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[Backerther]

Hi Allen A
Have you been enjoying Lindberg PT109 and watching this forum still now??

I have the 4th kit available here for another conversion project since I got it at a far less price here in Japan than in foreign countries. Moreover, this hull of the kit is so suitable and easy to convert to a RC scale-like fast vessel as you know well.  
The hull is not necessarily symmetrical but seaworthy and has shown a stable characteristics on the water.
Oh, NO! I'm not a salesman of the Lindberg company at all but a mere salesman of a RC scale fast boating.

The kit this time is injection moulded one with white unusually as shown below.
I just have started to think what next I should build with this versatile kit/hull. This stage is also interesting if some good concepts should arise in my mind.

The hull size is fundamentally large enough to install 550 class of motor and 5000mAh 3S lipo by which most of fast scale boats
could be boosted away straight forward so easily on the lake.
On the other hand, it's small enough to carry to the boating site and to keep on the shelf.

One more merit I like for using it on the water is that the boat is not so detailed originally unlike italeri kits.
What next...what next ...what next is such a happy time for me, an old man to go on with in a spare time..

[Backerther]

I just started to assemble a couple of screw shaft supports by glueing two halves.
And I sanded the corners of the supports to be round, though no indication was made about this point in the assembly manual.
And I also provisionally fitted the relating parts to the hull to confirm if they should go well and the result was so so..

Screw props are not what are included in the kit, needless to say.
I'm going to make a couple of screw shafts and stern tubes later, not because they are low quality for RC boating but because
they are made in inch standard, namely 3.17mm..as well as a bit short for my intended configuration.
I will build this boat by mm standard and it will be 3.00mm in this case.
One of the difficult matters is to cut the threads precisely on each one end of screw shafts by hands, not by lathe that I do not have..

[swiftdoc]

Hi Kiyo, I just came across your new build log and will follow that with great interest!
Arno

[Backerther]

Thank you for your comment, Arno.
This boat is scheduled to be powered by a couple of brushed motors that I have kept for my PT-109JP (jet boat).
And tank type steering is also scheduled to be done by an ESC for the RC tank.

[Backerther]

Not good !!.....but... sufficiently available as screw prop shafts for my application of a fast patrol boat.!!
Anyhow, it's soooooooo difficult to make neat threads on 3mm brass rods by a die regardless of prior trials for more than 7 rods.
I have found myself to be so clumsy again by this work...!!

[Circlip]

 Different grades of brass give different results. Soft brass - poor, Hard brass - good.


  Why brass? Stainless steel better.


  Why such a long thread?


 Regards  Ian.


 As an addendum, thread length required is only 1.5 X D  so 4.5mm or 9mm if  4.5 thick locknut.

[Backerther]

Hi Circlip,
So nice to have your comment and opinion.
What you have mentioned in the first paragraph is truly correct.

I have used stainless steel rods for my full-fledged RC boats while brass rods were used for pla-model converted model boats.
That's because the brass rods were good enough for screw shafts and consequently made nice jobs in such pla-model conversion boats as to sail on the lake so powerfully, as often posted in this forum with pics and videos as seen below.

Bing 動画

In other words, stainless steel rods generally are over-specification in my understanding for such toyish ? RC boats...

The length of threads is simply and mainly from the thickness of the prop holes which will be shown later in this thread.

Kiyo

[JimG]

Brass shafts work quite well if you don't do too much running of the model. The Billings Smit Nederland used chromed brass shafts running in brass bearings. I managed to wear through the chrome plating and brass on brass meant that the shafts started to wear at the bearings becoming a loose fit and leaking. The shafts are pretty near horizontal in the hull. I ended up replacing them with steel shafts with a sealed ball race at the inside end of the shaft tube. Admitedly the boat had a lot of running time on it, it had taken part in two 24 hour sails by this stage and went on to do two more before being retired.
Jim

[Backerther]

Hi JimG
I'm so glad to have your nice comment and information on brass material based upon your precious experience.!!

I wonder how many times of sailing most RC boaters are enjoying in each year normally once completed, namely sailing times or its total hours throughout a year or its active life to each boat/ship...??
IN MY CASE, 3-4 times a year at most in each boat and less than 10 minutes (one Battery capacity) each sailing with 4-5 times a day...

Brass screw shafts haven't made me nervous at all about wearing issue for my pla-model conversion boats so far.
Instead, I have paid much attention to set accurate alignment and sufficient lubrication with care once completed.
Therefore, they are generally so calm on the water.
Lubrication seems to have made a good work with assistance of water to prevent from wearing...though some drops of water
RARELY found in the hull after sailing and I'm not sure where it is from, either the deck or stern tube.??!!!

Pics below (1 through 3)are some of my pla-model converted good runners with brass shafts on the water.
Pics 4 through 7 are my new and old flag ships with stainless steel shafts.

[Backerther]

Well, getting back to my mainstream of this thread, cheap and simple home-made screw set is now complete as in the pics.
But the performance is not so cheap as its cost as in the pic.  byuuuin!!! 
A 3mm brass pipe was cut to length for stern tubes which mated well with the brass shafts.
Grease filling posts are supposed to attach later, needless to say.

Being unsatisfactory threads to me , the screw shafts and props are well mated causing no "laughing revolution" actually.
In this sense, I may possibly say that threads making work has been done successfully...

I can go further to the next stage smoothly surpassing difficult work of thread making.

[Backerther]

And I just sat the screw sets in the hull together with associated parts to see if they should go well for getting accurate
alignment with the motor shafts later to be set. Almost of all, they were so so this time too for an old pla-model kit.

[Backerther]

And I made a couple of grease filling posts and also cutouts on both stern tubes as in the pics.
Thickness of the grease filling post to mate with stern tube is 0.5mm. A bit nervous to drill a hole precisely in the very center of the brass pipe.
The filling post at its lower position will play a role of a support for the stern tube.  

[swiftdoc]

Job well done, Kiyo   I understand that drilling the holes in the centre was a demanding task!

[Backerther]

Arno,
I'm so glad to have your friendly comment and also to have drilling work understood about how troublesome it was for a thin and slender brass pipe.

[Backerther]

I completed fully a couple of screw propeller sets after gluing grease filling posts as seen in the pics.
I easily imagine that many or most modellers may say or think why not by soldering them..??

From my experience to fix this portion, this method is sufficient, secure, easy and simple to block water ingress while keeping a
good strength because of a quality two-part epoxy and construction of the grease filling post.

Soldering is generally a bit nervous to use, locate precisely and neatly such parts as these during the work to me...
The worst is fear of flow of melted solder into the stern tube....to me who is clumsy..

[Backerther]

For next thing, I made a couple of heat blocking spacers to be set between the motors and motor mount made of soft plastic.
The motors are imagined from my experience to get easily hot (as they also indicate on their cans as caution) when running at speed.
After that, I just made some drilling works on the mount (originally a bulkhead) to set the motors after checking precise locations
of the holes for motor shafts using a simple template. I'm going to use as many parts of the kit as possible this time.
Finally, I assembled the motors and the mount provisionally to see if they should go well as previously marked on the mount..
Needless to say, I intend to set water cooling coils around the motors later for the maximum cooling effect.

[Backerther]

In the next place, it's one of the most nervous and troublesome works for especially building a fast Rc boat in my case...
Yes,! Seeking for the best positions of motors/motor mounts for the best alignment between motor shafts and screw prop shafts.   Unless this works or adjustment are nearly perfect, an intended fast RC boat will be a slow sailing boat unintentionally on the lake later..  
In addition to the above, I also confirmed a good accessibility into the hull which is also very important for practical RC boat in terms of service of coupling, grease filling, tiller arms and steering servo as well as motor/ESC change.

Finally, I checked motor revolution at 1.2V battery to see if it is smooth and calm at even low voltage. They went very well.
By this test I understand that a good alignment may have been properly done perhaps as a result.

Pic 1-3 show that tips of screw prop shafts are about to be inserted to couplings. Nearly OK about alignment...

[swiftdoc]

All looking very nice and crisp, Kiyo! What kind of couplings are these? Is the black ring material flexible in case of minor misalignment?

[Backerther]

Arno,

Thank you for a quick comment.
Yes, they are very good couplings for absorbing comparatively large mis-alignment. They are called "flexible beam coupling".
And "black ring" as you have understood is just a coiled slit by which a certain level of mis-alignment could be absorbed.
Mine is made of aluminum and I adopted them for this project of a fast patrol boat of Japan Coast Guard.
Less than 4 USD each including shipping here in Japan.

Kiyo

[Backerther]

Just for reference to let you know how this kind of flexible beam coupling is tough for a fast RC boat which I have used actually in my second PT-109 although the material is a bit tough plastic.
In addition, the coupling is smooth and calm in running.

The pics below show the test running of the motors and couplings leading to confirming if the alignment is properly done.
In this case, the screw prop rotated with 2000 RPM at 1.3V Nimh battery.!!!  Perfect for a practical RC boat!!! 
And the sailing pic and video attached endorsed this setting to be OK and the quality of the coupling on our local lake actually.

Bing 動画     <----Over 40 knots,? faster than the real boat..??   A MTB had best run fast and thence is worth being called MTB.??!!

[swiftdoc]

Many thanks for your photos, Kiyo. I was mistaken not having recognized that there are slits instead of rubber. I am using the Misumi couplings in my Falcon which runs at very low revs though, compared to your setup. You surely will add some supports to the shafts as in your previous builds I guess….

[Backerther]

Hi Arno,

Misumi's disk coupling is, so far as I know from my past experience, the best in any aspects to use for fast and tough revolution
of motors and thence I have used such disc couplings for my full-fledged RC boats as in the pics.
However, only one unsatisfactory with me is the price.!!! Therefore, I have used such low-cost flexible beam couplings as in the comparatively light weight pla-model fast boats with brushed motors. 
This coupling is specified to be capable of 24000RPM in the product specification by which I have chosen to use for my large lake going brushless fast boats. Calm, reliable and tough but expensive!

[Martin (Admin)]

Misumi's disk coupling :  https://uk.misumi-ec.com/vona2/mech/M1001090000/?ppc_keyword=flexible%20coupling%20types&msclkid=8f547be7c9501f8914bb1c5f90b0cd33&utm_source=bing&utm_medium=cpc&utm_campaign=ba-en-generic-keywords-rotarytransmission-uk&utm_term=flexible%20coupling%20types&utm_content=en-generic-flexibleshaftcouplings-new-uk

[Backerther]

And this is the very evidence that shows true value of Misumi coupling in my Najade. 
24100RPM with 3S lipo for some seconds for fear of excessively heated condition of the motor!!!!!!!      This motor has to be water-cooled.!!! 

[Backerther]

Provisional setting was done in a good result so that I finally fixed the drive rain permanently with epoxy for stern tubes
while motor mount with a glue gun as I have ever applied successfully with previous pla-model fast boats. 

With this work, I have turned the first corner of this simple pla-model boat at last.!!!