RC hydrofoil

by antoinef, published

RC hydrofoil by antoinef Jul 19, 2015
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June 2017:
The rudder assembly has been reworked to allow for a change in the pitch angle. I mounted to servos and mix them (V-tail program on the transmitter). You need two 624ZZ 4mm x 13mm x 5mm ball bearing.
I added a new set of back foils (symmetrical) as well.
The boat is much more stable now!
I thing that if you don't want to add the relative complexity of a mixing servos, it should work just by setting up the proper angle and fasten it in place.

Thanks for your comments and I hope that you guys will build it, it's a great project!


July 26th 2015: This is my latest attempt of a RC hydrofoil.

The profile is a Naca 63-412 (both front and back foils). The back foil has a 5deg dihedral for lateral stability. It's in two parts, glued together, in order to print the part without support.

The foiler is actually flying but on a very narrow speed range. Enough to make it lift itself and not too fast otherwise the prop is reaching the surface and starts to cavitate.

I would really appreciate any suggestion to improve it.

As mentioned previously, I’m working on a new hull, in four parts of max 15 cm so it would be printable on a variety of printers. Keep you posted.

Penny Express – Not 1898 pennies, but just one riding in style!

This is my entry to the MakeItFloat challenge.

I always wanted to make a RC hydrofoil, so what a great opportunity.

This is my first real project with 123D Design and 3d printing and I can tell you that I learned a lot.

This boat can theoretically carry 1’898 pennies, but I decided that only one would ride, so I had to find a very special place.

After 6 weeks of endless nights and weekends, about 100 hours of total printing time three prototypes and almost 40 iterations, what I expected to be a simple project finally started to lift up two days ago (video here; https://youtu.be/DgALh0y2N18).

I tried every thing that I can think of; changing the foil profile, size, angle without much success. I truly experimented Thomas Edison quote: “I have not failed. I've just found 10,000 ways that won't work.”

I wanted to do a simple boat, with an air propeller as propulsion with basic RC equipment, but my first prototypes acted more like fast diving submarines that flying boats. They were too heavy, too unstable and too small. I finally went for a more conventional marine setup. The hardware is easily available in any boat hobby shops.

In my latest prototype I reduced the thickness of the hull from 3mm to 1,6mm and almost double the overall size. It looks great and flies well.

This model is easily modifiable; the foils just interlock in the hull and can easily be removed and changed. There are 15 parts altogether and they can be printed without rafters or supports (PLA) in any printer that can print in a volume of 18cm x 18cm x 18cm. I will update the files to be printable on a 15cm height printer.

The hull of the latest version is in three parts that are glued together using 5 minutes epoxy. The front foil is in four parts allowing to print a large foil (modified Naca 4412-33 profile).

There are almost no RC hydrofoil models or plans available and very limited info on them, so I hope that this project will serve as a base for any one interested in pushing it further.

Thanks’ a million for the learning experience and having make an old dream come true!


Printing tips:
I printed all parts in PLA with a fill density of 20%.
The hull parts are all printed in a “vase” configuration.
The back hull is printed back down.
The middle part front down, and the front part back down.
The back foil has a flat bottom so it prints in one piece (very cool looking part ;-)
The front foil is printed in four parts, glued together with epoxy in the middle of the profile. I sanded the foil to have a better penetration.
The two front panels are glued in place with silicon once the components are in place. The back panel is just taped on with duct tape (the only one that I can find that actually stick to the PLA). This is not satisfying, suggestions are welcome!
The foils (front and back are just tacked glued in place with a little bit of silicon. Very easy to get out if needed.
The motor mount was design to fit a 960Kv 480 brushless outrunner motor. I will update it to a more generic support in the near future.

Design considerations:
The actual front foils are 4412-33 scaled down in thickness to 75% with a 6 deg positive angle. They are too powerful for the light wait of the boat using a 1800 mA 3S battery. I will try a dipper V angle with a 5 deg angle next. The front foils are inserted in to Dagger board housing with easy dimensions, so feel free to experiment and please let me know if you are making progress.

In this configuration, the boat has a very narrow speed range. I hope that the new foils will correct that.

Please let me know if you need more info.

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Hi I'm going to be making one, what sort of prop shaft did you use and where did you get it from?

Hi there,
I use a flexible shaft that I had.
It's better if the prop is parallel to the water surface, but a strait axle would probably work well too.

Hi. This is a neat design that I'm attempting to put together, but it looks like you are missing the file for the rear flex shaft mount that attaches to the bottom of the hull. Note that it is also not seen above in the Thingaverse file preview.

I was able to load the cad file into 123D and extract the missing part into a .stl. Thanks for including the original file.

This is an inspiration! I'm an RC flyer, but want to get into RC boats... but no ordinary boats... hydrofoils! Coincidentally I'm also keen to get into 3D printing. There are no RC model hydrofoil kits available, so 3D printing seems the logical choice. This design is inspiring me to make a start! I just need to get a 3D printer first...!

One day I'd like to 3D print a scale warship hydrofoil (perhaps even Sparviero-class) . Ultimately I'd like to integrate a pump to create a jetfoil, and autopilot (perhaps using Ardu-pilot or something Raspberry Pi based) with fully submerged (FS) foils... but I'm getting ahead of myself. I must walk before I try to run!

That said, 3D printed water jets designs are out there (and RC boats to go with them). Would you consider the next iteration of your model integrating such a water jet? I'd be pleased as Punch and happy as Larry!

I'm currently working on a FS foil design but it still not ready to be published.
I considered the jet design, but I finally decided to create a Z-drive that works beautifully well!
Regarding the stabilization, I tested the auto leveling receiver from HK that works well.

Sounds fantastic!!! Can't wait for it to be published!

Is the Z drive 3D printed too?

A receiver with built-in stabilizer is a fab idea! What about banking in sharp turns?

How are you monitoring flying height? Ultrasound?

Yes the z-drive is already printed and it works great!!

I'm not into turns just yet, but it works just fine on my rc airplanes, so I imagine that it should work there too.

Flying height is controled by :
1) the pilot ;-)
In calm water, it works fine
2) ultrasound is probably the best, assuming that you can find a sensor small enough to be underwater (facing up and front)
3) most probably the simplest is with a mechanical surface sensor (like on the Moth class sailboats)

Any ideas welcome!!

Regarding ultrasound sensors... I'd always assumed they would be mounted in the hull looking downwards (i.e. measuring range to the water surface beneath the hull). This would become the "altitude" for the autopilot/stabilization RX. It seems to me there are 4 criteria for such a sensor:

1) Low minimum detection range (ideally 0cm), but some are 3cm+ and most 30cm+
2) Waterproof (IP67)
3) Small size
4) Cheap

1 and 2 are available, providing you sacrifice 3 and/or 4! This is the greatest hurdle!

Feel free to join my new group "Maritime" for like minded boat enthusiasts.

I found the top of the rudder in the file with the other rudder. It is on the printer now.
The fin from the bottom of the rear hull does not appear to be in any of the files I can open with Sketchup.
That would be the penny express and the 123dx files. I think I have enough to get her on the water.

I am getting close to having all of the parts printed. Looking at the pictures, I see a fin under the boat and a top piece of the rudder assembly. Since I am not seeing them in the STL files, I think Cura has struck again and they are included in the files but don't appear in Cura. Can you put those in separate files so Cura can find them? I have most of a ship and am getting excited to see it run.

The middle section printed very nicely. I'm now out of filament. :) I will print the bow as soon as I get some more.

Yes, it is a Cura issue. The new file popped right up and looks great. I have started printing it.

great, keep me posted

I've spent the last week working with cura to tune a profile to my printer. I can show that it will print at least 200 x 200. Now that that is working, I still can't get cura to do the middle hull. I continue to get the motor mount but not the hull. Can I talk you in to posting the middle hull section without the motor mount so I can work around cura's stupidity?


Dear eskiphill,
Sorry for the inconvenience!
I recreated the center_hull part without the motor mount.
Let me know if it works better for you.
Kind regards

I just went through the download and unzip process again. The middle hull looks exactly the same. The printer is supposed to do 220 x 220 but Cura is configured for a Mendel 90 which is a bit smaller (190x190?) and I have yet to take the time to set it up correctly to match the printer. I am thinking that the problem may be that there are a couple of elements in the middle hull. The motor mount which is fairly small and then the much larger hull section. I get complaints from Cura when I load the front section which shows up as 191mm wide which exceeds what Cura thinks is the print size. It could be that Cura is finding the hull on the middle section to be too large and is not showing it to me at all. That would make sense with what you are seeing. The piece I see in Cura doesn't have any slots on the bottom and doesn't look like the picture I just found in your post. Hmmm. I think I need to define another printer to Cura - but not tonight. Thanks for your help!

I went through the files again tonight. There is a very clear cross section in 0001_front_hull and an equally clear cross section in 0003_rear_hull. The cross section of either end of 0002_middle_hull doesn't match either the front hull or the back hull. Looking at this shape I similarities between it and 0012_motor_mount but they are not the same. If I don't resize the models, the front hull is 191mm wide and the middle hull has a maximum of 46mm. They really don't look like they should match up.

Hi there,
I just downloaded the files and assembled them in my splicer (Simplify3d) and they match perfectly.
I then compared them with the ones that I used to print my and they are identical, so I don't know what wrong on you side??

The middle hull section doesn't make sense. It looks more like a motor mount.
I had to scale the bow down but it did print nicely. I would really like the 150mm version you talked about. Thanks for the inspiration. I hope to see mine on the water soon.

Hi eskiphill,
You are right, in the middle of the middle part is a motor mount, I should probably rev^move it as it is available separately.
Please share pictures of yours.

Congratulation, you designed a very well thought hydrofoil.
My intention was just a poor try to lift a (bit by bit enlarged) displacement hull a little to make it faster ;-)
This couldn't work because the propeller was to high. Additional the foils where to thick and cause too much flow resistance.
I am looking forward to see more of the further development.

Hydrofoil Boat RC (experimental)
by wersy

Hi Wersy,
Thank you for you comment and for the inspiration of your project (the first 3d printed one that I could find!!).
The Naca 63-412 profile seems to give good results, but the speed envelop is still to narrow to claim success.
I'll keep trying!

En un mot: superbe !
J' attends la suite avec impatience ! Bravo !

Merci, ce n'est effectivement qu'un début.
J'ai un nouveau set de foil qui fonctionne mieux, et je travaille sur la version en quatre parties de 140mm avec un design un peu plus moderne.

Hi first off awesome foil! I've always been amazed by this technology.

Now I'm pretty new to rc boats, but can you tell me what the prop extender/flexible axle is called?

Edit: ....its called flexible axle isn't it.....

Hi Nigete,
I'm using a 300mm long 4mm flex shaft. I found it at my local hobby shop, but I've seen one over at HobbyKing.
If you plan in building this project, I suggesst you'll wait a couple of days. I made some subtential improvments since satursday.
Thank's for you interest!

Oh that looks very good. I would like to make a model of the type hydrofoil who sailed betveen Copenhagen (Denmark) and Malmoe (Sweden) in the mid 70/80. You can see a picture here: https://da.wikipedia.org/wiki/Hydrofoilfart%C3%B8j
It is not a lot changes that shall be made on Your model. Sorry for my badly english.

Hi vandborg,
yes this is an auto-stable hydro, typical from those days and that geography. The Russians are the masters in that field.
Now the foils are fully immersed, but it requires stabilization systems that are for my next project ;-)

Hi tmightyquinn,
thanks, it's only a start, room for many improvements.