For who try/have tried direct drive with outrunner


i have one with 80 kv, and it was working well on my prototype… but i don’t have much data to support that , and i guess it just impacts the prop choice…:slight_smile:
Where are you getting your replacement bearing from?
What type are you using?
Ceramic doesn’t seem to be an option, and even if it was i’m not sure they could take the axial load.
Stainless steel seems to be the next best option, but I’m still hesitating between:

  • completely open greased with CorrosionX regularly
  • completely sealed but i’m afraid if water gets in…


I think it would be interesting if we could compare our direct drives @Mat I’m successfully using two 6364 motors which are 190KV. It works well the longest continuous ride I’ve had so far is 13 mins, i should be able to go 20 mins per charge but i had to stop it was getting dark…

I pull a peak of 160 amps so over 7500W and this is to get up I assume and over the course of the ride the average current is 2800 watts so roughly 60 amps average current, and this is cruising at roughly 25KPH. I need to adjust the prop design I think I aim to get it down to 2000W to cruise.

Do you have any data on yours?


not yet, but it’s getting close…
My prototype was without cooling just to check if the overall idea works… and i got absolutely no data from it except: it flies! :slight_smile:

i’m currently finalizing the new board and designing a new remote… one or 2 month away from getting back to the water…


It’s going to be awesome when it’s done! The pictures you posted of it look amazing it’s a sweet looking paint job and electronics enclosures.

The thing I like about these setups is there will never be a drivetrain related issue!

How much flight time do you expect from your 16ah 12s?


i have no idea… 20 minutes would be a good start… (that would be a 2 kw average…)
i planned the battery bay to be able to double the number of batteries if needed :slight_smile:


I think you could certainly get 20 mins with your setup, with the larger prop it should be more efficient than mine which has small props.

Do you know the bearing dimensions of the 80100 motor?


when you disassemble, you can read the size on the flange of the bearings, they are standard 68xx sizes,
the shaft is 12mm, so the 3 small ones are likely to be 6801 (12mm ID, 21mm OD)
and if i remember correctly, the big ones are: 6809 (45mm ID, 58mm OD)
but double check the marking/dimensions to be sure :slight_smile:

you can find them in a lot of different materials, but i would stay away from ceramic as 1: they are hard to find and 2: they don’t look like the groove is deep enough to be able to handle the axial load anyway…

The ones i’m running now are:

and i have a set of those in case things go wrong with the open design:

80100 direct cooling

Thanks for that Mat! I didn’t know they had so many bearings. I’m going to buy a 80100 to compare efficiency to the smaller 63mm outrunner.


I have highlighted in several topics that the most efficient e-foil drive system is a jet propulsion. However, I have recently found that the most efficient drive system is the one that consists only of the engine and the propeller (preferably a propeller with an injury protection).

Every engineer here therefore did very well that he started developing a system that does not have a gearbox but has only of engine and propeller. The engine that has a rotating casing is probably the best solution for the propeller. However, stator coil cooling must be solved very well. Then this system is likely to spread all over the world.

Propulsion system, which consists only of engine and propeller, has the highest achievable efficiency - for example, it may have the highest acceleration or longest voyage (or a combination of them). The production of this system is the cheapest (the most expensive system is a jet propulsion), it has the longest life and the least maintenance. The propeller can be optimized for pull, cruise length or speed. The only downside is that the right propeller can not be bought anywhere. Propellers must therefore be designed in 3D CAD and be produced on a CNC. The propeller must be optimized for a particular engine.


it’s a good point - the centrifugal forces are quite high inside there


Give us a hint more, about ideal propeller. Anybody here designed and tried a few, some apparently works better than other, even made in proper plastic and finished with epoxy, but a photo, a drawing, some tips about prop design would be way more usefull to community than to declare that we need the perfect prop.


Well i am happy with my 40mm motor and my gearbox , sure we can make a direct drive setup but we are missing propeller and the motor size between 56mm and 100mm inrunner , Virus designed a direct drive with a 56mm motor that work , but for the moment i think this motor doesn’t have enough torque for a 30km/h application …


No one has proven that a jet drive is the most efficient solution. In fact its the complete opposite. It requires the highest amount of power for the slowest acceleration and slowest top speed! It has been proven time and time again in the marine environment that it is in fact the most inefficient (want proof, take any prop driven boat engine, change it to a jet and see what happens). However it is simply the safest option.

An outrunner is obviously going to have more torque than an inrunner and in some ways be a better solution, but in a marine environment it will have a much shorter lifespan as the bearings and other parts of the motor are exposed constantly. Therefore the cost will add up in the long run.

Alexandre has hit the nail on the head. What the efoil community needs is an inrunner (Is is easy to cool and keep out of the harsh marine environment) size that is somewhere between where the existing ones are. Something in the 70-80mm range would be ideal.

Prop wise, why don’t you show us some of your props you have designed and built and show us how they are working in their respective environments. I’m sure we’d all love to see it.


My bearings and outrunner are exposed to seawater and i did not even wash them after use. The salt crystals crumble out of the motor when i turn it by hand after 2 weeks of no use. Today i disassembled the prop and assembled it again, there are stains on the machined aluminium surfaces and the stainless screws needed some WD40 to make the first turn. Thats all.
The big advantage is: You do not need any sealing which can easily give up. I use three simple stainless bearings with covering discs and some standard grease inside the hub bearing tube.
My experience is: anodized aluminium, epoxy and stainless steel are good enough for such application.
I bet there is no sealing which can withstand these circumstances longer than the maintainance free stainless bearings.
I saw a system with magnetic coupling to overcome the sealing problem. Guess what it needs? Bearings running in salt water.


Propeller optimization is a lengthy and complicated process.

The propeller can be optimized only for the functional prototype of the vessel’s propulsion system. Prior to optimization, the prototype of the drive system, the torque and the maximum speed must be determined. The propeller is optimized for pull, speed or cruise length (or combinations thereof). For propeller optimization, it is also important to know whether the propeller prototype will be made of plastic or metal.

It is not wise to make this whole process only for one vessel and its prototype drive system.


I agree if we talk about mass production, but the spirit here is more into DIY and experiment a new way to cruise above water, so prototyping is what we mostly do.
Nevertheless, softwares and lot of thoughts went down behind any of the prop tested, no matter for the configuration.
Power, speed and given power for given speed, hence torque, have been determined, more or less by any fellow builder.
Would be great to do that step behind, have an example, a sort of inspiration for passionate amateur prop designers here!
Go deeper into this prop optimization topic, I’m sure it will be greatly appreciated by the Efoil community


I guess the next step in direct drive outrunner will be a smaller diameter than my 63mm 6384. It would be nice to have around 50mm, e.g.
with a half Kv and doubled torque.
With such smaller motor also the voltage is lower, so no harm for human beings.
Lets assume a prop mounted directly on the motor or on its end.
We get a hub diameter of 50mm, 2200W, 4Nm, ducted prop diameter around 130-150mm, travel speed 15-25km/h with maximum 1000W. Peak thrust 25-30kg, maybe higher electric input power for some seconds.
Shall we start a new thread about such configuration? Anyone interested? Prop design will be crucial.


very interested. Great idea! I like the way you think. I hope to post my entire build soon. Just working out the board and remote now. Everything else is working…(6384 direct drive)


I think a new thread would be good, the information will be easier to find, rather in one big thread.

Do you think a 50mm out runner could have enough torque? It is certainly worth investigating!


The engine diameter of 40 mm is too small and the gearbox increases only the acceleration. For this drive system, therefore, a simple propeller is sufficient. A highly efficient propeller is not required!