the first post.

From an efficiency standpoint, it’s not the best solution, too much rotating surface in contact with the water. And some more losses due to the water moving around the stator inside the motor.

On the cooling side, it’s perfect, during my test in the water, the motor didn’t even start to warm up.

The main point that drive my decision was that it’s as hard to do a simpler design: no moving seal, no shaft coupler, no housing, no added bearings (the motor bearings are deep groove and can easily take the axial load) I just replaced the metal sealed original bearings by some open ones to ease cleaning/lubrication.

The only unknown that worries me a bit is corrosion. I’m riding in a bay open to the gulf of mexico which is half salty and as soon as it’s more stable, i intend to go try it in the waves on the gulf side :slight_smile: for now i’m betting everything on urethane spray coating on all metallic surfaces and regular copious amount of corrosionX HD.


Hey Mat thanks for taking the time to post this!
A couple of Q’s.

1.) Is this the ESC you are using?

2.) Do you consider it to be overkill?
3.) “completely open stainless bearing, soaked in CorrosionX”. What mod is this exactly? Aren’t the bearings already exposed? Did you consider ceramic bearings instead?
4.) What batteries are you using?

Great work!

mine looks a bit different:

from what i see, it’s programmed differently, the one you show seem to have more caps… dimensions are also different.

i’m saying overkill because i’m pretty sure i’m not getting even close to 400A. and it barely got hot after playing close to full power for a while but with a lot of stop and go.
original idea was to make sure it will never blow up, and potentially not need any cooling… not so sure about the no cooling anymore…
i’ll do more trial this weekend, and i’ll hopefully do longer flights, continuous lower amps instead of intermittent high amps… i’ll see how it goes…

the original bearings has metallic seals on the side, the one i installed have no side protections at all. CorrosionX is a spray i put on to protect agains corrosion (even if they are supposed to be stainless :))

Ceramic bearing would be better from a corrosion point of view, but they are harder to find. Even stainless ones are not that easy to get, mine came from UK.
Also, they are radial bearing that need to handle a significant axial load, and i was afraid ceramic couldn’t take it, from what i saw the groove are shallower, reducing further the axial load they can take.

the batteries are: 2x Turnigy MultiStar 6S 16000mAh 10C in series, they didn’t got hot either :slight_smile:


You mentioned 80-100 80kv motor. Is this the one? What do you mean by 80-100?

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yes, that one… i got the sensored version but i ripped them off.