Another Jet Propulsion Try

Hello Boris,
at the same place I tested my jetdrive yesterday :grin::grin:

That’s looking good! Can’t wait to see it in the boat!

Hey Thorsten, your jet drive looks great!
What components do you use for it (ESC, Motor, Impeller)

I will not… but the progress is very slow at the moment because i ran out of money and time for this project.

Hello Boris,

I used a Leopard 5692 motor with 600KV and a flydragon 150A esc from flycolor. Running on 12s

Hi Merten, i always try to focus on a simple design… so the jet drive is the best option for me, first i used the SSS 56114/500KV, i had about 150-160A when I hit full throttle. To much for a durable setup.Take care, the lower the KV of the motor the lower the max current… Currently I am trying to use a outrunner with a lot more tourque, and power…
I would share my CAD designs but they are not in a good shape because i already changed many things and I did not updated all the models

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150A is not bad no ? For what speed ?

I did not measure it but I would say without coming out of the water, it was about 35-40kmh

Been doing a lot of riding and testing and what I found is peak amps can be super high and kill your wiring/esc/connectors if not managed properly with quality parts or current limiting. 150A is a ton of juice and things wont last long with most ESC’s at that level.

Here are my findings:
There i a point where you get maximum thrust to current from your motor. Once you motor torque has maxed out and you continue to pull the trigger for more throttle the thrust stays the same or drops while the amps go from 150A to 191A. I have tested a ton of jet propulsion setups now and see this in EVERY test we do.

191A in our example gives less thrust as motor is flooded with to much current, heat, magnetic field and thrust fades, and at the same time you drain the life out of your battery SUPER fast.

How to reduce or better yet eliminate this? if your ESC has throttle settings you can set mad throttle to 75% and it just may happen to be near perfect. We did this with a few setups. Meaning a full throttle we would only draw 150A and get max thrust without the huge excess current for longer periods of time.

The best solution we found now if you ESC can do this we use our own custom VESC, and you can limit your current. Now we have completely eliminated excess current permanently so we have less heat, less strain on electrical system, and a dramatically longer batter life.

Our system peaks around 150A for me to get up riding 115kg (255 lbs), and then im cruising at 45A, or fast riding at 20+mph at 80A.

Hope this helps with tuning?

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Have you thought about a mean to focus the spray cone, sign of a better efficiency ?

That is about the bottom line what we found last year too, With impeller drive we could not get below 1,8KW with 100kg at optimum cruising speed. Then moved on with prop and the 1KW we need now is pretty harmless for batteries&electronics without fragile water cooling:wink:

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But yet there are some that seem to think that a jet is more efficient than a prop and gear (obviously not aimed at you) :joy::rofl::joy::rofl:

Well it has advantages though, but at the moment the eficiency is a big argument;-)

he was referring to the commonly spread statement, that any gearbox setup would be the most inefficient solution (compared to DD or jet)…
e.g. here and at many other places…

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Bottom line, jets are more efficient in terms of prop safety and durability. The bigger the prop the more efficient it is in terms of producing thrust. I do agree a prop with reduction gear may be more efficient but then you add in the cost of $400 reduction gear which dont seem to last that long, plus the drag of a large 3D printed duct, plus the fact that a 3D printed duct if you fell on it will not stop you from hitting the blade (they do break with body weight) and I think we all saw the injury/cuts this gave one fellow prop rider here on the forum a couple months ago - OUCH!!! it could have been a lot worse too.

There are mainly two types of users I find (competitive racers/perfectionists/those wanting perfect performance/ best efficiency) and those (who want something I believe is a smoother ride, same thrill/fun level, safer, and more affordable and don’t stress over losing a few minutes of ride time) especially if you can just toss in another battery pack.

I’m shooting for the most efficient setup possible for what we have designed, the motor company is helping with optimal kv motor for least Amps/RPM on the motor power/efficiency scale. This alone will improve our DD jet efficiency another 10-20% or more at cruising speed. Exciting times!

That quite simply has nothing to do with efficiency. Efficiency purely relates to the power you get at the prop vs the power you put in with the Batteries.

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ya I know haha I was saying jokingly. I knew it would get a response, relax :slight_smile:

@Toto44 We did test spray vs focused and spray works better for Underwater jets like we are using.

Good to know. Would you have efficiency figures in mind, % ?

We got just over 5% more with spray for the identical setup vs focused nozzle. Its not much, but every little bit makes a difference.