For who try/have tried direct drive with outrunner

I realy do like this your concept…
It seems to me that lack of power is not due to motor but due to impeller - it seems that not too much flow…
did you measure max amps while running this construction in water?

yes, 27amps while kneeling on it and full throttle

with 12c battery? then it is about 1,3 kwt -about half of max power for this motor…

I made some experience with outrunners 6374 and 6384 with 130kv from Alien. I used a 120A ESC, which blew the first motor. I use Epoxy 4 hour cure time in combination with a fridge compressor for processing vacuum to seal the stator. The rotor is hydro optimated. I use stainless bearings with ceramic balls and sealings.
With the 120A ESC i get good results when trying to glide on a F2 Stratos.
The problem is electrical windings end somewhere in the stator foot and its hard to get them electrically insulated fully. The original windings are interfaced there to 2mm^2 flexible wires. From there is another solder interface to single lead copper wires moulded into the fin. Tightened with Plastic70, a spray lacquer for insulation.
From the foot of the fin i have a flexible 3 phase 6mm^2 cable going over the rear of the board to the box seated on top in front of the driver.

Thank you so much for your feed back! Have you more pictures?

I have no fully understand if at the end, it has work or not.

Your first motor burn? Right? And what about the seconde one?

Can you tell us more about the type of propeller and battery?

Thank you

The second survived so far. The prop is the cheapest you can get, no name, 180mm diameter, i cut it down to around 160 on a lathe. The other parts are milled, 3D printing could also work. The first motor was hydrodynamical opimized, that was a failure.

Keep the epoxy coating thin. The seconds motor had more space between the windings, so cooling is much more effective. I run it in the mediterrainian sea, very salty.

The incomplete insulation at the interface makes it necessary to insulate anything else with IP68 or better, so there is no current through water where a person could be.

E.g. the so called safety switches have the problem, that they are not really insulated between inside contact and outside ambient, they only have a cheap and ineffective rubber cap, scrap. Tried to find a better one, talked to some experts, no positive feedback so far.
Battery box with BMS ZLA13, TF02N Shunt, Albright Relay, VESC-X and 32Ah 12s mounted in a frame.


Oh…so great. With so much battery you should drive a lot of time!

I have the following configuration, not yet tested!

Alien .otor 130kv 3.3kw
Alien esc 300amp water cooled
8s/20ah battery
Solas prop 160mm with 6"pitch
Foil: crazyfoil
Motor run in oil who is cooled by conduction

Can you tell me what do you think about my setting! It could work?
Thank you

I did not get it, which motor are you using?

Alien 6374 HEV Outrunner brushless motor 170KV 3300W

I’ve just started testing a Leopard 160kV motor with a Solas 7 1/4 x 6 prop. I went with a larger diameter motor to help cope with the torque required to turn this prop. At 36 Volts it pulled about 105 Amps static thrust. Soon I plan to test to see if the amps drop off quickly as the craft speeds up and the propeller unloads; I’m hoping it does.

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I am using this with sucess removed the sensor board. Travelling with estimated 12 or 15km/h using 2.4kW from Battery on windsurfboard without foil, velocity dropped after a minute or two, vesc stepped in by temperature degradation down to 1.2kW and held there for an hour. Sometimes pauses to cool down and have full thrust again. The box is not specially cooled and i have no plans to do so. Instead i plan to have the inner temperature rising 30°C above the surrounding temperature, which is normally rather cool at the water surface. By this i calculate up to 200-400W power dissipation through the walls of the battery box. Additionally i load the temperature capacity of the batteries by warming them up. When charging, i open the box and ventilate.

haha, strange concept, due to the fact i have a leakage at the motor and cannot accept any additional linkage from the box. And honestely i do not want to remove this leakage as it can only affect a small area, because all surroundings are plastic. Anyhow, how can i guarantee or prove, that the motor is electric insulated, and what do i do, when it is sending a warning always.

When you go testing, take it easy. Keep the Duty Cycle low, try not to overload, learn something before its broken and hang on, stay at site … Good luck :wink:


Hello! I’m a novice, and never had anything to do with the boards, and hydrofoils. Interesting is your experience, you write that you were walking at a speed of 12-15 km/h, is this the maximum speed for such an engine? Do you plan to use hydrofoil? Is it enough for a hydrofoil? I was interested in it is more powerful and the speed is closer to what is used in efoil’s with the reducer.

The drag is 60% higher with 80mm compared to 63mm. It would fit for a bigger prop, but that would add drag. Maybe it is suitable for higher weight.
The specs at alien are somehow weird. 6374 130kv says 10s max 80A max and 6384 130kv say 12s max 80A max which does not make sense to me, as a longer motor should have more copper to take more current and a shorter motor should be mechanically stiffer, allowing higher RPM. So its somehow contradictionary. Anyhow, the 6384 has a little more space between the windings, making it easier to cool. I estimate 100A phase current permanently for the 6384 if run underwater, so it has power up to 4.4kW.
At the moment i do not plan to use hydrofoil, maybe some hybrid integrated to the duct.
12-15km/h is not the maximum speed given by the motor and prop configuration, this was due to current limitation by the VESC-X.
For outrunners running underwater without reduction gear i recommend a controller with phase current limitation.
Maybe you find a configuration with a prop with less pitch, suited for 130kv and 44V, so you dont need phase current limitation.

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If you are going to attempt an out runner from alien I would suggest going with the water cooled version. The one you are looking at is for an airplane and gets cooled by the prop thrust !

Cheers, David.

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Those batteries are sexy haha! Where did you pick them up?

Maybe you misunderstood something, i have built a motor from an Alien 6384 outrunner which runs completely under water, so the windings are cooled extremely well. Swapped the bearings to stainless with ceramic balls and good sealings. Scroll up and read. Batteries are 6pc. High Capacity 4s 16Ah, 1.4kWh from HK.


Yeah I was misunderstood ha! Sounds awesome :slightly_smiling_face:

How much thrust did you get with this setup? Thats a big motor, do you have photos of your rig :slight_smile:

Have you tested this setup yet? I curious if a 3300w can turn a prop that size going direct drive.

For[quote=“VeFoil, post:27, topic:362”]
How much thrust did you

In order to have an efficient motor/prop system, I think either go with a smaller motor with a gearbox or, you go with a larger diameter motor to get more torque. I chose to go with a larger, direct-drive motor. My thinking was that with a nicely shaped enclosure of minimal wetted surface area, the drag would be comparable to a much longer smaller diameter enclosure required for a gearbox system.

I hope to have test data before long. I’m also thinking about buying the Alien C80100 50kV motor. Compared to the motor I’m using now, the Alien motor it is longer, heavier (almost twice) and lower kV. I’m hoping it will create more torque than the Leopard 8072 I am using at this time.

I am also intrigued by the magnetic gear reducer shared by someone else ( I can’t find the original post) in this forum. If it works as advertised it could make the small motor with a reducer more attractive to me.