BLDC electric motor jet engine for hydrofoil or surfboard

[@rostravelventure]

Great video! It all makes sense until you do a real-life test A guy like you is good to have on my team.

[@graphicstudio-dz2374]

Hi Itai, Thank you for this excellent video, very clear, instructive, especially about KV, how to choose the brushless motor and about tricks you reveal when creating and assembling your 3D model, very good job. I found your video very important, but it was difficult to find it on youtube, may be you need to put on a selection of good keywords, good luck

[@gkeepleft]

Awesome video! Such great explanations! Can't wait to see more videos like this. I love learning about water jets. I want to make my own electric wake board one day. And I need to learn more about making jets. This is the best video I've seen explaining it.

[@K2board161]

Love this video. Have you or anyone you are aware of. made this yet? Would be very interested in the real life test. Have you made the plans available?

[@IamNoel]

I'm looking for some new motors for my DIY jet board (see my channel for my build). I'm using two (2) 56102 600Kv motors with a 12S12P Li-ion battery pack. It's working, but the amps pulled is way more than I expected. The BMS in the Li-ion battery pack shuts down due to heat after 10 to 15 minutes running full speed. (Max amps measured is 380 amps when static testing!). By following your example at 4:50 (Imax/Kv = t) I calculate 126/600 = 0.21 at 126A for my motors (126 = Max Amps and 600 is Kv according to the data sheet of my 56102 motor). As this setup is running to many amps it would be better to use a SSS 56104 motor as (according to you calculation) the torque is more (0.263) and the amps used are way lower (ie: 126 vs 95 amps). Again. I have 2 motors in my setup, so double it! Question. Why do you have 145 as Imax and 800 as Kv in the example for the 56104 motor at 4:50 ? Should this not be 95 and 360 ?????

[@ItaiLeshniak]

Hey, Can you send me a link to your technical build video? I can only find videos were you ride the board. When you measure 380A, is this for the two motors? Do you know what RPM your motor is running when you are at 380A? It sounds to me that your propeller pitch is too high, I would start by lowering the propeller pitch before buying now motors. If you give me more technical info I can try to help.

[@IamNoel]

​ @Itai Leshniak Hi. Thank you for your reply. Unfortunately no build video, however the two jets I'm using are made by Mark from Youngster jets (link to his YT channel is in my last riding video.) He has some build videos of his projects. The jets are 53mm. We did some static testing with them, and one (1) jet pushes about 50 newton @ 5000 RPM, 100 Newton @ 7500 RPM, 147 Newton @ 11000 RPM and just over 200 Newton @ 15000 RPM. Anything above this it started cavitating (could be because the board was tethered down so no water was forced into the jets) The 380 Amps was measured again static with both jets / motors running at 15000 RPM. (the current will be a bit lower when the board is actually moving) We used a calibrated clamp meter for measuring the amps. Motors used with the above data are Surpass Hobby Rocket 56102 600KV motors. - Watts: 6300W - Max voltage: 50V - Max Amps: 126A - Rotor poles: 4 - IO: 1.8A - Kv(RPM/Volt): 600KV - Max RPM: 30000 The powersource is a DIY Li-ion pack. 12S12P. I used Sony / Murata US18659VTC6 cells (3000mAh / 30A) Totall is 36Ah. Fully charged: 50.4 volts. 1814 Wh

[@ItaiLeshniak]

@@IamNoel So if I understand this correctly you are running max at 15K RPM (in static testing). From that it sounds that you do not need the full 50V only 30V (RPM/KV + some losses). Can you run a water/ride test with only 30V (it will limit the system to 15K rpm) and see if you get the speed you want? what is the current with 30V? If you do get the speed you want at (15K RPM) this will conclude that you should convert to a lower RPM setup - you can convert to a 360KV motor (like a SSS 56114 / 360KV) with the 12S12P setup. It will give you a max of 15,000 (18K on paper) but almost half the current from the 600KV 30V setup. I hope I understand the setup correctly...let me know what you find. Also if you do order the 56112 motor notice that it comes with a 10mm or 8mm shaft so get the right one.

[@IamNoel]

@@ItaiLeshniak I was already thinking of changing the 12S (50 volts) to a 10S (42 volts) as the way things are setup now the board is way to fast! I did do some test with the max power limited within the ESCs (in the video it is set to around 65%), and it's way better than when running at 100% I also have live riding data from the BMS, but I do not think that this is correct. When we did the static test, we compared the BMS data at the same time with the data we got from the calibrated clamp meter. The more amps we started pulling the bigger the difference. So I do not trust the data from the "cheap" BMS, and will not use it! You mention a SSS 56114/360KV motor, and at the end a 56112 (i do not think that this motor exist)... But do you think that the SSS 56114 will be better than the SSS 56104?

[@ItaiLeshniak]

@@IamNoel SSS 56104/360KV will work very well. What BMS are you using?

[@DktheWelder]

innovative design ! very well drawn i am halfway through building my second jet unit but using a petrol engine for jet board I fabricated first one from aluminum but this next one is mostly 3d printed. Wont your design struggle to feed enough water in with it having to draw water around the gearbox ?

[@ItaiLeshniak]

Since it's under water I believe it will have to reach cavitation speeds for that to happen. I do not think I will ever get close to that speed.

[@DktheWelder]

@@ItaiLeshniak o cool , do you think your design would be more efficient than a Hamilton jet like a JetSki or jet boat has ? That is the style I am building at the moment

[@ItaiLeshniak]

​@@DktheWelder It will not be more efficient. The most efficient design is with no gear and where the jet output is outside the water, you should be blowing water out into the air and not against water.

[@doc-holiday]

Hi Great video i like the animation. Your calculations are all spot on. Just wondering when the real live testing in the water would be great to see what speed and amperage you would getting out. Since this is sort of a new concept it might be best to even take out a patent to protect your design. The only thing I wasn’t really happy with…was the gear profile. Using spur gear is not a wise solution due to the fact that high rpm is not suitable for this type of gear profile. I would have in my opinion gone to a gear shop and have them make you up one driver and a follower out of solid brass ( doesn’t cost much 2 gears would set you back about $80, and they would also way outlast you with the current one you have at the moment. Ask them to manufacture you a set of helical gears as used in all modern car gearbox then the rpm of the motor is more suited at these higher rpm speeds and then these gears can easily handle the force and help reduce the motor amperage even lower. Using spur gears in my opinion is a real no no in the real world…they are way too noisy. ( spur gears are best used for low speeds ) That why they are not used in modern cars. Go talk to a gear manufacture or a small machine shop and they will make you up a new set. On a last note thank you so much for the tutorial on the brushless motor selection, that was very interesting.

[@preszter]

Hi Itai, have you ever built this thruster or has it stayed as a concept only? I want to build an electric motor propelled catamaran (20feet) and I'm looking for a viable solution. Yours look like the one that could be ideal for my project.

[@ItaiLeshniak]

I did build it. I simply never had the time to edit the video. I will try to get it done soon.

[@preszter]

@@ItaiLeshniak Could you share the cad files so that I could build it as well?

[@preszter]

Also did you make any calculations what speed you can make out if in water?

[@Arkvis10]

is 56104 500kV enough to cause thrust capable of producing enough lift force to lift a 70 kg man on hydrofoil board?

[@ItaiLeshniak]

Yes, but you can buy the bigger version 56123 for a small premium.

[@Arkvis10]

@@ItaiLeshniak meaning 56123 500kv or 56123 230kv?

[@ItaiLeshniak]

@@Arkvis10 230kv

[@Arkvis10]

@@ItaiLeshniak what will be the least possible and safe RPM,VOLT,AMP,WATTS that will be needed to produce lift force for a avg 70kg man!?

[@ItaiLeshniak]

@@Arkvis10 Sorry but it was over 3 years, I do not remember anymore. I can tell you that the RPM should not be over 8K and Amp as high as the motor can go.

[@joedietrich2737]

no thrust bearing? no good!

[@ItaiLeshniak]

This double row angular contact ball bearings can hold axial load of almost 500Kg (1,000lb). There is not need for a thrust bearing. Even Sea-doo stopped using thrust bearing, they use the 28BWD01A Double Row Ball Bearing.