Topic: DIY Coupling for prop shaft (Read 9075 times)

lesfac · « **on:** December 18, 2015, 05:04:44 pm »

I thought I would try and make a coupling using rubber to provide the flexing element.

I bought some 10mm diameter silicone rubber cord off Ebay and tried supergluing it into metal bushes which were the ends of the coupling. The super glue proved to be no good so I have cross drilled the bushes and rubber and put in a 3mm pin.

I have fitted the coupling to my 49 inch Perkasa and it just remains to try it out

The rubber has a Shore hardness of 60 and may prove to be too soft as there is a fair bit of "rubber band" effect. However I am hopeful that the coupling will be able to stand up to the power of the Emax GT4020 motor.

Can anyone suggest a glue that will stick rubber to metal effectively?

southsteyne2 · « **Reply #1 on:** December 18, 2015, 09:50:22 pm »

Hi I have used this for years about 4 dollars ebay and may save your model and your life if you try swimming after it serious
Cheers
John

CGAux26 · « **Reply #2 on:** December 19, 2015, 12:32:14 am »

I am concerned that if the rubber starts to tear while the motor is running, it could cause the motor or stuffing tube to tear loose. Dis-ass-trous.

But I love your motor mount. That's how I make mine.

Martin (Admin) · « **Reply #3 on:** December 19, 2015, 12:37:14 am »

Quote from: lesfac on December 18, 2015, 05:04:44 pm

Can anyone suggest a glue that will stick rubber to metal effectively?

Evo-Stik 'Sticks Like Sh*t'

Everbuild Stixall

Loctite Power Flex Super Glue Gel

Martin (Admin) · « **Reply #4 on:** December 19, 2015, 12:39:32 am »

Quote from: southsteyne2 on December 18, 2015, 09:50:22 pm

Hi I have used this for years about 4 dollars ebay and may save your model and your life if you try swimming after it serious
Cheers
John

These John? http://www.ebay.co.uk/itm/New-CNC-5mmx-5mm-Top-Tight-Shaft-Coupler-Flexible-Coupling-Servo-Motor-Connector-/271560849612?hash=item3f3a49b8cc:g:Y9oAAOSw~gRVke3b

southsteyne2 · « **Reply #5 on:** December 19, 2015, 01:43:43 am »

Yes Martin had no problems for approx 4 years with live steam and 5 blade prop so plenty of load

Cheers
John

lesfac · « **Reply #6 on:** December 19, 2015, 08:38:38 am »

Thanks for the replies chaps.
As CGAux26 says if it fails I imagine the rubber will get chewed up. I will be careful where I use it while I sus out the reliability.
I am about to receive a 1/12 Severn lifeboat kit and have started getting bits together to fit it out. I won't risk my home brewed coupling in that. The metal coupling indicated by southsteyne2 and Martin are very inexpensive. I have bought 2 Emax BL4030 motors for the lifeboat. Do you think the couplings are good to handle the power produced by these motors? One thing about them that occurs to me is that they are very short and I wonder about the amount of engagement on the motor and prop shaft side.

southsteyne2 · « **Reply #7 on:** December 19, 2015, 09:44:50 am »

They are 1" long with 1/4" or more bore depth depending how much flex you want also locked by 4 grubscrews so all good
Cheers and merry Christmas and happy new year to all

Arrow5 · « **Reply #8 on:** December 19, 2015, 10:19:25 am »

They don't post to Scottish Highlands, wonder why ? All the way from other side of the world to get lost in Inverness or Fort William. We see a lot of this in spite of being on the mainline (rail) and air routes to London .

southsteyne2 · « **Reply #9 on:** December 19, 2015, 10:27:09 am »

Aye wi global warming might be the only place you will be able post to maybe time to invest in land ho ho ho

Cheers

Arrow5 · « **Reply #10 on:** December 19, 2015, 10:43:09 am »

Quote from: southsteyne2 on December 19, 2015, 10:27:09 am

Aye wi global warming might be the only place you will be able post to maybe time to invest in land ho ho ho Cheers

Weel dinna invest in a ski resort because it is plus5C at the summit of Cairngorm today

Nae snaw at aw, at aw.

an the River Spey flooded the Old Bridge Inn last week , oh michty me. Ah micht hiv tae emigrate

Crossie · « **Reply #11 on:** December 19, 2015, 12:26:16 pm »

Quote from: lesfac on December 18, 2015, 05:04:44 pm

I thought I would try and make a coupling using rubber to provide the flexing element.

I bought some 10mm diameter silicone rubber cord off Ebay and tried supergluing it into metal bushes which were the ends of the coupling. The super glue proved to be no good so I have cross drilled the bushes and rubber and put in a 3mm pin.

I have fitted the coupling to my 49 inch Perkasa and it just remains to try it out

The rubber has a Shore hardness of 60 and may prove to be too soft as there is a fair bit of "rubber band" effect. However I am hopeful that the coupling will be able to stand up to the power of the Emax GT4020 motor.

Can anyone suggest a glue that will stick rubber to metal effectively?

There are many compounds which will bond rubber to metal more or less permanently, however you have used silicone rubber and the only readily available material that will permanently bond to that is silicone rubber though there are here are hi-tech industrial methods of bonding silicone to metals. If you can abrade the inner surfaces of your metal couplings then thoughourly degrease them, and then assemble with Polyurethane sealer/adhesive [ the stuff used in car body shops] . A Nitrile rubber tube would be easier to bond . Your pinning method is a good, cheap solution

Trevor

CGAux26 · « **Reply #12 on:** December 21, 2015, 07:09:02 pm »

Sorry but it seems you are going a long way around what is an easy subject. The 3 piece dog bone couplings and the universal joint couplings both work very well, are easy to install and align. I have used both on several models and never had a problem.

lesfac · « **Reply #13 on:** December 21, 2015, 10:09:31 pm »

For me making a coupling is an experiment. I don't know if the coupling will be durable or a disaster but if it works I think it will be a smooth drive.
Model boats is a field full of make or buy decisions. Some guys make hulls from scratch and others buy fibre glass hulls. The same goes for boat fittings. Some people make them and some people buy them.

I will purchase proprietary couplings for the lifeboat I am about to start on because I am not confident a home brew would be "safe". If I was shure of the durability I would certainly make the couplings
Les

richald · « **Reply #14 on:** December 21, 2015, 10:29:50 pm »

Have a look at Mobile Marine Models couplings ...

http://www.mobilemarinemodels.com/safety-coupling-72-c.asp

they seem to be very similar to what you are working with.

I have one fitted to a brushless set-up - it works fine!
(flexible and quiet)

Richard

derekwarner · « **Reply #15 on:** December 21, 2015, 10:43:53 pm »

Les.....remember the motors you have chosen are 1300 watt output [each] ......

.........have you considered the torque these motors will generate?

[Torque Nm = W divided by 2Pi x speed] ……so @ [5000 RPM]...... = ~~ 50+ Nm]

I also found it interesting to see an alternate complete drive listed by ACTion electronics for the same 1/12 scale Severn lifeboat however using much lower powered motors [M48x25/1] and 15 amp in line fuses.......[motor data sheet follows]

Derek

inertia · « **Reply #16 on:** December 22, 2015, 09:36:33 am »

Quote from: derekwarner_decoy on December 21, 2015, 10:43:53 pm

I also found it interesting to see an alternate complete drive listed by ACTion electronics for the same 1/12 scale Severn lifeboat however using much lower powered motors [M48x25/1] and 15 amp in line fuses.......[motor data sheet follows]

Derek
I remember doing this diagram as a favour to the chap, who had volunteered to obtain a recording of the engine sound for us. I thought at the time that the motors were unsuitable for the model but he did insist, probably because he already had them. I don't know whether or not he ever used them in his Severn but I would hesitate long and hard before doing the same. "Rice pudding" and "skin" comes to mind!
Dave M

derekwarner · « **Reply #17 on:** December 22, 2015, 10:59:08 am »

Thanks DM....it appears that some 5 years ago, the issue of the power requirements for the Severn lifeboats were expounded at length

in our archives as below... Derek
__________________________________________

http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwiVzpH9pe_JAhXonqYKHclkCxIQFggmMAI&url=http%3A%2F%2Fwww.modelboatmayhem.co.uk%2Fforum%2Findex.php%3Ftopic%3D26166.0&usg=AFQjCNEJMfEhz6BDM5RT_fM-Yfe8Wpxihw

lesfac · « **Reply #18 on:** January 08, 2016, 11:08:54 pm »

Well I finally got to try out the coupling.
It worked fine for many full throttle runs up and down the lake
As a final trial I held the boat stationary and gave it full throttle and this did break the rubber out of the metal housing.
Plan B will be similar but using larger diameter (12mm) harder, nitrile rubber with a much shorter length of rubber between the metal ends.
Les

lesfac · « **Reply #19 on:** January 14, 2016, 04:54:01 pm »

Plan B
I bought some 12mm nitrile with a Shaw hardness of 70.
So harder rubber, bigger diameter rubber and less rubber showing between the ends.
I still pinned the rubber with 3mm pins. No glue.
It feels much stronger and rigid while still being flexible.
This feels much better than Mk1
Les

Martin (Admin) · « **Reply #20 on:** January 14, 2016, 05:23:08 pm »

Looks good!

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Author Topic: DIY Coupling for prop shaft (Read 9075 times)

inertia