Light Foil Assist Project - Cocoa Beach, FL

[Jimmy25]

Hi All,

I built this project because I wanted to understand how an efoil works all the way through. This is an exploratory build intended to develop the working knowledge and riding skills to determine what I will want in future builds. Between a full efoil, a foil assist, and a tow-boogie, I selected the foil assist for low relative cost and simplicity.

So far, I’ve ridden 21miles on this setup and it’s been an absolute joy to my friends and I.

Thank you so much for all the information you all have collected here!

Build Summary

• Board, mast, and foil: Gong hype first rise 5’, 85cm mast, 1300cm^2
• Motor: 6384
• Battery: 10s3p Molicel P42A
• BMS: Flycolor 160A
• Flipsky VX-3

Build Steps:

Schematic:

BOM:

Item	Name	Quantity	Price	Link	Total Price
1	Waterproof box	1	31.82	https://www.amazon.com/dp/B0131VGD1O?ref=ppx_yo2ov_dt_b_fed_asin_title	569.7
2	Battery Cells	31	150.35	https://www.imrbatteries.com/molicel-p42a-21700/	
3	Heat Shrink	1	6.99	https://www.amazon.com/dp/B0CWDSP8YS?ref=ppx_yo2ov_dt_b_fed_asin_title	
4	Fish Paper	1	11.8	https://www.amazon.com/dp/B00DJUHBIW?ref=ppx_yo2ov_dt_b_fed_asin_title	
5	Kapton Tape	1	10.99	https://www.amazon.com/dp/B07S2219CK?ref=ppx_yo2ov_dt_b_fed_asin_title	
6	BMS	1	13.6	https://www.aliexpress.us/item/3256806227374514.html?spm=a2g0o.detail.pcDetailTopMoreOtherSeller.1.23f43170aQ5r7t&gps-id=pcDetailTopMoreOtherSeller&scm=1007.40050.354490.0&scm_id=1007.40050.354490.0&scm-url=1007.40050.354490.0&pvid=99f8227e-2b1e-49b5-bedf-82c35970e9d1&_t=gps-id%3ApcDetailTopMoreOtherSeller%2Cscm-url%3A1007.40050.354490.0%2Cpvid%3A99f8227e-2b1e-49b5-bedf-82c35970e9d1%2Ctpp_buckets%3A668%232846%238108%231977&pdp_npi=4%40dis%21CAD%2119.92%2113.15%21%21%2114.39%219.50%21%4021032e4e17120108583173192eb5e7%2112000037095883027%21rec%21CA%21860052467%21&utparam-url=scene%3ApcDetailTopMoreOtherSeller%7Cquery_from%3A&gatewayAdapt=fra2usa4itemAdapt	
7	XT90	1	9.99	https://www.amazon.com/gp/product/B07C8LJMFP/ref=ppx_yo_dt_b_asin_title_o00_s02?ie=UTF8&psc=1	
8	10AWG WIRE	11”	16.98	https://www.amazon.com/gp/product/B0B9JBJ3LK/ref=ppx_yo_dt_b_asin_title_o00_s02?ie=UTF8&psc=1	
9	ANL Fuse holder	1	9.99	https://www.amazon.com/dp/B0D1QQ1NSD?ref=ppx_yo2ov_dt_b_fed_asin_title	
10	ESC Flydragon 160A	1	85.99	https://www.aliexpress.us/item/3256802066593278.html?spm=a2g0o.order_detail.order_detail_item.4.680ef19c9E8QiT&gatewayAdapt=glo2usa	
11	Remote Flipsky	1	71.5	https://flipsky.net/products/flipsky-fully-waterproof-remote-vx3-controller-for-efoil-esurf-ejet-boards-esk8	
12	Servo Wire	1	7.99	https://www.amazon.com/Connector-Splitters-Parallel-Extension-Airplanes/dp/B0CNDFCX6K/ref=sr_1_1?crid=BCJKYWI6GMWN&dib=eyJ2IjoiMSJ9.6Dq8DIb8i6vYF3WAT7os84FJGAnPFGJfoKGcUAV-xHlIvrFyW53t8ihumXfuHQa_3lMJX9ku_OoiUNlYmsdmWAt5aFD-OFZ6G2a8xic9-vYMoCpiqRXpapVDf79YALCxBPFvNx5qf1teQNDj61At-Ih-jTJYexEhrFjr7S_hOc1SXXNIs3m0-FNhlSkDwtW3_tyYS74KM0_GL6kfGJhXEblGWavQeH28wGR-2NJa2OhWglqvruzLa51-zvyCuEe9au1GudKkPRtKOZVGRrqVDUT52_n_DSOBpqwY4n1JZco.c6WK7MU08DlbvZDleC_CArTnIAoln21Nc7Bg3oWAJ6I&dib_tag=se&keywords=servo+3+way&qid=1726517851&sprefix=servo+3+way%2Caps%2C153&sr=8-1	
13	XT60	1	8.99	https://www.amazon.com/Pairs-Female-Connector-Silicon-Battery/dp/B07QH249CR/ref=sr_1_5?crid=1JKD9MHBBTFPS&dib=eyJ2IjoiMSJ9.DaKl1hZzxQ8-Gjv6GV5NmxUp5VJHcKB7cXGPDwDZ2U12B-YtqSr4S6F7zdHD7akF8NJSPqLglYjwGz523zxKgdhNzdIPIjn1ULBfj6WK5a_-7aaThXK6e8TC7b-7hRskG-bZVRNQI5zaV1hVrPMFmF1hqDSAp1R7radp8uDYf_XCDr1IqCPJLM2fZALaXZHwtYc9PjFuDLFudNY5pn-rRKrVS0y2jIU97iWEkDZayoY_PP0yqBljVk_ORnFshJ6V_kAibShXJPn_OIigjIlCWYjc97UvshaxQg5tRc-0wh0.LgkwJsrwo8EQj_DqNvHX86e6U2_KEtfB739m1rt9ABI&dib_tag=se&keywords=xt-60&qid=1726517989&sprefix=xt-60%2Caps%2C140&sr=8-5	
14	12AWG Wire	79”	15.99	https://www.amazon.com/gp/product/B0C6QXVHKL/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1	
15	20 AWG Wire	11”	6.88	https://www.amazon.com/BNTECHGO-Silicone-Flexible-Strands-Stranded/dp/B01M12PSJM/ref=sr_1_11?crid=3P0QXVXR04E54&dib=eyJ2IjoiMSJ9.wIY7N3lR2j0ATiIhyjYyOua-hD0r6PnaGyGf837cHRPTgulgHuY6BEYlD1WmLUtVOtouWfwvb5007Sln73_FNV6pl_OwEaw2bWF4Eu_iefk0hYe2RBuqabRf929YnQNAbT9rpZxLOPqoGkNs0ElARMx9nnbP5dEWELV1SBQn0ghw_BOjww0kYrm92cEr3X0fDny5zkBDRkb_4gCN-udeT9HWYHFFTTOUQ68dzat4Dr7Ii3uWsjgD9nVjbEujeElLtjjR3cgFXk24BWQ0VUoEa6msyoPSR3YxtCRau5BSykc.AlKviZBbEA_I1iwBl6mh7HRbOhqqD0iNcV1dnORLTjc&dib_tag=se&keywords=20+awg&qid=1726518161&sprefix=20+awg%2Caps%2C141&sr=8-11	
16	JST Connector Kit	1	6.59	https://www.amazon.com/eBoot-Connector-Female-Cable-Battery/dp/B01M5AHF0Z/ref=sr_1_5?crid=38I06M8LG93Q1&dib=eyJ2IjoiMSJ9.5cOA-WvPV6cbqxwGW00qOtSElvu1WTQytk5qH2sMxl9HreCDZbYqjzZmWojRkhBoWNiqa5GXHpXn1SSNfC_Uj6yMxbxKJ4FwHDAIqttNqTr0z4Ndh89PQtcK9ibAYXBZBQud-Bcsf1WUCbY21FyamMCKU6GEvjTSIIrs4aWJqIcaQukvqXcFpyOcKOgsN0u5d0ZhQLx69NH1GZc8RHj5YCX5KHzT3FpKya9o5iIPKvIMn7H-L8FAiAymSgfX-mAlRTU4ehbiv2tQ2IEIg7wtR-bJk2Ri-3VGcfpXkMqLOG8.ceXvqsDR_8xkFwSrm8zhBSA5ApnfLs5ecfAZVtOBCis&dib_tag=se&keywords=jst+connector&qid=1726514650&sprefix=jst+connecto%2Caps%2C128&sr=8-5	
17	Slide Switch	1	6.79	https://www.amazon.com/cart/smart-wagon?newItems=814ef67c-18e7-4df1-b435-d0e8b802e1e9,1&ref_=sw_refresh	
18	12AWG Wire	1	15.99	https://www.amazon.com/gp/product/B0C6QXVHKL/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1	
19	Waterproof Gland	1	15.99	https://www.amazon.com/dp/B07Z9C9Q5X?ref=ppx_yo2ov_dt_b_fed_asin_title	
20	MR60	1	14.99	https://www.amazon.com/gp/product/B07X223LK3/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1	
21	6384 Motor	1	49.5	https://www.aliexpress.us/item/3256805603300813.html?spm=a2g0o.productlist.main.1.7a903af32yclxb&algo_pvid=6baf69dc-2132-41c0-bf1e-60e01593d54a&algo_exp_id=6baf69dc-2132-41c0-bf1e-60e01593d54a-0&pdp_npi=4%40dis%21USD%2150.00%2149.50%21%21%2150.00%2149.50%21%402101ec1a17222634778685954e5cf0%2112000034362123246%21sea%21US%210%21ABX&curPageLogUid=RbODZv4mJoYq&utparam-url=scene%3Asearch%7Cquery_from%3A#nav-review	

Battery

• 10s3p Molicel P42A welded using Maaletrics spot welded 18ms pulse
• 0.2x 9mm Nickel strip
• Daly BMS wired to charge batteries per manufacturers schematic (XT60)
• Main discharge (DIS-C) is connected with 10AWG to cells (XT90)
• Covered in Kapton Tape
• Surrounded by fish paper for insulation
• Covered with heatshrink, this was initially a very tight fit and required the next larger size to be used
  
  

Electronics Box Assembly

CAD:

Front View

Rear View

Blue highlights from left to right:

• Heat Sink (external to box, held in place with 5200)
• ESC Flycolor 160A**
• 3D printed bracket epoxied to wall of enclosure
• SS Threaded inserts
• SS Bolts

**Not shown is thermal pad between heat sink and ESC

Electronics box

• Clear case is spare 21700 battery holder with 1 3.6V cell powering the Flipsky receiver, a JST charge connector , Xt-60 for battery voltage measurement, and a power switch for convenience
  
  

Fuse, motor mount, prop and foil:

• For now I’m using the Gong 1300cm^2 foil, but I have a vacuum bagged / 3D printed one shown here

• Huge shoutout to @Hangloose for the 6384 mount, it works great and saved me a ton of design time! One note to highlight in blue below was to replace the standard copper threaded inserts and replace them with stainless steel inserts to avoid dissimilar metal corrosion in water between the threaded inserts and the stainless steel bolts.
  

  

• Many thanks to @V_S, I have used your propeller printed with Pet-G, covered in epoxy and lightly sanded, I’ve printed 3x but have only needed 1 for +20miles! Do you by chance have a 10s optimized design?
  

  

Waterproofing the motor:

• Disassembly was easy if I inserted bolts into the motor stator partially and clamped the heads by the vice and pulled the rotor off by hand

• I filled the bottom cup (black below) with melted wax, waiting for it to harden, wrapped the stater with tape, poured in the epoxy (not thermal epoxy, I was curious if it’s really needed since this whole assembly is in running water) then I melted it out with a decent result.
  

  

• Replaced bearings with ceramic bearings (The original set was rusting when I took them out of a tank test in the garage)
  

  

Summary:
The project was a great success! It worked on the first trial in the water and I have been able to get 3 friends out riding so far with the hopes they will build their own! Since I already had a foil and board for wing foiling, the cost of ~$600 for the electronics has been well worth the upgrade. With a 65kg rider, the board rides for ~40minutes and has a range of 3 miles, it cruises at 11mph comfortably. 85kg rider was still able to use the board with a steady takeoff.

Improvements:

1. Insert electronics box flush into the board, it’s such a hassle for people learning to get around a box being on the board
2. Improve schematic and safety with battery contactors, a kill switch, and improved thermal dissipation on the wires (12AWG gets warm)
3. Replace MR60 connector with a twist lock waterproof connector (This can get pulled loose when falling off the board)
4. Find/Make a BMS that supports 12S
5. Add current shunt and ammeter for battery telemetry
6. Update XT connectors style to have pre-charge resistor to avoid pitting on battery plug-in
7. Add another 6s worth of cells, I want ~3x the range I have right now!

[Sky8fz]

Thank for detailed description of your project! May you please tell the total weight of your foil drive system apart from the board and foil itself

[Jimmy25]

Thanks @Sky8fz, of course!

**Total Weight  5.927(kg) = 13(lb)**
Ebox            3.661(kg)
Foil Pod Drive  1.623(kg)
Strap           0.460(kg)
Flipsky VX3     0.183(kg)

[mekanism]

Cool build, thanks for the BOM! You mentioned wanting to switch to a 12S BMS, was 10S not enough power? I ordered the same motor, ESC, and Remote but am still doing research on the battery, BMS and other parts.

[Jimmy25]

Hey @mekanism,

There’s a few reasons you’d want to increase the voltage: efficiency, build safety, and top speed are improvements from 10s to 12s.

My design case (10s3P): Eg 36V nominal and 40A will equate to 1440W. (P=IV)
P = power
I = current
V = voltage

Increased battery voltage case (12s3P): 43.2V nominal and 33.3A

Heat generated H =I^2Rt
I = current
R = Resistance
t = time

Since we have the current term multiplied by itself (I^2), even a small decrease in current will lead to a large decrease in heat.

So for efficiency, with less heat, the wire we choose can be smaller gauge, or it will give us more headroom on the wire choice we have. We size wire by the current it can hold at a certain temperature (use a lookup table for this). We can purchase lighter gauge wire to save weight, make routing easier with less bend radius required, and smaller wire means smaller connectors which are easier to solder than the large ones.

There’s additional benefits for a higher voltage dropping less percentage than lower voltage for the same conductor but we’ve got such a small length wire run that I doubt that plays a large factor. (Read about voltage drop in wire if this interests you)

The build safety is impacted because we will have less heat in the batteries intercell connections with less current flowing through them. Theoretically, the rest of the wires in the system as well as the batteries connections will also benefit from running cooler which will extend the life of the conductor’s connections and shielding from reduced thermal cycling (less cracking).

Finally speed, each motor has a kv rating and if you multiply that kv by the voltage, you’re roughly going to get the rpm of the motor. More rpm = higher top speed and more speed with less throttle, which increases range. Of course, there’s trade offs, so you get less motor torque with less current and will have to learn about properly designing a prop for each voltage which is why I was asking in my post if there’s a prop designed for 10s out there.

To answer your question if I don’t feel like I have enough power, no. There’s plenty of power with the 10s3p setup and I can even get up on foil with a battery voltage of ~32.5VDC when the flipsky controller gives the low voltage warning for a 10s battery (this is configured in the controller’s settings).

Best of luck on your build! Let me know how it goes!

[mekanism]

Thanks for the detailed response. You have me convinced to go 12s now. I have read through the foil drive assist diy topic and it seems others are heading in the 12S direction as well.

Would you still use the 12AWG wire with 12S to gain some headroom like you said or go up to 14AWG? Also, I don’t see many options for a 12S BMS, were you able to find something that will work?

[Jimmy25]

The battery current in each phase 12AWG wire I measured with the motor mast in a bench test submerged in water was ~15A max. It’s probably higher for actual use in the field because as soon as the water started to circulate in the bucket in my test, the current dropped to ~12A probably because the torque required to move the water dropped with the circulation of water .

12AWG wire has been used pretty extensively on the forum here and mine gets very warm to the touch, so I wouldn’t try to go with a smaller gauge at this time for fear of burning wire and shorting out in the water. (Not very dangerous at this voltage, just unpleasant)

A reputable source: https://www.engineeringtoolbox.com/wire-gauges-d_419.html

Says that for 12AWG wire up to 3 cores can handle up to 20A max (more wires together creates more heat and reduces the current carrying capacity before the insulation melts and you get a short/ burn out.) Note as well, we’re running this wire partially submerged in water and thus have excellent cooling for the wire run going down the mast.

I haven’t had many any issue with the Daly charger besides my power supply/ boost converter setup resetting when it hits 42VDC (fully charged 10s molicel cells).

As for a 12S BMS, I think this would work:
https://www.aliexpress.us/item/3256805498397420.html?src=google&gatewayAdapt=glo2usa

If anyone has a better source, please chime in!

[S_Roger]

If you’re in the USA and don’t want to order all the way from China, there’s batteryhookup. I’ve been using one of these as a charge-only BMS (actually the 10S version), they have many flavors to choose from:

Li-ion/Lifepo4 3s-20s 30a BMS WITH BALANCE

[s9tim]

I have been using 14awg wire thru the mast for three years on my boost setup without issue. Not saying this is the way you want to go. I do not efoil more then 30 seconds or so at a time, using 12s.

[Jimmy25]

Just more data points, with the setup I have, I’ve continuously efoiled on flat water for 3 miles with 2 starts and used the entire battery doing so.

[mekanism]

So with a charge only BMS I could technically not need to install a BMS to the battery pack correct? I’m still not sure how I want to build a battery, BMS, no BMS. Seems there are different views on this. I want reliability, and have read that on pack BMS’s tend to fail frequently.

[S_Roger]

Usually the BMS is built onto the battery pack, even for charge only. The diagram @Jimmy25 made at the top of this thread sort of shows it, but not the full wiring. You’ll end up with a separate charge port and discharge port. This keeps things simple when you have to charge.
You could actually have an external BMS that you connect when you charge, then you need to have external balance leads to connect and disconnect.
You could also split the pack into to 6S packs and use an RC balance charger to charge the battery in two halves. Then once they are charged (to the same voltage!) connect them in series.

[Foilguy]

Your correct in there are a variety of views on how to implement BMS likely driven by use case and design philosophy.

What is important to remember that it is important to have BMS involved in the charging process.

This site might prove useful in coming up with a strategy that’s works for you.

Learn About Batteries

[Larsb]

@Jimmy25

Since we have the current term multiplied by itself (I^2), even a small decrease in current will lead to a large decrease in heat.

Theoretically true but it’s good to put into perspective what small and large is. Play a bit with a power calculator and you’ll see for a dc wire it’s only a few watts that you’re talking about, even with a 14awg wire.

For the motor wires it’s naturally more since motor current is higher than battery current.
Kv x voltage and rpm: yes. But you could also use a higher kv motor (not optimal but for the sake of comparison). This will require higher motor current to reach same torque, if you wind a 1.2x higher kV then 1.2 higher armature current is needed, 1.44x the ri2 losses.

Regarding heating, each wire is conducting 50% of the time and this lowers the motor wire heating.
(this is true for six step commutation, foc is different and not possible to estimate like this, however foc is a bit more efficient so this calc is on the high side)

An example at 50% duty cycle, with scaled kV for 10s to reach 12s rpm, including scaled voltage and current, 14awg wires :

Difference is 64W here, 4% of 1500W, it’s with 14awg wire (which I wouldn’t use anyway). We could use 10awg and win back roughly 80W. Point is the same, no huge differences but 4% is too much in my opinion. As long as cooling is good enough you probably won’t be able to tell the difference.

Inside the box is more interesting with higher kv and current, esc and batteries will produce more heat that needs to be transferred to the outside.

[Leapnlarry]

Have you made a video about your build? Are there videos of other foil assist builds, i searched youtube but not much came up. im looking for a diy replica of the foil drive system, cant afford 5k. Thanks

[Jimmy25]

I have not made a video, but I can if you need it.

What do you want to see it in that’s not in the write up above?

[lishine]

Currently there is not one video on YouTube of a foil-assist build process. Only in action.