I would like your opinions and help.Will this setup push me into waves?Should I reduce the diameter of this stainless steel prop in order not to burn up electronics…this setup is for Foil drive assist with waves…I will not EFOIL.I just want help to get moving onto a wave then standup once on wave.
Board is 50 liters with mono wing(works great as lite wind kite setup and prone foil),prop is stainless 6.5 dia-6.5 pitch,motor is 45-30 …520 kv (4000w)…grinder reduction at 3:1(3000 rpm@prop),18 v battery,with a 200 amp esc.Please if you have any suggestions before I do a water test,let me know,I’d rather not burn anything up…I will attach a prop guard before testing.cant post video…
No folding prop: drag during touch downs,
No pod: drag during take-offs and touch downs.
Is your motor (salt) water proof or compatible ?
We can make a comparison since i don’t think anyone has this exact combination.
First looking at the relative load of the prop:
A 6384 is able to drive the common props for efoil in size 6”x6”
Propeller load is proportional to d^2 so there’s a difference of a factor of 1.17 from the prop diameter
Pushed water speed is proportional to the pitch so there’s a difference of 1.08 from the prop pitch
Then looking at the motor:
Motor torque capability is proportional to
stator d^2x(stator length) which for a 6384 is 54^2x52
Relative widths and diameters for the 4530 seems to be stator dia 45 and length 30 (so naming is not the same for these two motors)
Relative motor torque capability is then 2.5x higher for the 6384 motor alone but the gearbox on the 4530 will have quite a lot of losses, i’d estimate 20% so final result needs to be derated in favour of the 6384 —> 2.5/0.8 is 3.1
gearing is 3
Total relation 1.17x1.08x3.1/3=1.3
On a set of rough assumptions the motor size, propeller load and gearing could work, it’s 30% higher load vs motor capability when compared to a 6384 setup that we know works. With this small motor, even with gearing, it would be better with a smaller prop and lower pitch.
Then looking at the esc:
The motor torque is proportional to esc current and kV. The normal motors we use comes in kV 80-120, if we relate those to your esc drive then
(120/550)x(3*0.8) (geared torque per amp with losses) is 0.52 so the drive would need almost double the current from the esc for same torque. With a 200amp esc the current will be borderline to produce the needed torque.
We can also look at the torque as calculated from the motor parameters
T=9.55/kV*i so 9.55/550x200=3.47Nm
With gearing and gear losses that’s 8.3Nm at max current, not considering stator saturation and motor losses.
Looking at the velocity and power to lift:
The third part is power and motor size, can the motor produce the power (thrust x speed) to get on foil? The drive might produce the torque as seen above but will need to be able to produce it at the right speed to lift.
Since the foil needs a certain velocity to lift and the board drag needs to be overcome too that relates to a power level. Here the gearing might give you enough torque but at a third of the speed and speed could then be too low:
Max noload rpm is 18*550/3 = 3300 rpm at the prop. I have run my efoil with 6” prop at 100kv with 10s battery, this gives a low volt pack rpm of 3600 (that was with a really high lift / low speed wing though)
I think the theoretic motor rpm could work to get you to lift speed but it depends on your wing and the drag at that velocity.
Looking at the battery:
The battery needs to deliver the current needed to power the motor enough. Takeoff power ranges up to 3kW (depending on weight, wing and board).
3000w/18v is 170A from the battery. If you run rc lipo battery with 60c rating (which realistically needs to be derated to at least half, 30c) then Ah of the pack needs to be 170/30=6Ah.
On the capacity and runtime:
A small pack like this has little energy. 18V*6Ah is only 108Wh. It will give you some short pushes. Consuming 3000W at lift gets you 108/3000=0.036 h of lifts.
That’s a little over 2 minutes until pack is empty.
On the total:
I think it might work but for a calculation like this to be relevant you’d need to verify some data. It’s too close to be sure as there is too little margin in the results.
If the results had 50% margin to the 6384 drive then i’d say it works even with the uncertainties but now results show the drive is weaker than a direct drive 6384 by some amount.
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Foldable prop would be better…I don’t plan on touching down😁yes take off will be draggy…I drag a foot alot on wave take offs because soo much speed …but yes will be draggy…yes I epoxied both halves of the motor…but I didn’t change out bearings…
Thanks for the feed back…seems like I’m underpowered…but I have a big wing 1500cm floaty board and push from wave…but I get it…I’m under gunned…but I will definitely reduce prop diameter and surface…maybe trim diameter down to 4.5 inches and reduce surface area a bit on prop…does that sound better… obviously this is a very low budget build and hard to get a flipsky where I’m at…but the prop and motor were cheap and easy to find(the motor actually measures 56mmx50mm)…thanks again
You can check the propeller rpm in a tank with the drive as it is now to see how high the loaded rpms are. Some short bursts won’t damage the motor if you let it rest between.
Looking at some dyno graphs it seems the drive needs to get to something like 75% of theoretic rpm with the prop to get a reasonable efficiency, otherwise the drive is overpropped.
I think 4.5” is too small since the diameter has huge impact on thrust, it’s best to check what you have first and then reduce prop in steps, starting at 145mm dia and reducing 5mm per time
30kg of thrust has been mentioned on here as a ballpark figure to get up on foil without assistance from wave, you can measure this simply with a kitchen scale. I think you can probably get away with a lot less thrust than that on a foil drive since you have the wave to use and skills to utilise the foil well.