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How Safe is my Motor?


Jon
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My plain landed head down as a result of a battery failure (batteries failed to stay in the plane ) result was No Control No Plane.! While I was rebuilding and testing it the weather man forecast that there would be no wind or rain on 15 Aug 08 (one for the Guinness book of records iI think )

On this record winning day I was to do a complete mock A test with my instructor...I was so excited and no wind either WOW!

During the pre flight test my motor failed to reach full rev's and made a high pitched squeal and stopped...I tried again...and again... Grounded on the best flying day of the year....I couldn’t believe it I now have a new motor and all's well apart from the rain of coarse....

My question is based on the construction of the brushless motors....are they all like this?

Having pulled it all to bits I found that the very small grub screw an the front was a little loose and had thus caused the main shaft to move forward at full rev's.

After it had been secured the old motor still squealed at full revs... Why? is there anything I can do about it?

Also I note that the only thing preventing the shaft from being pulled out at full rev's was a little cir clip mounted on the shafts rear end!  Is this really safe? Or am I missing something?

Feel like I missed the whole UK summer flying period  !! (is it normal that it just lasted for one day )  

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Jon,

To be fair to the motor, if you've, er, "landed it firmly" nose first it probably could do with a new set of bearings ,at least, and probably a new shaft.  It's probably the bearings that are squealing and, if the shaft's slightly bent (you may not be able to notice this) it will force the bearing out of true as it runs.

In my experience, any prop strike can damage the bearings.  Shock loads cause them to brinnell.  Bearings are quite small on electric motors.  I just keep a few new ones handy.

What make is the motor?  Axi motors have a small circlip to hold the shaft in place, but this is backed up by a grub-screwed collar when it is rear mounted (i.e. for when prop load is transmitted through the circlip).  I've never known one fail, though.

Ed

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Hi Ed

Yes, I agree its a bit much to think it coud withstand such a pounding and as a newbie I can tell you its had a few .... Lesson learnt is to check the grub screw before each awitch on. (see 1st Pic below).....

Its a 500w motor and driven by 5000ma 4s lipo

But as for the Circlip (it is shown in the second Pic) it is as far as I can see the only thing stopping the prop from pulling the shaft out.... When I took it apart the clip just popped off at the touch of a screwdriver. I did not have to leaver it off.....

Intrested in your comment about spare bearings... where do you get yours from?

Jon

http://forums.modelflying.co.uk/sites/3/images/member_albums/29596/DSC00049.JPG





http://forums.modelflying.co.uk/sites/3/images/member_albums/29596/DSC00046.JPG


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The clip you have there is an "E-clip" and works in a similar way to a circlip.

The forces generated by the prop are transfered to the very edges of the clip where they sit in the groove.

Since this is a shearing load, the force required to break the edges are far more than a prop could exert, it would take something more like the force of an overly large hammer blow being really swung at it.

Like the others have said, a new set of bearings and a new shaft and you should be ready to go again. If you do not like the E clip, fit a suitable size circlip - it will not make any difference.

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Thanks all for you comments.... but should the E clip come off so easily ?     a width increase to the end of the shaft would make me feel a bit better..... I'v  always been worried about the prop flying off and hurting a fellow flier but having now seen what holds it in place I'll be issuing tin hats next time I'm at the field.

but where can I get Spares for it.... it came from BRC.... spoze I should start there?

Thanks anyway....jon

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Hi Jon,

I get my bearings from here

http://www.smbbearings.com/Framesets/Miniature_Metric_Frame.htm

You need the shielded type - it keeps the dust out.  You have to take out the old ones, measure them, then order replacements.  From memory, they're pretty low cost.

Regarding the E clip - I have to say, although I agree with what Andy says, it does look a bit minimal.  You could get a replacement shaft from Micron radio control (a Scorpion shaft) that comes with a grub screwed collar to hold it on.  They're only a couple of quid.  That looks like a 5mm shaft - they come in various lengths and have flats ground in to accept the grub screw.  You probably need a new shaft anyway.

Ed

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  • 2 weeks later...

Now heres one for you all....

I purchased a brand new motor as described above form BRC and fitted it ready for my next lesson.. after 2 weeks of waiting for the weather to break I finally got a call from my instructor " we are on.. John"..

I dashed off to the field... and guess what... yes, it made the same screeching sounds as before...grounded once more  I was gob smacked...

The first motor ran like a dream untill I was told I'm ready for my test...  now the new motor has the same problem and its never been in the air...

Yes, I did trial it (at full rev's too) at home but the problem only showed up when the instructor ran it up at full revs... its almost as if its about to cease up and stop... reducing the power free's it up once more and he did fly it at 3/4 rev,s but as soon as its given full power it screams out loud I will be in touch with BRC first thing in the morning.... assuming I can get them on the phone, its always busy...

The first one was purchased early this year and the second just 3 weeks ago could they be both from the same batch? but why did the first one run fine for so long Any clues chaps ??????????

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Hi Andy....

I'll try a thin oil....but i;m still going to ring BRC

PS.... I got an email telling me that there had been a responce to this posting and that it was from Eric Bray.... but I cant see in listed and nor can I see any of his other postings... You mentioned Eric above is that due to his posting on this thread... I cant see any thing from him

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Jon, not sure if this helps but I've heard of motors screeching if the timing of the ESC is wrong.....some ESCs allow you to adjust this timing & (I think I'm right in saying this) outrunners generally prefer "hard" timing whilst inrunners prefer "soft" timing. Check the maual that came with your ESC.....

Also how close are you to the limit of the motor? I've had a motor that screeched at full throttle when I had it loaded right up to its maximum...dropping the prop size slightly cured it....I notice you say your motor also only screeches on full throttle

 Food for thought maybe & perhaps will take the debate in a different direction....

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Thanks Steve & Timbo....

I'll also look into that... but would it also cause the motor to stall while screeching and if power is reduced but then increased once more for it to then restart as if nothing wrong? it will do this in flight as well as under test.

It seams as if its trying to pull forwards so hard and since its held by me or as a result of drag  while in the air the motor stains against its own bearings until the stress has reduced

Jon

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