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Old Apr 08, 2009, 07:50 AM
Checking CG is for NERDS!
Smokescreen38's Avatar
Joined Jun 2005
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Grub screws...do you trust them to hold your rotor on at 40,0000 RPM?

Yeah... I didn't like the idea of relying on those grub screws for holding a rotor on a smooth shaft (with no notch)...

I was testing my new Phase3 F-16 on the stand with 4S and Don's Coolwind 4000kv motor in the Eflite SA fan...The rotor held up fine under WOT on 3s but under the additional RPM, the rotor parted ways from the fan at WOT.

The shrill noise of the "vacuum cleaner on steriods" stopped instantaneously with a sickening "thwack." It was quite dramatic and I was glad to have taken safety precaution of standing to the side/rear of the plane.

The damage was minimal. The foam of the duct did an awesome job of soaking up the energy. It took a charasmatic pattern of slices and a final chunk near the cheeter hole (I should post a pic before I repair it).

Was this a case of me not tightening the grub screws enough?
Do you guys use some loctite in these situations? Which version?
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Old Apr 08, 2009, 09:26 AM
Time is Hobby
Northern, NJ
Joined Jan 2006
247 Posts
Hi there!

I make a plastic adapter that presses on. Depending on your motor/fan combo I could make you one...

PS- the set screws should have hold it on fine...

Many installed around the world running them w/out issues.

Sorry for the shameless 'plug' hehe.
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Old Apr 08, 2009, 10:15 AM
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Economy, Pa.
Joined Mar 2002
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S38 The grub screws should have held, all ways helps to roughen up the motor shaft a little with fine grit sandpaper, and clean with alcohol before assembly, locktite on the shaft and screws wont hurt (unless you get it in the motor bearing) and it's also important to use a good alen key when you tighten the grub's down. Of course, if you use locktite the chance of disassemble without damage is slim. (striped out grub or pulled threads in adapter) all depends on you
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Old Apr 08, 2009, 10:28 AM
Build it, don't buy it
foamnpacktape's Avatar
Calgary, AB, Canada
Joined Apr 2008
2,150 Posts
Grub screws, set screws etc. should be tightened, backed off, tightened again, backed off, and tightened one more time.
A properly designed set screw (not all are), will bite into the shaft and cut a groove in which to secure itself. No roughing up or cutting a groove necessary.

I have never used locktite, and never had an issue. That said for anything in that RPM range a little locktite for reassurance seems like a good idea IMO.

foam.
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Old Apr 08, 2009, 11:09 AM
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Economy, Pa.
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foam, what you post is very true! If the grub is proper, it will be hardened and the contact end will be pointed (for lack of a better word) to some extent & not flat. The purpose of re-tightening is to embed the point into the shaft so it doesn't slip.
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Old Apr 08, 2009, 12:17 PM
Build it, don't buy it
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Calgary, AB, Canada
Joined Apr 2008
2,150 Posts
Mike,
Yup, but I made sure to clarify with "properly designed". This is why it is important to buy the best grubs, the price differential only likely being a few cents. Unfortunately, I have no recommendations to make, but I would hope manufacturers of decent equipment would not choose to cut corners here, it is the least expensive of the parts, and the most important, the weak link if you will.

A properly designed grub will not have a point but rather a circular ridge in its tip. This circle cuts a circular groove in the shaft as it is turned. A point can not do this, it relies on displacing material through pressure, on a hardened shaft this is near impossible, and, as you suggested, roughing up, or cutting a groove is necessary.

Regards,
foam.

So take a close look at your grubs if they do not have this feature, search one out that does. Those that know of a good supplier, let us know. There are many pointed/flat, unhardened crappy one's out there. I usually make due with them (do as I say, not as I do ), but in the EDF world this is unacceptable.
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Old Apr 08, 2009, 12:31 PM
Build it, don't buy it
foamnpacktape's Avatar
Calgary, AB, Canada
Joined Apr 2008
2,150 Posts
Read your title, and that is what prompted me to respond to this thread. I have tried, but can't resist any longer:

Where'd you find a motor that will spin at 400 thousand rpm anyway.

foam.
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Old Apr 08, 2009, 12:51 PM
Checking CG is for NERDS!
Smokescreen38's Avatar
Joined Jun 2005
5,347 Posts
You guys are the best! Thanks to all of you for making the forum a great place.

I definitely learned something about grub screws today. I'm going to take a good look at them before I spool up the motor again...and at the very least, rough up the surface so the screws have the best chance to bite.

Whoops!! Yeah, if only it was 400,000 RPM!!
It would sound like a dentist's drill and probably cavitate pretty badly too...(pun intended!)

Wilson Co, I don't think the plastic retainer would help in this application... but can you show us an example? I can't picture how it would work.
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