Always nice to have a few spares around, but in the case of the Dumas Dog-Bones, these will likely go into new builds as they last forever for me. The end brass couplings come in several bores to match various shafts. If need be, the hole can be opened up or sleeved for small shafts.

At the very left edge of the photo you can see the coupling that comes with the Zipkits Springer. It has two rings with set screws and a piece of a "Tygon" type tubing about 2-1/2 inches long. A horrible design! Didn't last long for me on two Springers. Ah, the dog-bones to the rescue.

Lew
Florida 😎, USA❤️

Len, et al., the only time I heard of the Dumas dog bones loosing its ears was one of the SSMBC's members' experience. It was on his big Dumas boat when he was new to the hobby. I don't know how it happened. Most of my boats have these installed, some multi motored, including three in my heavy 47 inch PT61 gunboat. NEVER lost even one.
Lew
Florida ⛱️, USA 🇺🇸

I also use the Dumas dog bones. I once got a dog-bone with 4 ears at each end instead of the traditional 2 ears. Do not know were I got it and have not been able to find it again. The argument about the plastic ears is that they break easily but this may be a good thing since it prevents damage to the rest of the drive train. You can always replace the plastic ears by drilling them out and inserting metal pins. Works for me. Len

Simply put, there are various designs for couplings to use for misaligned shafts that don't take a lot of space. Not expensive either. Just need to do a little searching.

Also, the Dumas dog bones are popular, especially with me!

Lew
Florida ⛱️, USA 🇺🇸

https://images.app.goo.gl/GCUnc227hxyoZWmcA

https://images.app.goo.gl/L2cocPMvC83DvP3G7

Hi Spence, if this is the same topic as last time, you should have already checked voltages and currents.
Furthermore, I also take it for granted that battery-esc-motor are suitable for each other.
I would also rule out the propeller as a problem because 25 mm certainly doesn't seem like an excessive diameter to me.
The problem seems to me to be of a mechanical nature (or at least the cause which then also led to an electrical problem I mean).
Since the joint broke (provided he translated and interpreted well) then the problem must be there.
Well it may be obvious but the joint under normal conditions should not break (in any case it should not break immediately).
In short, we accept a discussion of usury and super-exploitation but this is not your case.
I imagine that, before breaking, it could be stuck or blocked or otherwise run very badly with strong vibrations (if it is not homokinetic). This may have generated a overcurrent.
In theory (according to what I have learned in the latest topics on the use of fuses in brushless motors) the ESC should be able to intervene promptly and save the motor. Maybe there are some settings you don't know (but neither do I unfortunately).
But let's go back to the possible cause of the joint: why did it break?
To avoid interpretation problems (Google translates all "joints" the same way and doesn't make me understand anything) does your joint have one or two joints?
To avoid repeating the same things, I'll give you the link to the previous discussion on joints.
My message is number 24 (the part highlighted in red in the photo), perhaps it could be useful and interesting to you.
Bear in mind that I prefer perfect alignment between the propeller shaft and the drive shaft.
Misalignment can lead to problems that must be resolved effectively.


However, you who have your ship at hand look for other possible causes that have broken the joint, even trivial ones.




https://model-boats.com/forum/134878

Thanks Lew I don't think I have space for two UJs but your advice and Len's have helped immeasurably. I was starting to get quite frustrated this afternoon when I realised that the reason for the shaft coming loose was because everything was slightly out of line. I will get a flexible coupling of some sort. Thanks again, Spence.

Totally agree with Lew. Almost impossible to get great running with one u-joint but it can happen. Len

Spence, many people make mistakes by using only one u-joint. One can get lucky though if they get perfect alignment. A single u-joint only works great with angular alignment plus whatever slop is in the shaft ends (usually the motor shaft or the prop shaft & tube). This includes any cushion mount for the motor. But, this is almost zero tolerance.

For visual illustrations check out (search) "radial and angular misalignment" then images.

Best to use two u-joints or a flexible coupling that allows for misalignment.

Lew
Florida ⛱️, USA 🇺🇸

Hi Lew, the prop. shaft does turn smoothly and I did test out of the boat. Propeller is 25mm and Iam testing on a test bench out of the water. Battery is a NiMh 7.2v 4500 mAh. Using just one universal joint. I am posting a photo of my set-up although I am now using the Quicrun ESC. and the different battery. Cheers Spence.

Can you post a photo of the setup? You said universal joint, are you using one or two? Without the motor attached does the prop shaft turn smoothly using your fingers? Should have some resistance with the packing grease. How big is your propeller? Always best to test the esc and motor together before installing in the boat. Let it run forward and reverse for a bit, especially with new motors.
You need to supply more information in order for us to help pin down possible issues.
Lew
Florida ⛱️, USA 🇺🇸

I don’t know if this post has any previous posts, but it sounds like it may be a motor over voltage situation.

Double check the motor specifications and adjust the battery voltage accordingly.

Good luck