Thanks for measuring. I was pretty sure it should be 1608 size by caliper measurement from @Jordi.
Regarding the value your measurement seems to fit the 30B code nicely. I will search for some fitting component tomorrow. Looks like I have to get the controller back out of the box to resolder 
it was glued so nicely.
Anyway thanks again!
@lishine thank you for raising that point again.
I just replaced the resistor with a 1608 2kOhm. Worked fine and the size seems to fit well in comparison with your picture.
It seems the change improved a problem I was observing with the throttle response. Before the motor accelerated to full speed fine but holding the remote down it reduced the speed after a moment. I thought it had something to do with a protection feature when not under load (in the air). Now this issue is fixed.
By the way I also measured 1,7k once it was installed.
Great 
Build is done - I’m just waiting for the nearest lake to unfreeze for the initial test session.
I’m really happy with the result, only some minor holes in the bottom edge:
After a little sanding, filling of the holes and a thin epoxy coat it looks alright - no filler to save some weight - most of the carbon is covered by the Bopla box anyway
I changed the BEC for pro version and made a little mounting plate. This plate also fixes the antenna in a known spot to make it easier to match the external antenna. The antenna extension is made just from a antenna cable and potted in some printed parts.
One small addition I really enjoy - I configured a WIHA stubby with all the Bits needed for my assist system.
That’s it for the moment:
Very brave cutting up your lovely appletree board.
I hope it works a dream when the lakes thaw out! Looks great and likely inspiration for me to do a v2 after my v1 FD assist style lunchbox on board.
Initial testing went okay today. I used around half a battery lying on the board. Due to connection issues I had to hold the remote directly on the box. So standing up was not easy. I will try to improve my antenna extension for the next session.
Anyway the power is good and no issues with overheating - with the water still freezing cold it would be hard to overheat anyway I guess.
https://www.instagram.com/p/DG8DnuaMf5f/?igsh=OG4zMzBobWx1NDRp
wow nice work… really fine
coud I ask you if the battery it’s build by your self and the size?
12s? 20mah?
Battery is a 12s3p setup with Molicel p45b and self build of course. So it has a total of 13,5Ah.
Had a really fun session lately. About 1 to 1,5 hours on my lake learning how to get on the board and even doing some transitions to pumping Mostly on the Indiana 1200 H-AR with condor XS stab.
While I can’t wait for the first chance to hit some waves the development ist ongoing 
The idea is a submerged jet drive - mostly for safety reasons. I started with an SSS5684 800KV. Stripped it to a bare stator and rotor. Then replaced the shaft by a longer one. Designed my own waterproof housing which was done by JLC. Based on some pictures and basic calculations I designed a 60mm turbine. Printed also by JLC in Nylon. First test in the rain barrel gives me hope that the system works.
The most critical point is the shaft seal. In dry run it quickly heats up the shaft just from friction. So maybe switch to a ceramic shaft seal in the next iteration.
For now the next step is to get on the water and check if I can get on foil.
As an engineer I would love to see a comparison between the jet and FD prop. A basic test bench with load cell and power meter is probably what I want to do for the next winter project. This should help to do some improvements in my jet design.
Wow, that’s a very nice looking jet drive! I hope the nylon impeller can hold up to the power and load requirement. I imagine it has thicker blades so it maybe it can.
I believe I’ve read here somewhere that the jet drives are mostly less efficient, at least when compared to a well matched motor and propeller. I think it’s mostly anecdotal evidence and not tests though.
I have not seen any data on the efficiency matter yet - at least not a side to side comparison on an efoil. My main concern is safety - especially once I think about letting someone else use my board - this overrules efficiency in any case.
There are products on the market making it work - so I should be able as well.
Also I would go the minimalist-foil-assist route - just enough to get me on foil and a few 100 meters to the next wave.
Here you can see the cross-section of the impeller - 3mm at the thickest part. At the moment it is plenty strong although relatively flexible and reasonably cheap to be printed at 2,28€.
At this price I can afford many test setups to find the optimum rotor by trial and error - best case on a test bench. Same for the stator 
I have one more point where I could use some advise.
Currently I use these shaft seals in the PTFE or NBR material.
This leads to excessive heat built up in the shaft. Is this problem ignorable since cooling is good in the water anyway or should I worry about quick wear? Please keep in mind this is not meant as 100% efoil but assist only.
Alternatives would be:
Fair point that efficiency isn’t always the primary consideration.
One of the places I’ve seen jet/prop data is from Fliteboard’s foil time calculator:
They state it’s based on rider data they have gathered. So not controlled test data, but likely averaged real world data that I suppose their owners can upload.
How did you fill the motor between the magnets with epoxy without flowing away?
I used Epoxy with a lot of micro balls and spinning it every now and then slowly until it was hard enough.
Can you provide more info on why you needed disassemble your ESC? I bought a FlyColor Xcross HV160A ESC and it doesn’t work, just wondering if it has the same issue as yours.
@mekanism
I accidentally ripped off a component when I disassembled the aluminium cooling plates. I did this in order to mount it in that aluminium clamp to get cooling on both sides MOSFETs.
If you did not mechanically work on your ESC and something could have been broken off in a similar way I expect it to be a different kind of problem.
Had a great time on vacation and emptied a total of 15 full batteries. I had the Indiana kid aspect wings with me, also calle “ride”. With the 1500cm2 wing I was able to do quite some pumping and training of transitions. The smaller 950cm2 wing was getting really fast and fun, but quite hard to pump, since only mod aspect ratio.
No issues with the Bopla box. Great recommendation @hangloose
Only some small corrosion on the aluminium where it is close to the carbon board and water likes to stay in between.
Have a look on IG
Now working on some further ideas - smaller/ lighter battery and waist mount.
I sketched up this design quickly. The idea is to pott only the cell terminals, strips and wires. Benefits could be better cooling of the cells an lower weight since less potting material.
What do you think about it?
@Bzhwindtalker you have a lot of experience with potting batteries - any issues with gases from the cells?
Well I mostly potted some old batteries, and had some self discharge issue, I can not tell if from potting or just the cells.
If you have no need for structural holding, maybe some kind of foam or silicon would be more suited.
Here is the kind of stuff used by tesla in their packs :
Seems like you had a great time
@heiguga @S_Roger
Sorry for not replying.
I was and still am busy with a new propeller driven assist design. I’m trying my best to get it finished for vacation next week.
The Jet drive is giving me a hard time. So I started with quite a lot of pitch. It turned out that the motor was not producing enough thrust and current limit kickin in already way below 30% duty cycle on the motor bridge. With a high speed low torque motor that means making only little power. I had this configuration once in the lake and I could only taxi around slowly before the motor cut off.
So I lowered the pitch resulting in broken rotors - as you might remember they where Nylon SLS printed.
Latest addition is a metal rotor I just received this week. It should neither flex nor break and this will be the last chance for this motor/ jet combo from my side. If it won’t work I’d rather switch to an outrunner configuration with jet. Main reason being better weight to power ratio.
