90mm DIY jetpump
Greetings Frank
Very nice as always , may I ask how do you figure the blade angle and diameter of the nozzle ?
I have it no angle 
I feel it 
I make 40ty year rc models, rc Heli, and boats and I have the Graupner 50mm jet pump only bigger built 
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@JetboardCologne That looks great You have done a an amazing job with that the impeller is my other target that I need to look at as I’m not convinced 6 blade prop is efficient looking at space between blades and pitch.
I’ve been looking at other available motors and it seems you can’t get 300kv -500kv in an 80mm without custom work. So Im Thinking of requesting a 400kv 83100 be made around 7-8000w, what do we think?
I would really like to just throw money at a tp100 and call it a day but sadly without redesigning the dropped section in the board it just won’t fit.
Sadly my last outing resulted in me drowning my 400a esc so I’m on the bench till I get parts back. (When a hatch is described as waterproof I really wish it actually was)
And that would be OK on a flier 400a With water cooling?
Have you seen this build already?
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I don’t recommend buying this MP motor.
I was tempted to buy one myself too since it seems to be a much cheaper version of the TP100, it’s basically a Chinese clone, however, longevity and quality-wise is incomparable to the TP.
I know I’ll buy a TP in the future, just by looking at the magnetic wire on that beefy motor you know it’s built for big amps.
Yes definitely nice build but there’s a ton of modifications needed if he wants to get decent speed, better impellers, intake, batteries.
I’m talking about the guy in the video,
A lesson I’ve learned from my own project is that your jetboard intake must scoop water as you go, (impeller should be almost fully submerged until you reach planing speed, then, during planing, your impeller/nozzle should be about half in the water ad half in the air) many diy’ers kinda skip this part (me included) to “avoid drag” and so they build the bottom way too flush with the intake expecting the jet-pump to magically suck and lift water off the surface, it’s not how it works, you reduce your potential speed significantly.
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I’m back at it with the 100mm motor configuration.
Working on a multistage prop to achieve a goal of around 100lb/s flow rates… if the motor can handle it. Ill chime in with some cut-ways as I get to them. So far it looks around 200lbf thrust @ around 75fps.
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Here’s a snapshot. Likely going to increase the impeller a bit to get a little more velocity. A goal of around 80-90fps with 200lbf of thrust should get anything moving 30-40mph on the water.
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(confused in metric 
)
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All good friend.
80fps = 25m/s
200lbf = 890newtons
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So you’ll need >20kW , which ESC are you using?
Not necessarily.
My last design made 40lbf at about the same speed pulling 2kW. Shooting for 10kW.
The math doesnt add up. Even with a 100% efficiency
I would check the maths.
We’ve already tested the low power variant and measured power output and power draw. Look above 100 messages or so.
Working on a multistage prop to achieve a goal of around 100lb/s flow rates… if the motor can handle it. Ill chime in with some cut-ways as I get to them. So far it looks around 200lbf thrust @ around 75fps.
In metric that is:
flowrate 100 lb/s = 45 kg/s
vel 75 fps = 23 m/s
Force = flowratespeed = 4523 = 1030 N → ok
Power required (100% eff) = 1/2 * 45 * 23^2 = 12 kW
But then you’ll have losses in your esc, motor and propeller, so you’ll probably be at >15kW? Doesnt your CFD program give you the input power?
and It becomes even worse if you aim for your 80-90 fps your’re aiming for.
Problem is that the energy depends on the square of velocity, while the thrust increases linearly…
If you want to have 5 times the thrust with the same “efficiency” ( thrust/watt) compared to your smaller jet , then you’ll need 5 times the are to keep the same velocity. That’d bring your larger jet to 64mm * sqrt(5) = 140mm, so it might be better to switch for a propeller then??
(btw, i’m just talking about static thurst here. In any case, if you’re looking for speed, looking at static thrust is not really useful IMO, jets are meant to be used at speed, so i don’t know how useful it is. If you want acceleration, then it’s great to have this large area, but the drag will be huge at higher speeds)
I don’t disagree with the power calculation. I came up with 12kW as well.
The thought was to shift flow rates or thrust to the desired 10kW. Meaning we could settle for 150lbs of thrust if its at a higher flow rate.
At 48 volts this puts us at 200amp draws. We simply can’t do more than that. More than 48v is dangerous and more than 200a will melt wires. Hell 200a will melt wires if the water cooling isn’t effective enough. Not to mention beat up the battery nicely.
My CFD is more focused on flow characteristics, and this is where my greater efficiency came from on the last design. I make sure to avoid random pressure potentials, and cavitation. It allows me to tune the pitch of the prop to allow for the least force on the impeller, while maintaining the higher flow speeds.
This is a completely different impeller design to the last so you start to lose me talking about simply increasing the size of the jet. I haven’t fully decided on the size yet, but know that I’m working below 100mm still. Pitch and RPM characteristics greatly effect the output of the jet as well as the impeller shape itself. There are many ways to skin a cat with a jet. I’ve seen at least 3 different ways to pressurize water within a jet all dictating 3 different impeller shapes.
Electric motors still have a ‘moment of torque’ to them, and within this process I’ve not seen making an impeller larger than your stator work out well for anyone. It will over-torque and draw amps to the moon. WITH AN IMPELLER SETUP - I cant say the same for open propeller designs.