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AlignRC Thunder Power RC
flyboy1985

Senior Heliman

mohnton pa

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hey guys, 126 flights on this 700mx motor , and yesterday , first pack of the day , 23 sec into the flight , I'm doing a piro flip ,
all of a sudden halfway around the flip , it seems like my motor cut out?!>?

landed hard, was about 25 ft up and lost almost all hs before I had her upright and all but level,

boom bent ,ever so slightly (have spare)
broke right side of my assault skid ( heard there not to flexible)

other than that I thought nothing of it, infact at the field I first thought it was due to the motor pinon set screw backing out.

thought this to be weird as I loc tight all my screws and never had this happen before , and so many flights in ,

well today I started pulling the motor to reset the set screws , well wouldn't ya know ,, the shaft is snapped!

wow , ok , this is cool lol ,, first time for everything eh>?

well now heres my problem ,, I cant seem to find a source for this replacement shaft ,, I don't want to order over seas , so any help on this I'm greatful for,,,

going pro , one crash at a time

09-28-2016 07:05 PM
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Steff Giguere

rrProfessor

St-Eustache, Quebec, Canada

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Happened to me in the past with a Kontronik motor. Kontronik wanted me to return the motor to Germany for them to change the shaft....bought a Scorpion shaft to replace the Kontronik shaft, changed it myself.
Now I only fly Scorpion motors.

Team Synergy, Rail blades, Team Scorpion, V-Team

09-28-2016 07:16 PM
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flyboy1985

Senior Heliman

mohnton pa

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ive heard of this happening if the alignment isn't perfect , you will get a lot of stress on the shaft and than once metal fatigue sets in , its a matter of time before your align , katronic, scorpion or even hk motor shaft will just fail and snap,

so that being said, maybe kontronik motors aren't so bad and maybe you had an alignment issue>?

either way it sucks , and I still need to figure out where to get a new shaft

going pro , one crash at a time

09-28-2016 07:27 PM
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flyboy1985

Senior Heliman

mohnton pa

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so heres what I found and I'm gonna try,,

the 750mx motor shaft is 2.5mm shorter than the 700mx motor shaft,,,

they use the same bearings and same diameter shaft ,, soooooo,,,

I'm gonna get a 750mx motor shaft and throw her in my 700mx,, in theory it should be just fine , .......

going pro , one crash at a time

09-28-2016 09:11 PM
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Dr.Ben

rrMaster

Richmond, VA, USA

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Should be fine. Do please check for any frame misalignment, because shafts with counter bearing in use rarely just snap. The side loads supported by the counter bearing are immense, esp. with our helical transmissions. Around the time the Georges start sourcing his shaft material from Europe because he too was having issues with shafts breaking (that's why the about tripled in price), they measured the side load being applied to a motor shaft. I recall it being several hundred pounds. With these kind of forces in play, if the frames flex or are not aligned, you're at risk for snapping a shaft regardless of motor brand.

Ben Minor

Team Synergy Team Futaba Team Kontronik USA
Progressive RC

09-28-2016 11:45 PM
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flyboy1985

Senior Heliman

mohnton pa

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@ dr ben,

I thought bout frame flex, but if that were going on , wouldn't my main gear show wear ? or fast wear on one or more sides of the main gear?

mine snapped right up at the bearing,, actually maybe a little father in than the bearing , and my counter bearing isn't blown out like I would have expected to see with that kind of force ,

got love our toys

going pro , one crash at a time

09-28-2016 11:58 PM
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Dr.Ben

rrMaster

Richmond, VA, USA

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A reasonable thought. The maingear won't show flex wear unless it's horrible because the usual amount of backlash between main and pinion will allow for it. In the days of the engineering abortion known as the Stratus, you could load the model's driveline in a hard pull and hear the mesh change, but we never had issues with premature main gear wear.

Hopefully your issue was a fluke and will not repeat itself. That kind of in flight failure is surely unnerving.

Ben Minor

Team Synergy Team Futaba Team Kontronik USA
Progressive RC

09-29-2016 01:31 AM
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flyboy1985

Senior Heliman

mohnton pa

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I sure hope it was a fluke , only time will tell , ill be sure to keep an update once I get and install the shaft so if anyone else wants to see it retro fit they can ,

thanks again for all you're advice

going pro , one crash at a time

09-29-2016 01:58 AM
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icanfly

Elite Veteran

ontario

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got a pic of the failed shaft and motor?

so if I'm not mistaken those motors of a 700 are pushing 100bs of force to the main gear during 3d? sport? tic tocs? piro flips? in general?

It's an Align 700 no doubt from the mx description and it was said if the support bearing is out of line with the motor breakage was inevitable. 128 cycles on the shaft is good/bad/ugly I don't know. I have an mx Align motor so I'm interested in knowing more and if Scorpion went to great lengths to supply a better steel shaft at 3 times the price, from Switzerland (?) and no matter what all motor shafts of any manufacture are potentially going to suffer the same fate it tells me a few things I would look at in my own endeavors to make motor shafts for a few project helis I have. I also want to protect against your sort of failure with a few solutions I imagine should lessen the issue and worry.

The fact the shear happened inside the motor bearing actually suggests the bearing was faulty and would allow the shaft to bend repeatedly, constantly, when the gear is engaged. An out of round main gear will also add to the problem as the motor shaft is being vibrated as the pinion climbs and recedes the main gear teeth in each rotation, then you have a harmonic and a destructive resonance. In a 450 that detail is insignificant due to it's weight, on a 700 of over ten lbs you'll have a resistance of ten lbs or so dampening the effect and you may not see it without a vibe analysis.

Someone told me today they went to a funfly recently and was told they were beyond the ability of an Align product to perform at the ability level the flyer was able to achieve. I recommend he look at more boutique level manufacturers who pay attention to the heli and not final business bottom dollars where qc takes a back seat, hint hint.

It's said in fs circles a heli rotor is a resonant system, and so the tail is also and the two are intrinsically linked via main gear and pinion and shaft to the motor bell.

Sounds like the Scorpion shafts are dom chromo btw not carbon steel annealed which I believe the mx motor shafts are but I can't be sure without someone sating this with absolute certainty from real metallurgical testing.

Do you remember a time when Align's 700 series tt tail shafts vibe'd like crazy with several disintegrating too from a critical rpm limit and harmonics throughout the heli manifesting in the failures, another shaft of sorts at high rpm linked to a very powerful 11 or so hp electric motor bell?

Lastly but not leastly, balance the motor bell before you reassemble the motor, with new high quality bearings OF COURSE, and add some loctite in the bearing when it's finally put back together so it won't ever vibe in the bearing, or overheat if the bearing fails and the shaft turns inside the inner bearing race.

Cammon, if you fly that hard to break shafts you must be flying pretty solid 3d.

09-29-2016 02:22 AM
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flyboy1985

Senior Heliman

mohnton pa

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I just tried to take the clearest pics I can , the break is right at the bearing , maybe 1-2mm before ,, but not much ,

going pro , one crash at a time

09-29-2016 02:44 AM
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flyboy1985

Senior Heliman

mohnton pa

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ill be honest tho ,
this crash cost me 5 bucks (landing gear)

including the motor shaft give or take $23

it could have very easily been a $200+ crash had my blades hit and I didn't save it , thank god ,,

but it troubling to think this is happening , like I said 100+ flights in , I think we can say the shaft was true to the gear and not causing the failure? , but who knows,,,

I fly 3d ,, I try my best to beat the hell out of my helis, I don't ever just hover around , I get bored to easy , but regardless, I'm no bert k . so I doubt I'm stressing the shaft by flying, who knows lol ,

its possible the bearing was failing in the motor but wouldn't the motor mount and pinion support stop that?

my buddy has a shaft so worn , the front bearing don't seat , it wobbles inside the bearing , like a 1.5mm gap , infact ill have to take a video to show you , seeing is beliving ,and he flys just hoving around , nothing crazy , but still , his never snapped , and even I told him no good dude,,but yea I see your point ,

just sucks our toys are so expensive , yet made so cheaply

going pro , one crash at a time

09-29-2016 02:53 AM
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icanfly

Elite Veteran

ontario

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ahh yes the old milled shoulder weak point. At least we see what to look out for. See that tiny little black circle right where the sheared metal with pinion is? That's the weak spot on the whole shaft and right where all the stress between pinion and motor goes.

I'm exploring custom motor shafts and merits of atm, good to have posted so we can see first hand what might happen.

Kind of interesting, in the recycling business you learn how to tear metal apart finding the weakest points and twisting until it shears, often where it's thinnest and or a partial tear has occurred exploiting the stronger metal surrounding the weak spot in order to concentrate the energy of the shearing action. I could break that shaft with a vise and pipe wrench real easily, it'd break where yours did every time.

09-29-2016 03:03 AM
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flyboy1985

Senior Heliman

mohnton pa

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maybe I should look into another companys shaft ?
maybe a scorpion will fit , or kde,, on the bocca bearing site theres the bearing size for the 700mx motor , also with other compatable motors in the market, the link here , click on" also fits", you will see what I mean

http://www.bocabearings.com/bearing...s-700mx-all-all

going pro , one crash at a time

09-29-2016 04:03 AM
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RappyTappy

rrProfessor

North Denver, Colorado

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This is maybe just a fluke thing I have to say. Maybe that bottom bearing is bad on the motor and caused the shaft to heat and cool repeatedly causing heat stress at that point of the bearing.

Either Way though could just be luck of the draw. I member berry talking to a guy at a fun fly and he had a brand new TDR snap its main shaft right at the top bearing and it was all over.

09-29-2016 06:17 AM
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icanfly

Elite Veteran

ontario

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I just did a search on all accounts and got almost nowhere except a whole motor on ebay Gartt http://www.ebay.com/itm/Gartt-530KV...VMAAOSwGtRX0S2D . If you look at the shaft closely you'll see the transition from pinion shaft to collar is round and not abruptly square, this is the proper way to make them. Chances are the gartt shaft will fit the mx and if you email the company or try to get the info out of someone who owns the gartt motor you might have enough info to assert the fit. Maybe gartt will sell you a shaft.

Now, if you adjust the mesh with the main gear on the motor plate does the lower motor shaft bearing support also follow the distance inward/outward from the main shaft? If not the shaft would have been bent back or forth at all times right where your failure occurred.A chassis engineering oversight, Lynx has an upgrade motor mount I saw on ebay http://www.ebay.com/itm/Lynx-Align-...WAAAOSwdzVXuI-A but I can't be sure the lower bearing support is adjustable with the motor gear mesh adjustment.

Thanks for bringing this to our attention op.

09-29-2016 12:03 PM
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flyboy1985

Senior Heliman

mohnton pa

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oh yes the good garret motor ,
I thought of buying one of these but didn't want to go over seas,
I think its the same as the 700mx , same specs and all ,

I don't know about a fluke thing, ,, there are many reports of this failure , but I'm hoping youre right ,,

fly on my friends

going pro , one crash at a time

09-29-2016 01:49 PM
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helifanatix

Veteran

Fountain Valley, CA

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As Ben said:
- There's misalignment
- There's flexing

Your conclusions & speculations are based on what you know at the moment.

You would know if it's cheap material if you can see worn area on the shaft at the bearing.

Take time from this incident to think about learning to auto.. it's possible at height if you know how to do it right

- Scott

09-29-2016 04:27 PM
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icanfly

Elite Veteran

ontario

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regarding misalignment if the lower bearing plate is not adjustable to follow the meshing of the pinion with the motor plate this would cause bending of the motor shaft. 6mm with lateral force of 100lbs and the score line where they break, sorry that's sort of like scoring a glass pane before it's broken while being sized, you get the idea.

At least this lesson has taught me of two issues at the motor to be made aware of, how about you?

09-29-2016 04:57 PM
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flyboy1985

Senior Heliman

mohnton pa

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@ helifan,

I dunno if you read my thread , by the time I relized the motor wasn't spinning the gear , most hs was lost,, id say being in the middle of a piroflip and bringing her back around and down with only broken skid and bent boom? id said that was a save wouldn't you?

kinda like a owb failure id soppose,, by the time it happens and you relize it , its already halfway too late.. but again , id say I did a good job..

I think maybe frame flex,, and or milling flaw?

either way , I'm trying to make sure this cannot happen again ,

going pro , one crash at a time

09-29-2016 06:52 PM
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RappyTappy

rrProfessor

North Denver, Colorado

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If there is many reports of this, then seems like a defective design of some kind, I would shelve it personally and spend my money on a different motor rather than spending money trying to fix a defective designed product with a known common failure.

09-29-2016 07:26 PM
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