Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Tutorials & "How Tos" ... => Topic started by: GG on October 25, 2019, 04:27:46 pm

Title: Spring Motor Couplings
Post by: GG on October 25, 2019, 04:27:46 pm
Trying to install two RE385 motors into a destroyer model recently and a problem was encountered.  They were to be connected to "Radio Active" brand of propeller, tube and shaft assemblies, perhaps not the most sophisticated items but perfect for small models and they feature neat plastic props that are well matched to direct drive from these motors.

The problem was the small diameter shaft of around 1/16 inch (1.6 mm) in diameter.  This is adequate for the modest power in such models but not so easy to find commercial couplings to connect motor and prop shafts together.

In other models I've successfully used tubing for this job.  The only precaution needed was to ensure that the tubing would firmly grip with no signs of slippage.  My usual test being to keep the propeller stationary with a couple of fingers whilst increasing the power supplied to the motor.  If the coupling failed to slip then I could be confidant that it ought to be reliable in normal sailing.  This whole process was completed in a few seconds since a stalled motor is rarely a happy motor.  Also , as I value my fingers, it is not some thing to try with more powerful motors!!!

This time, no suitable tubing could be found to grip both motor and propeller shafts.  I did end up using a rather messy looking combination of tubes slipped over each other but it was not a pleasing sight. Something better was clearly needed, which led me to rummaging through my boxes of potentially useful (sometime in the future?) bits and pieces.  This successfully located two pairs of brass Collets, one pair matching the prop shafts, the other the motors shafts.  How to connect them was also found in these boxes, a couple of small springs.

Joining the springs and collets was the next thing to sort out.  Adhesives might have done the job but couplings can have an arduous life so I opted for soldering.  With the surfaces to be soldered cleaned and coated with a little flux the only problem left was how to keep them aligned.  Securing the collets on a rod, with the spring between them, was the obvious answer.  The rod was of the same diameter as the prop shafts so to keep the collet that would be secured to motor shaft properly aligned, a short length of suitable diameter brass tube was slipped over part of the rod.  A 100 Watt soldering Iron soon produced a strong, if not exactly the neatest of joints between springs and collets.

These homemade couplings ran smoothly with no noise and coped effortlessly with the stalled prop test.  Yes, I might well have been able to find some commercial couplings to do the job but this would have robbed me of the satisfaction of creating my own solution.  Plus, it allows me to counter Mrs Guest's criticism of my habit of hording apparently useless items....!
Glynn Guest
Title: Re: Spring Motor Couplings
Post by: Mark T on October 25, 2019, 04:51:48 pm
What a great solution I never would have thought of that.  Just goes to show its best not to throw anything away as you never know when it might come in handy.
Title: Re: Spring Motor Couplings
Post by: Shipmate60 on October 25, 2019, 10:19:01 pm
For small motors and shafts have you thought of jewelery box couplings.
The ones for the spinning ballerena.
I have use these in plastic models and as long as you don't go mad astern work fine.

Title: Re: Spring Motor Couplings
Post by: chas on October 25, 2019, 11:34:39 pm
It's great to see others making running gear, we are modelers after all. I haven't bought a prop shaft or  coupling for a long time, including my quick brushless powered models. And no, I don't have a lathe or any special skills.
    The spring coupling was once quite popular, I think it was Kielkraft that used to sell them way back in the 1960s, very good they were too, as a youngster I had one that lasted for a very long time.
    Thanks for sharing that Glynn.


Title: Re: Spring Motor Couplings
Post by: roycv on October 26, 2019, 08:46:44 am
As a source there is the old method of holding up a lace curtain, a long spring, still got about a foot left on my one.

 If you are only using a few watts then hard neoprene tube works well, first heat it up in hot water and it then goes quite soft.
If you have a Huco type coupling and the centre has broken then there are plastic tubes that will make the connection.  These can be used to lengthen the connection as well.
Sometimes the plastic splits on the splines, I have repaired these with a dozen winds of strong thread, treated with a 2 part resin glue.
In the dim and distant past we had metal ball and socket couplings but these can frequently cause interference on the older radios.  SHG did or perhaps still do an all plastic dog-bone coupling where the lining up of motor and prop shaft are not so critical.
Of course if looking for a small motor for a boat do not overlook the motor in a broken servo especialy for the plastic magic size models.  These motor only need a plastic tight fit tube as a coupling.


Title: Re: Spring Motor Couplings
Post by: malcolmfrary on October 26, 2019, 10:13:49 am
For thin shafts, and the very short shafts poking out of ex-servo motors, I get couplings at 5 for 1.  The guy in the shop thinks he is selling gas lighters, unaware that the spring under the flint has tapered ends which grip well on a range of shaft diameters.  Collets not needed, but the ends of the shafts do need to have a minimal gap between them.  Works with either direction of rotation with low power motors.
Thinking out loud, is this a use for the spring out of the middle of a dead pen?  I usually lose my pens way before they become dead, but they must be around somewhere.  Surely?