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Nov 05, 2019, 04:34 PM
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Kayaker's Avatar
Originally Posted by sundogz
Kayaker, do you use the hybrid (SS/Ceramic) bearings in the stator? Was wondering how they hold up. I've been using/recommending full ceramic for the stator and sealed stainless up front.
Full ceramic bearings can get expensive. Boca full ceramic to fit the 45mm jet are $128 USD each:

My stator bearing, $11 USD, with ceramic balls and 440c races is holding up well with one greasing per 20 hours. It now has 50 hours and still going. The front bearing got replaced at 40 hours from noise.

Im trying to get the front bearing to last longer so I used a long shaft to true up the jet bearings to match the motor bearings and glued both jet bearings in place. I put mold release on the bearings. This is like line boring. I dont know how much this matters as most people will not put 40 hours on a boat.
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Nov 05, 2019, 06:29 PM
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Originally Posted by Kayaker
Full ceramic bearings can get expensive. Boca full ceramic to fit the 45mm jet are $128 USD each:
Yeah, I don't know why Boca full ceramics are so expensive. Here are some 6x15x5' (45mm jet) full ceramics you can buy straight from China for $11.90 w/free shipping. I only buy Bocas when I can't find them elsewhere. I have experienced pitting in hybrid bearings, but don't periodically grease them like you.
Nov 05, 2019, 08:21 PM
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I wonder how those Chinese bearings stack up as far as accuracy against a name brand? I know that there are a lot of cheap bearings out there with horrible movement thanks to large tolerances.
Nov 06, 2019, 09:56 PM
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Originally Posted by MiteyF
I wonder how those Chinese bearings stack up as far as accuracy against a name brand? I know that there are a lot of cheap bearings out there with horrible movement thanks to large tolerances.
Maybe I have just been lucky to get good bearings from the various Chinese vendors on Ebay. In any event, IMO it's worth taking a chance on $12 Chinese counterparts compared to dishing out $128 for Bocas when they're going in a toy boat. I would like to buy American, but 1000% markup is . And since Bocas are made in China, guess where most of that 1000% 'markup' is going? Not to middle class laborers, but to a few good marketers and some stock holders would be my guess.

Ebay and Wal-Mart are two of my favorite stores. I absolutely do not think 'paying more' means 'getting more' in today's world, and get a tiny thrill buying the same or better quality for less money. I have played American made Fenders and Gibsons and compared them to the overseas manufactured counterparts and they are virtually identical - except for the price. Anybody who disagrees wants needs you to believe otherwise (when he goes to sell his instrument) and will argue the point till the cows come home.
Last edited by sundogz; Dec 29, 2019 at 05:17 PM.
Nov 14, 2019, 03:31 PM
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Here's an example I got in today. They are full ceramic 6x15x5's that are for the stator of a 45mm FJD that I plan to install in a 38" boat (post 2390) soon. I got them from this vendor on Ebay for $11.50 each shipped. I just picked the cheapest bearings that had a shielded side that I'll install facing the impeller (water lubricated). They are packed nicely and are silky smooth - no 'runout' that I can tell. They'll do fine, and cost a less than those from Boca. They came from China so took almost 3 weeks to get here, but I had plenty of time considering the money I was saving.
Nov 27, 2019, 10:33 AM
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Watch that seal tightness on the shaft

Have you noticed that your motor is pulling more amps than you expected? Consider that the seal you use may be causing performance problems! Even if you remove the inner spring (if so equipped) on the seal, and even with grease lubrication a new seal may be so tight on the shaft that it will require considerably more amperage for the motor to spin it up. When assembling, spin the greased shaft with your fingers to check the resistance. It does not need to be tight on the shaft to keep the grease in, it just needs to be snug. And you want it barely snug - it shouldn't be able to spin freely.

It will free up on it's own with enough use - but being lubed with water on one side and grease on the other this may take a long time to happen. You can fix this easily enough by wrapping sandpaper around a suitable drill bit chucked into a drill. Insert it into the seal and spin it 5-10 seconds, then remove and try it on the shaft it until it lowers the resistance to a comfortable level. If you go a little too much you can re-install the inner spring to snug it up. I've had to do this to both a 35 and a 45mm pump and it made a remarkable difference in performance. Definitely worth checking out considering the possible increase in speed and longevity of batteries.
Jun 25, 2021, 09:42 AM
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Re-opening of the FJD thread (sticky)

Michael (UnusualRC) now has the telemetry and data gathering equipment to properly test and evaluate the different parts of the FJD. He has my Proboat Recoil with the 45mm FJD in it as a test bed.
He has also been bitten by the 3D printer bug! and has a new Prusa printer with which he can make the new parts as he tests them. This has been a long time coming and now we can get some hard data on the different stator outlets, impeller pitches, etc. and make this drive truly one of the best - if not the best available. We have re-opened the FJD thread (sticky) for posting related info. Thoughts and comments are welcomed - this should be quite an interesting subject. Sdg
Jun 25, 2021, 10:46 AM
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It took me a while to find time to pick up the project again.
Now I have and can use Dave's Recoil 26 as a test-bed.

You might know the original Recoil 26 as brought out by Pro-boat, features a 3S set-up with a surface prop and motormount cooled outrunner.
Total weight was 1400 grams/3.0 pounds

I have added FrSky telemetry sensors to this model. I have put them in a waterproof (not submersible, but keeps most pray out) clear plastic tray.
Here are the sensors:
  • RPM
  • Current (A)
  • Total lipo voltage (V)
  • Voltage per individual cell (V)
  • GPS longitudal, latitudal, height
  • GPS speed (KPH)
  • motor temperature (C)

This hull with the 45mm FJD, 4092 inrunner (1250kV) and 4S set-up (2x 2S 8Ah) hits 2600 grams/almost 6 pounds!
Keeping it float is the main goal here. I have another 2S battery to make it a 6S set-up, however it does not fit in, nor does the deck stay above water when I tried...

4S is fine, since the maximum theoretical (unloaded) RPM is around 20.000 rpm.

Thanks to kayaker (Robin) I got data from different motors and battery counts, which I am very grateful of.
Still testing myself was the goal, and finally I did some testruns with Dave's original set-up.

Started on 4S (8Ah and 30C), 40mm pitch impeller (out of nylon 12) and 33mm stator exit diameter housing. Here is the video including telemetry data.
Special note about the GPS sensor. It is a copy you will find in most smartphones, so not particulary accurate (speed 0.1 m/s). That day it had a 0.5 second delay I did not compensate in the movie.
Reason is the boat simply does not want to run in a straight line with the CoG on the original position. Putting it more up front does make it go better in a straight line, yet steering is terrible to the level of almost no control at lower speeds, extremely aggressive at high speeds. In despite dual rate set to a lower value.

For some good testing I need to run in a straight line at least for a 100 yards. A later check on google earth when I plotted the route showed there was hardly any straight line. Those who look straight are all at lower (sub 25KPH) speeds.

Free Jet-Drive project 45mm impeller, 40mm pitch, original stator with 40° LE angle (10 min 59 sec)

I did already a maiden with the same set-up, but forgot to turn on data logging....
So next I removed the activation on the Tx from a switch to the power ON switch.

Luckily my transmitter has a large LCD screen which shows me the real time speed, as well as it memorizes the fastest measured value.
That was 45KPH/28 MPH

The data logging interval was set to 1.0 second, which I now consider to be too less.
The next test will be with the 30mm pitch impeller and data logging set to every .5 seconds.

So far these are the results:
  • 10.000rpm = 60A, 20-25KPH
  • 15.000rpm = 130-150A, 35-40KPH

I cannot get the motor above 15.000rpm. The Esc. can handle 220A, however I could not find a sensor which can handle more than 150A (the Esc has data logging with these numbers, but I need to hook the Rx cable to my PC)
150A on 4S is when fully charged 2.4 kW.

In other words, more power is needed, or more optimization of the current design.
I choose to walk the last path.

As can be clearly seen in above video towards the end, the exit jet-stream is wide. Not a nice straight column of water. Robin (Kayaker) already had some nice footage of that.
If you look very closely a spiral direction can be seen. Found out the direction is the opposite of the impeller rotation, so this must be caused by the 40 stator vanes angle. That must be reduced.
Grail made some new stator housings for this jet, which I think is a better solution.

This will be one of the first things I will change, thanks to owning a 3D printer myself now.

Also I have water leaking issues inside the hull.
If you use waterproof electronics, no issue. With my Esc, Rx and telemetry sensors a serious issue!

In order to find out what is causing the leakage, I have put a GoPro inside the hull. I have tested this in a basin I made in my garden.

See the footage here:

testing inside hull part 2 (12 min 18 sec)

Since then I tape the hatch shut with electrical tape.
Dave and I found out a spring is missing on the rubber axis seal, which is probably causing the water leakages from the axis.
I will try to order some new.

This topic is meant to improve the drive.
This time I use real life data to see what works, and what does not.

Next test is the 30mm impeller, if the rain clears I will have a go any moment!
With this impeller the RPM can go up and hopefully the current more down. That is if the blades will hold. The less pitch, the less curvature which add structural stiffness to the blades. For this size pump, and probably the 35mm as well a printed steel type will be the best. However SLS printed by a third party in Nylon 12 plastic is a good way of trying out new impellers, yet keeping the prices reasonable.

I calculated that this will pump more water with 20.000rpm than the 40mm impeller at 15.000rpm.
Let's find out.

Feel free ro respond! The more eyes investigating the footage, the better!
Last edited by unusual_rc; Jul 11, 2021 at 04:57 AM. Reason: Changed youtube URL to better version concerning telemetry
Jun 26, 2021, 08:02 AM
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Rain all day yesterday...but this morning it was dry.
Unfortunately, a huge colony of Goose took over the children's swimming pond.
They create so much poo that walking is becoming a nightmare, and the water quality drops significantly.
I am sure they will shut it down soon. A pity for testing.
Nevertheless water in abundance in my neighbourhood. But this is a nice sheltered location.

Installed the D45mm impeller with a pitch of 30mm this time.
Blade thickness of all impellers I have tested so far (pitch 40mm is the other one) is 1.6mm.

I was worried about blade flexing, and if I interpreted the telemetry data correct, this is actually happening.
Probably also with the 40mm pitch impeller.

From idle to full throttle you see the RPM go to 18.000 revs a minute, and quickly dropping to 16.000.
Also the current goes down a bit. Here a sample:

Interesting to see when I take some throttle back, the current goes a bit up and RPM is increasing.
Speed is also increasing with 3KPH.
So something is happening with the impeller is my best guess.

Now I get a pretty steady 100-108A with 16.000 RPM and a speed of 29KPH.
This is not at full throttle, but on 50/60%

To limit blade flex ordering a metal copy at Shapeways is one option.
Or I need to order them printed in Nylon 12 with thicker blades, or with a progressive wall thickness down to the hub.
Another option is to print a stator with less progressive pitched statorvanes, like Greal already made in another topic.

Less resistance can also prevent blade flexing.
So better flow through the stator could also solve or limit flexing.
That will be my next step.

Maybe I will use one of his 6 or 7 bladed stators. Kayaker already had good experience with these.
Jun 29, 2021, 03:24 PM
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Made some progress with the 30mm pitch impeller and original 33mm stator-housing, versus a new designed shorter stator-housing with less angled stator-vanes:

Original stator-housing
Recoil FJD 45mm 30mm pitch impeller test with original 33mm stator-housing (7 min 20 sec)

Newly designed stator-housing
Recoil FJD 45mm with 30mm pitch impeller and new design 5 blade stator-housing test (7 min 37 sec)

Besides the less angled LE (15 instead of 40) and 5 instead of 4 stator vanes, also it is 10mm shorter.
Plus the original exit angle of the nozzle itself was 0 (perpendicular with the impeller axis), this one is 5

Jun 30, 2021, 09:39 PM
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In the same way of shorter vanes , here are the stator of the TFL 40mm jet ...
It's 17 mm long for a 46mm "body"
Jul 01, 2021, 02:12 PM
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Originally Posted by Denis BE
In the same way of shorter vanes , here are the stator of the TFL 40mm jet ...
It's 17 mm long for a 46mm "body"
Many thanks Dennis for the detailed picture!
This is more like the MHZ 64mm drive stator vanes, but those are longer.
See the picture:

Can you provide more data?
You are using the FJD 45mm impeller of what pitch, and scaled to exactly 40mm diameter?
What is the end diameter?
And I see a tripod like cross in the exit nozzle hole? What is that?

Just estimating from your picture the acceleration factor (surface area of working area of impeller, divided by the surface area of the exit hole) seems to be low. I am curious what those dimensions are.
Jul 01, 2021, 03:56 PM
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Using a TFL stator and impeller in a 3D home printed jet drive would simplify a lot of things. I just ordered them from Banggood to see the possibility's.

Stator, $34

impeller, $43

two stator bearings, $14
Jul 01, 2021, 04:06 PM
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Those stator vanes are shaped like a NACA airfoil, rather than most stators even in jet turbines. Compare with the 64mm MHZ surfboard drive stator shape for example.

Finding the right shape, angle an size of the stator will be hard to find out. A lot of prototyping and testing, or getting into CFD (computed fluid dynamics) simulation
Jul 01, 2021, 10:36 PM
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The end diam of the TFL is 28mm and the "tripod" is a support for fixing the stator.
The blades are 7mm long and it may also help to straighten the flow ???
My 40mm impeller is a 39/35 upscaled to 40mm but nothing is tested yet in 40mm , I must make a hull first . Will be 80x34cm
Maybe for the FJD 45 ???
For data's , the vanes of the 35mm alu jet are 22mm long
Here also a pic from the MHZ jet4 stator ...

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