For who try/have tried direct drive with outrunner


Thank you PowerGlider. I was really happy to see your response. It seemed like I was was getting more power out of the ESC than I was putting in. What you say really clears up some things I misunderstood. I am still trying to wrap my head around how each parameter effects the others. I will probably try to go with lower pitch smaller prop, and start reading about how to rewire to lower the KV on my out-runner.


Imagine 2 motors 56mm 100KVwith this setting :!-)


Been browsing this website for months in anticipation to building our hydrofoil. For simplicity’s sake we were planning on using a motor for direct drive in the hydrofoil and I picked out the Alien Power System c80100 130 kV 7kW. I am not worried about the amount of power it has, but more about the cooling aspect of it. Our initial plan is to use a snug aluminum tube to house the motor, and disperse the heat to the ocean environment. After reading through the forums and seeing all the water cooled and oil cooled set ups, I’m a tad worried about our methodology. Does anyone have any experience with this motor?


Similar discussion here, providing some solutions:
Direct drive outrunner with direct water cooling


you cant press an outrunner into an AL housing because the outer motor housing needs to spin with respect to the stator and the stator need to not spin with respect to the housing.

The whole outer bell rotates on an outrunner


Yikes, of course. I want to stick with either the c80100 130kv or one of the APS series posted in this thread. One of my goals of the build is to create a less complex propulsion unit. Just a few printed housing pieces, prop and motor. Less complicated. I would like to run the motor directly in the water and am leaning towards the APS 6384S, max power of 4kW. Since we are on a budget I want to be very confident in my purchase, any experience in running any of these motors directly in the water?


I bought an Alien 80100 50 kV motor. Just started flume testing, but so far it is performing very well. The plan is to optimize the prop for this motor as much as possible in the tank then later in the spring continue optimizing the prop in actual hydrofoil use.

The first test I did was for actual kV…actual kV is 65.

In the tests so far the motor “barely gets warm” at cruising thrust levels.


My plan is to mount my 83100 water cooled core motor inside a dry aluminum pipe. There is just enough clearance for the out-runner to spin inside the pipe. I already bought the pipe from McMaster Carr. The Pipe is 3.5" OD. I don’t know if the water cooled core is going to be good enough to keep the motor from burning up. I’m currently having more problem keeping my water cooled ESC cool. I have been testing the motor in my test tank. It has tons of power. If I step on it I see thrust over 100 pounds. Unfortunately it is going to burn up my ESC because of too much phase current. I have turned down my 7.25 X 6 Prop to a diameter of 5". That helped, but not nearly enough. I’m just not going to get there with the 180KV motor. I have disassembled the motor and I am in the process of learning to rewind it to a much lower KV.


If the water cooled core is not adequate I am also considering adding some kind of light oil inside the pipe to help with cooling.


I have some questions about rewinding my 83100 Out-runner. But first I need to bring who ever is interested up to speed. My plan was to carefully pull off each winding and document every wrap. Before I did anything I measured the max free running rpm = 8535 @ 45.53 Volts. So the KV =187.5 .
Removing the wire requires quite a bit of effort. The wraps were under each other and covered with a hard epoxy film. It was kind of a disaster. After I was done I weighed all the wire and calculated what must have been the number of winding on each pole. 12 poles, 14 magnets, The 3 phase wires that exit the motor contain 180 strands of magnet wire that measures 0.008 in. So the phase wires must each contain 90 strands because the phase ends are joined when they exit the motor. Delta winding. Each of those 90 strands are wrapped around the relevant 4 poles 4 times.


On the Alien website for the 80mm bldc out-runner motors,
it say WIRE WINDS: What does wire winds mean?



nice that c80100 50 kv is beast. Did you take any further steps to waterproof it, or are you still housing it with the aft pod like in your sketch a few months ago?


So the D means Delta winding.
Are you sure about:

180KV with 6D sounds like your motor…
Instead of pulling of the windings you could have just changed Delta to Star and get ~100KV.

How many KV is your goal?


I do recall seeing the sketch you speak of. That was not from me. Any how at this point I have not done the water proofing. I have done all my testing in the test tank I built. The motor has always been out side the tank. I installed a very long shaft in the motor so I could reach inside the tank with a 1 piece shaft. Progress has been slow.


I do think the D stands for Delta. But I don’t understand why the wire winds number does not consistently get bigger as the KV gets smaller. Maybe there are errors in the specs posted on the Alien web site.


The delta to star thing I figured out about 1 day too late. It would have been a little tricky because there are 180 wires running together in the same bundle all epoxied together. But I wish I had known, I would have tried.


KV I want? I don’t Know. 50 KV might be too low. The smallest off the shelf boat prop with the highest pitch I see available is 7.25 x 6.5. Not enough top end speed, unless I go with very high voltages. I may bring all the leads out of the motor when I rewind it so I can try star and delta configurations.


I’m planning on running the motor dry in the pod. The pod has an aluminum tube center section surrounding the motor to help with passive cooling. The gap between the motor and the aluminum is about 1/8 inch.

I bought the motor with a long shaft so I will not have to add a shaft extension. The tail cone of the pod will have a bearing and a mechanical seal.


I guess it is an error. If you take the 4D aside it would match the theory…
Still there are some other effects like the number of strands per wind decrease, because you can not just have more winds (which space should they use), but that does not directly affect the KV but the maximum amps and thus the torque.

100KV at 12S with 6.5 pitch should be around 40km/h, how fast do you want to ride?


I agree, I think 100 KV should be what I shoot for.