Dust in Motors

Discussion in 'Cinestar 8' started by georgemcnabb, Feb 28, 2015.

  1. georgemcnabb

    georgemcnabb Member

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    Hi Guys,

    Was doing a shoot in a carpark today. The carpark was basically a bland lot. With no tarseal.

    So I took off from the ground with a huge cloud of dust & same when I landed.

    The motors (4012 Tiger Motors) are now making a slight scratchy sound when slowing down or when I spin them with my hands.

    Any solution for this? or am I just being paranoid?
     
  2. Steve Maller

    Steve Maller UAV Grief Counselor

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    If you have an air compressor you should definitely try blowing the motors out. Crunching sounds are no good. Failing the compressed air, you might have to disassemble the motors and use the air to get into all the parts of the motor (especially the bearings). But depending on the material that got into the motor, you may need to replace one or more of the motor bearings.
     
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    To avoid this problem in future, George, purchase a 10 foot square tarp (Gary insists it has to be blue, but I think, this time, he might be wrong :) ) and then weight down the corners and the middle of each edge.

    This becomes your takeoff and landing zone. If you do vertical takeoffs and landings, the propwash holds the tarp down. If there's any significant crosswind, or you use a 45 degree ascent/descent, then you can blow the tarp away unless it's weighted down.

    When I first start the motors, I let them idle to blow the tarp clean. For landing, as I say, I come in vertically, and hover above five feet above the tarp -- which has the effect of cleaning it and allowing any accumulated dust to blow downwind before I land.

    Steve is right about the "crunchy" stuff -- the only thing that can cause that is dust in the bearings. There really is no other moving part in the motors.

    Andy.
     
  4. georgemcnabb

    georgemcnabb Member

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    Will be going to the hardware store today to get that tarp. I dont know anyone with a compressor. May need to stop in at a bicycle store or something like that and awkwardly ask to use their air o_O

    Thanks for the help guys, lets hope I dont have to take the motors apart.
     
  5. Steve Maller

    Steve Maller UAV Grief Counselor

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  6. georgemcnabb

    georgemcnabb Member

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    Alrighty, so seeing it's the weekend I had some time to try and solve this.

    Took to it with a massive amount of air from a compressor but no luck. So I guess will have to take the motors apart & replace bearings which is a real pain.

    What are the risks of giving it another flight as the motors are and seeing if the dust just comes out itself?
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    If the motors still turn freely by hand (even if they sound crunchy) I don't think there's much risk that they will suddenly seize up, but I'd stay low to the ground for the first few minutes to see if the dust clears itself. Personally, that's the kind of problem that never seems to fix itself for me....

    Andy.
     
  8. georgemcnabb

    georgemcnabb Member

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    Yeah doesn't look good. Just going to order all new bearings - no one has 8 sets in stock though :(

    Pain in the ass but I have learnt my lesson!
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I've purchased bearings from Boca Bearings. Be sure to get APEC #7 quality.
    The person I emailed with back in 2012 was Gareth Burrows gareth@bocabearings.com -- he may no longer be with them, but he was super helpful. See http://www.bocabearings.com/

    Andy.
     
  10. georgemcnabb

    georgemcnabb Member

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    Ill check that out. They dont have the tiger MN4012 specific bearings though huh?
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I'd contact them and they may know the dimensions of the bearings required. I don't think there specific bearings for the MN4012 (beyond they have to be the correct size).

    Andy.
     
  12. georgemcnabb

    georgemcnabb Member

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    Ok, so the saga continues...

    Tracked down bearings from T-Motor direct, they arrived and I installed them...annnnnndddd it still produces the same noise.

    One motor also feels like it isn't spinning smoothly - I am so frustrated and am just chasing my tail haha!

    What are the repercussions of just continuing to fly the rig like this?

    Im starting to think the dust isn't in the bearings either.

    Thanks for the assistance guys
     
  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    George:
    As you probably figured out when you took the motors apart to replace the bearings, there really isn't any other place for the dust to be...you got me scratching my head....could the shaft be bent on that one motor that doesn't spin smoothly? Is the "cogging" particularly bad on that one motor? You've got good reason to be frustrated -- not that that actually helps anything, though!

    Andy.
     
  14. georgemcnabb

    georgemcnabb Member

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    Yeah I thought may be the shaft too but the chopper has never had damage, or any dings.

    I may just give it a few test flights and see how it performs. And just try live with it.

    Would the dust cause any failure or just vibration?
     
  15. Janne Hoglund

    Janne Hoglund Member

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    I had nearly the same problem, but among the dust there was some small parts of magnetic metall.
    To get rid of them the only slution was taking the motor apart, locating and picking the small pieces out one at the time.
    Those motor magnets are really strong ones!!
     
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  16. Steve Maller

    Steve Maller UAV Grief Counselor

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    I've seen this before. You have to clean the motor windings carefully so you don't damage any of them. You can look on the magnets (on the outside "bell" portion of the motor) for tell-tale scratches that'll indicate something in the windings.
     
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I think the risk with dust in the bearings is that the bearings would seize up in flight and motor would slow down dramatically or stop entirely.

    The metal pieces in the bell is an interesting problem: it suggests that perhaps with wear/crash, the bell of the motor deflects far enough that the stator (with the coils on it), comes into contact with the neodymium magnets attached to the inside of the bell and shaves off some metal (either from the pole pieces on the stator or from the magnets). Either way, I suspect you really need to get rid of them!

    Andy
     
  18. georgemcnabb

    georgemcnabb Member

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    Yeah i did take a look in the bells and couldnt see much. I will try again, how do you recomment cleaning the windings? Im almost considering just replacing all the motors. which is a pain but when you have a machine in the air this valuable its a no brainer
     
  19. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    George:
    It's a bit of a labor of love to remove any crud that might have accumulated on the magnets -- I've found that just using a lint-free rag lets you wipe off some of the smaller magnetic particles -- but it's not easy as the neodymium magnets are pretty strong. I also tried using a larger neodymium magnet in the hope that that might work. All that happens it that you end up fighting to separate the larger magnet from the ones on the motor bell! :(

    As to the windings, they should not have any permanent magnetism so I've used everything from a toothpick to soft toothbrush.

    Can you just confirm one thing though: Are you finding that the motor is literal just hard to rotate or are you feeling strong "notches" as you rotate it? Or is there a crunching noise/feeling as you turn the motor? Sorry for the Spanish Inquisition, but I'm just trying to learn from your experiences as this is a rather unusual situation -- given that you've changed the bearings and that didn't fix the problem.

    Andy.
     
  20. georgemcnabb

    georgemcnabb Member

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    Hey Andy sorry for my delay. Its basically just a crunching/gritty noise, only when I spin the motor and it starts to slow
     

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