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Old Aug 29, 2007, 08:51 AM
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Rimfire outrunner evaluation

Recently there have been reported problems with the 28-30-xxxkV model of the ElectriFly Rimfire outrunner motor throwing its prop shaft. This motor has an integral prop-saver propeller mount on the front. In some applications, the motor has to be mounted behind the firewall and a prop adapter fitted to the prop shaft behind the motor.

I needed a 1000-ish kV motor of 150 watts for a plane I am planning and decided to purchase a Rimfire 28-30-950kV to evaluate this motor for my own curiosity. The prop shaft on some of these motors has been reported to be a loose fit, and the two prop-saver screws, which also serve as setscrews to secure the shaft, have loosened, allowing the prop shaft to separate from the motor. On the motor that I evaluated, the prop-saver screws were tight, and the prop shaft was a tight press fit in the outrunner bell and required tapping with a hammer and pin punch to remove the prop shaft. Discussions to the contrary, it appears that the design of the motor is adequate with two screws and a press fit of the shaft in the bell to secure the prop shaft. I would speculate that the failures of this motor may be due to loose manufacturing tolerances between the prop shaft and the bell. This is unfortunate, but is covered under warranty. This would be easy to check before use by loosening the prop-saver screws and seeing if the prop shaft can be moved by thumb pressure. If the shaft can be easily moved it would obviously be a good idea to not use this motor for flight. See image rimfire001a-rimfire010a.

Dr Kiwi recently observed that this motor has a circlip groove on the far end of the prop shaft and speculated that the shaft could be turned around and the circlip placed in the new groove to keep the shaft from pulling out in flight. I disassembled the motor to evaluate this idea. As it turns out, this idea works very well, and will allow the prop shaft to be placed either in the front or the rear of the motor, depending on how the motor is to be mounted. I did not replace the circlip while checking the fit of the shaft for the rear-mounting of the motor, but you can see how it is to be placed on the shaft. See images rimfire011a-rimfire016a.

I plan to use this motor mounted on the firewall with a collet adapter to mount the prop. I placed the circlip on the end of the prop shaft and pressed the prop shaft in from the rear of the motor and had about 0.4 of shaft in front to use with the collet adapter. See images rimfire017a-rimfire020a.

While the motor was disassembled I evaluated the construction of the motor. The motor appears to utilize typical techniques for the design and construction of an outrunner motor: it uses a laminated, insulated stator pressed onto the backplate which contains two shielded ball bearings which the propeller shaft rides in, and the shaft is a press fit into the outrunner bell, which has magnets epoxied to its inner circumference. Within my realm of experience, it appears to be typical of the current crop of inexpensive outrunner motors from China.

--Bill
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Old Aug 29, 2007, 09:00 AM
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A most excellent, practical, common-sense, evaluation, Bill. Congratulations on a job well done.

Do you think I can claim royalties on the reverse shaft/circlip idea? It is great to see the proof of the pudding, in the eating.

Cheers, Phil
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Old Aug 29, 2007, 09:04 AM
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Sure, submit the claim to the Chinese. I'm sure they'll respond right away...

--Bill
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Old Aug 29, 2007, 11:19 AM
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You pretty much summed it up Bill. I obviously got one that was not a tight press fit. The problem I had is that I only had the motor for 3 months and GP didn't honor the warranty. I still have the motor with no shaft except the one I got from GP.
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Old Aug 29, 2007, 11:53 AM
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Scooped

Sorry Doc, I'm afraid I got the scoop on you. I suggested the snap ring and groove idea back on Aug. 18, in post #4, of the "Do we need safety standards" thread in the Motor design section. Yours didn't show up until Aug. 21, in post #231, of the "Rimfire potential danger" thread.

Those royalties $$$$ are on the way now. They're so close I can smell the greenbacks!!!

What's really scary is the idea is so obvious and simple, yet "they" didn't do it.
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Old Aug 29, 2007, 12:27 PM
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I read you post Ken and you're absolutely right. A very simple modofication could solve the problem.

John.
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Old Aug 29, 2007, 12:59 PM
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Quote:
Sorry Doc, I'm afraid I got the scoop on you.
Nope, no soup for you. You said "A simple snap ring and groove in that end of the motor would prevent..." Keyword: would prevent (if added).

Kiwi said: "I just looked at the photos in Post #20. The exposed shaft has a circlip groove near the tip..., noting that the shaft already had a groove that could be used. Keyword: has a groove (that can be used).

Advantage: flightless bird.

I notice that other Chinese motors have a similar unused snap-ring groove at the end of the shaft. I'll wager the snap ring grove is designed to be used like that, but this was not passed on from the design team to the tech writers.

--Bill
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Old Aug 29, 2007, 01:40 PM
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Soup and scoop!

The fact that there was a groove already in the shaft simply means someone other than the Kiwi meister put it there. The idea to use it at that end, was verbalized my me three days before the good Doctor even knew there was a groove! The existence of said groove on the supplied shaft is no more than a good coincidence!

Advantage and Match!! The Ken meister

What a shame, an unused groove just sitting there waiting to be utilized.
Wait till Dave Matison finds out how easy is was to fix his problem.

Ken
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Old Aug 29, 2007, 02:54 PM
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Aug 03, 2007, 09:10 AM Report This Post to a Moderator View your Warnings #12
Dave Matison
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Posts: 376 I called Electrifly, yesterday, and spoke with Jake. Jake said there was no record of my conversation, last week, but said he would send me a new motor and he gave me some kind of claim number (the fellow last week did not give me such a number). This is truly odd, in my opinion, since the guy last week said something like, "I have one here on my desk that did the same thing."

Well, who knows, but I'd say to anyone if you have one of these motors to tug on the shaft a little bit before use to make sure it does not come out with simple (light) hand pressure.

Aug 03, 2007, 01:08 PM Report This Post to a Moderator View your Warnings #17
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Posts: 377 Mike, my dead stick skills are poor and my gear was crushed and the bottom wing broken. Because of your postings, I reinforced the motor mount and that was not a problem, but I had two "failures:" the first during static testing (when the prop almost struck my eye) and the second during flight. As a novice in the field, I guess I should have stopped at the static test but I simply didn't know any better: I tightened the screws on the prop saver after reinserting the shaft and, in retrospect, unwisely flew the plane.

Here is the tip-off, in my experience: if you can remove the shaft by hand, even by tugging, beware!

As to vacations, well, maybe the E Guru guy left right after he commented on my posting, here.

TO TAKE YOU WAY BACK (at least in this industry), I just completed a Graupner BO 209, with an Axi 221226 and FOUND YOUR "ANCIENT" review invaluable!

Regards, Dave (hoping the Guru comes back and answers)

Aug 03, 2007, 06:25 PM Report This Post to a Moderator View your Warnings #21
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Posts: 377 Bill, the motor fits into a "tripod" mount with the shaft forward and the "integrated" (non-removable) prop adapter facing rearward as depicted. I was told by someone at Electrifly in the first phone call last week that the prop adapter screws do not hold the shaft and DO NOT go down to the shaft: I verified the latter by measurement (as close as I could!). I was also told that an "e clip" "inside" should prevent this but it's beyond me where that clip should have been (there is one in "front" of the shaft, outside the housing). [B]My speculation is that my motor had a defect in fabrication of some kind.[/B] I appreciate your research and believe me, it is as much a mystery to me as it appears to be to you. Regards, Dave

Q.E.D.

AND,

Aug 09, 2007, 08:45 AM Report This Post to a Moderator View your Warnings #46
Dave Matison
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Posts: 377 Quote:
Originally Posted by Bill Harris
Not really. As builder and pilot, it is your responsibility to check and verify the suitability of all components on the aircraft. Since you had a failure of the prop shaft during static testing you should not have flown the aircraft with this motor that had a known problem.



Bill, go back and read all my postings and those of the engineer. What more would you have had me do? I did tighten the screws that E Guru contends are adequate. The engineer casts doubt on the entire design or so it would appear. Here is what I said:
Mike, my dead stick skills are poor and my gear was crushed and the bottom wing broken. Because of your postings, I reinforced the motor mount and that was not a problem, but I had two "failures:" the first during static testing (when the prop almost struck my eye) and the second during flight. As a novice in the field, I guess I should have stopped at the static test but I simply didn't know any better: I tightened the screws on the prop saver after reinserting the shaft and, in retrospect, unwisely flew the plane.

I believed I had cured the "problem." Any consumer is held to a reasonable consumer standard, not a "perfect consumer" standard. What more would you have had me do? I well remember a BMW case (products liability) in Alabama and your own home state only holds a consumer to a "reasonable man" standard in use of the product.

So, in HINDSIGHT, was it unwise? Yes. Measured by a reasonable consumer standard was it unwise? I doubt it.
Of course, I'm not asserting a legal right to a new DR-1, just a moral one.

As I said, likely my "group" is the majority, future market (those who use, rather than fiddle), and if the manufacturers wish the good will of this group, well, "nuff said."

Have a great one, Bill, and thanks for your comments.
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Old Aug 29, 2007, 03:22 PM
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E Guru, does this cure void the warranty?

E Guru, should this cure be incorporated into the manufacturing process?

E Guru, it appears to be a cheap, efficient cure, so why not use it?
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Old Aug 29, 2007, 04:45 PM
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Wouldn't the cost in "yuan per hour" (one guy in China tugging the shafts) be de minimis relative to the potential harm?
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Old Aug 29, 2007, 06:51 PM
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Quote:
Originally Posted by Bill Harris
Nope, no soup for you. You said "A simple snap ring and groove in that end of the motor would prevent..." Keyword: would prevent (if added).

Kiwi said: "I just looked at the photos in Post #20. The exposed shaft has a circlip groove near the tip..., noting that the shaft already had a groove that could be used. Keyword: has a groove (that can be used).

Advantage: flightless bird.

I notice that other Chinese motors have a similar unused snap-ring groove at the end of the shaft. I'll wager the snap ring grove is designed to be used like that, but this was not passed on from the design team to the tech writers.

--Bill
Thank you for the support, Bill.... but personally I don't give a damn who thought of the idea first. As long as it prevents someone from losing an eye ... I'll donate all my royalties to KenSt's charity of choice!
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Old Aug 29, 2007, 07:20 PM
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Well, what did the inexperienced modeler say to the ... manufacturer?

"I'll keep an eye out for you!"
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Old Aug 30, 2007, 04:23 AM
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It's a good idea no matter who noticed it. I don't think that the prop shaft is a major issue, though. The elastic bands on the prop saver wear and fail. Prop adapters loosen and fail. The downside to the ARF revolution is that there is a crop of new flyers who do not have the experience to recognize and solve the problems that anyone runs into with RC flight.

--Bill
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Old Aug 31, 2007, 04:32 AM
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http://www.rcgroups.com/forums/showp...postcount=3233

Here is a good description of how to press the prop shaft out of an outrunner. Most designs are similar to this.

--Bill
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