Check if motor screws are touching motor winding

One common issue quadcopter pilots tend to have with mini quad motors are using screws that are too long, and they can make contact with the winding/wires inside the motor.

What happen when screws are touching motor winding?

Due to the fact that carbon fibre is conductive, if screws are touching motor winding it could cause short circuits. One or more of the following problems might happen:

  • Motor overheat – some motor(s) run hotter than others even COG is perfectly centered
  • Motor desync – no matter what PID numbers you try, you just can get rid of oscillation/vibration
  • Causing interference and noise to FPV video even if there is LC filter or filtering capacitor in the system
  • Motor Burn-out / smoke without any obvious reason

If the screws are too long it can also permanently damage the coils in the stator, so be aware!

How to check if screws are shorting motor winding?

Simply use a multimeter, and turn on Continuity Test Mode. It’s a handy feature on Multimeters and it makes a warning beep when a short circuit is detected (and display OL and Ω). Cheap Multimeter doesn’t have this feature but you can instead check for zero resistance for short circuits.

The Multimeter I use can be found here: Check out our list for more quadcopter tools.

Use one probe to test the motor screw

And use the other probe to test one of the 3 motor wires (just need to test 1 because all 3 motor wires are connected inside the motor). If the motor wires are soldered on the ESC, simply test the solder joints.

If the motor screw is touching winding, a short circuit should be detected. Repeat this for all the motor screws.

How to determine the correct length of screws?

Generally speaking, the length of screws is determined by the thickness of the carbon fibre arms. For 3mm arms, I use 5mm screws; for 4mm  arms, I use 6mm screws. If you don’t have shorter screws, you can also use 1 or 2 washers.

Another good way of checking is described here:

Check here for more useful tips on quadcopter building/flying.

13 thoughts on “Check if motor screws are touching motor winding

  1. Tobias

    Hello, I have recently purchased an Emax Babyhawk r 2″ and right away i noticed overheating on two motors. Only a short test hover. Both counter clockwise motors. i have checked all screws and none appear to be touching winding. I back out each screw and checked just in case there was something i was not seeing. The short still exists. The short exists through multiple screws on each motor. I removed the stack so only the four in one esc and motors attached. Still shorts on all screws.Then removed 4 in 1 from frame so only motors attached to frame because it appeared esc components were touching in spots. Still shorts at those screws. I have thoroughly checked all the soldering and seems clean. The short also exists through frame to esc solders on the same two motors only. I am completely stumped at this point. Any Ideas what could cause this? Thanks in advance.

  2. Ben

    If you have flickering OSD issues… this^^^ triple check your motor screws are not shorting.

    My OSD would start flickering as soon as I armed my quad and video would intermittently black out for 1 second. Finally found the issue when I armed on the bench and let the motors spool up. Motor2 was hot to touch after 5seconds with props off! Motor screw was shorting on winding’s.. This article finally resolved my flashing OSD issue. First quad ive built and the last time I make this mistake. Thank you!

  3. Fjmm

    I tightened the screws on my stock hglrc batman220 and at the end of my flight motors started stuttering and got really hot. When trying to arm again it flipped on me – then worked again for some LOS testing.. turned out on two motors the screws were touching.. and that with a bnf drone… well…


    I’ve noticed today that the flight controller screws also have an effect on the motors for some reason. My Motors were getting so hot I replaced every screw beneath the motors and still got very hot. It wasn’t until I change the flight controllers 4 screws to those plastic ones and now my Motors don’t even get hot after torture Punch outs. I think I’m the first person who’s ever had this happen to them LOL

    It was a rmrc newt frame with Emax 1106 motor and a F3 Magnum stack from a baby hawk r

    1. Oscar Post author

      The original screws were metal? My guess is the original screws were probably passing more vibration through to the FC.

  5. Bobby Fuller

    1st thanks for this resource and all the work helping the comunity. I checked this on my quad and am confident that i did not have the screws too long, however i realized my vtx antenna mount does ground to the frame and i can detect some resistance from the frame to my motor leads by way of the vtx mount. I am thinking this may be the cause of my desync and that i should insulate the antenna mount from the frame? The way i had mounted the antenna actually only grounded to the frame intermittently most likely during the hard turns which are when my desyncs occur. Thanks

  6. Kit Jones

    I did this test on my quad. I ended up removing all the screws and the motors from the frame entirely and still had continuity between the motor base and the motors wires!

    1. Oscar Post author

      how do you do the test if you have removed all the motor screws? LOL
      were you testing with the frame? then it probably means your electronics is somehow shorting the frame…

  7. Dave

    Another ill effect of this, it causes interference in video that can’t be removed by any ordinary means. No LC filter etc helps. I have found this by a very long and painful process.


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