For who try/have tried direct drive with outrunner


Thanks guys for your input. I’m gonna make the mounting plate aluminum, with the fuselage out of aluminum as well, then find a way to connect the fuselage to the printed mast pieces. It seems I under estimated how hot these motors run, last thing I would want to do is melt my entire propulsion unit. It’s nice to get some experienced help! Back to solidworks I go :grinning:


Maybe it is better to flip the design, so the mounting plate for the motor is near the seal and the prop. Of course you need to run the wires somewhere. Otherwise you might need a coupling and additional bearings for the seal, because the distance from mounting plate to the seal gets too large.


For inspiration let me share that outrunner design. You might have seen some of that in a video before. I tested it last September with a PLA case as mentioned above and it burned down the SK3 motor immediately. Like you suggest @PowerGlider, I have the outrunner mounting plate towards the back. Cable routing challenges lead me to this fuselage-attached design instead of the previous mast-mounted ones. It was very solid. For the test I just taped the cables to the fuselage and fed them through the existing hole in my mast. I still like the simplicity of this design, it’s only 2 printed parts (shell and threaded lid) plus the prop. It was watertight during my short test. Problem was the cooling, so it will need a re-design with parts that can be made in aluminum. Tempted to pick this up again some time… right now I am working on a belt drive though, need to stay focused :slight_smile:

Timing Belt Reduction

I went back to the drawing board, replaced the fuselage and mounting wall with aluminum. The holes seen in the printed pieces are just temporary place holders (there is no room to screw on any nuts and bolts!) until I figure out a way to connect the fuselage and mast/shaft pieces together.


Looks a lot like what I am trying. I have not modeled the parts forward of the motor yet. I black aft motor cap has 2 seals back to back, and 1 bearing.


I am letting it sit at about 3 foot deep under water for a day or so looking for leaks.


Hi @pacificmeister. Thanks for sharing the info about the SK3. I’ve also purchased this one SK3 6374, 149Kv. Can you please reply to this questions below:

  1. What was your SK3 KV - also 149 or higher?
  2. Is it 12S setup?
  3. Do you have any feeling about amps in full throttle?
  4. In those 30sec of running, did you feel enough power to take off?


out of curiosity, how are you connecting your aluminum fuselage to your printed pieces? It looks like just adhesive?


Hi @Antonbit
1 - yes, same 149kv version
2 - yes
3 - Unfortunately I wasn’t able to log or read anything.
4 - It felt quite powerful but died before I picked up enough speed. Hard to say. Could work with the right prop, wing, board and a not too heavy rider.


At this point it is just a very tight fit, no adhesive. I had to press the parts together with probably 80 pounds of force. I can’t pull them apart. I will probably eventually secure the ends with a few tapered screws.
I can get it apart by applying compressed air to the oil fill screw that is built into the black printed part. That cause the ends to pop off.
I took it out of the water tank today. No leaks!!!


If you can apply compressed air, then you can use a slightly modified radiator testing gauge to determine the sealing.


Then what would I do with that giant test tank I built?


i am using this sk3 149 on my e-skate, nice motor, running on 4S , i recall may be 50A uphill with my 100KG :slight_smile: , rpm drop fast and bad efficency (70% if i remember right) , it is powerful enough for an e-skate, for an e-foil may be, but i has to be mounted with a thrust bearing, the motor bend with just the tension of the belt drive


i use this:

to test my engine builds


Hi @pacificmeister please share your design files I will try to adapt it to my motor and props.


@Antonbit, here it is Let us know how it goes. Good luck!


sorry for digging a pretty old post…
i finally tried to run a 80100 wet… and i’m getting in the same 100w range in air, and 1kw+ in water. without prop attached…
the water was jumping all over :slight_smile:

in the end, did you found out if it was expected?
and any way to mitigate the water “friction” and lower that unloaded power?

i’m planning on trying to block some of the opening… only thing i can think of to help…


Would be interesting to know how hot it got at 1kW despite being in water.



That test taught me two important things:

  1. The motor spinning in water will pump the water very effectively and waste way too much power.
  2. Minimize all wetted rotating surfaces. Do not spin anything in water other than the propeller. Even a propeller integrated into a spinning tail cone is a bad idea in terms of energy wasted.


it didn’t run for long… there was water everywhere my bathroom :slight_smile: but it stayed completely cool, the energy went into spraying my bathroom…
issue is that i sprayed the motor with Corrosion X before … and i might have put too much, so now my bathroom won’t corrode either…