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Jun 17, 2008, 10:27 AM
Registered User
Thread OP
Alert

RFM Spinner + 2kW + RFM 20x13 = No good!


Hi guys,

a word of warning.

Please be very careful when using the RFM Twisted Yoke spinner along with big props and some kWs. I did use the 38mm one + RFM 20x13 folding prop + 2kW (Neu 1512/1.5Y/6.7/F+10SA123) and crashed & ruined my "just maidened" Big Ceres E on her 5th flight last week because of failed screw in the spinner.

Martin
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Jun 17, 2008, 11:03 AM
Registered User
epwierman's Avatar
Martin,

Ouch!!! That really hurts. Sorry to hear that. :-(

We might learn something here if you are able to share what start up and brake setting you had set in the ESC.

I know the latest esc's have user defined settings that can go a long way towards keeping this critical area intact. The FAQ section on Neu's site addresses this for Castle controllers. For hotlining, we can be even more conservative with softening up the start and stop of the big blades.

I feel your pain.. Rudy makes some of the finest gear going. Getting the whole package to work without any weak links can be a daunting challenge sometimes. Even one landing where a blade strikes an object could cause an undetected fracture, leading to a later failure. I've had similar failures when blades have failed, leading to separated spinners / motor mounts / etc.

We often put our hearts and souls into these things, so it's always a bummer to lose a plane; especially one as nice as this.

Eric
Jun 17, 2008, 11:21 AM
Registered User
Thread OP
Eric,

thank you for your words. I forgot to add the most important thing - both blades are in perfect shape/condition - the one thrown away has some scratches on it, but that's all. It means it was not caused by the broken prop.

By some ironic twist of destiny we've even found the broken screw on our field - within 15 minutes after the crash. But it took us more than two hours to find the motor+esc+prop as it was thrown around 300m away from the "landing" spot. At least there are no doubts about the cause of the failure now.

We've used Jeti-Hacker Master ESC 77A Opto. If I am not mistaken it was set to very soft start and very soft brake aswell.

Martin
Jun 17, 2008, 12:10 PM
Ain't Dutch? Ain't Mutch!
Kimble_Schmitz's Avatar
Does that look like a hollow bit on the inside of that screw?

Are you saying it was a bad screw?

Still hard to believe the Big E is dead.

Joe
Jun 17, 2008, 12:23 PM
Registered User
Thread OP
Quote:
Originally Posted by Kimble_Schmitz
Are you saying it was a bad screw?
Yes, that's exactly what I think now. And it makes me even more sad.
I cant tell there was a hollow bit inside the screw, but the fact is the screw is broken and the Big Ceres E is gone. Maybe we have exceeded some strenght limits of the screw - the forces on twisted yoke spinner are much bigger than on a regular one, who knows. In this case Rudi should issue some warning on his site. But since we didnt hear about thing like this in the past we didnt expect the spinner's screw to be the weakest link of our setup.
Or maybe it was just a bad luck.

Martin
Last edited by PiNa; Jun 17, 2008 at 01:35 PM. Reason: spell check
Jun 17, 2008, 12:35 PM
sloping addict
Protocooler's Avatar
Wow I feel the pain for you !

I guess it's time to throw away these rubbish rolled metal (I think) screws and use only machined steel screws instead.
Mind you, I had 2 months ago the same issue but with a car (the real car with a JTD engine) screw break down exactly the same way on a pulley axis (tension pulley for accessories belt) - It could have killed me because this belt actions the assited steering, I got lucky as it gave up when I was just parking !!!!
Exact same failure and exact same rubbish screw - just 10mm diameted instead. Crazy they don't use good steel screws, at the risk of killing people (really). I keep the broken screw on my desk as a souvenir !!!
Jun 17, 2008, 01:08 PM
Registered User
Lenny970's Avatar
Martin,

Sorry for your loss.

Are you sure it was the screw that failed? It looks like the non-threaded side of the yoke broke first, allowing the screw to bend and break where it threads into the opposite side. If so, it's not the screw's fault.


Lenny
Jun 17, 2008, 01:40 PM
Registered User
rcelectfly's Avatar
Martin,

If you know anyone who is a metallurgist a quick look at the parts under a microscope would probably tell what happened. It would be interesting.

Chuck
Jun 17, 2008, 01:49 PM
Registered User
Thread OP
Quote:
Originally Posted by Lenny970
Are you sure it was the screw that failed? It looks like the non-threaded side of the yoke broke first, allowing the screw to bend and break where it threads into the opposite side. If so, it's not the screw's fault.
Lenny,

when you look closely on the broken yoke you will see an imprint of the screw's head on the outer side of the non-threaded side. It means that the screw broke first. If there wouldnt be any imprint of the screw's head I would believe it was non-threaded side of the yoke that gave up and broke.

Martin
Jun 17, 2008, 01:49 PM
Ain't Dutch? Ain't Mutch!
Kimble_Schmitz's Avatar
Lenny, if what you say it true, the yoke would not have been bent the way (direction outwards) it is.

It was the screw looking at the picture i am sure.

Infact, i am rather suspect of all the RFM screws. I think they could be the reason for the many RFM spinner failures we have seen to date.

Rudy needs to get better screws and put out a warning!!!

While he is at it, he could add a warning not to push normal 16x16 wide, 17x18 and 18x19 beyond 4KW as this is where they start to crack at the root.

You need the reinforced props for that, or the slim props that are much lighter.

Joe
Jun 17, 2008, 02:00 PM
Registered User
Thread OP
Some over-flashed pictures taken from a different angle.
Jun 17, 2008, 04:09 PM
One Idiot is plenty...
Dbox's Avatar
Martin,sorry for your loss.
But You are not a first one with twisted yoke spinner falure.
I dont know what broke first spinner or skrew.
Plane is gone as well as battery/controller.
Yuri.
Jun 17, 2008, 04:37 PM
Ain't Dutch? Ain't Mutch!
Kimble_Schmitz's Avatar
Okey, that is enough for me.

Heavy blades and RFM twisted spinners are out!

Joe
Jun 17, 2008, 05:08 PM
Boom goes the dynamite!
verticalflight's Avatar
Martin, that would hurt to lose a plane that like. Your photos of your S14 are on my desktop... it sounds like it failed pretty quickly after first use.

Yuri did yours fail soon after using it, or did you fly it for sometime before failing?


Quote:
Originally Posted by Dbox
Martin,sorry for your loss.
But You are not a first one with twisted yoke spinner falure.
I dont know what broke first spinner or skrew.
Plane is gone as well as battery/controller.
Yuri.
Jun 17, 2008, 05:33 PM
Registered User
Lenny970's Avatar
Quote:
Originally Posted by PiNa1971
Lenny,

when you look closely on the broken yoke you will see an imprint of the screw's head on the outer side of the non-threaded side. It means that the screw broke first. If there wouldnt be any imprint of the screw's head I would believe it was non-threaded side of the yoke that gave up and broke.

Martin

Martin,

Now that you mention it, I do see the imprint of the screw head and your assumption makes sense.

Lenny


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