I would like to add motor into my inflatable 12,6ft SUP (13kg + 80kg me) to be mostly used on lakes, rivers, potentially sea and that would give me reasonable speed (around 20km/h if possible)
My total budget is limited to 500USD.
After reading through the forum and seeing that most of you are now opting for low kv 65161 motor run at 12s, I was trying to find something close to it but not at such high costs.
Motor I am looking for should be if possible:
inrunner (problems fixing outrunner motor onto the fin)
used as direct drive
12s
as low kv as possible
used with smaller propeller/lower pitch to tackle higher kv than you usually use (70-100mm?)
So far I came up with:
Flipsky 56115 200KV (strangely this motor been pulled down from all sites except flipsky, did not see anybody trying to use it here, no reviews either)
SSS 56114 360KV (10mm shaft)
APS 56115 100KV (pulling only 50A at 24s, so probably not so much power)
As for ESC, I am planning to use Flipsky FSESC 200A 60V ESC matched with Flipsky VX2 remote control.
What are your opinions on this build? I have never build anything to be used on the water, so propellers, attaching propellers (do I need some extension shaft or can I fix propeller right on the motor shaft?), waterproofing stuff…all this is something totally new for me.
I will be using small 4s lipos I used to fly with on mini quadcopters. In total I have 18 pcs of 4s 1300-1800mah (12x 1300, 6x 1800mah) lipos which should give me 7800 mAh 12s lipo. Not the neatest solution but for the start I would like to use what I have
As for attaching motor onto the fin I plan to do something like this, even though 3D printed solution from [rcjetman] looks super neat and enables outrunner motor use.
I tried my Efoil setup ( FR motor ) without the foil , my board is around 90L , same setting :
With wing and flying : 35km/h
Without wing : less then 15km/h
So my guess , I would go with high kv ( support more amp with big wires )
Small prop like 100mm
You will loose around 20-30% at least all included ( rpm power prop slip vs pitch and speed )
So do that math : battery voltage , max rpm , supposed top speed vs pitch ( most prop have a ratio 0.8 to 1.3) and looses
Here in the forum there is a 2 sheet prop “flipsky” 3D file that works very well and effectively with the 6384 120kv.
Depending on the number of cells, reduce the prop to 0.9 to 0.8 in diameter and pitch.
With 6s and org. Size is already 25km / h possible.
Greetings Frank
Appreciate you showing me how to the the theoretical speed math.
Unfortunately all those motors are outrunners and I still did not figure out how to safely and securely mount them onto the fin, compared to inrunner motors. At the moment best option seems to be 56115 200kv from Flipsky even though there are no reports about usega/reliability.
May I have newbie question about mounting the prop on the motor? Do I have to use some king of prop shaft with bearings (something like this?), because motor shaft on most motors (56115 flipsky for example) is very short, unlike 65161 that has long motor shaft.
If I was to use this 80mm ducted prop (30% cheaper than 90mm) with 1.2 pitch, according to thrust tables lower on the page, it should give me almost 3000W of thrust.
When using this RC boat speed calculator, and entering 200kv motor (flipsky 56115) and 80mm 1.2 pitch prop, it is giving me theoretical speed of 31km/h.
How do I calculate amp draw with particular prop size and pitch to be able to determine total runtime with my 7800mAh 12s lipo I am to build from 18 4s lipos? Calculators give me runtime around 5 min @80Amps which is extremely short.
i have already seen these propellers and wonder why they are not used by more people? I find that the ratio between the required power and the speed of rotation gives a high thrust.
5min runtime @80A is realistic. 7800mAh is not the biggest battery for such an application. I think the most people here in this forum use batterys with 40Ah (40.000mAh)
Prior to any real calculations I guessed I would get with such “big” battery 30min runtime Probably just influenced by flying mini quadcopters where single 4s 1300mAh lipo gave me 2min flight time and speed up to 120 km/h… so I guessed having 18 of such batteries could give me definitely more than just 5 mins of sailing
Do you think there could be a way to mount that duct right onto the motor?
After doing FOC in VESC tool I have limited ERPM to 60k (motor has 12 magnets) and since producer lists this motor with “max amps 80A” I have set Motor current max to 80A.
Here comes strange thing:
1st test:
on full throttle it was taking only 50A max and speed was 13km/h max.
2nd test other day:
on full throttle taking only 35A and max 10km/h max.
When I go over 25A there doesn’t seem to be big gain in speed, maybe 3 km/h but there is appearing strange sound - could that be caused by possible cavitation? Prop is mounted on fin which brings it quite close to the bottom of the board. I have no prior experience with propellers in the water so it´s difficult for me to find out what is the culprit.
Will changing ERPM limit open up possibility to draw more amps or there is some other limiting factor?
