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Old Jan 10, 2015, 01:30 AM
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JurassicJet's Avatar
United States, WI, Chetek
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Collet adapter on larger brushless motors?

Hello:
I fly generally larger aircraft with most of them utilizing 6 cell power. For example, I have some Motrofly 4320's and 4325's (380kv). The Motrofly has bolt on prop adapter which I have complete confidence in. The Motrofly are beautiful motors and of the highest quality with superb support from Ken. That being said, they are spendy motors and I am looking for other "less expensive" options for "beater" airplanes, but still in the large category.
I have run across a number of motors in the 4025 range that use a collet type prop adapter. That just seems to be ludicrous to be turning a 16 to a 19 inch prop with a "squeeze on" system that holds that prop.
I am looking for your feedback or personal experience with collet prop adapters on larger equipment. Do they work? Is there a safety issue? Should I be concerned? What about a dab of red Locktite on the shaft to really lock that collet on?

Thanks for any advice in advance.
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Old Jan 10, 2015, 03:20 AM
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Here'a a current thread on collets - they come up frequently.

In the motor size range you mentioned with 6S, 16x12 prop I use Hyperion and OS motors, which use stub shafts and collets. From my perspective, not ludicrous at all - quite the contrary. And the high performance geared motors for F5B are using even bigger props and 5kW + with collets. Also consider that high power setups using collets have been around a lot longer than the fairly recent move to backmounted outrunners with adapters bolted to the bell.

While people have preferences and pre-conceptions, I can't recall many posts in a bunch of threads over many years complaining that collets don't hold firm. But as I said, personal preferences can be strong for either method.
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Old Jan 10, 2015, 10:24 AM
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Thanks Scirocco for that info and the link. Interesting discussions. I don't know why I never thought of the router bit analogy. I have been woodworking for 25+ years and never had a router bit come loose, and I have used both 1/4" and 1/2" collets on some fairly large panel raising bits.
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Old Jan 10, 2015, 01:21 PM
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Quote:
Originally Posted by JurassicJet View Post
Thanks Scirocco for that info and the link. Interesting discussions. I don't know why I never thought of the router bit analogy. I have been woodworking for 25+ years and never had a router bit come loose, and I have used both 1/4" and 1/2" collets on some fairly large panel raising bits.
Yeah, those collet mounts are extremely reliable. Putting one on a 6 mm shaft tightly, and you need a gear puller to get it off from the motor shaft.

I've found one of those automotive battery terminal pullers works well for this purpose.

FYI, I've got two of the Hacker A60 motors in my models. These A60 motors use 8 mm threaded shafts, like a 70 sized common glow engine.
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Old Jan 10, 2015, 01:43 PM
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The collet type mounts are a wonderful thing. They do require some attention to detail in making sure they fit right (no excess play or clearance between the shaft and collet fingers) and are mounted intelligently.

One irrefutable proof about collets used with props is that if the collet is too loose or loosens in use it can slip. And on a tractor mounting the prop can pull a loosened collet and prop assembly off of the shaft.

The major problem with the aluminum collet type prop adapters that are most commonly used in electric RC is that if they are over tightened there is a danger of over-stressing and breaking threaded prop shaft portion of the adapter in the threads where the prop nuts clamps the prop in place. So some caution is needed when tightening the prop nut.

As an old machinist I know collets and how to use them. I have used a number of them for mounting props and have never had one loosen in use or come off the shaft in flight. I have used them on shaft from 3.175mm (1/8") to 6mm on brushless motors, properly made I would use them on larger shafts without any trepidation.

The best way to loosen a collet's grip is to support the adapter by the collet closer and strike the loosened nut to release the collet closer's grip. The use of gear pullers and the like is not a good way to do it.

This is quoted from a previous post:

The collet should be a no play sliding fit on the shaft, it should not tip or move radially relative to the shaft.

1 - Degrease the shaft and the collet interior, side the prop shaft/collet onto the motor shaft

2 - Slide the collet close/prop hub over the threads and up against the taper on the prop shaft/collet

3 - Slide the prop over the shaft, and the washer, then nut, and tighten the nut finger tight.

4 - Grip the motor housing, collet, and prop with one hand and tighten the nut just until all the play is taken up. When you get to that point, grip the housing firmly and tighten the nut a tiny bit more, like only 1/16th or 1/8th of a turn at the most.

5 - Hold the motor housing and try to turn the collet adapter and prop as a unit on the shaft. If it rotates a little (don't go very far) go back to step 4 and tighten the nut another 1/16th of a turn or so. At this point you are right at the point where excess tightening cal actually stretch the threaded portion of the shaft and it can break.

6 - Once the adapter and prop resists being turned on the shaft when moderate force is used the collet type adapter is adequately tightened and ready to use.

If you want to improve the collet's grip on the shaft, you can degrease both parts with alcohol. And you can take a small piece of 200 grit emery cloth and stroke the shaft lengthwise to put almost microscopic striations on a highly polished shaft.

Another thing that will help prevent collet slippage is to dust the shaft with powdered rosin after de-greasing and before sliding the collet onto the shaft. You can get the powered rosin in a small bag from a bowling alley or sports supply store (bowlers and pitchers use it to improve their grip on the ball).

If the prop is loose on the shaft you can wrap the shaft with tape to take up the play. If the prop is to tight you can drill or ream it out. And you should balance the prop too.

From this point on, when you loosen the prop nut the collet will not let go of the shaft, it will retain it's grip and the prop can be changed. But don't over tighten the nut when you put it back. If you want to prevent the prop nut loosening you can put a split washer under the nut and on top of the flat serrated washer that is against the prop. Or you can put a tiny drop of blue (not red!) Loctite on the thread where it emerges from the nut.

To get the collet off you will normally have to remove the nut, washer, and prop, and put the nut back on just enough to protect the threads on the end of the shaft. Then grip the prop hub/collet closer in a pair of padded pliers jaws and hit the nut on the end of the shaft with a wooden hammer or block of wood. That will force the tapers away from each other and the collet will slide off easily.

If your collet is not a no play sliding fit on the shaft (i.e., if you don't have the right size prop adapter) none of the above will work and you won't be able to tighten the collet enough to get it to grip the shaft. It will probably break along the threaded shank first.

Jack
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Old Jan 10, 2015, 03:59 PM
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If I had a problemwith collets, it was due to poor mfg practices, not the collets ability to hold.
A while ago, I found several collets with oversized bores, and some motors with undersized shafts. As anyone realizes you cannot slide a 6mm shaft into a 6mm hole. The shaft has to be slightly smaller to fit thru the motor bearings, like 5.98mm. I've seen shafts as small as 5.95mm on motors.
If the collet happens to be reamed to 6.02/6.03, you will have the devils time getting it to hold. I bought several collets from different mfg's at the time and found them all wanting at the time. I contacted them all, only one responded and shortly had a redesigned collet that worked fine. I've since run 2000watts on a 6mm collet without issue. It really helps if they have a crosscut relief pattern instead of a single cut in the collet rear to squeeze onto the shaft. Just my findings Doug B
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Old Jan 11, 2015, 12:21 AM
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Collet Puller

This is what I use to pull collets off of motor shafts. The unit consists of an old lead acid battery terminal cable puller, with a nut to prevent damage to the collet threads. It would be wise to put a tiny 2-56 nut over the end of the shaft to prevent damage to any internal threads the collet shaft might have. The gear puller jaws has to be tightly held against the collet while pulling it off. Otherwise it will just slip off.

As for tapping the shaft with any sort of hammer, leather or otherwise, those motor bearings are highly stressed, and have a lot of load/RPM on them for their size. Hitting the motor shaft with something can put a lot of instantaneous stress on those bearings, and can result in ball denting the bearings.

(Don't ask)

The photo was taken on a bare shaft, along with rubber bands on the puller to make it possible to shoot the photo with my camera.
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Old Jan 11, 2015, 12:22 AM
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Collet Puller

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Last edited by vollrathd; Jan 11, 2015 at 12:24 AM. Reason: Removed because of accidental duplicate posting.
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Old Jan 11, 2015, 01:08 AM
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And then there's a specialist tool, particularly useful if there's very limited clearance between the collar and a spinner base for example. http://www.aircraft-world.com/en/p10...hp-adap-pull02

of course I only have the 5/6mm version and forgot to add this to my last big order

Regardless of method, some judicious heating can help a lot - I use my heat shrink gun. The greater circumference of the collar means it expands fractionally more than the collet itself, thus easing removal of a stuck one, even thought the actual expansion is minuscule. And aluminium has a higher coefficient of expansion than steel, so the motor shaft itself expands the least.
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Old Jan 11, 2015, 05:28 AM
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I use tapered collet adaptors on motors up to 4250 size and have abolsute confidence in them. In fact I prefer them to the bolt on adaptors ...

Interesting the pullers shown for removing the collets that are 'hard-on' ........... they only remove the outer collet but leave the actual shaft part behind. THAT is the part I have difficulty with ... Often I can remove the outer but the shaft part is a real pig to get of ! Pullers above cannot remove that part as they rely on pressing on a shaft separate from the part to remove. Just remarking ...

Nigel
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Old Jan 11, 2015, 09:27 AM
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"..As for tapping the shaft with any sort of hammer, leather or otherwise..."

When I do that I am restraining only the prop yoke /closer or hub/collet closer, the motor itself is not resting on a surface and it's motion is not restrained. And the blow stuck is a light sharp rap. It will not damage a bearing unless it is struck with way too much force and the motor is resting on something.

It is not the only way to get a collet to release but it works very well.

If collet is too snug to slide on or off a shaft easily, either the collet or shaft is mismatched. Some shafts will have an invisible preservative coating on them that is applied to keep them from rusting. It is like a lacquer or something similar. Lightly polishing the shaft will remove that and it can change a too tight fit into that desired no play sliding fit. I do it by lightly gripping the shaft in a drill motor's chuck and putting a couple of drops of light oil on a piece of 600 grit emery cloth and polishing the shaf while running the drill motor.

When I make replacement shafts I often use High Speed Steel drill blanks. Those have a ground finish and are typically sized to a tolerance of about five ten thousandths of an inch.

I have received brand new motors with shafts that were not very well made or sized. Collets can vary in size too of course. If there is an image of the shaft you are thinking about buying, sometimes you can spot poor quality shafts.

The image is an example of a poor quality shaft. Those shafts are not ground to their finished size and may not have even been heat treated. That is what I would expect to get if I bought mill finished drill rod. If you look at a typical HSS steel drill, the finish seen on the gripping end of the shank is what you would see on HSS drill blanks.

Jack
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Old Jan 11, 2015, 11:09 AM
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Excellent information so far guys! I REALLY appreciate everyone's input and has helped put my mind at ease for utilizing collets on larger aircraft/motors.
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Old Jan 11, 2015, 01:52 PM
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Quote:
If collet is too snug to slide on or off a shaft easily, either the collet or shaft is mismatched
I find that the inner shaft part often tightens up and refuses to slack of when outer is removed. That's the problem - nothing to do with mismatched.

I would not 'polish' a shaft with emery cloth, personal opinion ... collets are designed to have maximum contact area to work .. even 600 grit will introduce slight burring of surface ...

But the condition of shafts for collets has been an endless argument ever since they came out for drills and for us ... One camp say absolutely smooth as baby's bum ... other saying burr it ...

Me ? I clean shaft of with spirit and thats most I ever do ... never use emery on it ...

Nigel
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Old Jan 11, 2015, 04:10 PM
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Originally Posted by JurassicJet View Post
... Do they work? Is there a safety issue? Should I be concerned? ...
Since they work ok on +15cc IC engines hammering away on props ... and have been doing so for tens of years.

Vriendelijke groeten Ron
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Old Jan 11, 2015, 04:16 PM
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Originally Posted by Ron van Sommeren View Post
Since they work ok on +15cc IC engines hammering away on props ... and they have been doing so for tens of years.

Vriendelijke groeten Ron
Hi Ron ...

I've never seen a collet adaptor on an IC engine ... all IC engines I've seen have a threaded end to the crankshaft to provide the prop shaft ...

Just asking ...

Nigel
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