M-Jet 60 - 3D Printable Jet Drive for Electric Surfboards 3D print model

Do you think using two EGO POWER+ 56-Volt, 5 Ah 5 Ah Lithium Ion (Li-ion) Batteries would be suitable to power both pumps for a sufficient amount of time?

This battery looks too small and I am not sure if the Li-Ion type can provide enough discharge current (expect maximum current ranges 200-300A). I would suggest looking at for example 6S 10 000mAh and running 2 of those in series.

Do you only need one ESC for both motors?

No, each motor must have its own ESC.

Do you think if you scaled the pump up, you could use just one to power a surfboard?

Firstly, scaling the pump up brings complications. All fastener sizes, bearings, shafts, seals, motor mount, servo mount all become incompatible and possibly generating non-existing requirements for dimensions of these parts. Solving this requires a lot of additional effort. Secondly, if you scale the pump up, you need an accordingly more powerful motor and accordingly lower KV. In our application, KV should scale with (-0.5)th power of size. Power requirement scales with 3.5th power of size. Static thrust scales with 3rd power of size. This means for example: 1.2x size -> 1.73x thrust, 1.9x power, 0.91x KV. If you do both of these steps successfuly, then you can use a single pump to run the surfboard and possibly have better results than with a single pump. Let me know if you need some more help with this, feel free to send me a private message too. Stepan

Could you please send a link to the motor and battery you recommend for your design? I'm making a jet-powered surfboard, but I am a little confused about what motors and batteries to get.

Hi, I bought your jet propulsion data and am currently planning a jetboard. I want to use three jets to make the board very powerful. For the battery, I plan to use a 12S Li-ion 44.4V pack. However, I’m unsure about the motors. RClifeon used SSS 56123 500kv motors to build a fast board, but it runs quite inefficiently. He mentioned that with his 44.4V 16Ah batteries, he rides for an average of 3 minutes, which means a consumption of around 14kW! Especially considering that my Jetsurf board with a 100cc engine reaches around 60 km/h with approximately 8 kW. I would like to build the board more efficiently, so I'm considering using 360kv motors. The question now is whether I can still reach my desired speed of 50 km/h with these 360kv motors, which have a no-load speed of 16,000 rpm. Have you ever measured the jet velocity? I’m concerned that while the 360kv motors might generate enough thrust, the jet speed may not be high enough. Do you perhaps have a completely different motor recommendation for me? Additionally, I’d like to know if the jet propulsion system is fully waterproof. I’m considering using a shaft seal instead of the O-ring. Best regards, Jan

Hi, there are multiple considerations to be taken into account. 1) The 360KV motors will indeed run more efficiently than 500KV motors, but they will also produce a bit less power output. 2) The M-Jet 60 on 44.4V powered by sufficiently large 360KV motor will achieve around 20kg static thrust at approximately 40kph exit velocity. Such setup will likely consume around 4000W per single pump, so 12000W in total. 3) Despite using 3 pumps, the exit velocity will be limiting, and I don't think 50kph is achievable. RCLifeon did 44kph with higher KV. I have some different options to suggest. The M-Jet 60 was developed in 2021, and since then the M-Jet designs advanced. The M-Jet 30 and M-Jet 35 are designed for RC boats (30mm, respectively 35mm impeller diameter), but they have features which make them more efficient. You could buy the M-Jet 30 or M-Jet 35 and scale it up to 200%. There are many problems arising if you attempt to change scale of any M-Jet design. All fastener sizes, bearings, shafts, seals, motor mount, servo mount all become incompatible and possibly generating non-existing requirements for dimensions of these parts. Solving this requires a lot of additional effort. The M-Jet 30 and M-Jet 35 come with a STEP file which includes all parts *except* for the first stage and second stage. If you work with CAD, you might be able to modify some dimensions for bearings to make it work. Eventually this can result in a better pump than the M-Jet 60 and achieve your goal. Stepan

M-Jet 30: https://www.cgtrader.com/3d-print-models/hobby-diy/other/m-jet-3d-printable-jet-drive-for-rc-boats M-Jet 35: https://www.cgtrader.com/3d-print-models/hobby-diy/other/m-jet-35-3d-printable-jet-pump-for-rc-boats

Thank you for your response. I’ve given a lot of thought to finding the best solution to quickly build a functioning board without extensive testing. If I use three M-Jet 60 units with either 500kv or 360kv motors, I’d certainly have a working board. I also considered scaling one of your jet drives or designing one myself. CAD is not an issue for me as I’m a mechanical engineer. However, if I scale the M-Jet 30 or 35 to 200%, there are no existing reference values for suitable motors since the same RPM as before scaling is still needed to achieve the same jet speed. Ideally, it would make sense to develop an 85-90mm jet specifically for a surfboard that operates with a power output of around 10 kW, similar to Jetsurf’s 90mm system. However, that would require extensive testing again to determine the appropriate impeller pitch, nozzle diameter, and suitable motor. The clear advantage would be the superior efficiency.

I see. Glad to meet a mechanical enginner. Then calculating appropriate power and RPM for an upscaled pump won't be a problem for you. When scaling up, there might be multiple options to choose from but what I set is constant thrust to weight ratio. If you do the physics, you'll find that RPM scales with (-0.5)th power of scale, power input scales with 3.5th power of scale, torque scales with 4th power of scale, thrust scales with 3rd power of scale and exit velocity scales with 0.5th power of scale. When calculating RPM and consequently motor KV, remember that loaded RPM drops to 80-90% of the nominal Volts*KV value. Reference points (without acetone smoothing): M-Jet 30 25000 loaded RPM 1300W shaft power 5.8kg static thrust 19.4m/s exit velocity; M-Jet 35 20000 loaded RPM 1300W shaft power 6.8kg static thrust 19.6m/s exit velocity. You might ask why the 35 is better - at such small scale, boundary layers on all surfaces are disproportionally more important than at bigger scales. The 35 is bigger which gives more space between the walls where the flow can develop without being hindered by wall friction. When upscaling to 200% this won't be as relevant, and both 30 and 35 might perform the same if both are scaled to 60mm. Of course, a single 85-90mm pump would perform the best.

Thanks for the info! I think the M-Jet 60 is already a solid foundation. I’ve played around with it in my CAD program and made a few adjustments, such as separating the stator and nozzle and thinning the stator fins since I might print it in aluminum. Additionally, I removed the two-stage setup and am using only a single stage. I'm leaning toward scaling the jet up to 85mm and adapting the impeller to fit the motor I plan to use. An 85mm jet has roughly the same cross-sectional area as two 60mm jets. The MP83100 8kW water-cooled outrunner motor seems like a candidate. It’s fairly affordable, though it’s questionable whether it can sustain 8kW continuously. My plan is to use a 16S battery system, around 60V. This setup would only be worthwhile, of course, if an 85mm jet offers significantly better efficiency than two 60mm jets. If the 60mm jet could be optimized with the SSS 56123 motors at 500kv or 360kv to generate 30kg of thrust at 4000W, that would be an attractive solution as well. I might need to dive into CFD simulations to refine the design further. Do you think it’s possible to make the M-Jet 60 significantly more efficient by better adapting the impeller to the motor, thinning the stator fins, and optimizing the nozzle for the motor? Could a 25% efficiency improvement be realistic? I also wonder why your stator fins run the full length to the end rather than just a short segment, like in more traditional setups such as Jetsurf and Jet Ski designs. The M-Jet 35 seems quite different in that regard too.

Alright, sounds good! It is certainly possible to make the M-Jet 60 more efficient by some modifications, reducing vane length is a good idea. 25% is a lot but if you scale it up it should be more efficient from the start already.