Hand-Wound Brushless Motors Revive Grounded Quad

You’re happily FPVing through the wild blue yonder, dodging and jinking through the obstacles of your favorite quadcopter racing course. You get a shade too close to a branch and suddenly the picture in your goggles gets the shakes and your bird hits the dirt. Then you smell the smoke and you know what happened – a broken blade put a motor off-balance and burned out a winding in the stator.

What to do? A sensible pilot might send the quad to the healing bench for a motor replacement. But [BRADtheRipper] prefers to take the opportunity to rewind his burned-out brushless motors by hand, despite the fact that new ones costs all of five bucks. There’s some madness to his method, which he demonstrates in the video below, but there’s also some justification for the effort. [Brad]’s coil transplant recipient, a 2205 racing motor, was originally wound with doubled 28AWG magnet wire of unknown provenance. He chose to rewind it with high-quality 25AWG enameled wire, giving almost the same ampacity in a single, easier to handle and less fragile conductor. Plus, by varying the number of turns on each pole of the stator, he’s able to alter the motor’s performance.

In all, there are a bunch of nice tricks in here to file away for a rainy day. If you need to get up to speed on BLDC motor basics, check out this primer. Or you may just want to start 3D printing your own BLDC motors.

Thanks for the tip, [thjubeck]

34 thoughts on “Hand-Wound Brushless Motors Revive Grounded Quad

  1. “originally wound with doubled 28AWG magnet wire”
    “25AWG enameled wire, giving almost the same ampacity in a single, easier to handle and less fragile conductor.”

    Skin effect at high RPM makes the thicker wire much less effective. That’s why they had the double wire originally.

    1. “Skin effect” has nothing to do with or in this situation–unless, that is, your motors are being flogged in the MHz (Mrpm) range).

      You, and indeed, most ‘hackers’, and ‘makers’, need to stop grasping at neat-sounding technical phenomena which you don’t understand, and which, when exposed to the harsh light of reality AND WELL-ESTABLISHED science and engineering, reveal only that you don’t understand the phenomenon you’re using to explain the problem.

      The following is an excerpt on skin effect, from a wire-and-cable manufacturer of DC-to-GHz product which has been in the business for probably close to 100 years–

      “…This unusual effect on wire and cable has been cited so many times by so many people that most readers don’t even know what it means [sound familiar?]. So let me have a go at it.

      “Skin Effect happens in all wire and cable (or in any metal object that conducts a signal, such as a trace on a circuit board or antennas, etc.). When the “signal” is DC, it uses the entire conductor, with the same amount of current flowing in the center of each wire as on the outside of the wire…. Table 1 below shows how much conductor is used at 20 kHz, pretty much the highest audible frequency, and compares that to various wire sizes….

      “Table 1

      “Basis:
      Depth at 20 kHz = 18.4 mils (.0184 in.) Radius x 2 = 36.8 mils (.0368 in.) Diameter
      Amount of conductor used at 20 kHz, based on conductor size

      Conductors Diameter % of conductor used
      24 AWG 0.024 100% at 20 kHz
      22 AWG 0.031 100% at 20 kHz
      12 AWG 0.093 75% at 20 kHz
      10 AWG 0.115 68% at 20 kHz

      “You will notice that even for largest wire size, the difference between the inside and outside of a conductor is a few percentage points…”

      Hey, he’s only an expert; what does he know?

      1. LoL. Unless you an Dax argue about this regularly then I’d say you’re getting all fired up over nothing. On the other hand, where can I read more? You gave quotes but not actual source. And before you get upset; I really do want to read more, I’m not challenging your source.

          1. I’m going to guess that the thicker wire leaves a less dense wrapping; so given the limited space inside the housing it is more efficient size-wise to go with thinner parallel windings than a single thick wrapping.

        1. It’s the very same reason why you can can fit more sand than rocks into a glas. You can fit more square dia with more thin wires than with one thick. Just wind a motor yourself and you will know.

      2. You are correct, but skin effect is not the only frequency-related effect in play. Proximity effect is usually a bigger factor in windings.

        I don’t know much about these motors, so it may still be a moot point.

      3. Great information, and exactly what I was thinking when I read the “skin effect” claims above. How about you don’t be a dick about it next time? There is literally no need for that.

  2. FYI, those are extraordinarily crappy clones of EMAX redbottoms which are popular high-performing motors in the FPV racing community. The EMAX motors draw over 30A apiece at 4s/5s voltages with 5″ props so I’m not surprised he’s burning the windings with his setup.

    1. I actually never ran these motors one time before rewinding them. I simply wanted to show that for about $25 and a good bit of your time, you could actually make a really decent motor. Some that you could probably compare up to some $20 motors that are out there; and I’m talking $20 a piece.

      If you look at the Mr. Steele Silk motors, for instance, that TBS makes, they use the single strand winding method as well. Now the real Emax red bottoms use three strands of good quality enameled wire, that are wound around each tooth of their stators.

      Now I can’t go into all the science behind which is better, but I can look at who uses what. Everyone knows that Mr. Steele is going to use a motor that has his brand behind it, but he was a huge part of the development of those Silk motors, and doesn’t just use them because someone stamped his mustache to the side of them. Now he is probably the best freestyle pilot out there, for sure the most known. Racers, however, use motors like the Emax red bottoms. They say that the Silk motors do not have as much top end throttle, but they do have that nice, smooth low end throttle… … the kind that freestylers like. I happen to be at the freestyling stage for right now, so I prefer the single wound motor; not just because it’s the easier to handle, one strand windings, but also because the motors frequency and noise levels seem to be greatly reduced.

      Either way, I’m just a guy who likes to do things, just to see if he can do it. So that’s another BIG reason why I rewind motors; and, quite honestly, the MAIN reason. I’m a hobbiest, so I want to make as much of my hobby as I can.

      Anyways, I hope the vids did help some people; I certainly did enjoy learning about some of the science behind these things, and I strongly encourage anyone to go read up on this and rewind some motors for yourself… …just… …because you want to see if you can.

      Thanks,
      BRADtheRipper

      1. I am not picking here, but the old saying you can not polish a turd comes to mind. I would suspect if the motors are wound with crap quality wire, they cut corners or built to a cost on literally every other front as well, from bearings to magnets, to the adhesives they use, and even the materials the motors frame is made out of.

        That being said, it is very cool that you have taken the time learn how to rewind small motors. Have you considered applying some of what you have learned to home brewing alternators for alternative energy?

        1. I haven’t, but given the crazy stuff I’ve looked into since getting into this hobby, it mite not be too far away.lol

          As for what you said before… …Yes! These motors do suck on alot of other points. But, they’re all points that can be managed. Thinks like balancing for instance (I will be posting a video on my channel on how I go about that), they are not well balanced at all. The bearings did surprise me, however, but time will tell how they hold up. I’ve already had some pretty major crashes though, and they’re taking it like a champ…. …heck, I’ve already ordered a couple more sets:-P

        1. Wow. I’ve lost so much of my proper grammar since I graduated.lol. My grammar teacher would have freaked!;-P

          Thank you for pointing that out; I will never make that mistake again.

  3. I’ve got a bag of bad motors that could be revived with rewinding. I’ve rewound one motor. Given their price, I can’t see doing any more of them unless someone puts up plans for a 3D-printed motor winding machine.

      1. Has to be run by an Arduino or the haters would get left out of the comments, and where’s the fun in that?

        Unless, of course, the author misspells a word or gets a minor fact wrong. Then all hell will break loose. :P

        1. Don’t worry, we’ve got yawnhairy to pass the time while we wait for that.

          He committed a cardinal sin by actually quoting facts and figures. Even better, he did it without providing a link to the source for us to fight over :)

          1. Get your tights in a wad much, and often, do you? The answer for you is “Too much; too little.” Caffeine; meds. Fix it.

            Steve Lampen, “Understanding Skin Effect and Frequency”, The Right Signals Blog, belden.com.
            Posted on 13 Dec., 2012.

            Tear yourselves to pieces.

          2. “Get your tights in a wad much, and often, do you? The answer for you is “Too much; too little.” Caffeine; meds. Fix it.”

            Stupid Jerk. This is why non-techie types think we’re all antisocial assholes with no sense of humor.

    1. I know.lol. I don’t know that was happening, either. I was recording on a completely different device that was even plugged in. Working on a new mic setup, anyways.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s