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Sep 07, 2021, 12:56 AM
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Originally Posted by sundogz
Up until now I've only imagined a rudder like that, I have never seen one. Interesting! Cutting off the end of the nozzle helped back-spray? After the taper there is no increase in pressure (to speak of). Oh well, whatever works! Yes, you are doing it right to get proper comparison measurements.
IMHO adding a rudder to a jet-drive is always a sign that something is wrong.
Good (trimmed-out en well designed) jet-boats do not need them!
Special applications aside like this vintage "neck-snapping" drag-race boat!

The current FJD stator-housing does not feature a funnel shaped nozzle exit, like we designed it back then.
Our consensus was water should exit parallel to make the most efficient transition.

When I tested the shortened 5-vaned version of the stator-housing with a 5į incline angle on the exit, it was noticeable the jet-stream was much more parallel/straight. Agree that this is not proper proof that this incline is causing the jet-stream to be more straight. I believe multiple factors play a role here. I am far from finished testing more options here.


Nevertheless I have to deal with a jet-stream, which is fanning out.
The only way to channel that is having a more tapered nozzle.
The current nozzle was already like that too.

Beware the exit diameter of the steering nozzle is 2.0mm bigger than the exit nozzle.
Still is runs wet all the time (no Proboat RiverJet show-off here )

The more I talk about it, the more I want to redesign the steering nozzle/stator-housing!
Also 6S is calling...as is a larger hull
Last edited by unusual_rc; Sep 07, 2021 at 03:09 AM.
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Sep 24, 2021, 06:58 AM
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Motor-mount added and metal 45/40mm impeller


Small update!
The model is ready to hit the pond again.

Thanks to Denis_BE, who was so kind to send me some M3 inserts for 3D printed parts.
You can push them in with a small soldering iron with ease.
Quite a strong bonding!

I glued the support to the original Pro-boat battery tray with epoxy.
Reason is PTEG does not bond well using CA.

I have an issue with the mapping of the throttle channel with the Swordfish 220 + Esc.
Whatever I do, it goes full power just of centre of the stick's travel.

Sundogz kindly send me a USB dongle to update the firmware of the Esc.
However on my previous Windows 7 machine I was never able to bring it to live.
Now there is a newer version of the software available from Hifei...you need to plug the Esc into the USB dongle without a motor attached.
I soldered it on, to reduce IR, no bullets

Anybody an idea?

What I can do is change the endpoint in my transmitter as a work-around.
Sep 24, 2021, 09:17 AM
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sundogz's Avatar
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That is a strong looking support, indeed! I am assuming you were able to repair the front mount to satisfaction?
Sep 24, 2021, 10:40 AM
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unusual_rc's Avatar
Quote:
Originally Posted by sundogz
That is a strong looking support, indeed! I am assuming you were able to repair the front mount to satisfaction?
It only has a wall thickness of 4 perimeters, and a straight ribbed structure inside of 20% infill. Yet it is very sturdy!
Also these inserts are a great addition. So easy to bolt stuff to your prints!

Indeed the front mount was really thorn apart. Layers were separated off each other. Because those breaches have a large surface area, gluing it with epoxy makes it very strong again.
Used a wood working clam again to enforce the bonding of the epoxy, using small wooden boards.

Nevertheless radial movement of the motor was still possible, as it was before. With this motor-mount it is quite solid.
Now the ABS hull is warping a tiny bit. Small, but large enough to not use the solid coupler I got from Denis_BE too. In the right size 5mm to 6mm diameter axis.

Maybe I can have a go tomorrow morning. Today there is some strong wind, tomorrow way less.

So curious how the metal D45/P40mm (.9) impeller will perform. This will certainly solve the "flexing blade" issue, if this is causing the decrease of efficiency at the high rpm/power.

If this is a success, I might cram in another 2S to see how the D45/P35mm (.8) impeller will perform with even more power! However the risk of sinking becomes a serious one with so much weight in this relatively small hull for a 45mm drive.
Oct 05, 2021, 01:38 AM
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Quote:
Originally Posted by sundogz
Up until now I've only imagined a rudder like that, I have never seen one. Interesting! Cutting off the end of the nozzle helped back-spray? After the taper there is no increase in pressure (to speak of). Oh well, whatever works! Yes, you are doing it right to get proper comparison measurements.
I suspect it's back pressure from the increased drag of a longer nozzle. Drag of course being ever more critical as the velocity increases.
Oct 05, 2021, 01:46 AM
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Quote:
Originally Posted by unusual_rc
IMHO adding a rudder to a jet-drive is always a sign that something is wrong.
The nozzle thrust vectored steering and add on rudder steering are quite different. The first requires jet motor RPM and a primed pump to work, the second requires straight line boat speed to work.


So you have to consider how you want the boat to behave when you throttle down, suck air off a wave trough or through heeling over excessively in a turn. Also, dual rudders lend themselves to complementing a non Hamilton Jet reversing flow where the reverse bucket turns with the jet and the redirected thrust is still in line with the nozzle.
Oct 05, 2021, 11:22 AM
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Quote:
Originally Posted by grael
The nozzle thrust vectored steering and add on rudder steering are quite different. The first requires jet motor RPM and a primed pump to work, the second requires straight line boat speed to work.





So you have to consider how you want the boat to behave when you throttle down, suck air off a wave trough or through heeling over excessively in a turn. Also, dual rudders lend themselves to complementing a non Hamilton Jet reversing flow where the reverse bucket turns with the jet and the redirected thrust is still in line with the nozzle.
It's only meant for straight line stability. Not for cornering.
And another question will be: will the fin be deep enough in the wash from the stern of the boat?
I noticed the bottom of the Recoil is not flat as one would think, the rear 4 to 6 inches are sloped up.

A ride plate is the solution here, with or without additional fins like the Thrasher v3.

If I add the ride plate now I render my measurements of previous runs pointless. In most RC jet boat applications a ride plate enhances top speed.
Last edited by unusual_rc; Oct 05, 2021 at 02:15 PM.
Oct 19, 2021, 03:29 PM
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42kmh and 100 to 110A of current usage.
At slower speeds even less current draw than before.

So Nylon 12 versus Stainless Steel/Bronze 3D printed impellers: 0 - 1

Even the sound is better, so the "versatile plastic blades" must be flexing for sure with 1.5kW of electric power!

Soon the video and more information.
I am getting close to the 45kmh I am aiming for on 4S with this hull!
Last edited by unusual_rc; Oct 19, 2021 at 03:48 PM.
Oct 22, 2021, 03:04 AM
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The video of the metal impeller


Here is the full video, I might make a shorter version later:

FreeJetDrive45 test P40M S3376 42kmh @ 105A (17 min 41 sec)


I would call this a successful test!
What Sundogz and I expected, is more or less shown here: With so much power plastic impellers are not the correct choice!
Might sound like a no-brainer, however the reason we went the Shapeways versatile plastics route (Nylon 12) was cost.
Although metal 3D printing has become much cheaper, the impeller used here costs around Ä40,-/55USD.
The plastic one a fraction of that price.

Nevertheless I think for all drives from 25mm and up metal is still the best choice, if you want some serious speed.
For scale models, do not bother and go for the versatile plastic ones!

Test results:
  • Current draw limited from 160A to 110A maximum
  • Increased top speed from 36 to 42kmh
  • Motor temperature stays very low (in other words, it could work harder, calculated an motor efficiency of 87,5%)
  • longer run-time with less strain on the lipos
  • steering improved with added small fin to steering nozzle
  • steering still bad, difficult to estimate corner radius
  • spins do not occur thanks to the fin
  • straight line stability still an issue. If you look carefully you see the model chine-walk several times
  • full throttle spontaneous direction changes limited, but still present
  • FrSky GPS sensor working on 1Hz maximum and with a 7.0 second delay still sucks! (compensated in the video)

Next step
I am not finished yet with this hull, although the end is visible on the horizon.
Still it makes a lot of water, over 150cc this time. And I even changed the bad oil seal with a brand new one (quite an operation, as you estimated it would be Dave )
Also visible on the video, the backspray might be the cause of this. A no backwash design as Sundogz already made is wanted.
However, it could also be that there is a leak somewhere in the drive itself, in the inlet housing.
A basin test in the garden with a camera in the hull might be needed. However weather is bad lately.

My next test will be the same nozzle and impeller, but added a ride plate and hopefully something to prevent or deflect the back-wash.
I am convinced the boat will become faster and more controllable with a ride plate. The fin will be rendered useless, which is fine.

I can conclude that a small fin on the steering nozzle helps, but not a lot.

Issues
  • possible leak
  • steering nozzle back-wash on lit and holes for water-cooling and steering. Lit is difficult to tape watertight at the rear
  • Esc (Hifei Swordfish 220A plus)

I have reprogrammed the Esc again.
What's happening?
  • Since I use it, the LVC never works (using the FrSky telemetry sensors instead, programmed an alarm per cell Voltage)
  • Clearly visible in the last part of the video, the current graph slopes down while the throttle stays constant. Return the throttle position to OFF resets the Esc immediately, and full throttle is back...and the sagging starts again
  • I have tried several times, but I cannot get the full throttle path programmed correctly. At 50% throttle 100% of the power is there already. Instead I have reprogrammed the path on my transmitter. Good work-around, but not as it should of course.

I do have the Usb dongle to read-out the Esc, and to even update the firmware.
However in order to do so I have to unlink the motor (not using bullets, soldered on for less resistance) according to the manual.
The programming card works as is, but does not help with the LVC or the sagging of the current at the end of the run. Mind you, when I stopped I still had more than 3,6V/cell measured with my calibrated charger.

Will open a new topic for this on the appropriate forum, but if anybody has a clue?
It is a fine Esc, but the sagging of the current is the most annoying issue.

Current LVC settings is AUTO, have tested 4S as well without result, cut off at 3.3V.
Also CUT OFF TYPE is set to gradually reduce power (SOFT) instead of instant cut-off (HARD). I might put it back on that last setting.

I would love to test the 35mm pitch metal impeller I still have, which is meant for 6S with this set-up.
This hull is just not capable of handling that added weight.
Oct 22, 2021, 12:53 PM
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Well, improvement indeed! And high speed turns are much better. Still a bit of hopping (more subtle, like pushups), but that may be because the correct COG cannot be obtained with those large batteries/motor/pump in such a tight space . This may sound redundant (I seem to be saying this a lot lately) but a finned ride plate would do well in this application.

Sorry about the speed control, you may just have a dud there. But perhaps someone else has experienced these same problems and can direct you to a proper adjustment. Great job on the motor mount repair, it seems to be holding up well. I wouldn't worry about that little water ingress, but then you have some pricey equipment in there now!
Oct 22, 2021, 02:09 PM
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Thanks Dave!
Indeed I think efficiency of our FJD pump design increased with just a few subtle changes (stator vane LE AoA from 40į to 15į, slightly thinner stator blades, exit nozzle incline of 5į, zero back-wash nozzle (to be mounted)) and strong metal 3D printed versions of the impellers.

Indeed I think a lot of RC boaters with a jet-sprint would be pleased with the sharp full speed cornering the Recoil can do now.

I think it is the sharp V- angle, the long and relatively sharp spray rails, the long an narrowness of the hull. But above all it does not run fully planing due to the large water intake (almost 1/3rd of the rear bottom surface), which is good for cornering, not so for top speed.

The CoG is as Proboat designed it. Found the original position of the propeller driven version and could get it there too, although much heavier (2,6KG versus 1,3KG of the original).

Indeed some fins under the ride plate will solve the chine-walking and straight line stability.

No apologies necessary for the Swordfish. It is a fine and beloved Esc. among model boaters. Never had a Esc which behaved like this. I will investigate it soon more deeply. I still have a watercooled 160A Esc spare by the way.

I was thinking to create with the 3D printer some holders for a pool noodle around the model, to create a RIB. Can fix the holders with glue to the model, the pool noodle with some tie-wraps. This will enhance flotation for sure, and probably could handle the added 2S pack to create 6S. Theoretically 55kmh should be possible then.

Still wonder if the next drive will be the 35mm or if I keep this 45mm size. Denis_BE is pushing almost 10 pound large hulls with a 40mm drive with modest amp-draw. The Recoil now proofed this is possible with our drive too!
Oct 23, 2021, 02:48 PM
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Kayaker's Avatar
Quote:
Originally Posted by unusual_rc
Clearly visible in the last part of the video, the current graph slopes down while the throttle stays constant. Return the throttle position to OFF resets the Esc immediately, and full throttle is back...and the sagging starts again
I had similar LVC and Over Heating shut off problems with my Swordfish Pro+ 240 amp HV ESC. Now I only used my Swordfish for recording highest RPM under load. I use a program box to get the RPM. I changed to Flier for my boat ESCís because the Swordfish has no revers. I think the things I tried that helped with my Swordfish problems are:

The Swordfish doesn't come with a capacitor bank so you have to add one to avoid LVC if you use old batteries or small batteries in a small boat. Big oversight from Swordfish. Almost all ESCís come with a capacitor bank. Everyone with a RC jet boat runs batteries that are too small.

I set the Low Voltage Cutoff to 2.5 volts per cell. This effectively turns off the LVC so I just used telemetry to know when to quit. For testing I donít let my batteries get below 4 volts resting per cell. This keeps the numbers comparable. With the Swordfish I still had LVC cut off so I changed to Hard Cut Off to make sure my recorded numbers are good. With Soft Cut Off itís hard to know what is happening with amp readings going down.

When static testing I use 3 times more battery mAhís. My boat canít float enough batteries so I add a float.
Last edited by Kayaker; Oct 23, 2021 at 02:57 PM.
Oct 23, 2021, 06:50 PM
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MiteyF's Avatar
Quote:
Originally Posted by Kayaker
Everyone with a RC jet boat runs batteries that are too small.
Not everybody!
Oct 24, 2021, 07:05 AM
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unusual_rc's Avatar
Quote:
Originally Posted by Kayaker View Post
I had similar LVC and Over Heating shut off problems with my Swordfish Pro+ 240 amp HV ESC. Now I only used my Swordfish for recording highest RPM under load. I use a program box to get the RPM. I changed to Flier for my boat ESC’s because the Swordfish has no revers. I think the things I tried that helped with my Swordfish problems are:

The Swordfish doesn't come with a capacitor bank so you have to add one to avoid LVC if you use old batteries or small batteries in a small boat. Big oversight from Swordfish. Almost all ESC’s come with a capacitor bank. Everyone with a RC jet boat runs batteries that are too small.

I set the Low Voltage Cutoff to 2.5 volts per cell. This effectively turns off the LVC so I just used telemetry to know when to quit. For testing I don’t let my batteries get below 4 volts resting per cell. This keeps the numbers comparable. With the Swordfish I still had LVC cut off so I changed to Hard Cut Off to make sure my recorded numbers are good. With Soft Cut Off it’s hard to know what is happening with amp readings going down.

When static testing I use 3 times more battery mAh’s. My boat can’t float enough batteries so I add a float.
Thanks Robin for your reply!
I can indeed live without VLC because I use telemetry too, and added a programmed verbal alarm.
Reverse is something I do not need, although I can understand for your 3D steerable nozzle a fitting and working reverse bucket is a true design challenge (although if you can mix on your transmitter, I think there are possibilities it can... different discussion )

So you noticed this "sagging" of the current with throttle kept constant too?
So CUT-OFF set to HARD?
I tried that a couple of weeks ago, but cannot remember it worked
Focussed too much on the VLC.
Need to try it again.

Thanks so far!
And no, I have 4S 8Ah lypo's in my boat, capable of 25C discharging.
They are huge!
Agree I see often too small lipo's being used! All depends how much current that you use.

By the way, as far as I can tell this particular model has two capacitators build in.
Last edited by unusual_rc; Oct 24, 2021 at 07:14 AM.
Oct 24, 2021, 03:13 PM
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Kayaker's Avatar
On low voltage of 4s you can have voltage sag from wires and plugs when you hit full throttle. A capacitor bank may stop LVC from tripping. A cap bank also gives instant throttle response.

My Flier 180 amp 12s comes with a good cap bank but R-Snake recommends adding more. Here is what they say about adding a 5 cap pack to it: ďTo optimize its function, it is recommended to use two or even three cappacks in parallel, doubling or tripling the amount of capacitors.Ē

https://www.ebay.com/itm/26517281530...Cclp%3A2047675
Last edited by Kayaker; Oct 24, 2021 at 03:20 PM.


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