For who try/have tried direct drive with outrunner


Awesome results there! The board looks perfect for testing, i.e a nice stable platform to balance on before getting up to speed. Is this DIY?


Yes, a DIY board. Not sleek, and it was pretty heavy, but as you noted it made for a very stable launch platform. It has been retired. I found a windsurf board that is now being modified for my next version efoil.


Thanks.I think I will go the route of modifying a windsurf board also. Need to research glassing techniques…


Bravo! Maybe you could use a prop with lower pitch and then apply more voltage. I think, your prop has higher pitch than mine, and the kv of your motor is also higher. Amazing, that it lifts already at such low speed.


Great work and videos!
Im about to test some new motors and custom designed props specifilaly for efoiling setup and speed in my testing pool… exciting times!


I was thinking about this the other day and I also saw it posted on another thread somewhere, but why not use two outrunners driven by two ESCs? Have them mounted on top of each other? Wouldn’t that definitely resolve the lack of torque issue of single outrunners?


Running two motors, two ESC, more battery packs… sounds like a ton of potential issues and extra costs. It would likely work, but it’s also a ton more work to build two units and run them together, don’t you think?


Well, I come from the e skate world, where dual motor setups are quite the normal.

In theory yes, it would be more complicated. You’d need double the ESC, and you’d need to have a good enough battery bank to ensure proper C rating discharge.

In theory, the motors would be splitting the load and overall would be less stressful on the system while only using slightly more wh.

3d printed parts are easy to make and design, and also outrunner motors running in open water is a simple design.


I’m not sure if this has been covered:

The stator and rotor can all be corrected with epoxy, bearings replaced with ceramic and stainless, etc… but the shaft? How do you treat that block of carbon steel?

Are you guys just taking standard outrunners rotors? Or are you removing the magnets and putting them in a new rotor assembly with a stainless shaft or something?

Do we even need shafts? Wouldn’t a balanced load be held in place and just rotate? has anyone tried this?


I thought I should point out that I do not think it is wise to plan on running any electric motor in open water (especially higher voltage motors). The huge risk here is the degradation of the insulation materials and the increased leakage currents of the windings. Motors off the assembly line can have up to 3.5mA of leakage current total to be considered safe for consumer products. I have personally performed tests on stators submerged in saltwater and saw appreciable increases in the leakage current due to the fact that saltwater is a great conductor and even acts as a capacitor in the circuit. It only takes around 30mA of current to cause bodily harm and this risk is not worth taking. Beyond the health effects, open water operation of electric motors will lead to premature failures of the insulation materials and the motor itself. If you intend to run water into the electric motor than you should take steps to properly pot the windings and laminations, otherwise a waterproof enclosure should be built for the motor to run dry.


yeah I’m with ya there. which is why I’m building an inrunner setup :stuck_out_tongue:


Hello Vincent
i have the same wing from a aquaskipper,does it work correctly?
If yes i can do test with different size



I dont know u have some trouble with my motor and haven’t tested it yet!


ok thanks for your answer
merry christmas


I sent an email to alienpowersystem, they told me that their 80mm outrunners are waterproof and can be used under water :

So we can use outrunners underwater ? No need to add more epoxy resin or anything right ?


Read his mail carefully. Motors copper is always insulated, otherwise it will not work at all. However, the mechanical forces on the windings will be higher Underwater, so it is a good idea to fix them with epoxy or other resin. Otherwise the isolation will suffer from mechanical friction.

He states: Connections have to be out of the water. As there is normally a solder interface between copper stranded winding being isolated individually to flexible wires gathered together in one single isolation, this interface needs to be protected. Normally it is a cheap piece of heat shrink without a special thightening. Sometimes this interface is outside of the motor, sometimes it is between aluminium hub and stator iron, unreachable without disassembling of the motor. As the iron stator is usually glued to the hub, this can be a problem. You need to make it watertight. e.g. by using epoxy or other material.

Waterproof has a lot of meanings and is not a norm. Sometimes it means you can use it in the rain for some time. Insist on IP numbers, like IP68 while it is running under full load. The 8 means it is protected against permanent full submersion. 7 means it is protected for 30 minutes against full submersion.


I did run a 80mm Alien and an 80 mm Suppo under water with no problem. With the Suppo I changed to titanium shaft and ceramic bearing. The Alien I did not do anything so the bearings did get rough after a while.
I believe the copper windings continue out to the connectors without any joint in the motor. The problem is that the motor is very heavy to run in the water, it used 30A without propeller. I can not garantee that it is safe to run the motor like this in the long run since I do not know what kind of voltage spikes comes from the esc even if the battery is only 50V… .


One more thing: That the motor is not suffering from water does not mean, that you are protected against electric shock. Risk is a function of voltage and salinity of the water. If you have the risk that there is a connection of a motor phase to the water, you must have additional measures to protect against electrical shock, e.g. a completely isolated housing for the batteries and ESC and cables with no electrical connections to the ambient. To run electric current through your body you need two poles. If these two poles are inside the motor it will only harm the motor, not you. But if you touch a part on your battery enclosure with a linkage to battery + or - or a 5V or what else derived from the battery, while standing in the water and having a leakage from the motor phases, this could kill you.
This is also a risk in case of accidential damages of your
motor leads,
rotating or stillstanding thightenings,
battery or ESC case,
tightened plugs,
sensor cables and sensors, even hall sensors,

The problems arising from these requirements are hard to fulfill at any time under all circumstances.
With voltages below an unknown value (i have searched a lot for internet information, but did not find any recommendations) the risk is neglectible, you might feel something strange in your finger. At this event i stopped testing and got things done better. But the risk is evident, that the current could rise and harm you deadly. Especially if some mechanical breakdown occurs.

So the standard rule is: Protect anything metal (and carbon) and all cavities and build an isolation around all electrical parts. By this at least you will keep the leakage mechanically small and thereby the electric resistance high. A small crack or hole in some coating has a different resistance than a tinned wire hanging loose in salt water. If salt water enters the motor compartment and get contact to e.g. flexible cables, there is also a contact to the inner aluminium wall, of the mast or the fin box, any plug and cable needs to be tightened.

An additional measure could be a detection system which can measure the leakage, but for this, you have to install some anode into the sea water, connected with very high resistance to the battery. But i guess, that a simple reading of the voltage over the high resistance could deliver a lot of positive false results. So there is needed some intelligence, some considerations and before all that testing.


Tighten the head of the rotor. Make a round cap of plastic. Test it, than drive small holes in the outer diameter and test again.


See my response above -

Motor windings are insulated with a varnish, but during the winding process this finish is always being scratched. The scratches will result in increased leakage current and/or phase to phase shorts.