Hey everyone, first post of a lurker here. Been in this hobby for about 2 months and flying daily. 

I have a BetaFPV TwigXL https://www.racedayquads.com/collections...se-your-rx

All parts I’m using are stock, with the exemption of LEDs I connected to the FC. I’ve flown it for about a month without issue but today had 4 propellers explode unexpectedly. 

The first time it happened was about 15 seconds after putting them on: I was hovering in place and both of the back 2 propellers exploded at the exact same time. The prop screws remained in place, but the props were no where to be found. I was able to locate one of the blades, which was severed at the base.  You can see a photo of the prop blade and how the motor screws are still intact below.  

I replaced those props, and thinking that I may have torqued them too tight, I made sure all props were tightened sufficiently to stay on, but not with a lot of force. I also inspected the quad and battery cables to see if there was any evidence of the props coming into contact with something, and there was not.  I then flew for about 3 minutes, and another prop blew up. This one had been split in the middle along an imaginary line where the screws are inserted. Note that I was not at high throttle when any of these exploded - the timing seemed very random. 

I replaced that prop, and inspected the others carefully to check for any visible signs of damage or weakness, and didn’t find any. 

I flew for about 5 minutes, then another prop blew. 

I’ve flown this quad almost daily for a month and this has not happened prior. The props that blew today were from 2 separate sets (And colors), which makes the potential of a manufacturing defect lower. I was not having any signs of significant vibration or other issues while flying. I am using Gemfan 3016s, which are the ones spec’d in from BetaFPV with the quad. 

Anyone have any ideas on what would be causing this, and what I should do?

Edit: One thing I just thought of: I did use loctite blue on the propeller screws for the first time today.  Perhaps that added stress on the props after it dried?

Edit 2: I believe the 4 props that exploded may have been from all 4 motors separately (vs the same motors repeatedly). This leads me to believe the loctite may be contributing, since I only used it once per motor.

this can only be a bad prop badge, report it to the seller or the manufacturer, they should reblace it.

if you store them on a bad place heat/frezee/heat/freeze... , they can go worse...
but as the should be able to spin 50000 rpms and more under load, your describtion only match a faulty product
even if they worked totaly fine befor, on tma faulty product some „softeners“ in the plastic can go bad over time

So it turns out, the prop on each motor blew once - but not again. Didn’t matter that they were different color props from different packs either.

I flew 5 battery packs today and didn’t have any issues.

This leads me to believe that the loctite I put on the 4 props once when installing caused the breakage. The props I put loctite on broke, and after replacing without using loctite they didn’t break again. Note that these are the motor and prop types with a 1.5mm center hole and 2 screws next to them, for 3 holes total in a row - so there is a line in the center of the prop that may be more fragile than the single hole types.

I honestly don't see how Loctite could cause a prop to explode. You put a drop on the very end of the threads of the bolt and that thread then goes into a threaded hole in the motor. Even if some of the loctite got onto the inside of the plastic holes of the prop as you slid the bolt through them, Loctite is plastic friendly and it's actually also designed to be used on plastic threads as well as metal ones.

I still believe that you just got unlucky and that there was a manufacturing defect in those particular props that went bang.

(05-Aug-2020, 09:07 AM)SnowLeopardFPV Wrote: Loctite is plastic friendly and it's actually also designed to be used on plastic threads as well as metal ones.

I think it depends on the type. 242 (the typical blue stuff) has some caveats.

Quote:"Not for use on plastic parts, particularly thermoplastic materials where stress cracking of theplastic could result"

Source

Looks like you are right. Some of the thread lockers are definitely fine around plastics but I guess it depends which one you use. I still find it strange that freshly fitted props would explode after 15 just seconds. I would expect any chemical softening/hardening of plastic to happen over a reasonable period of time and not just seconds or minutes.

(05-Aug-2020, 10:11 AM)SnowLeopardFPV Wrote: Looks like you are right. Some of the thread lockers are definitely fine around plastics but I guess it depends which one you use. I still find it strange that freshly fitted props would explode after 15 just seconds. I would expect any chemical softening/hardening of plastic to happen over a reasonable period of time and not just seconds or minutes.

If I recall correctly, I used a fairly generous amount of loctite which may have made it more likely to cause an issue.

You know there are always many suggestions as to the cause, but AUW is never one of them.  You have to remember that the rotors,(some call incorrectly props      ) carry the weight.  If your quad is heavy for its size, the weight it carries can result in blade failure.  Not dissimilar to overloading the tires on your car.

what battery do you use?

650mah Racedayquads 4s lipo

I think I can confirm blue threadlocker is the culprit here. I had a couple props/bolts fly off on a new 3inch build. So bought Blue thread locker to lock them down.

This one.

https://www.phaserfpv.com.au/products/pt...dlockerzap

Now the bolts stayed on but props kept breaking, I crash a lot, maybe the props aren't great quality... Tried another brand of props. Bolted them on with a nice dollop of threadlocker and left to to dry.

Came back to bench 30 minutes later and props had cracked in two and were sitting in pieces on the bench. I hadn't even powered the quad!

So now i want to know, what is the best loctite type thing for small props and m2 bolts?

i fly small motors with t-mount over years, i dont see a need for locktite.

i had screw flyaways only a few times on a settup and tune which causes very much vibrations and the bell material wasnt that nice.

i would try some different m2 screws befor add any locktite. good screws and okish quality motor bells does work without any addition. tighten them again after first flight is something usefull.

Holy cow just today I installed a new set of 4” props on a Brand new avant. I used locktight for the first time on my screws. Normally I just check them often. This time I used team losi racing blue and was sloppy putting it on the screw and sliding thru the hole.

Half way thru the first battery a rear prop broke in flight and left the 2 screws in place. The little shim that goes in the prop was still there.

I agree on not using loctite for props. I’ve never used it outside of the exploding prop incident in the original post and never had any loose screw issues. I would just add the prop screws to the standard periodic screw visual inspection every 10 or so flights.

The base for most thread lockers is Acetone, which is a hardcore solvent (it's basically nail polish remover) and will damage paints and plastics very quickly.

Here's an example picture.. I found Here:



It's likely that the thread locker soaks into the plastic an softens it quite rapidly, this coupled with the fact that these props have 3 holes in the centre means the loctite would quickly saturate the plastic holding the prop to the quad and in turn break off.

If I was you I would purchase screws with the blue preapplied locking patch, or purchase some of the locking patch glue so you can apply it to your screws and let it dry before putting the props on.