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Author Topic: Scorpion propeller adapter  (Read 2591 times)

Offline Matt Piatkowski

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Scorpion propeller adapter
« on: August 18, 2018, 03:05:54 PM »
Hello,
I am using Scorpion aluminum collet style propeller adapters for the 5 mm. OD shafts of my electric motors.
When the propeller nut is torqued lightly, the 3 blade carbon composite propeller blades rotate reasonably in one plane. When the propeller nut is torqued sufficiently (please see below for explanation), at least one of the blades is clearly off the rotation plane.

Sufficiently means that the static force of five pounds cannot remove the collet from the shaft. Lightly means that 2.5 Lbf. static force can remove the collet from the shaft what means that the prop. with the adapter can slide off from the steel motor shaft in the middle of the maneuver with potentially catastrophic effects.

I know that the prop adapter aluminum shaft is bending in proportion to the applied torque because the thread on it reacts the torque this way.

Simply put: sufficient torque will always bend the Scorpion's aluminum prop. adapter threaded shaft causing the prop. out-of-plane-of-rotation imbalance.

I  wonder if anybody found the cure for this? The stainless steel threaded adapter shaft will not bend so much but it weights three times more...

Your opinions and suggestions are, like always, appreciated.
Regards,
Matt

Offline Fred Underwood

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Re: Scorpion propeller adapter
« Reply #1 on: August 18, 2018, 03:25:31 PM »
Thread size M6 or M8.  Hyperion makes both, but I'm not sure about Scorpion.  Some use the Hyperion 5mm to M8.  I use the 5mm to M6 with Xoar wood 2 blade without difficulty so far.  Tightening on wood vs APC or Carbon feels a bit different.
Fred
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Offline Vitalis Pilkionis

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Re: Scorpion propeller adapter
« Reply #2 on: August 18, 2018, 04:17:41 PM »
Hey Matt,
I'v just had the same situation as you  ;D
I'v got a new hollow prop from Tomasz Jadczak, which came with 6mm central hole predrilled. I did not want to drill it to 8mm, so I ordered a new Scorpion collet prop adapter with 6mm prop shaft. And while I tried to mount it with a prop I faced with just the same problem as you - prop turning was not true and I could see adapter wobbling to sides. I tried to put another prop from other manufacturer I found the adapter and prop turning true. So apparently a problem was in the new propeller. I measured the hub at three places and found there a huge diffecence in thickness. I did not want to sand a carbon prop, so I glued a patches of thin (0.6mm) ply to both sides of the hub. I firstly carefully sanded patch on the back side of a prop until true turning of a prop was achieved. And then I sanded the patch on a front side to get both sides of a hub parallel. Now I can torque a nut with a full force and the prop and adapter both run true.

Greatings,
Vitalis

Offline Matt Piatkowski

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Re: Scorpion propeller adapter
« Reply #3 on: August 20, 2018, 11:09:47 AM »
Fred,
Please see the attached.
Hyperion prop. adapters look exactly like short Scorpion prop. adapters I have.
They are too short for my model and I had to use the long one.
There is most likely some place in China turning these and they sell to whoever wants to buy them.

By the way: the short adapter has much better transition from the threaded to the unthreaded shaft. Less stress concentration and thicker final shaft to the collet.
I do not understand why they (whoever they really are...) did not use the same design for the long adapter? 

Vitalis,
Igor's 12x5x3 electric prop I am using has the hub of reasonably constant thickness. At least when measured with high quality, steel caliper. Pol-Props ( I have many different types and styles) have unfortunately a bit poorer quality and some variation of thickness across the hub that is possible to measure using the caliper.

At this moment, I do not know how to fix the problem but I will find out. There must be something CAUSING it but what?
Thanks,
M



Online Howard Rush

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Re: Scorpion propeller adapter
« Reply #4 on: August 20, 2018, 01:05:41 PM »
Thanks for the tip.  I'll avoid Scorpions.

These work: http://www.icare-rc.com/prop_adaptors.htm#MPJet_collet_prop_adapter
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Offline Vitalis Pilkionis

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Re: Scorpion propeller adapter
« Reply #5 on: August 20, 2018, 01:26:03 PM »
Matt, can you confirm that shaft on the short adapter has two different diameters?
If so, I wonder how can I fit a prop without drilling it?  ::)

Vitalis
« Last Edit: August 20, 2018, 02:15:21 PM by Vitalis Pilkionis »

Offline Matt Piatkowski

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Re: Scorpion propeller adapter
« Reply #6 on: August 20, 2018, 03:09:03 PM »
Vitalis,
I have three of the short ones and yes, there are two different diameters on the  smooth part of the shaft: 5.85 mm. on the length of ~3.0 mm. and 6.95 mm. on roughly 5.50 mm. 6.95 mm. is, therefore, the minimum required diameter of the hole in the prop. to fit this adapter.

The long Scorpion adapter needs min. 5.96 mm. hole in the prop.

Go figure!

Can anybody explain why the people producing these adapters could not standardize the most important dimension?

Comment: Pol-Props will fit long Scorpion adapter smooth shaft diameter without drilling but, if you want to use the short adapter for whatever reason, you can ream the prop. holes carefully - not drill but ream by hand (ref: https://en.wikipedia.org/wiki/Reamer). The hubs in Pol-Prop are all hardwood and reaming will not damage or chip the carbon composite covering this wood.




 

Offline dennis lipsett

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Re: Scorpion propeller adapter
« Reply #7 on: August 20, 2018, 03:56:38 PM »
You could look at the precision aerobatics site and check their collets They are made in Germany. Need I say More. Oh it's a 3D rc site and might interest you in seeing really light construction. reaonably priced.
A 5 mm Collet adapter is about $8.00
www.precisionaerobatics.com

Dennis

Offline Matt Piatkowski

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Re: Scorpion propeller adapter
« Reply #8 on: August 29, 2018, 12:53:59 PM »
Guys,
After experimenting for the last week, I have found the explanation and the reasonable solution to the problem.

First, let me restate the problem the way I see it now: when ANY collet style propeller adapter is used, the combined effect of torquing the prop's mounting nut AND the adapter's shaft bending stiffness AND co-linearity of the collet under preload, may cause the prop's blades to deviate from the desired plane of rotation. This behavior is random, depends on the angular position of ALL the pieces that are squeezed and may or may not manifest itself. If it does, one of the 3 blade propeller's blades will be bent out of the ideal plane of the prop. rotation more than 0.002" that can be measured by a good quality metal caliper.

Please see the attached. In my case, the addition of the hard rubber washer, separating the prop AND the aluminum prop. support ring solved the problem.

All the 3 blade carbon composite props I have (see the attachment, please) rotate now true and well.
By "true and well" I mean that the blades tips stay within 0.002" from the theoretical plane of rotation.

Regards and Happy Flying,
M








Offline Randy Powell

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Re: Scorpion propeller adapter
« Reply #9 on: August 29, 2018, 02:47:05 PM »
I've discovered that you have to be careful about the washer on the prop nut. I've had to flip them over so that they don't impinge on any of the prop blades. It can cause exactly the problem you describe.
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Offline Vitalis Pilkionis

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Re: Scorpion propeller adapter
« Reply #10 on: August 29, 2018, 03:33:54 PM »
I'v just received all three options of 5mm to 6mm adapters that Hyperion offers. As you can see in the photo below they are all different. Even two hyperion adapters in a middle that looks almost the same, in close view look like made by different method. It also looks like Scorpion adapter is made of different grade aluminum (sturdier). The cheapest one at the bottom obviously is the worst in terms of construction and quality. I would use only first three and avoid forth.

Regards,
Vitalis

Offline Randy Powell

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Re: Scorpion propeller adapter
« Reply #11 on: August 29, 2018, 03:59:06 PM »
I use Brodak and Randy Smith spinners. The cone on the spinner is 1/4-28 thread. The collet adapters are problematic. The ones I use are 5mm for the motor shaft and are usually 6mm on the prop side. So I finally made some prop nuts that are 6mm on one side and 1/4-28 on the other so I can use regular aluminum spinners. Something of a pain.
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Offline Steve Helmick

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Re: Scorpion propeller adapter
« Reply #12 on: August 29, 2018, 04:28:25 PM »
Avoid adapters, use glow engines!  S?P Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Matt Piatkowski

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Re: Scorpion propeller adapter
« Reply #13 on: August 29, 2018, 06:01:38 PM »
Hi Vitalis,
After my latest "discovery" I consider the problem solved.
Whatever adapter you will be using for the carbon composite props., try the hard rubber washer - it works.

I suspect that the root cause of the initial problem was the way in which aluminum pieces interacted with the carbon composite surfaces in bearing. A very small deviation from flatness, perpendicularity or parallelism of mating surfaces was immediately converted into localized stress and deflection.

The addition of the rubber washer softens this reaction and allows the mating surfaces to accept the unavoidable manufacturing imperfections.

My Scorpion long adapter works well without the rubber washer with any two blade wooden prop. The prop. support ring ridges bite into wood, crush it locally and the prop's hub sits flat and true filling the grooves between ridges.

Carbon composite prop hub surface is too hard for these ridges to bite into considering the safe bearing force caused by torquing the mounting nut.

Following Randy's observation, I would also suggest to always round and/or chamfer the sharp edges of the prop. nut washer and check if the diameter of this washer is not too large for the given carbon composite prop.
 
Happy Flying,
M




 




Offline Vitalis Pilkionis

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Re: Scorpion propeller adapter
« Reply #14 on: August 30, 2018, 06:16:36 AM »
As I mentioned earlier I came out with another solution - two patches of thin beechwood ply. I sanded them down so that hub got flat and parallel.
This method seems a little better to me as I always remove prop at the end of a flying day and on the next day I don't have to bother about the same problem again.

Cheers,
Vitalis


Offline John Rist

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Re: Scorpion propeller adapter
« Reply #15 on: August 30, 2018, 06:54:45 AM »
Avoid adapters, use glow engines!  S?P Steve

Avoid slime go Electric.  LOL!   LL~
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Offline Matt Piatkowski

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Re: Scorpion propeller adapter
« Reply #16 on: August 30, 2018, 08:54:57 AM »
Hi Vitalis,
By gluing the beechwood ply to the carbon composite hub you are also "softening the interface" what is good for alignment.
I bet a raspberry candy that you can see the imprint of the ridges and grooves of the prop. support ring on the ply.

Our information exchange here is a textbook example of good communication.

We have found two solutions to the annoying problem and we have learned something, haven't we?

Regards and Happy Flying,
M




Offline Vitalis Pilkionis

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Re: Scorpion propeller adapter
« Reply #17 on: August 30, 2018, 11:15:37 AM »
Yes, we have!  :)!

Best wishes,
Vitalis

Offline Wolfgang Nieuwkamp

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Re: Scorpion propeller adapter
« Reply #18 on: August 30, 2018, 12:04:38 PM »
For an adapter with left handed thread I used the construction shown. The three M3 screws can be nicely tightened from the front side, and the prop nut may be tightened normally.

Regards, Wolfgang

Offline Matt Piatkowski

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Re: Scorpion propeller adapter
« Reply #19 on: August 31, 2018, 11:07:32 AM »
Hi Wolfgang,
Please see the attached. The Cobra on the left has the screw-on (or bolt-on) prop. adapter similar to the one you have shown on the drawing.
The Cobra's adapter is very well machined and is mounted using three short screws. Such adapters, like I wrote before, have "separated functions" and this allows to better maintain the prop. alignment while the prop. mounting nut is torqued.
The use of such adapters is, however, restricted to the motors mounted FWD of the firewall.
Cobra on the right is mounted AFT of the firewall and the motor's design does not allow for use of the screw on (or bolt on) adapters discussed above. There exists another type of the "separated functions" adapter, like the one used in the MVVS motors, and this one can be used in the motor's AFT of the firewall configuration. We can (can we?) call the MVVS type adapters "Slide on prop.adapters". Like you probably know, such adapters usually use one or two small worm screws for the attachment to the motor shaft - a connection considered by some as not strong enough.

Regards,
M

 

Offline Wolfgang Nieuwkamp

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Re: Scorpion propeller adapter
« Reply #20 on: August 31, 2018, 01:19:53 PM »
Hello Matt,

please look again at the drawing. The three screws are not attached to the motor. The screws just pull the ring forward to tighten the conical part to the shaft, so it is ideal for normal motor mounting.

Regards, Wolfgang

Offline Wolfgang Nieuwkamp

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Re: Scorpion propeller adapter
« Reply #21 on: August 31, 2018, 03:06:46 PM »


Better picture?

Regards, Wolfgang

Offline Matt Piatkowski

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Re: Scorpion propeller adapter
« Reply #22 on: August 31, 2018, 03:21:14 PM »
Hi Wolfgang,
I can see it right now! Very interesting idea in which the adapter functions stay "disconnected".
I would love to try it on all my motors and they all have 5 mm. OD shaft. Is there any way I can buy it from you for shipping to Canada? Are you using 2024 aluminum alloy for the assembly or something "softer", like 60YY series alloy?

If you can sell it, I will need longer threaded part. I will send you the length required for the plane I am flying right now.

Aha...what is the threaded part OD? What hole in the props. I need?

Happy Flying,
M

Offline Wolfgang Nieuwkamp

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Re: Scorpion propeller adapter
« Reply #23 on: September 01, 2018, 04:56:24 AM »
Hello Matt,

5 mm OD shaft OD is OK. The material is free cutting aluminium, AlCu4MgPbMgMn.
The threaded part is M 8, I have standardized all my props to 8 mm, using an old Fox reamer....

Since I am only equipped with a small Chinese lathe (ergo no CNC) I need multiple hours to make a custom adapter. Just send me the dimensions you need, then we can discuss how to proceed. PM wnieuwkamp(at)compuserve.com

Regards, Wolfgang


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