Direct drive outrunner with direct water cooling


Has anyone tried this ??

3200W is probably a little low considering Alien ahs a tendency to overstate specs, but looks like he made an outrunner motor inside a waterproof case that could be perfect for eFoils.


I don‘t see how this motor is cooled, otherwise a 7Nm motor for 120£ is good.


I am tempted to try this one. But I am very sceptical how the cooling is supposed to work. Maybe they put an outrunner inside and filled it with oil? That is my only explanation. I doubt they could build an inrunner at those specs and dimensions. If it is oil filled, we could let the oil run up and down the mast for additional cooling. My mast has two empty chanels inside. We could also elongate the motor tube for more cooling.


Hard to tell how this should work regarding the cooling and also the sealing. Material exchange is the most effective way of cooling, recirculating a gas is uncommon. On the other hand i see a niche for these encapsulated motors, as they are unique and for a minute they will last, maybe also 5 minutes is possible. You should have some temperature recognition. By measuring resistance of the windings or by a dedicated sensor within or nearby the winding or by a model. The magnets strength can suffer starting at 80-100°C.
These motor manufacturers come from the RC world, where air models are so overpowered you can believe a 1 minute full power sequence is always followed by an empty battery. You have the motor cooled by the downstream of the prop. With cooling the windings by water directly i contribute to the situation. The motor is under water, so how can i make the mass exchange to transfer heat so i can get 4kW from 1kg motor mass producing 30kg thrust at standstill? Where is your interface which has high thermal resistance? Eliminate it to get higher duration current capability and higher torque.
All these modern motors are made of high quality materials, available since decades, but now at affordable price. I built some motors for electric vehicle before using cheap base materials from automotive 850W blowers, there is a difference in material and design.
If you have new or better or other solutions to get the heat out of the windings, please let us know here.
I am trying to optimize it (to my feeled needs) in this thread with the help of you all, and even if i am not answering directly often, i read your posts and think over them. Thanks


So here are some updates of my direct drive direct cool build:

Find the innovation!

I found a way to balance this prop together with motor:
I use a single ball bearing without thightenings, removed the grease with ethanol, oiled it again to make it run a smooth as possible. I am lucky i can support the motorpropspinner in its center of gravity. I use an original motor hub for this and put a single very long M4 screw into the back plate and clamp this in a bench vice.
Beneath this stands a bench grinder with some inbalance. If i run it, the motorpropspinner will start to vibrate slightly and move the balls in the bearing, diminuishing the friction in the bearing and the motor will swing in like a pendulum. You can add or substract weight. Time consuming and in the end its not perfect, at least its much better.

How to get a good and effective propeller

So I guess it would be wise to have the cables submerged in water too. I am designing a similar motor pod but with water flowing through the nose cone. Not sure if the mast attachment is the best idea anyway. Pacificmeister did a prototype where it gets attached to the fuselage. Why not mou t it right in front of the front wing?


The red parts turn, the others not. I made this cutout in the fin to get a good design, where everything is intersecting saving a lot of space and at the same time providing support, some degree of protection for/from the prop, and a low drag. Flipping the motor into forward direction could work as well if you want to underride patent but has some drawbacks as you loose the mast as a part of protection. I think this design can be adapted to foil and mast easily. Make a longer nose cone so the cutout in the mast gets small or vanishes, put a prolonged tunnel over it.
One could also integrate the foil, mast, part of fuselage, motor holder and motor into one part, to come over the simplistic approach of modules.
Development could also end up with lots of modules stacked at the mast, like Doppeldecker foil surrounding the motor(s).
Who knows. For the moment i have this design, lets see what it can do. The old one is also in good shape, i can compare them maybe.
I plan to test in Hyeres starting end of month.

P.S. Did you find the innovation visible in the two pictures?


P.S. Did you find the innovation visible in the two pictures?

Not really.


We have three ball bearings, one at the hub and two towards the end. Between them is a cavity where the axle rotates. By sealing the single ball bearing at the hub this cavity has only one inlet left through the double bearing. I added a grease fitting, a pipe and a sealing with an o-ring to be able to maintain the ball bearings when i use them in salt water.
Next step would be to put a real sealing over the double ball bearing (which are semi-sealed, 2RS Stainless).


thought yall would like this video…


Funny Video!
I fixed my nano-x remote, one issue was with the crystal, and the second with the On/Off switch of the transmitter.

I resoldered the crystal, that helped a lot, but still it was not reliable enough, sometimes loosing the binding when i only touched the switch or just shake the transmitter. So i swapped the switch, now it works well.

We already had discussions about a kind of cruise control, with analog or digital throttle in combination with a dead man switch on the remote, which you need to hold while cruising.
I do not know why, but i somehow ignored benjamins videos too long. So the solution for these features is already ready! Have a look:

Nunchuk VESC control:

I will definitely upgrade to wireless Nyko Kama nunchuk which is widely used for the nintendo wii and in the ESK8 scene. Note, you can only use it with the VESC, which has a special input and code for the receiver.


That video of underwater Iron Man would have some great information if there was anything posted. They solved the waterproof remote issue, direct drive issue, waterproofed the battery box, seem to have the correct size propellers for the motor, and have proper protection from the prop. They mentioned they used it for about 4 hours before having to recharge. Seems like they solved most of our issues. Anyone know these guys?


They are using a 120mm 4 blade EDF that hobbyking used to sell. Unfortunately it is no longer made


Hi @powerglider. Did you have a chance to test your new setup? Thrust and speed? Will appreciate your feedback on the alien 100kv motor (powerglider motor).

What is the fin type you have used?

Many thanks!


Hi there,
yes i tested it for some minutes until the battery box became untight because of a mechanical overload to the cable. As it was in choppy sea with strong wind it is hard to judge it.

I was not able to glide permanently, the maximum power consumption from battery was 1800W. I think the new design was overshooting, by reducing both the diameter and the Kv. Maybe i can test tomorrow in calm water to get reproducible results and compare the old and the new motor/prop setup. Too early to make conclusions, fine tuning might be necessary.:thinking:

The fin is made from high quality glass fiber, US/standard fin box. You can find high quality easily today, because a lot of windsurfers have grown old and sell their old but high quality equipment for peanuts.


Great! Thanks for such a prompt update!

Sounds like there is a room for bigger prop to get more power from the system ( unless it just became more efficient comparing to the old setup). Interesting to know the speed of the board, can you measure it next time? (Can be done with smart phone, taken with you to the ride).

Good luck and awaiting for new updates


Maybe i should try outlet vanes.

What you think?


As outlet vane? Since intake is kinda done by your fin and prop closure supporters.


Here are some more pictures of the ducted prop 140mm inner diameter


Propellers and Ducts

Can someone recommend an app for android for recording the GPS data with high resolution? Is GPSlogger a good solution?