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Quad motor suddenly stopped/stuttered - my Quad flipped - was ok before

Quad motor suddenly stopped/stuttered - my Quad flipped - was ok before

My Quad suddenly flipped? Looked like one side flopped down. It seems OK but randomly flips? The flip looks like a motor just stopped or drops down.




Land - Cut throttle - don't fly - Motors won't just stop unless they are damaged/bent/wiring compromised by mis-use or crash impact or incorrect assembly ; so check for any hot ESC's immediately or any hot motor? Then take the copter back to your workshop. Be aware of the difference in pre-crash damage and post crash evidence - Check for : -

  1. Wires internally - are wound Delta - so each stator winding has a pair of much thinner inner wires ; one wire may be broken/pulled/bent internally in a motor, from a crash ;  or the wrong (too long) screws used ;too-long screws can cut the windings 
  2. use a DMM  https://www.carbonbird.com/products/uni-t-pen-sized-dmm to measure/check  
  3. the internal resistance Ω between all 3 input wires - 2 at a time - 3 readings should be identical 0.150Ω - what do you get Ω?
  4. the wires may have been overheated/melted and are shorting to the stator? Resistance from any wire to GND should be >250K Ω - thats around the resistance of your skin holding the motor when you test it.
  5. that sharp carbon has not cut the insulation of any ESC or motor wires - use a diamond file to dull down carbon edges 
  6. Wires GBC side - check to see if a lead wire has been broken - pulled - snapped off or weakened near the GBC side  - re-solder all 3 of the GBC if unsure - ALWAYS use FLUX paste to prevent a dry joint.
  7. Wires connection JST side - check you have not pulled out any of the ESC JST connectors in a crash
  8. The ESC's control motors and a motor hesitating can be an ESC driving it - so check that ESC to see if female GBC are broken from a crash - the ESC GBC must be firm on the pcb -  you may have bent/snapped the ESC outlets off the PCB from excess man-force - use INOX lube to ensure the GBC slide in without force
  9. Heat - RED motors running 5x4x3 or 6x4.5 props are limited to 5 secs of full power WOT per minute flown - high amps cause heat -  overheating a motor can cause the wires to melt and magnets to loose their magnetism
  10. BEC heat - For a small Knife size quad you only need one ESC BEC red wire connected after calibration and snyc of the 4 ESC - see above in "instructions" - you only need one BEC red wire
  11. Mechanical stoppage - if the motor is jammed - open it and check the magnets are not damaged or broken from a crash.  In some instances people have damaged their motors by letting FOD enter, something ferrous/magnetic get sucked inside by magnetic attraction force, from their work bench - then when they spin it up with the FOD spinning around inside  :(   (foreign object - damage) thereby cut the windings - be very careful with FOD - this means after a crash use a dry paint brush(or air nozzle)  to brush sand and dirt out of the motor BEFORE trying to run the motor.  Also untangle any grass wrapped around a motor in a crash - just using throttle after a crash can burn out your motor/ESC if it is not free to spin.  
  12. Check the shaft of the motors is not loose - grub screw(s) must tight - use Loctite
  13. Check the Prop & Prop adapter nut is actually tight
  14. If your LiPo was lower than you expected you may have reached VLC (voltage low cutout) on 1 ESC before you expected to - alway check your LiPo with a CELL meter before takeoff ; or in flight with a Cell Telemetry such as FVLSS
  15. NAZA and your props and motors are out of balance - it will flip after 4-5 mins because the IMU is being vibrated - go balance your motors and props

After making any changes and before flying do a full power test, ie do a hand maiden test - GND test for power - observe WOT limits - usually 5-10 secs on the ESC depending on the prop size

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