Flight Controller will not Arm
Various flight controllers will not arm for different reasons. Here are a few problems to look for when diagnosing your flight controller not arming.
Ensure the flight battery is fully charged. If your drone has a battery monitoring system, the flight controller may not arm when the flight pack voltage is below a certain threshold.
Compass & IMU Not Calibrated
The compass (magnetometer) can fall out of calibration if exposed to strong electromagnetic interference (EMI). Ensure the compass is far from batteries, motors, magnets, and other components which may create EMI.
Follow the calibration procedure for your flight controller to ensure your compass and IMU are properly calibrated before flight.
Bad GPS Signal
Some flight controllers equipped with GPS will require a good signal before arming to ensure they have a home location to return to in the event of a radio control system loss of signal (LOS). Leave your drone turned on but disarmed for a couple minutes with a clear view of the sky to ensure good GPS signal before flying.
Motors Spinning the Wrong Direction
Most flight controllers will spin the motors at slow speed when armed, ensure your propellers are spinning the correct direction.
Brushless AC Motors
To change the direction of rotation for a brushless motor, swap any two wires connecting the motor to the speed controller. This works by changing the order of phasing in the three-phase brushless motors.
Brushed DC Motors
Alternatively, if your drone uses DC motors (Parrot.AR and some smaller drones), first check that your propellers are installed on the correct motors. These motors are factory installed and are not likely to be spinning the wrong direction.
Drone Flips on Takeoff
Probably the most common cause of confusion among new pilots who have built their own drone, flipping on takeoff and be easy to fix but hard to diagnose. This is because there are a few different problems which can cause this to happen.
Motors Spinning Incorrect Direction
Flight controllers expect each motor to spin either clockwise or counter-clockwise, depending on which spot they are located. Check you flight controller manual or data sheet for motor spin direction notations and make sure your motors are matching what the flight controller is configured for.
Propellers Installed Incorrectly
Propellers should spin in the direction that forces air downward with the concavity of the blade curved down. Check that your propeller is spinning the correct direction and is not installed upside down.
Flight Controller Orientation
Some flight controllers allow you to mount them on their side, at an angle, or on their back. If you have mounted your flight controller in an alternative way, make sure your flight controller knows this by adjusting its configuration accordingly.
Radio System Failure
Antenna placement is key to success for any wireless system. Power, antenna quality and placement, and clear line-of-sight are all important to good signal strength.
Using an amplifier to increase your signal strength can lead to significant distance increase. However, these amplifiers saturate the receiver at close range. With the receiver used to such strong signal, any minor block in line-of-sight can cause the radio connection to fail.
Propeller Flies Off in Flight
As funny as it may sound, this does happen occasionally and can result in significant damage. Self tightening props are available from a few different suppliers are can ensure your propellers never come loose. Loctite Threadlocker can be used on prop securing bolts to prevent them from coming loose during flight.
Battery Life is Significantly Short
Batteries should be stored at room temperature, in the shade, with low humidity. High temperatures and humidity can damage the chemistry inside the cells, causing the battery to lose capacity resulting in shorter flight times.
Manufacturer Defective Batteries
Some manufactured batteries may be defective, we've seen this with a few Phantom 2 battery packs. Contact your manufacturer for a replacement if you feel your battery may be defective.