Thank you for this perspective. For the newbies trying to gather this all in, what kv range on the 6374/6384 motor is ideal for a faux assist with a rider 215lbs/99kg on a prone setup). From what I understand this is a combo arrangement with the prop style and size as well. You insight is appreciated!
Hi,
The “standard” Kv range is 120 to 130kv. Th FD engine is 130kv i believe and that has plenty of grunt… You also need to consider what ESC to use as this will determine what power you get from the engine vs battery consumption. This subject is also vast…lol
In terms of props alot of people use a prop/hub designed by “enzymlefax” which you can download off Thingiverse. This is a good setup and produces good thrust. I note your weight and you could limit the effects of this by getting the correct foil setup…i cant comment on which foil as this choice is dependant on many variables but the standard FD setup should work to easily punt you onto a wave with most foil setups if you take the basic “variables” (skill, weight, style, discipline, cost etc) into consideration
Another option is to build/use a higher voltage battery…your weight will not be an issue with more voltage and hence more power and longevity…see FD Gen 2. One of the guys that owns it is around your weight and he burns around on his …endlessly.
Hope that helps
K
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Voltage is not a universal solution to thrust. You’re covered by enough voltage in a 8S setup and the normal props used here.
If you can’t lift then first items to look at is a large enough board, large enough foil and some riding skills.
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I’ve ridden 6s to 12s on an assist and I can tell you I wouldn’t touch anything under 10s again. I’m 95kg and the difference between 8s and 10s is worlds apart if you want to ride high performance gear.
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Sure, there’s a difference but not ”you can ride endlessly” or anything like that. If so, we would all be riding 20s1p packs
So, seems like some data went missing, to summarise what was there on the foil drive efficiency topic:
The current per cell in a pack with the same number of cells is the same regardless of how they are connected at a defined power level
12s3p at 3000w is 23A per cell
9s4p at 3000w is 23A per cell
This follows from the fact that each battery shares the load equally, same number of batteries, same load per battery.
If we add more batteries with one string of parallel batteries the relative difference is large since battery internal resistance goes down. With a moli p42 pack and a 12s3p vs 12s4p pack the internal resistance goes down from
12x0.016/3=0.064ohm and 305W losses at 3kW
to
12x0.016/4=0.048ohm and 228W losses at 3kW
This is a 3% gain in efficiency from the extra batteries
To compare with the resistance losses in the rest of the system:
For a 10cm connection length of 8AWG wire the resistance is only 0.00041 ohm and at a 3kw the difference in current is
3000/(8x3.6)=104A
3000/(12x3.6)=69A
Resistance losses difference is 0.00041x(104^2-69^2)=2.4W This is negligible to the battery resistance losses - which are about 100 times larger.
On the esc side the losses are also small, at least with a good esc. An example is the APD 120f with 0.0011ohm resistance and a 7w difference in the esc resistance losses, about 40 times lower than the battery resistance losses.
On the motor drive side the losses from voltage and current is the same regardless of the DC voltage since the esc balances the output vs the load and throttle command, this is if it can do it with the current and voltage available. That’s a big if for drives that don’t reach foiling speeds😄
the difference that is worth the effort: propeller and motor drive efficiency. Getting up on foil is the most energy consuming part of the drive and limiting the time to get up is the key goal for a foil drive. With your system maxing at 3kW during starts you’ll consume half the energy if you get up twice as fast. I think this was the main point from @Jezza and the driver for the foildrive systems to go to higher voltage levels.
Of course all this is also highly affected by the size of your board, your foil and your skill level. As always, optimisation gets more important if you’re at the extremes.
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Proper theory.
You should pin that somewhere so people can learn the basics instead of reading through millions of replies.
Maybe add phase wire current, stall behaviour and saturation.
Or even add kv, propslip, speed and you’ll complete the manual.
.
That said I do prefer higher voltage. Punchy on throttle. Less heat. Cheaper components.
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That should not be pinned. It’s completely incorrect for various reasons which I’ll provide with real world data when I get a chance…
It will also lead people completely astray in their choices and solutions…
There a very good reason you prefer the higher voltage and the data will show it.
Here is the breakdown…
Lars incorrectly assumes that the power required with series cell count increase stays the same. This has led him to argue with me about it previously but unfortunately those posts are lost. He also tried to tell me I’d regret not reading properly, however it was him that did not read my reply to @cephalofoil correctly with respect to the power required at 10S vs 12s…
I will use my system as my example as I have data on it:
Slingshot WF1 24L board
Gong Veloce XXL foil
6384 140Kv motor
The cell voltage under load will change based on how many cells you have in parallel but is reflected in data…
- If you incorrectly assume power requirement stays the same with series increase, you would think the following
- Now lets look at what actually happens.
When you increase the series cell count, what you do is add extra RPM to the prop eg. adding 2s to a 140KV motor will give you 2 x 3.6V x 140 = 1008rpm extra at any specific current value. With a 4" pitch prop on an assist and a slip of 13% this equates to an extra 4.8kph which is a MASSIVE difference and explains exactly what I see in my data.
When I moved from 10S to 12S I saw my total current through the system drop from 80A (10s) to 60A (12s). Resulting in the following
As you can see from the real data, I gained a lot of efficiency by upping series cell count instead of parallel at 10S. The 12S gets me out the water and onto the foil much faster too because of the increase in RPM.
If I wanted to add more ride time on my 12s setup, I could add cells in parallel, but it would increase the weight by ±800g which I don’t want.
It should also be noted that increasing your series count is FAR cheaper than buying a new larger board to solve getting on the foil faster!
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You convinced me I’m going 12s
Don’t care much for the public display of beef. 
I think basic physics are a good way to rationalize what is happening in a system and everybody should have that knowledge.
Jezza your 10 to 12s data displays valuable real life experience in finding the sweet spot of optimising electron to thrust. Don’t forget that upping the voltage gives a bunch extra torque to swing that big ass prop round 
In my boating experience I’ve found that upping rpm is in particular good for improving top speed.
I’m also a big fan of max voltage, why?
-easier to regulate for the ESC mosfet
-less amps means less heat = better efficiency = more playtime
-less amps means thinner wires & connectors
-less amps means cheaper ESC
-less amps better for motor
-higher voltage = more Torque
The only reason I can think for lowering voltage is reducing weight or cheaper battery.
But for that you can also go for low capacity high voltage setup.
@NortheastFoiler Please still do the math about kv, rpm, prop size, etcetera to make it work 
or ask, people will help.
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For me it’s not about that at all. I’ve seen advice lead others down a costly path of new equipment etc (circa up to $1000) whereas upping the voltage is actually the cheapest and easiest option.
I also think some forget that the idea with assist is to try get as close to analogue foiling as possible with as small as possible swing weight in the board.
Funnily enough because I gained efficiency going to 12S, I actually removed one row parallel and saved 500g because I dropped from 30 to 24 cells.
When I completely maxed both systems I ended up with only 10% less time on the 12S which I didn’t mind.
If I really want extra run time, I can always use a split lead to run in an extra 12S row or 2…
@jezza Seems you’ve got it backwards if you calculate power used from the loaded battery voltage, that’s including the voltage drop from the battery resistance losses and that’s larger on the 12s battery. Recalculate 
If it would be a correct calculation then a battery that drops to 2v during load would seem to be more efficient…
Let’s stay vegan in the future. It gets tiring.
@BasNL i think a lot of the points you mentioned aren’t significant, as my calculations show. It doesn’t mean that the value of going to higher voltage isn’t there but that it’s due to other reasons, one of them being simply that output power of props is proportional to rpm cubed for a given propeller. That means that the output power will be a lot higher if you reach a higher rpm with the higher voltage. Therefore it’s really interesting to see which rpm was achieved in the systems if you’re comparing voltages with the same propeller. Maybe @Jezza has this data?
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I am convinced and I am going to reconfigure my 8s3p into an 12s2p to try. My question is the BMS. The picture I saw of one of y’all’s setup before the server crashed had just the BMS leads on the battery, which is what I plan to do cause the 12s BMS’s I have are not huge, but much larger than the 8s. How do yall setup from the charger through the BMS with it being external?
I used the current and resistance of the battery to calculate power loss in battery. So the power loss in the batteries are correct.
Where I was lazy and I’ll admit it, I never actually calculated the correct cell drop and so on the conservative side gave 3.6 (12S) and 3.8 (10S) as the cell voltages.
In reality the correct cell voltages are 3.72 and 3.77 respectively. The 12S still wins…
I do have some RPM data fishing about. I am also hoping to get out this week with some new props so that should provide further data
I tried calculating, there’s some weird math going on, is this all from theory or from measured values?
If measured then i’d be interested to see how you replicate the exact same conditions to get up on foil, and the curves you get the voltage and current data from.
Same cells? Same prop? Same unloaded voltage?
The current values are real world max values at takeoff and during powered up carving.
Batteries all start at full voltage. Technique used is the same, pull trigger, throttle curves all the same and only stand up once the board has shot out the hole and on the plane. It’s by far the most efficient way to get up as weight distribution is optimised.
From the real world current you can then calculate the rest of the power losses through battery etc and total power used etc…
Cells all the same…
If you meant the photo of my battery, then I do not use external bms for charging, I use special chargers iCharger x12 and Ev-Peak A9.
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Ah ok. Thank you for the clarification.
I would like to use some calculator that could help us compare, given the same prop and motor, different voltages, also giving the motor phase current, as that is a killer of esc and phase wires on overloaded setups.
wonder if any of the airplane sims can be adapted.
http://www.drivecalc.de/
OR