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Nov 18, 2021, 03:17 PM
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Gala jet rib, Rey pulling a ringo with her jet boat (4 min 12 sec)

Enjoy..... Interesting idea about using a gyro, not sure how you go about it.
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Nov 18, 2021, 05:01 PM
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unusual_rc's Avatar
Nice movie!
Was that full throttle all the time?

Does your model porpoise?
Mine only chine-walks, which is quite irritating. It also shows this sudden change of direction without touching the rudder. In my movies I show real time both trottle and rudder values, as a proof it does out of the blue.

Seriously I think vertical trim is key here.

I do have an Rx with build in 6 axis gyro (not 9), because it was a bargain and can be turned off, even from the transmitter. For flying it is almost a sin here to use one in a fixed wing airplane
Nov 18, 2021, 11:47 PM
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Not on full throttle, the ringo rides better at lower speed, not as bouncy. No porpoises to be seen in our lake😂 Have we found the cure?🤐
Nov 19, 2021, 04:33 AM
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Quote:
Originally Posted by returntohome
Not on full throttle, the ringo rides better at lower speed, not as bouncy. No porpoises to be seen in our lake Have we found the cure?
So there is more power spare, good to know!


Indeed we call porpoises "brown-fish" in Dutch. I think the name for the boat like behaviour resembles the way these little dolphins swim

A gyro is one of the things to try. However as with model airplanes and cars I find it a bit of a cheat, although the technology is great.

Still vertical trim might be the solution on your scale model. Ride plates on anything semi or non scale.

Watched the official broadcast of the world championship marathon jetboat racing in NZ last night from 1997! Wonderful boats, no one had a turbine in the day. And boy, these highly modified v8 engines broke down a lot.
Again it was obvious that almost all of these very fast jet-boats had vertical trim, and all had it a bit up at top speed. Easily noticeable by the huge jet-stream behind the vessels!
Spectators on bridges had to be careful

By the way, very inspiring concerning a future scratch build model. Need to create an efficient mixed flow pump then, although some of those old boats still used multi-stage axial pumps. Today all use mixed flow pumps to reach speeds way over 200km/h or 120 landmiles/h!
Nov 19, 2021, 04:58 PM
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I thought this comment was funny from another forum where i showed the ringo film.....
think she's trying to drown him! :lol:... Never look behind to see if her ken is okay! : At the beginning he is relaxed, then he raises his hand to say that things are going too fast, at the end he clings on as best he can! ... There is a problem of divorce and division of property!
Nov 21, 2021, 02:20 PM
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Gala A500L Jet powered Rib, Jumping the pipes (1 min 18 sec)

Got a bit daring today egged on by some fellow club members..🤣
No luck yet with turning left, but I've just realised I can swing the pressure cone left and right and as I do the linkage to the nozzle compensates keeping the jet straight.!
Nov 21, 2021, 02:34 PM
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Quote:
Originally Posted by returntohome View Post
https://youtu.be/86UxkujjJ5I

Got a bit daring today egged on by some fellow club members..

No luck yet with turning left, but I've just realised I can swing the pressure cone left and right and as I do the linkage to the nozzle compensates keeping the jet straight.!
Very cool footage!
Nice jet-stream visible in slo-mo behind the vessel!

Hope you solve the steering issue soon!
Nov 22, 2021, 03:06 AM
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Shots from the videos 🤣
Last edited by returntohome; Nov 22, 2021 at 09:05 AM.
Nov 30, 2021, 01:18 AM
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After my c of g exercise I had not only moved the battery into it's rearward home but also stuck some lead in the back. I had a brief try at the lake, but the nozzle and compressor fell off and sank, but it did seem promising in those short runs. I need to redraw the compression nozzle, maybe with bosses to take the screws as this is where it cracked. Small slots rather than holes allow for tilting the nozzle upwards.
Nov 30, 2021, 11:06 AM
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Back to the drawing-board, but it sounds like you are on the right path now to get this design right!
Dec 01, 2021, 08:06 AM
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PLA is not that good for mechanical parts, PETG is a bit better. (nylon and ABS too, but they are harder to print)
But, if you only have PLA (or want to stay with it), you can try to anneal it, for 10~20% more strength.
You may find some guidances about this here and here
Dec 01, 2021, 04:54 PM
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Some tried to cure the FJD parts this way, to make PLA water-tight.

For me the drawback is the risk of shrinking and warping. The sand method sounds as the best of the worst!

I had big issues printing my new design steering nozzle out of PTEG. Needed 3 attempts to get a usable one. And boy, the differences in strength are huge! First 2 broke like it was made out of China, the last was strong, but needed some post processing (knife and sandpaper).

Yet I have good experience with tight tolerances.

Next I printed something from a brand new spool of PLA for my little one.
When I tried to remove it from the bed, it was still warm. It deformed like candlewax!
Luckily it was still stuck to the magnetic plate, so eventually it cooled down straight. Then I removed it from the bed plate.

Nevertheless I have my doubts about PLA for the pump parts. But I will try to make a few out of it, just for testing!

What about the more tough PLA?
Dec 02, 2021, 01:39 AM
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Jerome that seems an awful lot of trouble to just get a little stronger. Being new to printing I need good results to gain confidence hence pla. My latest print took about 10 hours, it's one half of the New gearbox with the propeller up front. 100 per cent solid should make it waterproof, and it's high impact pla, even though the fin is thin at the bottom it won't bend. I have discovered it's best to let big items cool on the bed so they don't get warped.
When I dismantled the prototype gearbox a tablespoon of water came out, must have been inside the skin, also even though I cleaned it oil still ouses out.
Dec 02, 2021, 02:54 AM
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I did some tries with different sorts of PLA, it do give more strenght, high impact or not. The best (or the least worse) results I was able to achieve, regarding accuracy and strenght, was by using the cheapest plaster I was able to find and encase the part in it before baking.
Anyway, I have small boys at home, soon I found that repairing toys/random broken stuffs with PLA, even if I gave my best at hardening it, was like putting a bandage on a wooden leg. But I had some success, some parts lasted for a few weeks
Now I print everything with PETG, with a simple anet a8 and a glass bed, it's far harder and last longer, even after a few weeks outside.

I only have the inlet housing of a Bermylizzard jetsprint still in PLA (epoxy coated), so far it didn't broke. PETG is not that hard to print, compared to PLA. It's sticking much better to build plate, and cura default PETG settings are enough to achieve good results. For post processing, a really quick heat gun exposure will remove most, if not all of the stringings. Supports will require more work (z gap value help about this), but parts will last far longer.
Dec 02, 2021, 11:30 AM
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Quote:
Originally Posted by nwalker
Now I print everything with PETG, with a simple anet a8 and a glass bed, it's far harder and last longer, even after a few weeks outside.
You confirm my thoughts about possibly switching to PLA for my jet-drive parts.
According to my personal experience PTEG is not as easy to print as PLA.
On my machine (Prusa mini+) PLA is really turn-key: add the 3D part to PrusaSlicer, apply the corresponding manufacturers settings, slice and print.
No tweaking, change settings, nothing.
Just 99% correct prints.

For PTEG there is no manufacturers profile available, only a generic.
(except for Prusament PTEG, of which most parts of their printers are made out of. Have not tried that yet)

I have to tweak a lot!

But it depends mostly how many details I want into the part.
10 degrees Celcius printing temperature difference makes a whole of difference in stiffness and brittleness.
Up till now I get almost stringing-less prints, which are not that strong.
Or highly stringed, oozed models, which need some degree of post processing. But they are perfect concerning strength and flexibility.

Retraction is key here concerning the stringing and oozing. But I have not found the sweet spot yet.


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