RC India

Hey, the R/C tips and technique section is filled with posts of materials to build rather than some tips. It's been a long time since I have seen a help tip on RCI. So, here I present you something I learnt in my hobby that may help you.


Flying my FPV plane with gear inside worth ₹₹₹₹ Felt awesome. Giving all my trust to the great powerful Turnigy 1100kv motor feeling safe. And, snap I heard a sound.
Is anything broken? My plane is falling , fast. Is my battery down? Nope. My plane with a near average glide characteristics. Got  down fast. Thought my gear was broken. But it wasn't. Thank God!
When I reached home, I found that when my motor body was still. The propeller spun. Given the plane is fat pusher. At home, I restarted the motor and till 1/3 throttle, it worked perfect. I increased the power to 50% and snap. I heard and the sound of metal chafing against plywood of my poorly built third grade motor mount. Till that time, I blamed my adapter for being loose. Something was wrong with the motor shaft. I removed the propeller and took the motor and gave a closer look. The shaft wasn't broken. But, the shaft just comes right down when I force the shaft down. You could say. Dude, a motor is made for a normal plane. Not your funny looking pusher. But I need to suck in every ounce of what I spent. You could call me Kanjoos. But,have I lost my faith to the best brands of RC?
Realistically speaking, It shouldn't have done what it did.
So, Then I tried lifting the outer ring. Viola, It came right out. Feeling heartbroken for my lost teeny weeny ₹1000 I searched the whole of web. Found a little hint on refitting it using Super glue. Truly, I hate it. I hate all forms of CA. It may be good for you. But, It ain't good for me. Its smell suck. You could say that my favorite epoxy has worse smell than it. But I still hate it. And, CA won't bond tightly again with CA, so if I failed sticking my motor with CA. I am doomed with that. That's why I love epoxy. So, What I did was I Stuck epoxy everywhere on the motor where the shaft contacted the motor body. And specially at the bottom part ( that U ring or C ring , I don't know what it's called). Left it for a day. It's stronger than ever. And will take a lot of beating. Sorry for the long story, thought It would be easier for you to read If I wrote it like a story.
Conclusion: Most motor manufacturers stick the shaft to the motor with cheap low quality CA, which can be broken easily by us.

So, In short:  When you buy a motor, before using it, remove it and give it a bath of epoxy at the right places (beware , only the right places) especially the C ring or U ring. So, Your motor body will last till the coil burns. And, If you want to rewind the motor, It's not that hard to break the epoxy bond. Epoxy also makes it easier to reapply and still be strong enough.

Admin edit:
In post #19, the author backs off from these recommendations...

Please provide some images and videos.

Sorry but problem not clear.  :headscratch:
Shaft loose in outer casing?

When we use a motor for a pusher plane, the stress on the shaft is the opposite of what it was designed for. As, the C ring was made for the shaft to hold on to the motor when the propeller pulls it forward with the whole plane. When the thing happens in the opposite, the whole thing relies on the bond of the C ring with the motor with the help of the CA glue which was used to bond the C ring to the motor.
So, What happened was , the C ring got broken from the motor due to low quality Glue from the factory. So, Using epoxy at first ensures there is a good bond.

The C ring you mention is the C ring/ E ring/ circlip on the shaft at the end opposite the prop?

Yes, I didnt knew the real name of that.

Capture an video and photo then give in the reply of this message. videos and images will help user to understand.

Okay, let me do it tomorrow.

A circlip is a fastener element, and is not designed or meant to be attached to a shaft with any sort of adhesive. It is meant to nest in a groove, precision  machined for it specifically under close tolerance

Any sort of adhesive use, cyanoacrylate, epoxy or otherwise is just jugaad and is absurd

How is the shaft attached to the motor?

Light press fit

I mean , the when motor spins, what keeps the shaft attached to the motor? My shaft became loose and it started spinning on its own without the motor spinning.

When you say "shaft attached to the motor " you mean attached to the rotor, or the entire rotor-shaft assembly within the motor?

If to the rotor, it's a light press fit

If the assembly staying within the housing (stator) on one side a circlip is used. If it comes off, change the circlip, or if needed, change both shaft and circlip (if the groove has got worn - unlikely usually)

If the press fit to the rotor gets loose, you can use a retainer like Loctite 638

http://www.loctite.in/loctite/retaining-5298.htm

These kind of failures only happen on a defective (bad quality) motor, or if it has been misused/abused

There is a screw!

There is a set screw at one end, and a circlip at the other

But his question is (now) specifically targeted at the fit between rotor and shaft

@al ham shari,

At last someone mentioned the screw! Thanks, Ambattuhari.
(Added a better pic)
Perhaps you could check a few things:
1. Do your bldc motors have a grub screw to hold the shaft to the outer casing/rotor? All of mine have.
2. Do the shafts have a flat for this grub screw to hold?
3. Remove the E clip/C clip/circlip at the other end of the shaft. Then pull the front end of the motor away from the back end, and see how much effort it takes.
4. Run the motor with a tractor prop after removing the clip at the end of the shaft. If the front end flies off, I’ll replace the motor at my cost.

The clip HAS NOTHING TO DO WITH ATTACHING THE SHAFT TO THE MOTOR.
It just prevents the rear bearing from falling off.

And you were talking about pusher configuration where there is no tension load on the shaft at all!

Sir, could you consider withdrawing all this ‘epoxy bath’ recommendations?

Regards

😁

Sent from my Moto G (4) using Tapatalk

Sorry, got it now.I didn't actually tightened the screw. I applied epoxy there, that's why it doesn't come apart. So epoxying the whole C clip thing is not needed. I have epoxied the ( necessary part) but didn't think about screwing it in.

So,
Your whole conversation is paraphrased into nothing!
You again made wrong recommendations.
I don't want to say this but please please please research before posting.
You never know which newbie may follow your advice!
One of my planes has a motor with the c clip missing.
Just as Iyer sir stated, It flies just fine.
Regards.

Yes, Loctite 638 Retaining Compound is designed for the bonding of cylindrical fitting parts, particularly where bond gaps can approach 0.25 mm. Ideal for use where high dynamic forces or cyclic loading is expected, for eg: shafts, gears, pulleys and cylindrical parts that

- High Strength (4200 Psi)
- Fills Gaps Upto 0.25mm
- 180oC Service Temperature
- High temperature resistance
- High strength on all metals, including passive substrates (e.g. stainless steel)

https://www.tryloctite.in/products/retaining-compounds/loctite-638