Welcome to foilassist.diy

is a sub $300 foil assist possible?

Hello, my name is Jerome. My goal was to build a motorized foil assist unit for under $300 USD, and I did it! Now I want to share my experience and knowledge with anyone that is interested in doing the same.
The primary function of my foil assist is for boosting into swells that are otherwise uncatchable. Its speed and range is similar to commercially available units but for a fraction of the cost.This is my project documentation website. I have developed, compiled, and documented this information and it is available for everyone. All in one place. No more hunting through threads, searching endless websites, pricing multiple parts sources, or worse, finding untrustworthy information.My basic build journal is all here for FREE on the website. Just click on the buttons at the bottom to navigate. The premium PDF Build Journal is just, $49. It has more detailed pictures, wiring and pinout diagrams, code hacks, maintenance tips, pitfalls to avoid, and the entire BOM with product links.

SUMMER IS ALMOST HERE.
LET'S GO!

• BUY PDF

AVAILABLE MAY 16TH, 2026

PROVEN

After many fails and iterations I was able to achieve success. Even though this unit is built with foil assist wave catching in mind, to date, I have logged over 20 miles riding in efoil mode (flat water) and I have just started. I have many many more miles of wave riding to look forward to.

mission

The challenge was to build a fully functional foil assist unit with a $300 budget. They said it could not be done.Simplicity at its core, only the essentials. That is my build philosophy. Complexity offers more failure modes. Sure, I could add all sorts of "features" such as a telemetry screen on the remote or a BMS. At worst, those are potential points of failure with added cost. At best, they are just conveniences. But the reality is that "features" do not enhance my ride, my foiling experience.This is my personal build journal. It is not an "instruction manual". However, if you follow along, you will see exactly how I did it, what materials I used, where I got them, and how I assembled them. You can use this info as a blueprint for your build. You can modify it as you like, such as use a bigger 6384 motor, or a 65111 inrunner motor. You can use a 12S4P battery configuration for more range, or use a commercially available remote control with this build. You could even integrate the enclosure into your board! Use this information to inspire your build and guide you along the way.The success of this challenge is a big middle finger to the haters, the naysayers, and the gatekeepers who not only doubted this could be done, but discouraged others from daring to create, problem solve, and imagine. To those trolls and negative goons, I say stay in your box, the one that keeps you and others from progressing. This is for all who dare to think outside the box and imagine what can be done.

BILL OF MATERIALS

Below is the Bill of Materials list with prices for every part used in my foil assist unit, everything down to the nuts and bolts, hook up wire, and even teflon tape. This is an extensive list but keep in mind that prices and availability can change. I have receipts for all of the items I used for this build. I ONLY used BRAND NEW parts. These are NOT estimates.

The entire BOM product links are listed on the premium PDF. It can save hours and hours of searching the internet. How much is an hour of time saved worth?

Note: The free information contained in this website is my build process. The premium PDF version adds build details, photos, temperature settings, pinout diagrams, tips, tricks, pitfalls, and product links. The PDF is my personal build journal which can be used as a blueprint to build yours. It is not a traditional "instruction manual". It is a very detailed account of how I took an overwhelming pile of parts and methodically assembled them into a high-functioning foil assist unit. My journal documents what worked for me. If it worked for me it can work for anyone. Obligatory legal disclaimer: The operation and safety of any build is the builder's responsibility.

ESC

ELECTRONIC SPEED CONTROLLER: I chose the Sequre SQESC 12200. I selected it for its impressive 200A current rating, its 5S to 12S battery capability, lightweight size, price, AM32 configurability, and easy setup. This is a good quality ESC and works well for this purpose. It even comes with heat shrink tubing for the terminal pads and a signal wire harness.This ESC is not VESC configurable. VESC is an awesome tool, but in my opinion it is incredibly overkill and complex for foil assist or eFoil use. It is like using an aerospace grade flight controller to operate a kitchen blender to make a margarita — totally unnecessary. For a foil assist, an ESC only has to spin a motor, one direction, with no brakes. That's it.

The AM32 settings I used are shown below.

The complete itemized bill of materials for the entire build is on the BOM page.

BATTERIES

This component holds all the power — literally. There are many horror stories involving lithium-ion powered devices. Before I started my build, I had heard of exploding vape pens, cell phones, eBikes, hoverboards, and Teslas. I chose to treat the lithium-ion battery with respect, but I did not fear it. By being careful and knowledgeable of what I was doing, I was fine. I have not had any battery accidents. Knock on wood. What follows is exactly what I did to make my 11S3P 46.2V battery pack. With over 20 miles of successful riding, this battery building method has proven to be safe for me.

I opted not to use a BMS because I routinely monitor my charging process. The BMS, in my opinion, is a battery nanny for people who don't know how or don't want to manage their battery. I bulk charge my battery/cells, and I have had ZERO issues or events. Educate yourself on battery management. Jehu Garcia on YouTube is an excellent resource for battery knowledge. https://www.youtube.com/@jehugarcia
My battery charging process is detailed in the premium version PDF.

The complete itemized bill of materials for the entire build is on the BOM page.

THROTTLE TX

REMOTE CONTROL: This is the transmitter unit. It’s designed to be rugged, easy to make, inexpensive, and completely waterproof. I used a 1" PVC riser as the body and a standard e-bike throttle for the controller. I chose this type of throttle because it uses a Hall effect sensor to send signals. This means the signal mechanism is immune to sand, saltwater, and corrosion. I completed the steps below and ended up with a throttle transmitter/remote control that I made from scratch. It works great, is very rugged, and was easy to build. If it works for me, it will work for you.Notes: I used PVC parts because they are very easy to source and they are completely waterproof, obviously. PVC should be available at every hardware store. The only variable might be the shape of the cap. It really depends on the manufacturer. But the 3D model is very simple, so it can be modified easily.I designed the throttle behavior specifically for foil assist and eFoiling. The code for the ESP32 module-controlled throttle is entirely my own creation. My concept is a response to the challenges of full-range throttle control. My concept is called Compressed Range Gearing with 4 Speeds (CRG/4S).How CRG/4S Works
Instead of using the entire throttle signal range, CRG/4S compresses the usable range into four distinct gears. This eliminates the need for the lower and upper extremes of the throttle signal, which are often either too slow or too aggressive for stable riding.For example:
The lower range of the throttle barely moves the propeller, so it’s excluded.
The upper range (e.g., 7854 RPM at full throttle, 46.2V x 170 KV) is unnecessary for most riding scenarios. By focusing only on the middle, usable range, CRG/4S provides precise control with four clearly defined speed settings.The 4 Distinct Gears of CRG/4S
Each gear is designed for a specific phase of eFoiling:Gear 1 – Slow Taxi
Ideal for getting the water moving under your hull.
Provides stability at low speeds.
Gear 2 – Planing Speed
A steady, stable speed to help you transition to kneeling or standing. The board is on plane
and very stable. Smooth speed without sudden lurches.
Gear 3 – Lift-Off Power
Designed for takeoff and cruising.
Doubles as the cruising speed—just set it and enjoy the ride.
Gear 4 – Boost Mode
A high-power boost for when you need extra speed or to escape tricky situations.
Also doubles as a cruise speed when the battery voltage sags.Why CRG/4S Solves the “Porpoising” Problem
When I first tried my friend Gary’s genuine Foil Drive, I loved the experience—but as a beginner, I struggled with hunting for the right RPM. It was either too fast or too slow and, I went up and down like a propoise. The throttle felt like an on/off switch.
CRG/4S eliminates that porpoising—just direct, predictable control in every gear. Bonus: It gives you increased efficiency, extra runtime, and more fun!CRG/4S is Customizable and Open-Source. You can adjust the code to suit your weight or riding style. Feel free to tweak it and share it!
You can find the code below.
Have fun riding!

The complete itemized bill of materials for the entire build is on the BOM page.

Here is how I built my throttle:

• FREE THROTTLE BRACKET 3D FILE - CLICK HERE

• TRANSMITTER CODE FILE - CLICK HERE

The code for the ESP32 S3 based transmitter is provided below. My build journal PDF details how I upload the code to the ESP32 module.

#include <espnow.h>
#include <WiFi.h>// =====================================================
// CRG/4S ESP32 S3 SuperMini 4-Speed Discrete
// Hall Throttle: Pin 4 | 810–2943 (12-bit, 3.3V)
// V260509 GOOD
// Output: 0–32767 CRG to RX
// foilassist.diy
// =====================================================// ---------- Packet ----------
struct Packet {
uint16t throttle;
uint8t deadman;
};// ---------- RX MAC Address **(BE SURE TO INSERT YOUR SPECIFIC MAC ADDRESS)----------
uint8t rxMAC[] = {0x4F, 0x00, 0xAD, 0x04, 0x64};espnowpeerinfot peerInfo;// ---------- Hall Sensor Throttle Signal ---------- USE PIN 32 ON WROOM MODULES, OR PIN 4 (OR 5) ON S3 MODULES
const int THROTTLEPIN = 4;// ---------- Throttle Calibration ----------
const int THRIDLESAFE = 810;
const int THRFULLSAFE = 2943;
const int THRFAULTLOW = 600;
const int THRFAULTHIGH = 3300;// ---------- Deadzone ----------
const float DEADZONE = 0.05f;// ---------- Gear Thresholds (auto by throttle position) ----------
const float G2 = 0.05f + 0.2375f; // 0.2875
const float G3 = 0.05f + 0.2375f * 2; // 0.5250
const float G4 = 0.05f + 0.2375f * 3; // 0.7625// ---------- Discrete Gear Speeds (fixed CRG output per gear) ----------
const uint16t SPEEDG1 = (uint16t)(0.40f * 32767); // 13107
const uint16t SPEEDG2 = (uint16t)(0.60f * 32767); // 19660
const uint16t SPEEDG3 = (uint16t)(0.80f * 32767); // 26214
const uint16t SPEEDG4 = (uint16t)(0.95f * 32767); // 31129// ---------- Send Rate ----------
const unsigned long SENDINTERVALMS = 20;
unsigned long lastSendTime = 0;// =====================================================
void setup() {
Serial.begin(115200);analogReadResolution(12);
analogSetAttenuation(ADC11db);
pinMode(THROTTLEPIN, INPUT);WiFi.mode(WIFISTA);
espnowinit();memcpy(peerInfo.peeraddr, rxMAC, 6);
peerInfo.channel = 0;
peerInfo.encrypt = false;
espnowaddpeer(&peerInfo);Serial.println("TX ONLINE");
}// =====================================================
void loop() {
if (millis() - lastSendTime < SENDINTERVALMS) return;
lastSendTime = millis();int raw = analogRead(THROTTLEPIN);// ---------- FAULT CHECK ----------
if (raw < THRFAULTLOW || raw > THRFAULTHIGH) {
Serial.println("THROTTLE FAULT — SENDING ZERO");
Packet pkt = {0, 1};
espnowsend(rxMAC, (uint8t *)&pkt, sizeof(pkt));
return;
}// ---------- NORMALIZE ----------
float norm = (float)(raw - THRIDLESAFE) / (float)(THRFULLSAFE - THRIDLESAFE);
norm = constrain(norm, 0.0f, 1.0f);// ---------- DEADZONE ----------
if (norm < DEADZONE) {
Packet pkt = {0, 1};
espnowsend(rxMAC, (uint8t *)&pkt, sizeof(pkt));
return;
}// ---------- SELECT DISCRETE GEAR SPEED ----------
uint16t crgOut;if (norm < G2) {
crgOut = SPEEDG1;
} else if (norm < G3) {
crgOut = SPEEDG2;
} else if (norm < G4) {
crgOut = SPEEDG3;
} else {
crgOut = SPEEDG4;
}// ---------- SEND ----------
Packet pkt = {crgOut, 1};
espnowsend(rxMAC, (uint8_t *)&pkt, sizeof(pkt));Serial.printf("RAW:%4d NORM:%.3f CRG:%5d
", raw, norm, crgOut);
}

RECEIVER

The receiver is the connection between your finger and the propeller. Its primary job is to receive the throttle signal from the transmitter and translate that signal and feed it to the ESC (motor controller).I selected the ESP32 development modules for my remote control system. The advantage to using this particular microcontroller is that it has a native radio on board, therefore it has Tx and Rx capability built in. It uses ESP NOW communication protocol.Why should anyone care? Because it has no latency, and it pairs instantly. What does that mean? It has no lag time and instant throttle response! And, it is easy to configure.Below, I outline the steps I used to prepare the receiver.

The code for the ESP32 receiver is provided below. My build journal PDF details how I upload the code to the ESP32 module.

#include <espnow.h>
#include <WiFi.h>// =====================================================
// V260509 WEBSITE RX HYSTERESIS SKETCH
// ESP32 WROOM DEV MODULE
// foilassist.diy
// =====================================// ---------- Prototypes ----------
void writeIdle();
void disarm();// ---------- Packet ----------
struct Packet {
uint16t throttle;
uint8t deadman;
};volatile Packet incoming;// ---------- Output ----------
const int OUT1 = 18;// ---------- PWM ----------
const int PWMMIN = 1000;
const int PWMMAX = 2000;
const int FRAMEUS = 20000;// ---------- Safety ----------
const uint16t RXMAX = 32767;
const unsigned long RXTIMEOUTMS = 500;unsigned long lastRxTime = 0;
bool armed = false;
bool linked = false; // CRITICAL: Signal only starts after first packet// =====================================================
void onReceive(const uint8t *mac, const uint8t data, int len) {
if (len == sizeof(Packet)) {
memcpy((void)&incoming, data, sizeof(Packet));
lastRxTime = millis();
linked = true; // "Wakes up" the signal output
}
}// =====================================================
void setup() {
Serial.begin(115200);pinMode(OUT1, OUTPUT);
digitalWrite(OUT1, LOW); // Stay flat-low at bootWiFi.mode(WIFISTA);if (espnowinit() != ESPOK) {
while (true) { delay(100); }
}espnowregisterrecvcb(onReceive);
Serial.println("RX ONLINE — STANDING BY FOR TX...");
}// =====================================================
void loop() {
// SAFETY GATE: If no packet has ever been received, keep PIN LOW.
// This allows the ESC to beep its "No Signal" alert.
if (!linked) {
digitalWrite(OUT1, LOW);
return;
}// ---------- FAILSAFE ----------
// If we lose connection after having been linked, or deadman is 0
if (millis() - lastRxTime > RXTIMEOUTMS || incoming.deadman == 0) {
disarm();
return;
}// ---------- ARM ON ZERO ----------
if (!armed) {
if (incoming.deadman == 1 && incoming.throttle == 0) {
armed = true;
Serial.println("RX ARMED");
} else {
writeIdle();
return;
}
}// ---------- DRIVE LOGIC ----------
uint16t crg = incoming.throttle;
if (crg > RXMAX) crg = RXMAX;int pulse = map(crg, 0, 32767, PWMMIN, PWMMAX);noInterrupts();
digitalWrite(OUT1, HIGH);
delayMicroseconds(pulse);
digitalWrite(OUT1, LOW);
interrupts();delayMicroseconds(FRAMEUS - pulse);
}// =====================================================
void writeIdle() {
noInterrupts();
digitalWrite(OUT1, HIGH);
delayMicroseconds(PWMMIN);
digitalWrite(OUT1, LOW);
interrupts();
delayMicroseconds(FRAMEUS - PWM_MIN);
}// =====================================================
void disarm() {
if (armed) {
Serial.println("SYSTEM DISARMED");
armed = false;
}
writeIdle(); // Fall back to 1000us (Zero Throttle)
}

MOTOR

The ubiquitous 6374 BLDC motor provides the thrust for this build. It is the standard size motor that many commercial foil assists use. They are readily available and relatively inexpensive. They are so inexpensive that I could buy 17 of them for the price of a commercial replacement (~$700). So hypothetically, I could buy a new motor each season, for 17 seasons, for the price of one commercial motor. In other words, I don't sweat it if it craps out after good use. But, I address the topic of maintenance and bearing replacement in the premium PDF.

6374 BLDC motors come with a long shaft that will need to be removed. The shaft interferes with the mounting to the foil mast. It is not difficult to remove. Follow the steps below.

3D PARTS

3D printed parts are satisfying to make! I use a stock Creality Ender3 printer. You can pick them up on Facebook Marketplace for around $50 used. Once I got my bed leveled and set up it worked fine. Also, Ender3 parts are super cheap and readily available.
The great thing about having a 3D printer is that you can make unlimited spare parts and modifications.I use PLA filament. Haters will say PLA doesn't work for propellers. They will say, "what about the UV exposure"? Keep your parts out of the sun when not in use. They will say, "You have to use Nylon or CF (carbon fiber) reinforced filaments!" Nylon is flexible and less rigid than PLA, and CF-reinforced filament has been exposed as marketing hype. They will tell you that you can't do this and you can't do that.Some people will say you need to coat your parts in epoxy, and you need to fine-tune and balance your prop blades. I didn't, and my parts are working fine! I ride mine all the time, zero issues with excessive vibration or out-of-balance blades or separating layers.In fact, I have only had 2 parts fail during this whole process, and both were my fault, not the fault of PLA filament.
Failure 1: The propeller blade snapped off at its base. The cause was incorrect print orientation. I stupidly printed the blade in a vertical orientation, and the layers were in a concentric pattern. Of course it would snap off! Duh. Print orientation is IMO the most important factor in making a strong and reliable part.
Failure 2: I had been post-session rinsing my motor with fresh water (totally fine) and finishing with a spray of WD-40. The WD-40 spray got on the propellers and weakened the PLA; they eventually failed. My fault again. DO NOT USE WD-40 ON PLA. I only use Corrosion-X on my motors now. It doesn't seem to affect the PLA, or it hasn't yet (it's been months). To date I have over 20 miles of riding on PLA propellers with ZERO FAILURES!I ignore the haters, naysayers, and gatekeepers because I'm too busy foiling.

1. Download the STL Files
- I found the STL motor mount and propeller files online at Thingiverse.com and downloaded them to my computer. Where necessary, I modified them to fit my needs. I have provided the Thingiverse links at the end of this page.2. Prepare the File in Slicer Software
- I opened the STL file in my slicer. I use Cura as my slicer.
- I positioned the part on the virtual build plate to optimize print strength and quality.
The most critical factor IMO regarding the part's strength is print orientation.*
- I adjusted settings like:
- Layer height I used 0.3mm for faster printing and strength.
- Infill density I used 100% for strength.
- Supports (enabled if the part has overhangs).
- Print speed (slower for better quality, faster for prototyping).
- I sliced the file to generate the G-code.3. Prepare the 3D Printer
- I cleaned the build plate to ensure the part would stick properly.4. Start the Print
- I transferred the G-code file to the printer via SD card or USB.
- I started the print and monitored it for the first few layers to ensure it adhered correctly.5. Post-Print Finishing
- Once the print finished, I carefully detached the part from the build plate.
- I removed any supports with pliers or a knife.
- I sanded rough edges if needed for a smoother finish.6. Final Checks
- I inspected the part for any defects or issues. If they look good then they are ready to install.

Cura Slicer settings and other detailed tips are provided in the premium PDF.
Links to free 3D part files are provided below.

• MOTOR MOUNT - CLICK HERE

• PROPELLER - CLICK HERE

• THROTTLE BRACKET (1" Diameter version)- CLICK HERE

• MAST CABLE GUIDE - CLICK HERE

enclosure

I used an IP67 rated enclosure for this build. I have tried all sorts of enclosures, such as handgun cases, hinged and unhinged electronics enclosures, aluminum, and plastic. I even tried an ammo box. The most important thing to consider is that the enclosure must be rated IP67 waterproof or better. Secondary is size. Of course, I tried to keep it small and light. There is always room for improvement. This enclosure is what I used for this version. It works very well. No issues. I only needed to make one penetration for the phase wires. The steps below document how I did it.Of course, I don't prefer to have a goofy box sitting on the deck of my board, but future solutions are coming. For now, the will to ride is stronger than my dislike of a deck mounted box.

ASSEMBLY

Almost finished and so close to ride time!

PICTURES

COMING SOON!

SOAPBOX

COMING SOON!

COMING SOON!

skunkworks

COMING SOON!
TENTATIVE SKUNKWORKS RELEASE SCHEDULE:

SUB $300 J-DRIVE STANDARD 5/16/2026
SUB $350 J-DRIVE DAILY DRIVER 5/18/2026
J-DRIVE PASSPORT FOIL ASSIST 6/1/2026
SUB $400 eFOIL J-FOIL 6/15/2026
SUB $250 J-DRIVE LIGHT 7/1/2026
TWIN-TURBO 5065 8/1/2026
J-DRIVE MICRO BOOST 8/15/2026
J-DRIVE TOW-BOT 8/30/2026

THE BLUEPRINT

AVAILABLE MAY 16TH, 2026

$49

• BUY PDF

Welcome to the J-Drive build journal. A few things up front:
This premium PDF has added build details, detailed photos, temperature settings, connections, code hacks, pinout diagrams, tips, tricks, pitfalls, maintenance, etc. The PDF is my personal build journal, which can be used as a blueprint to build yours. It is not a traditional "instruction manual". It is a very detailed account of how I took an overwhelming pile of parts and methodically assembled them into a high-functioning foil assist unit. My journal documents what worked for me. If it worked for me, it can work for you.

Note: I do not offer technical support — no email, no calls, no DMs, no exceptions.
Not because I don't like people. Because answering questions takes away from my other projects, riding my foil, and time with my family. I'm not willing to make that trade. Fair warning, fair deal.

AVAILABLE MAY 16TH, 2026

$49

• BUY PDF

Obligatory legal disclaimer: The operation and safety of any build is the builder's responsibility. "By purchasing you acknowledge this is a personal build journal for informational purposes only. Builder assumes all responsibility for their build and its operation."