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Author Topic: Motor to prop coupling  (Read 701 times)

stuiegonefishing

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Motor to prop coupling
« on: November 12, 2017, 09:56:52 PM »

hiyall..my first post.. I really hope someone can help please..I have a miss Greco 17inch version and am in the process of converting it to brushless.. I have all the components but the drive couple is doing my head in.. I can not get it centred properly and the vibration is very bad.. can someone think of a flexible solution.. I know it sounds daft but I was thinking of a bit of rubber tube, but obviously getting the power out of the motor to the prop will cause slippage..cheers for reading and hopefully a good fix :-X :-X :-X
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jarvo

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Re: Motor to prop coupling
« Reply #1 on: November 12, 2017, 10:44:00 PM »

HI Stuie, your idea is good, you will need some stiff straight rubber tube, fairly thick walled. Cut to length, then drill locking pins through the rubber and the connectors, the pins will need to be fairly thick to allow for the torque of the motor from cutting the rubber.


The alignment of the motor and shaft is critical. Lock the coupling with a piece of copper pipe clamped around the coupling with a couple of jubilee clips, this will hold it rigid while you align the motor and shaft then glue them into position without any movement until the glue sets


Hope this is clear and helps


Mark 
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chas

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Re: Motor to prop coupling
« Reply #2 on: November 12, 2017, 11:26:08 PM »

The solution jarvo suggests is fine, but as he says correct alignment is vital with any coupling in this type of model.  What is not clear is why you are having trouble aligning the motor and shaft. can you clarify your problem?
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stuiegonefishing

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Re: Motor to prop coupling
« Reply #3 on: November 13, 2017, 05:23:58 PM »

Thank you jarvo and thank you chas.. the problem is a very limited amount of space in the hull and limited material, in the original coupling and the replacement I have bought,.. itís a mini coupling thatís only 20 mm long and 9 mm diamiter.. I have drilled the center and drilled extra holes for 2 more grub screws to help center it(what a pain that was).. just canít get it straight enough.. it may be down to me being too ham fisted and impatient..
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Chris57

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Re: Motor to prop coupling
« Reply #4 on: November 13, 2017, 10:14:11 PM »

I use car nitrile fuel pipe over the splined ends of the brass inserts of huco type couplings, after making everything as straight as possible. No slippage on the splines ( so far) and less noise than the conventional universal joint.


Chris B
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oldiron

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Re: Motor to prop coupling
« Reply #5 on: November 14, 2017, 03:23:21 AM »

rubber couplings can be used with success as long as there's not too much torque. Hoever, if people would use cardan joints the way they ares upposed to be used, we wouldn't see any missalignment and vibration problems. But no one ever does.

John
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Martin (Admin)

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Re: Motor to prop coupling
« Reply #6 on: November 14, 2017, 10:58:58 AM »

rubber couplings can be used with success as long as there's not too much torque. However, if people would use cardan joints the way they are supposed to be used, we wouldn't see any misalignment and vibration problems. But no one ever does.
John

How should they be used?!?


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Tug Fanatic

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Re: Motor to prop coupling
« Reply #7 on: November 14, 2017, 11:15:00 AM »



How should they be used?!?



This is my understanding. You should have 2 universal joints connected by a linking tube - like an old car propshaft. The input shaft & the output shaft should still be parallel but can then be slightly out of line.


The one universal favoured by model boat owners is a very poor substitute as we rarely get exact alignment and the reality is that the motor & propshaft never have absolutely no play. This is why I use belts or gears.


Like this:
https://www.aliexpress.com/item/1pc-RC-Toy-Car-Spare-Accessories-Cardan-Telescopic-Universal-Joint-Climbing-Car-Transmission-Shaft/32810670038.html?spm=2114.search0301.3.46.d05QH6&ws_ab_test=searchweb0_0,searchweb201602_0_10190_10192_10073_10130_10152_10151_10557_10537_10539_10055_10154_10056_10155_10059_10312_10179_10314_10534_10313_10533_10060_10084_100031_10083_10184_10547_10107_10307_10548_10341_10065_10142_10340_10068_10343_10541_10342_10562_10301_10345_10103_10102_10344_10303_10325_10324-10102,searchweb201603_0,ppcSwitch_0&algo_pvid=1a070c75-abac-497d-9bf6-fb48b15c59d6&algo_expid=1a070c75-abac-497d-9bf6-fb48b15c59d6-6


Ideally it should also cope with some for & aft movement of the motor or prop shaft which is why your car propshaft/ drive shafts have a sliding joint..





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grendel

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Re: Motor to prop coupling
« Reply #8 on: November 14, 2017, 12:33:45 PM »

I used a model car front axle joint in mine
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oldiron

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Re: Motor to prop coupling
« Reply #9 on: November 14, 2017, 12:41:21 PM »

I used a model car front axle joint in mine

Excellent!!  Good to see some one getting smart

John
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oldiron

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Re: Motor to prop coupling
« Reply #10 on: November 14, 2017, 12:42:33 PM »


How should they be used?!?


Martin, I you remember, Irish Car guy and I did an extensive thread on the proper use of universal jints a couple of years ago.

John
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oldiron

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Re: Motor to prop coupling
« Reply #11 on: November 14, 2017, 12:44:16 PM »



This is my understanding. You should have 2 universal joints connected by a linking tube - like an old car propshaft. The input shaft & the output shaft should still be parallel but can then be slightly out of line.


The one universal favoured by model boat owners is a very poor substitute as we rarely get exact alignment and the reality is that the motor & propshaft never have absolutely no play. This is why I use belts or gears.

Ideally it should also cope with some for & aft movement of the motor or prop shaft which is why your car propshaft/ drive shafts have a sliding joint..

  Congratulations, some one else has got it.
Can't understand the way the rest of model boaters don't get it.
Look under your cars guys, The drive shaft there says it all
John
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Martin (Admin)

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Re: Motor to prop coupling
« Reply #12 on: November 14, 2017, 01:25:14 PM »


OK, fair enough. I've never had a problem with a single UJ myself but then again, I'm fastidious about shaft alignment!

See:
  http://www.modelboatmayhem.co.uk/Builds/Puffer_Jan/1ndex_Puffer_Jan.htm

 
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Tug Fanatic

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Re: Motor to prop coupling
« Reply #13 on: November 14, 2017, 02:02:45 PM »



I hear you Martin but I have seen so many out of line models and heard so many complaints about inexplicable vibrations etc.


Each to his own but when you think of the time & money a model boat costs I cannot see the necessity of the short cut.


One odd thing is that the US modellers had an easy answer with the Dubro Dog Bone coupling but the idea never caught on here.


http://www.dumasproducts.com/product_info.php?cPath=39_86&products_id=289

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Martin (Admin)

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Re: Motor to prop coupling
« Reply #14 on: November 14, 2017, 02:12:28 PM »


Some time ago, I saw a nice model on the water, I said to a modeller;
"What kind of sound generator are you using?"
"Sound generator? I haven't fitted one!"
"....Ah!"    :embarrassed:
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oldiron

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Re: Motor to prop coupling
« Reply #15 on: November 14, 2017, 02:14:35 PM »


I hear you Martin but I have seen so many out of line models and heard so many complaints about inexplicable vibrations etc.


Each to his own but when you think of the time & money a model boat costs I cannot see the necessity of the short cut.


One odd thing is that the US modellers had an easy answer with the Dubro Dog Bone coupling but the idea never caught on here.


http://www.dumasproducts.com/product_info.php?cPath=39_86&products_id=289

  That's a proper coupling. Done with a correct coupling, worrying about shaft alignment is a thing of the past.
And I'm in Canada , and I get it. I wouldn't put a single cardan joint on my cars drive shaft and expect it to work, why would anyone do it with a boat and complain about vibration?

John
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oldiron

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Re: Motor to prop coupling
« Reply #16 on: November 14, 2017, 02:18:26 PM »

Review this thread from a couple of years ago , and it will tell you all about coupling shafts and what to do ands not do:

http://www.modelboatmayhem.co.uk/forum/index.php/topic,33847.0.html

John
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Bob K

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Re: Motor to prop coupling
« Reply #17 on: November 14, 2017, 02:56:31 PM »

Double dog-bone couplings are nice in theory, but very noisy.  The plastic dog-bone tends to rattle in the brass cups, even with zero end float..
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Tug Fanatic

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Re: Motor to prop coupling
« Reply #18 on: November 14, 2017, 03:00:22 PM »


Nothing changes - what was true a few years ago is still true today.


How does nylon "rattle" in brass with a properly set up coupling?
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Bob K

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Re: Motor to prop coupling
« Reply #19 on: November 14, 2017, 06:42:04 PM »

I have two boats with double dog-bone couplings, both very noisy.  And, yes, the shafts and motors are accurately aligned.  In fact, if you can get alignment "perfect" there is no need for a coupling, but in real life you do need them.
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Stavros

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Re: Motor to prop coupling
« Reply #20 on: November 14, 2017, 08:06:07 PM »


Simply contact Steve Tranter Model Boat Bits and he will Make you a solid joint of whatever length you need and shaft dia as well


Dave
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RAAArtyGunner

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Re: Motor to prop coupling
« Reply #21 on: November 14, 2017, 11:44:40 PM »


I hear you Martin but I have seen so many out of line models and heard so many complaints about inexplicable vibrations etc.


Each to his own but when you think of the time & money a model boat costs I cannot see the necessity of the short cut.


One odd thing is that the US modellers had an easy answer with the Dubro Dog Bone coupling but the idea never caught on here.


http://www.dumasproducts.com/product_info.php?cPath=39_86&products_id=289

Yes, I have those and Billings use that type in their kits not to mention US makers such as Lindberg.

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chas

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Re: Motor to prop coupling
« Reply #22 on: November 15, 2017, 09:04:23 AM »

I'm not sure how any of this is helping the poster. As I understand it, there is only space for a 2 cm coupling, and there is a problem with the drilled hole for the motor end of it. If I have read this correctly, you are trying to get that end straight and in line using grub screws. I don't think you have much chance. I would start with a new coupling, with the correct bores that are a tight fit on the shafts. Have a look at the couplings Dave Millbourn uses in his models, they can be bought an short lengths, use a good solid rubber insert and are proven.
    I'm presuming that the 2 cm mentioned is the gap between motor shaft and the prop shaft, if so, you will also need to measure the total gap between motor end and the prop tube to find out the length of coupling that will fit in.
  Lastly, on couplings in general, dog bone couplings are available in the uk, shg models sell them.
Chas
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chas

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Re: Motor to prop coupling
« Reply #23 on: November 15, 2017, 10:04:57 AM »

I've just realised that I wasn't very clear about the couplings Dave uses. Google model boat bits and look at microflex couplings. if you aren't sure if they are suitable give them a call / email and see if they can help.
Chas
http://www.modelboatbits.com/MICROFLEX-COUPLINGS
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Bob K

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Re: Motor to prop coupling
« Reply #24 on: November 15, 2017, 10:16:34 AM »

I am using rubber block couplings for my latest build, extremely quiet and effective.  :-))
http://deansmarine.co.uk/shop/product_info.php/cPath/5_12/products_id/192 for four big Buhler motors.
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