Efoil Build in Missouri

My homebuilt electric hydrofoil. - YouTube

Equipment: Total Cost: ~ $1087

  • Fresh water (I live in Missouri)

-old kneeboard I had laying around - $0

-Hydrofoil- Gong Allvator Rise M70 (front wing 70cm wide, volume1500cm², rear wing 45cm wide, volume 270cm², Mast - 80cm (select the “kitefoil” for the 80cm mast) $342.49 (shipping included)

-44.4v 12s 2kwh li-ion battery (used ev battery from batteryhookup.com) - $200

-130kv 65121 flipsky brushless motor, 3700w peak, 2000w continuous - $269

-Flipsky FS75100 ESC ( uses open source VESC software) - $130

-Apache 3800 water proof box - $54

-moto z2 force ( VESC display - any old android phone) $0

  • Vanpro RC car/skateboard controller - $23

  • xt-90 anti-spark connector - $1 (10 for $10)

-8awg silicon wire to extend motor wires $69 (this was 50’ so I have a lot left over)

-motor mount (mast clamp) - pine 2x4 and aluminum flashing I had laying around, I may attempt to 3D print a better solution in the future.

-propeller - 7 1/2 x 7 propeller that was included with the flipsky 65121 motor, it is far too big. I’ve cut it down to about 110cm or 4.33" - I’m currently only getting about 1500rpm drawing 70 amps from the battery (50v fully charged). This motor has ~5N/M or torque, its bigger brother, the 65161 has ~9N/M or torque from what I’ve read.

I haven’t gotten up on it under its own power yet. I’m still tweaking things. I think I may need a bigger surf board.

I can only load one photo at a time because I’m a new user, although I’ve been lurking for at least 3 years enjoying all of your posts!

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My mast clamp looks pretty janky, but it is actually quite solid! It’s made from a pine 2x4 and some aluminum flashing.

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Here’s a screen capture from a 30 second ride showing my power usage and rpm ( divide erpm by 6) so I peaked just under 2000 rpm pulling around 80 amps from the battery, I have the motor amperage limited to 120amps. I required an assist from a boat to get going, although once up I do have enough power to ride. Does anyone think a 2 blade prop would give me better efficiency? I then removed the prop and rode behind the boat, and I have to say, the motor does add a lot of drag. I plan to 3d print a better mount, change to a paddle board so I can start standing up, and find or print a 2 blade propeller. Any ideas or suggestions are appreciated!

Here is the link to the screen capture of my vesc data.

Electric hydrofoil ride, with boat assist to get on the foil - YouTube

Sorry about the low quality, not sure why it is so grainy. I also have a video of the ride, will post it later.

I think maybe your board is too small to get on foil for the amount of power avaliable. For reference I need 180 - 200A at 16s to get up on foil with a 5ft board 130mm thick at 115kg. Once on foil it drops down to 30 - 40ish amps. A bigger board, more streamline motor mount and better prop will definitely help

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Thanks for the reference point, that helps! I weigh 80kg and my board weighs 30kg, so pretty similar. I have different batteries that could save about 5kg at the expense of range as well.

Lol I mean my fat ass alone weighes in at 115kg :sweat_smile:. Board with bat and foil is roughly 30kg.

Question for others using VESC regarding motor RPM.

I’m running at 50 volts, My ERPM is maxing out at 18000 which indicates 3000 rpm 18000/6 poles is 3000rpm, I’ve verified that is correct using an android app that uses a strobe light function to check rpm (really easy effective way to check rpm). With a 130kv motor I should get 6500rpm at 50v right? I measured ~30v AC between motor wires at full throttle. Am I missing something? Is the KV rating wrong? What should the voltage between two of the motor wires be from the ESC at 100% duty cycle? I’m in FOC mode, max ERPM is set to 50k, and I’ve checked other minimums to see if something is limiting my rpm.

Success! The two blade propeller did the trick. VIDEO LINK ABOVE

The two blade 9-spline propeller fits my flipsky 65121 motor with only very minor modification and some electrical tape on the shaft to make it fit snug, also adds some dampening. It was originally 7x4 3/4 but I cut it down to 6" diameter, crude hack saw job but there doesn’t seem to be any vibration!

I had longer rides, but that was the only one that I got on camera.

Takes 75amps to get on foil, then it drops down to 30 or so.








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Here is another video, with VESC real time data. About a one minute ride. I need to add some water cooling or improve my passive cooling.

Adding water cooling. I could have bought a CPU cooler but I like to use what I have lying around. Going to test it out later today hopefully!




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