Choise of Brushhless Motor


HI Guys,

I would like to launch this topic for discussion: Motor for the Propulsion Unit.

I have been analysing most of the builds posted in this forum and it seem that everyone it’s been using pretty much the same motor: SSS 56104/500KV Brushless Motor ( From this link it can been seen that This motor can have a output of 11000W.

I have also seen that most of the builds have a battery pack with a 12s14p configuration. This configuration will work at approximately 48V and if we admit that the current will be around 90A ( Very high current!!! Most of the batteries can’t work at this current) the maximum electrical power that is delivered to the motor is 48 * 90 = 4320W. Basically, we will use less than half of the motor capacity. This over-dimensioning of the motor really freaks me out and there’s another issue with SSS 56104/500KV Brushless Motor : at 48V the motor will run at 500*48= 24000 rpm (witch is freaking HIGH!!!) and this introduces the need of implementing a gearbox (most of the guys use 5:1 planetary gearbox). I have to admit that these set-up seems very inefficient and can lead to a lower lifetime of the propulsion Unit

I gave some thoughts on this issue and to avoid the implementation of the Gearbox and the over-dimensioning of the motor i think that it would make much more sense to chose a motor with a Lower KV value and a lower power (since we are not using 11000W anyway). I was able to find a supplier of Inrunner brushless motors : Alien Power System and in this supplier i was able to identify two motor that could be used for this Hydrofoil apllication:

Admitting that we are using a battery pack with a 12s14p configuration i feel that these two motors are more indicated for this application.

Now i would like to hear everyone’s opinion on this.

Hereby some discussion Topics:

  • Do you agree that these two motors could be used in this application? If so, what motor out of these tow you would chose?
  • DO you think by having a much Lower KV value i could avoid using a Gearbox?
  • In the links of these two motors it can be seen that the motor Torque is 4.8 N.M. Does anyone know what is the torque of the SSS 56104/500KV Brushless Motor? ( i failed to find this information).
  • Does anyone know Alien Power System? Do you know if they are Trustworthy?


I have been running my setup above 20000rpm for a couple of Month without any problem , for the sss motor , the given numbers are for max output since you will be running a sss with gearbox to half of its max voltage for 24k rpm and half for the max amp to limit heat, you need a 12kw motor to have a good 3000w set up…


BUt what is your opinion the Motors that i have posted? Do you think that they could be used for this application?


Most of us have same question, we all would love to avoid gearbox. Few of motors are directly from aps and some esc’s. Some1 just bought 56200 from aps and will try it direct drive. Merten also had some tests with low kv inrunner direct. Therr is another user who tried 56115 and in his experience isnt working, 2 much current/not enough torque. Me personaly been tempted do make 2:1 gearbox (basically Merten belt but with steel gears planetary compact design) and try under 200kv inrunner (almost doubling the torque and hopefully slicing amps down) for a propulsion unit. Unfortunately, i had to stop with my experiments cause of some personal issues but hopefully ill get back on track as soon as its resolved.


Look at @Mat or @jakebarnhill1 builds! They both used a direct drive set up with the APS 80100 motor. They waterproofed it with epoxy so you can run it without a sealed aluminum tube (see instructions for that on my build post; they were provided by Mat). At the moment, I think this motor, the APS 80100 80kv or 130kv, is one of the only motor that has proven success. I’m personally going to use this set up on my build! However, I was wondering if I should run it at higher voltage 13s or 14s.


I am new to this forum. How can i see their build?


Oh welcome. Search function works great! Just try keywords “direct drive inrunner or outrunner”, “56200”, will give u nice choice of threads. I recommend reading through whole thread from start to finish, there is some great and helpful info not directly related to topic sometimes. :+1:
Also, under user signature there is part list of their build, u can also check topics they started(their builds) if u click on their nickname.


Thnaks for the hELP :slight_smile:


As the aliens came to earth by their own drive system and settled and opened a shop, their products must be outstanding.


I’m building based on the 80kv APS motor. I’m buildning with 18S. Customised ESC from APS that can take up to 22S.

Ice now in Sweden so testing this in late march


Try the 56200. Skip the aluminum tube and match the 3D prints to the diameter of the motor.


Do you have a link for the 5600 motor ?


Why are you wondering that you shouls use a 13 or 14s? Whats battery They uses? Did their build had trouble with power?


google is your friend.


Since I am building my own battery pack using 18650 cells, I can customize how many cells I want to put in series. I was initially thinking to use 12 cells in series or 12S like most builders here. However, if I go with the APS 80100 80kv version, I might want to consider higher voltage/more cells in series to gain more thrust and speed once foiling. I’m still debating whether it would be worth it to increase to 13s or 14s. If anyone has any experience with the APS 80100 130kv or 80kv, I would greatly appreciate your input. General guideline from my understanding: more cells in series=higher voltage=more power=more thrust=more speed=slightly more dangerous too though.


Dos you know if it is possible to use this motor with direct Drive? What votage and current?


Another benefit is lower current = less heat. I am starting to build with the 80100 80KV. I would like to go with a dry pod. I don’t know if it will burn up. I just did a quick and dirty measurement of the KV at no load. It fluctuated between 75 and 78.


But what values are you aimimg for the voltage vs current?


I already own 2 -20 amp hour 6S batteries and charger. 12S (44.4 VDC)should work fine. My foil lifts at low speed. If I ever build my own battery I will probably go 14S just because I want to try it.


would you consider going with the 130kv version or the 80kv is better?