keep your multi-rotor safe…

1.   Motor Wire Fracture

Cause
Vibration causes fatigue failure of the wire.
Solution
Normally fractures before the solder joint to the bullet connector or the ESC wire. 

Secure the joint well before and after the connector by wrapping tape around joint and around the motor arm. I use self-amalgamating tape which is non-adhesive (only sticks to itself).

Some motors are more susceptible to this problem than others. I used RC Timer 2830-14 750KV motors for many hours without a problem, they are a very smooth and powerful motor but the motor wires are thin and relatively fragile.
 

Well supported motor wire joint.
 

Self-amalgamating tape.
 

RC Timer motor.  Smooth and efficient, but weak wires.
 

Cause
Vibration
Solution
When assembling your multi-rotor, check all threaded joints are tight and apply non-permanent thread lock to all metal to metal threads.  Check motor grub screws, they hold the motor together but are often hard to spot and are often forgotten.  Balance the props and reduce vibration as much as possible.

3.   Low Battery Voltage

Cause
Flying beyond safe flight time.
Solution
Programme your timer for 80% of the maximum run time the battery can sustain. Use battery low voltage alarms and on screen displays to alert low voltage.

4.   FPV Feed Stops

Cause
Likely to be an intermittent connection into the video transmitter. If you use GoPro live feed out for FPV, be aware that when the GoPro battery is exhausted, the camera switches itself off leaving you with a blank video screen!
Solution
Pay attention to all video leads and joints.  Where possible solder video leads directly onto the video transmitter and other devices. Avoid connectors in the video feed where possible, they can be unreliable.  Keep video leads as short as possible.

5.   Propeller Failure

Cause
Using damaged or poor quality propellers.
Solution
Use good quality props, paying the extra can save your multi-rotor from an expensive crash.

Failed propeller.  This one failed in flight without warning.  It was almost new and had not been crashed or stressed previously. 

Genuine APC next to equivalent lower quality propeller.


6.   ESC Failure

Cause
Various causes but most likely is running all ESCs with their BEC wires intact. Excess current or voltage can also cause failure.
Solution
Use reliable ESCs and disconnect the BEC (red cable) from all but one of the ESCs. I use RC Timer and Hobbywing ESCs.

 
An example of a high quality ESC.

7.   Elctrical Intereference

Cause
High currents into and out of ESCs generate signifcant noise, which in severe cases can cause servos to loose sync, and receivers to experience reduced range.
Solution
Keep the RC receiver and its leads away from ESCs and high power cables.  Avoid routing receiver cables alongside and in contact with ESCs and their input and output wires.  

8.   RC Control is Lost

Cause
Flying beyond safe range, interference, poor antenna installation, poorly oriented or sighted TX antenna.
Solution
With multiple causes, the only safe thing to do is to carry out thorough range tests. This articleis a good starting point.  Keep video transmitter antennas and radio control receiver antennas as far apart as possible.  Use frequencies that are less likely to interfere with each other.  Keep the FPV video transmitter power to a minimum, overdriven video transmitters cause widespread and spurious harmonic interference.

9.   Connector Failure

Cause
Wrong choice of connector for the application, poor installation and wear and tear.
Solution
Any connector can and does fail. Make sure you use the right connector for the job and make sure it is terminated and installed correctly.

Servo leads are particularly vulnerable. The pre terminated ones are better quality, if you need to shorten or extend a lead, do so by soldering the lead.

Male “Deans Type” plugs do wear out. The springs become straight meaning they are not so securely connected from a mechanical and electrical perspective.

10.                     Solder Joint Failure

Cause
Cold solder joint.
Solution
Use a hotter soldering iron. Use the right type of solder and become expert at soldering. Multi-rotors have many solder joints, anyone of them could fail if not soldered correctly.

- Please add YOUR experience –

Comment below and I will add your ideas to this article.