Flex coupler to solid shaft ?!?! - RC Groups
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May 07, 2012, 05:35 PM
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Flex coupler to solid shaft ?!?!

I read a post by someone saying they “used a Octura flex coupler to a solid shaft”.

Has anyone else done this? Did you have any problems arise when you did it? Was your engine mounted solid or did you use rubber mounts? Which way would be better as I can see pros & cons either way.

I have a couple of vintage rc boats with solid shafts but unable to find u-joints with a 1/4-28 thread to a 3/16 solid shaft to upgrade engines. I thought about connecting straight to the solid shaft with a flex coupler but was not sure it was a good idea.

Most of the u-joints I found are for electric motors and do not list the thread size. Who has a 1/4-28 (for .21 Rossi & .61 Webra crankshaft thread sizes) u-joint for a 3/16 solid shaft?
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May 07, 2012, 10:10 PM
RC boat Rock Star
I rarely see solid shafts used in the US any more. Some engines come with part of the U-joints attached from the factory but they usually get tossed. You might want ot think about switching it over to a flex cable setup as it shouldn't be that hard to do but will require some new hardware like a different strut.
With a solid shaft you would need a solid motor mount but it'll really vibrate everything inside the boat.
Which Rossi .21 do you have? I had the Niagara version, killer motor once it gets broken in but figure on putting a good gallon through it to get there.
May 08, 2012, 05:39 PM
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I am trying to avoid the cost and time of refitting them with flex shafts when the straight shafts are still in good condition (Not broke, don't fix syndrome) and only need the part like what your talking about that usually gets tossed... I ordered a catalog from Octura. Someone has got to have a 1/4-28 threaded u-joint.

I'm still wondering about the flex hex to straight shaft, as I had a very well known rc racer / boat maker / Hobby store owner recommend I go that way in an email reply today.

I have an older Rossi 5 port redone by RB Mods. I'm amazed at the power that you can get out of the Rossi .21
May 08, 2012, 06:43 PM
RC boat Rock Star
They're probably one of the most under-rated engines out there. Most racers will run Nova Rossi's, CMB's and back in the day, MAC's. Mine was fast as it was in my son's race boat and had shown the big names the way around the course.
I really wouldn't know where to find those parts stateside any more as this kind of setup is still used a lot on the other side of The Big Pond in FSRV classes, western Europe mostly.
May 10, 2012, 01:53 AM
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Any of these of use to you, here?
May 11, 2012, 02:58 PM
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coriolan's Avatar
Originally Posted by w3bby
Any of these of use to you, here?
May 12, 2012, 08:57 AM
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Originally Posted by coriolan
Why confused? The link goes to a selection of flexible couplers that mate an engine to a hard shaft, one of which is 1/4 UNF (which I believe is 1/4-28). They are admittedly to a 5mm shaft but it may provide a workable solution....

Here's another solution but again to metric sizes and another.
May 12, 2012, 09:58 AM
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coriolan's Avatar
Sorry I didn't see the link at first!
May 13, 2012, 06:08 AM
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It's all good, i have a screen at work where link colours can be a little vague, easy to miss at times.....
Jun 04, 2012, 12:22 AM
Registered User
Thank you for the replies...

w3bby, Thank you for the links. I bookmarked them for future reference.

I was able to get Universal Joints from:
Octura Models Inc
7351 North Hamlin Ave
Skokie, Illinois 60076
(847) 674-7351

They do not have a website or do anything online, just by phone or mail. They pretty much have any RC model boating hardware or supplies you would need. Just not the convenience of doing it online. I don't have any hobby shops close to me and most of the online shops carry Octura parts but can not give you a detailed description of it like the Octura catalog does.

Thanks again,

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