Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[Dave_S.]

I am in the process of renovating an Aerokits 46" crash tender. I bought the model ready built and it had an MFA Tornado motor installed. I am replacing this with a more powerful brushless (42-50 500kv out runner) which I will be using at a probably max of 800 watts which should produce a performance similar to a good .60 glow engine.


The Tornado motor (157 watts) had been installed using a standard red plastic Huco style coupling. I have no experience of using a coupling with a motor producing over one horsepower, but the Huco coupling doesn't look like it will be up to the job - or will it? I


I'd be interested to hear from anyone with experience of using a fairly powerful motor in a scale or semi-scale model, especially in regard to the coupling. I doubt that I'l be using full throttle very often, and will be accelerating in a smooth and progressive manner, but would like to know that the coupling is not going to fall apart if, for example, I am required to go from full power forwards to reverse in order to avoid an obstacle on the water.


Thanks, and looking forward to reading the replies.

[Martin (Admin)]

What are your shaft sizes?

Solid rubber ones can handle a lot of power ....




https://www.ebay.co.uk/itm/201677538423?hash=item2ef4eb0477:g:-RUAAOSwDk5T-053&amdata=enc%3AAQAHAAAAoBpMyEborHHIu2sS%2F3igVvZ5t8aca6nhBiiELI9L69T%2B1NeNiuGpDJUV5ZqtpjR%2FMBBkdyO4bXYocd433fnlMP6AOcu4OPpg76MkH2oEtmw5p00VXEO2ocwtQkbinChuU9VXJmmHl4kYM0qQJ9cPcLcoaWg9djt5vok7RK8atxjrwj8Bf9Re0mYlMGk5ttKkXEtZXj%2F6ntPPqdafYPWO180%3D%7Ctkp%3ABk9SR6zY5cemYQ

[Dave_S.]

 5mm threaded (shaft end) and 5mm plain (motor).


Good point, I hadn't thought of them, I shall get in touch with Steve and see what he suggests.

[Martin (Admin)]

Also see Prestwich Models:

https://www.prestwich.ndirect.co.uk/hdwrrubbersetc.htm

[Dave_S.]

Thanks again - another supplier I had overlooked. Used to buy from them when I was running IC boats years ago, and therefore hadn't considered them for electric.


I've sent a message to Steve at Model Boat Bits and will see what he says.

[Dave_S.]

Thank you for your suggestions, Martin. Steve from MBB relied to my query very quickly (as he always does) and says that the Powerflex couplings were originally used with IC boats, so I have ordered a coupling and an alignment tool to help with the motor installation.


Excellent example of how useful a forum like this can be!

[Circlip]

Are you REALLY sure about the thread Dave? O/D of M5 is usually 4.9mm and 2BA 4.7mm and although 0.2 mm is only 8 thou., It makes a huge difference in alignment with a powerful motor.


  Regards  Ian.

[Dave_S.]

Thanks, I'll let Steve know…

[Dave_S.]

He hasn't anything in imperial sizes. I think I might just have to bite the bullet and change the shaft. If I can get new bearings made up to slip into the the current shaft tube, I might get away with not removing it, as it looks a big job as it is well glued in place.


I'll see how the coupling fits and take it from there.

[Dave_S.]

Just spoken with Steve again, and he has the ideal solution - all I need to do is send him the end bearings from the shaft tube and he will make a pair that will fit but have 5mm bore, so I can replace the shaft without major surgery to the boat.


Problem solved!

[Martin (Admin)]

What great service!   

[SteamboatPhil]

Steve is the Man 

[Andyn]

There was recently a discussion about couplings over on the MBM Facebook page, my comments there were that electric motors should not be fitted with flexible couplings. In my experience, all they do is induce vibration. The very best way of coupling an electric motor to a solid shaft is by using a solid coupling, and aligning everything perfectly to suit.


The rubber bobbin couplings are second worst only to the red plastic huco couplings. Rubber isolation bobbins are NOT aligned. They are designed to isolate vibration in exhausts and other applications where rotating is not something that they need to do. You can try to align a rubber bobbin coupling until the cows come home, you’ll never get them to run true.


Should you wish to fit a solid coupling to your model give me a shout and I’ll make you one

[Dave_S.]

Thanks, Andy, as the Powerflex coupling is already on its way here, I'll give it a go, and if I can't get it to run smoothly, I'll take you up on your kind offer.

[Circlip]

With nuts and washers, you should be able to pull the new bearings into the existing tube using the 'Old' shaft.


  Regards  Ian.

[Martin (Admin)]

The rubber bobbin couplings are second worst only to the red plastic huco couplings. Rubber isolation bobbins are NOT aligned. They are designed to isolate vibration in exhausts and other applications where rotating is not something that they need to do. You can try to align a rubber bobbin coupling until the cows come home, you’ll never get them to run true.

Very Interesting Andy!   

I'm guessing that the inboard end of propshaft needs to be FIRMLY supported?

 
 

[Dave_S.]

The chairman of my club runs a very powerful large scale boat, I'll ask him what he uses for couplings. I do know that the whole boat is very well put together and runs very well too.

[ooyah/2]

Dave.
I used to run a flash steam boat ( OOYAH) and to get a coupling to withstand the high torque I copied a coupling same as the 120MPH hydro of R.Kirtley's which I have always known as ( Dog and Bone )
it with the ball end drilled and tapped to fit a 3/16 "dia St/Steel  and the engine had a lock nut with a slot to take the ball and bar.
On the pic of the engine is the lock nut that pulls the main shaft and the bottom half of the engine together.

The other pic is of the prop and the angled main shaft and the prop shaft parallel to the water line and lock nuts on each end of the prop shaft, the main shaft has locking collars to prevent any pressure to the engine,
I don't know of any where that this type of coupling is available to buy.

Hope that this helps.

George.

[Andyn]

Very Interesting Andy!   

I'm guessing that the inboard end of propshaft needs to be FIRMLY supported?

Not really no, though I’d hope any propshaft is firmly in the model...


 Was recently speaking to Ian Folkson, he has now ditched top end bearings in his 3.5cc geared multis in favour of running a 5mm shaft directly from gear through to the prop, with a PEEK bushing at the prop end. Quite a few races have followed suit. [size=78%]Wouldn’t be entirely impossible to do with an electric motor either, as long as it was a 4/5mm shaft in the motor you could replace it with a long piece of shaft straight to the prop. [/size]

[JimG]

Sounds like the shaft set up in the old Sloopy fast electrics. No inboard bearing only an outboard one. There was a solid coupling between the motor and the shaft, used a 2mm wire shaft hard soldered into a 4mm prop adapter. Allowed the shaft tube to be only 5mm outer diameter.
Jim

[Umi_Ryuzuki]

Maybe something similar to these?

[Backerther]

In my case of conversion to motorised Rc boat made about 8 years ago....This is just nearly the same case of mine as Dave S is now trying to convert to electric powered boat.
My 1m class Jupiter F-99 used to run with 60 nitro engine (Japanese Enya make) with 60mm dia. props very well while
currently powered with 2,200 KV(1,200W) brushless motor, water-cooled and 47mm dia.Props which sailing video is as shown below.
Diameter of the prop shaft is 4.5mm while that of the motor is 5mm.
The subject of this thread is the coupling and mine are disc couplings as shown below.
The same type of coupling has also been used very well in my 105cm cabin cruiser Najade as seen in the pic below and no problem was found at all up to today in both Jupiter F-99 and Najade.
This disc coupling is specified to be capable of rotating over 24,000RPM and I tested it in my Najade build as in the following pic.
I hope above will be of some use in your conversion project to motorised boat.!!


1/2;1m class Jupiter F-99.
3; Disc coupling in Jupiter F-99.
4; Another disc coupling in Najade.
5; Revolution test with Najade.   Reaching easily over 24,100RPM but I became a bit afraid of its number of 24,100..., though an alignment had been perfectly set up with no vibration previously, needless to say...!!   
6; Najade leaving a long wake.
7; Screw props of JupiterF-99

Video is JupiterF-99;
https://www.youtube.com/watch?v=fj0o7ci3xj0

[Dave_S.]

Thank you all for your suggestions. Definitely getting plenty of options to consider, many of which are familiar from the days when I ran IC boats, so ar definitely strong enough, especially as a brushless motor should be more or less vibration free.


Backerther, your conversion seems to be a similar size boat and similar power to mine (my motor is rated at 1350 watts max) - do you have any further details of the coupling you used?


I can see the reasoning behind Andy's ideas, but replacing the motor shaft with one 12" longer is beyond my capabilities. I am not convinced that a completely rigid system is going to work in a fairly old wooden hull, as it is not likely to remain as stable as a GRP or carbon hulled racing hull.

I have considered using gears or substantial belt/pulley as a coupling, probably 1:1 ratio, as there is plenty of room in the crash tender.

The only problem now is that the more I think about the many ways of getting power to the prop, the less is getting done! I'm sure I'll get this on the water before the spring, though. There is little else to do it other than sorting out the drive system.

[Backerther]

 Hi Dave_S.
This is the additional information of disc coupling similar to mine(double disc type).
My type is MCGL20-4-5 and I enlarged the 4mm hole to 4.5mm to suit the prop shaft.    


https://in.misumi-ec.com/vona2/detail/110300119910/?PNSearch=MCGLC&HissuCode=MCGLC&searchFlow=suggest2products&Keyword=MCGLC&isReSearch=1#


Kiyo

[Circlip]

Went through the flexible coupling saga back in the sixties with a Racer powered Adamcraft seaplane tender, EVEN correctly aligned the ultimate system we eventually adopted was the RipMax universal Ball and Socket. Result/ Never a problem again. Commercial version of what George (Ooyah/2) has described. Reason you cant get them as standard any more? Red plastic peril was probably cheaper to make, but useless for 'Proper' power units.

  Regards  Ian.


 Other advantage to this type is that NO endthrust has to be compensated for.