In that point I don’t agree. I think if done properly, a single jet can be cheaper and on top of that more efficient too. For example I would use the same battery and the same ESC (Flipsky).
Single jet:
Alien Power Systems motor: 200€
Flipsky ESC: 300€
–> 500€
Dual jet:
Surpass Rocket Motor: 2x100€
Flipsky ESC: 2x300€
–> 800€
Do you guys think 350 KV will be enough for a jet drive?
you are right until you include weight and torque
exemple: onean carver board, first “cheap” esurf: 1 jet but 2 motors, now going 2 jets 2 motors
I don’t understand. 1 jet with 2 motors?
Yeah torque is a problem right now with one bigger jet.
But shouldn’t be the weight of a single drive less then of a dual drive? Mainly because of one less motor and also one less jet and a smaller case?
yes 1 jet with two outrunner in a serie
weight: the person on the board, not the same if 60kg or 90kg…
Single jet (say, MHZ 64) with a 350kv (water-cooled outrunner) motor is great as long as your setup can handle 200A continuous, that if you are looking for speed of course.
Thanks !
I would consider following points for your setup :
Lampuga boards are suing Lehner Motors Torqstar 7025 :
You can customize your Kv as you wish. Not sure you will have enough torque to drive a 80mm impeller or bigger with a SSS motor. Lampuga is also using 93mm impeller I think.
Make use of following calculator to size your jet and motor depending on the desired speed :
https://endless-sphere.com/forums/download/file.php?id=177188&sid=1c188c180776bcecb343943f70b816f3
File from following link : Technical discussion around jet surf board | Endless Sphere DIY EV Forum
Interesting !
That’s why I can’t turn the impeller by hand 
Re: I would move the jets closer to each other. You might get a benefit from this as done by Onean
This is for us the closed as we can put them together. Any closer, and the jets will start stealing water from each other at the inlet causing cavitation
Re: I would make sure the nozzles are place right at the water surface and not deeper. All the Ejets on the market are done this way.
This is in our case also setup like this.
Re: I would move the jets closer to the end of the boards. You may want to reduce the transparent plastic part 1-2cm.
The transparent tubing is there to keep the water jet coming out of the nozzle nicely close together.
In our case it does generate more thrust.
Re: I would design a custom part that might be 3D printed and placed on the bottom of the board. This would help you benefit from the water being pushed in your jet the faster you go
This is something we could try.
Re: I would make a static test and record the thrust.
Yes we are working on this. Soon we will have some true values.
What waterjets are you using? any site that you can share or if it is 3D printed maybe you have a STL to share?
BR
Magnus
The static push results are in.
Motor(s) used: Surpass hobby 56102 600KV
ESC(s): Flier. Model: ESC 240 16S
6S6P (LiPo 4500 mAh Zippy compact )
12S12P (Li-ion Sony/MuRata VTC6 & Ant BMS)
More data will be added when we have the VESC’s installed.
The static test has been done like so (see image)
Hi Magnus.
They are from Youngster Jets. See: https://www.youtube.com/channel/UC3R46Y_HAi_KgBaoQEYsSSg
When talking about KV ratings… I assumed the target KV for a jet drive should around 500 KV.
Not necessarily. It depends on the Jet size and thrust desired. I obtained 50lbs of thrust out of a single 65mm jet running half the voltage (6S - 22v). That was with a SSS56114 at under 100amps. I did that with 2kw versus youngsters 5kw, so if we rated efficiency i’d win. But we’re looking for overall power output.
There are four things that have to all come together as a science here.
RPM - absolutely determines max performance of a specific foil
JET SIZE- think of this as torque for a jet. You can throw more mass behind you faster with a larger jet and that creates higher thrust. Move more water at the same speed is always more thrust.
MOTOR SIZE - the power behind the jet. Diameter creates torque and length supports amperage. Windings creates KV and KV somewhat defines final RPM.
AMPERAGE/BATTERY - the most important. What your battery can handle in terms of draw is going to be what your motor can pull from it in a given instant and that will decide the overall power-draw you can achieve. Now i’m going to say if this thing runs 30 mins straight… your amp limit to the battery is 150 tops. I don’t care how many batteries you run in parallel, the two wires powering the esc is moving 150amps… and unless that wire is 4ga or larger… it will melt after 15 minutes. So plan on each esc only being able to handle around 150amps (but plan for less). You have C ratings with different chemistry as well. LIPO has the highest power/weight while LI-ION will have the best power storage but worst power/weight. On the flipside LIPO can run 50-100C while LI-ION really doesnt like more than 10C so you need a larger pack. All these variables.
These things all go hand in hand and effect one another. You could have a lower KV motor designed to run higher voltages and thus lower amperage. The larger the jet the more torque it requires, the larger motor, less kv, higher voltages etc.
@kuban_fpv just for my understanding about jet unit : is there a way to match thrust needing for top speed and weight ?
just for my understanding about jet unit : is there a way to match thrust needing for top speed and weight ?
There may be some calculators out there somewhere but not that i’m aware of. Lots of variables to consider!
A few members reported in an other chat, that a single 64mm jet from MHZ isn’t enough for getting up to decent speeds.
The problem is finding a motor powerful enough for such big jets.
Maybe that is why the trend is to go with two smaller jets?
I wish I had the money to built one… I think the problem facing with 64 MHz is that max rpm is too low , I think we need at least a 450kv on 12s to achieve value close 16krpm
Great Numbers on the sss motor. Which jet was that?
Those are pretty decent results (nearly same thrust as 1x 64mm impeller from Onean - 226N you VS 240N Onean) !
I am looking forward to your field test and see what speed you will be able to achieve !
My guess is you will be able to hit 40kmh but maybe not 50kmh.
