Small Bolt Drive Shaft Problem Advice Needed

[Basstronics]

Measure twice.

The stock motor is not the 2.3mm it advertises to be!

At least not mine. Another person confirmed theirs is 2.2mm as well.

[SweetAccord]

Octura makes a collet for a .098 cable as well, but the motor end is 1/8" (540 car motors), you can cut a short length of brass or aluminum tubing to sleeve the motor shaft and it will work just fine. Just notch through the tubing so the set screw goes right to the motor shaft, not just the tubing.

Wparsons is correct and that was my first mod. when I was into removing the drive line and greasing (now I use oil). I changed as it was just big and heavy and ran close to the hull but worked like a charm. You can see my old pic in my album that was in my Starship (I need to update, LOL).

On Amazon you can get stainless steel tubes to make that coupler work as that is what I did, for the motor side and use loctite on it and you are good forever and the stainless steel tube when hit with a allen screw holds well. In searching for something smaller and lighter the Etti was just right for me. You can make it work too.

[SweetAccord]

Is this the one and you enlarge the 2mm end to 2.3mm or there abouts for the .098 flex?

Product ID: etti-a006
Etti Coupler 3.175 to 2mm
In Stock: 8

Yes that is it! It's not a direct fit for the stock motor as I'm not using it. I'm using these on Tacon motors and it's a direct fit on them. I measured, on the stock motor you need to bore it out one side to fit the motor shaft, the other side you can cut a 1/8 copper tube (slit it so from one side to the other so it can compress) and slide that tube into the other side and the flex cable will go into that and it will compress when tightened down but you have to make it fit but it holds tight! I did this so it's small and has less rotational mass than anything else and is lighter and can be removed easily and no flex drive damage from the screws. If need to remove the drive line ( I don't ever) then I can and the flex cable is not grubbed in. What does Jeff Wohlt now have? I asked him long ago and he said he don't do anything this small.

[SweetAccord]

Measure twice.

The stock motor is not the 2.3mm it advertises to be!

At least not mine. Another person confirmed theirs is 2.2mm as well.

Mine is 2.27 mm, that is right. By the way I'm "Research" on RC Universe. I may be the "other guy".

[CaptPJB]

Yes that is it! It's not a direct fit. I'm using these on Tacon motors and it's a direct fit. On the stock motor you need to bore it out 1mm one side to fit the motor shaft, the other side you can cut a 1/8 copper tube (slit it so it from one side to the other so it can compress) and slide that tube into the other side and the flex cable will go into that and it will compress when tightened down but you have to make it fit but it holds tight! I did this so it's small and has less rotational mass than anything else and is lighter and can be removed easily and no flex drive damage from the screws. If need to remove the drive line ( I don't ever) then I can and the flex cable is not grubbed in. What does Jeff Wohlt now have? I asked him long ago and he said he don't do anything this small.

Thanks for the explanation on how to make the Etti work
Peter

[SweetAccord]

Thanks for the explanation on how to make the Etti work
Peter

No problem. But see what Jeff can make if he can as a custom direct fit is best, let us know. I spent months looking and there is just nothing else that comes close but the Etti when modded.

[SweetAccord]

I also forgot to mention. If you go to the .098 cable, and you want an identical motor coupler, the one from Minicat racing works. I have them (spares from boats) and tried it on the stock Bolt motor and it's fine.

[SweetAccord]

The biggest change to make on this boat including the drive, is to replace the busing in the strut and use a bearing. That works wonders!

[Basstronics]

Mine is 2.27 mm, that is right. By the way I'm "Research" on RC Universe. I may be the "other guy".

Is that measured with a caliper or a micrometer?

I measured mine with a micrometer w/friction thimble and mine is 2.2 mm. Not 2.3mm. Not 2.2X mm- it is 2.2mm exactly.

I sent Jeff a print for these couplers and he didnt seem interested in making them or it was going to be some time until they got made.

There is nothing ground breaking about them. 3/8" Dia x 7/8" lg. Motor end is drilled 3/8" lg and flex 1/2" lg. Add set screws.

[SweetAccord]

It's cool bass. I measured with a digital caliper which is accurate as I have other projects with factory spec values and my caliper matches exactly to their values. For example I have different motors with screw spacing that is factory spec of 16mm and my caliper is exactly on that value. It's accurate to 0.001 mm. A micrometer would be more accurate but the difference in tolerance of 0.07 between 2.27 and 2.2 is so small there is no effect. Human hair is 0.05-0.06mm so you can't even see or feel the difference. So we are literally "splitting hairs".

Also on these motors I would not look past that the shafts are all off in size so a difference of 0.01-0.07 is not surprising as these are not high quality motors and mass produced. If you look at the shaft, it does not even looked milled down very well compared to others I have so I don't feel your measurements are off nor mine.

[Basstronics]

Im going to disagree here on multiple basis's.

I cant comment on your background but let me share some of mine. I was a Machinist (trade school trained) now turned Design Engineer. I have run a variety of machines and have worked on more materials than a human being can remember... I have done many bearing journals down to .0002" micrometer and dial bore gauge as well as a bench micrometer on tungsten laser rods down to .0001" with a scope for porosity. I have also received a certificate thru Federal Mahr on fine surfaces.

A caliper is in no way even remotely accurate to .001mm. A caliper is known to be accurate to around +/- .001". You can easily see that variance depending on pressure applied and where you measure on the jaw. That is why micrometers with a friction thimble provide the most accurate readings.

Claiming you have compared caliper readings for bolt spacing to the stock spec is irrelevant. Tolerances and machine inaccuracies can void that out as qualifying as an accurate basis for true measurement. Furthermore compounding that is how it was measured?

.07mm is enough difference- its a huge difference. These boats and spaces are tight enough that every little bit counts. Between my coupler to my brass stuffing tube/teflon theres about 1/8". Now if Im .003" off in my coupler, when you wrench down on the screws it will throw the concentric off balance. This will make wobble on the flex end. The bottom line is the more you are off on the motor end the greater the wobble will be on the flex end.

The best coupler is one size to size or a collet type as far as run out goes.

The smaller the sizes and distances the more critical the tolerances becomes.

its design 101.

I would highly advise anyone with these motors to measure with a micrometer to ensure you have an accurate coupling.

And just for poop and grins:

2.2mm = .0866"
2.27mm = .0894" (+.0028")
2.3mm = .0906" (+.004")

[Basstronics]

Oh and last part...

I have a different motor with a true 2.3mm shaft (as verified by micrometer) and a coupler for that motor (airplane prop). You can see a big difference in wobble when placed on the small bolt motor.

[SweetAccord]

My caliper is mm not inches. Inches is a horrible way to measure anything it's is not precise enough. But if you want to go into .07 mm of a difference go ahead. I have to laugh.

[Basstronics]

Measurement is a measurement. I can convert it multiple of times and not loose anything many places out.

In my job we work mainly in inches and its not uncommon for me to scale things from metric to inches- which is a factor of .039370078740157 and thats by memory.

The part that you miss is the run out due to excessive clearance. When you amplify the clearance over the length it will produce a wobble.

Laugh as you will. I aim for perfection.

[Basstronics]

Its beyond .07mm thats whats your not getting.

I dont expect you to understand this as obviously you are not a machinist accustomed to such issues or an engineer who envisions such instances.

While it may not affect it that much it will have a negative effect to some degree. When you compound that with a wobble in the flex with not much free room for the flex it will amplify the issue more.

The principles of this is fairly simple.