I have started my build and have realized I might have screwed up quite badly…
I have have complete packs with 13s already built, with current limits that are extremely hard to change. I can discharge 40 A continuously and up to approx. 55 A in 10 second burst.
I have a Vesc 75200 and is quite familiar with writing FW to Vesc, so would not be to hard (even if would be good to avoid) to add some kind of 10 second burst current limit. Also have a Flipsky 6384 with 2 blade foldable alu prop.
I bought a cheap inflatable Cabrinha 110L board and I weigh around 90kg. Total for me and all stuff maybe 100-105kg. Already have a Neil Pryde surf glide medium (1226 cm2) foil.
Have I screwed up royally or will it be enough to get up (2kW at nominal voltage)?
Would 55A for 10 second (2,6kW at nominal voltage) be enough to get up?
Can a larger foil save me or maybe just more efficient propeller? My plan was to 3d print quite a few propellers anyway to be a reasonable efficiency.
Not possible to parallel unfortunately and definitely not comfortable with 26s voltage in this environment.
In theory I could modify some small things on the bms as a workaround but would really not want to do that for a few reasons. That is really a last resort, probably even better to build complete new battery.
10 second burst with 55A from Vesc is probably easiest, together with having as optimized prop as possible. But I don’t know what kind of prop design would be best (I am an electrical/electronics engineer). And with Vesc FW I still cannot get more the 55A.
Replacing foil would probably be second hardest and/or more efficient motor.
I have a suspicion that prop design is crucial for efficiency. Evaluating if motor/electrics work optimally is easy for me, but prop design is out of my knowledge zone…
I have seen rctestflights propeller competition, but that’s not right efficiency metric here I guess.
I think you would get feedback if you could explain a few things such as what your use case is - ie full efoil or foilassist - flat water - waves etc.
You are stating limits such as max amps for a 10 sec burst but not why you created it like this in the first place, you can’t run more P count but can double S etc.
Lots of people foil on Flite and Lift boards that are 100l or less, on foils with your surface area or less, and weigh same as you or even more.
Yes props are important but a highly efficient prop (extended battery use) may NOT be the right one to get you up a foil.
You are asking questions and we have to guess on the details.
The BMS act as in the way it does. I cannot change it… actually I have never been able to. I can only share what is does and that I would really like to use these packs. The rest of the board I can share everything about.
I can of course build new packs myself, heck even designing a BMS from scratch would not be to hard for me. But I am not sure that is within my budget, neither time or financially.
I cannot change either series or parallel in packs. I cannot parallel complete packs and I really don’t want to deal with 26s voltage. Those voltages are just to dangerous in a wet environment for my taste.
But my usecase is full efoil, not only assist. Driving around on the lake and in summer at the coast, not when to much waves of course. Mirror on the water is quite rare. A lot of people wingfoil in the area though.
If we define efficiency as thrust per unit of power at lift-off speed, I would think that what I am after here. To stand a chance to get up on foil after reading about what power levels people have here…
I am open to prop/drive-system/foil/board changes if anyone has an idea what could help or what to try first? How bad is the Flipsky folding 2 blade prop? My feeling is that it is quite poorly matched to 13s and that motor.
Around what peak (and continuous) power limits does Flite or Lift have? I did look as close as I could on a Lift board, but only spec I got was battery capacity… so kinda pointless.
So if your current BMS is creating your discharge limit why not stop using it.
Lots of people here ride rigs where the BMS is not involved during the ride - ONLY when charging. Let the VESC manage power during ride. If you start out the session with balanced good quality cells it’s not likely you will have any problem.
There are also techniques where you can get a “challenged” rig up on foil. Start downwind, catch a little wave to get board to release earlier etc.
A larger foil can help here to as generally speaking a larger surface area will create lift “quicker”
Because that means that I cannot use these packs given how they are constructed. The next alternative is to build new battery pack myself. Which would fantastic if I could avoid by optimizing anything else.
Assume I can push the current limit upwards, but want to do a little as possible. Is 60A at 13s sufficient? 2-3kW is quite a large range.
Wing is probably relatively easy to replace.
Maybe I should just slap the thing together first, test. From that see how far off and then start with bigger wing? What about propeller for max thrust?
Dude - it sort of feels like you have picked a bunch of random components without considering the whole picture which a seems odd for an engineer type person. There are lots of successful builds here that you could have and likely should model your build on.
You don’t really supply much detail about things like your battery (all that we know is that it’s 13S and has a BMS) and when you get suggestions about how to resolve things you push back on some other item and appear to have never Efoiled so you don’t have any practical experience to base your responses on.
Therefore I’m out but you might consider renting an EFoil for a few hours with an instructor to get a better understanding of what a good rig is like.
Dude - I don’t really see what is random about it.
Well, the random component are the already waterproof batterypacks that I have available as many as I want. But cannot touch any of the insides… I cannot disclose more about them, it is extremely high quality cells. From an electrical standpoint it does not matter, as long as voltage sag under load is manageable (which is insignificant here), voltage and current limits define the rest. Given as 13s and current limits above. What more specification is relevant? I cannot disclose more about the battery and I actually cannot see that any more specification is relevant.
ESC is sufficient, that I definitely already know. Rest is just limits in FW.
Propeller must be matched to system anyway (can’t be running in top gear). To get motor within good RPM range for electrical efficiency, these similar cheap motor manufacturers I have had experience with at work generally like to spec max current as when core saturates, not a good starting point… 4.4kW (in a quite poor spec sheet), at 2.5kW I should be in decent power range for electrical efficiency at 70% duty. Given 140kw, rpm for prop is more or less given. Pushing kv down more have some drawbacks as well at these diameters so what might be gained at prop would be losses in the iron.
That I thought I would get away with even 1,5kW from battery is based on friends that did some academic work on foils, even as little as 400W would sufficient to lift 100kg. Of course more losses but a factor 3 safety margin over wing drag. When reading here on the forum I am quite surprised how much power boards consume, that’s why I started the thread.
Board and foil setup was dirt cheap used stuff to have something to slap together the system on. They are easy to change. But do they matter that much?
Front foil of course have huge impact on take off speed, but just replacing the front wing (or even making myself is way less work then building a good battery).
I push back on changing battery pack or modifying existing ones. I know the limits of these packs inside out and I know what I can and cannot do with them. Having other packs is what I want to avoid, given the amount of work and tools I need to make a decent one safe enough for my comfort zone.
I have my VESC set up to 2200W limit and can easily get up with the Axis 939 (900cm²) and a 41L board at 84kg.
I guess having a fixed current limit is a bit worse, but this should be doable. Get it up to speed lying down on the board and only get up once fully on a plane.
Take a look at one of the earlier foil drive videos.
I think this is what you should do. You have the battery, if it doesn’t work out you can build/buy another one. It might work, as long as you don’t go into the wind.
I went and looked through some of my vesc logs, I can take off between 1700w and 2200w (just based on max power from the sessions I checked). This was on 80L Fliteboard air, 1280cm2 front wing, me at ~65kg. You are heavier, but will have a larger board and possibly a larger wing. You don’t have the margin most would try to build with, but it might work out.
Very interesting, I guess it is you build with a Flipsky 6384 as well? 12s? What propeller do you use?
It certainly is worse with fixed current limit like in my case, lower then nominal voltage (including sag) and power goes down further. But still very interesting that you can get up at 2,2kW already.
With a 100l board and a 1400cm or so wing you will be fine. A bigger board really helps get enough speed before you engage to foil. Once on foil with a good prop you can expect 20amps or so. Just do it!
