Troubleshooting Guide

Select a topic below to troubleshoot your 3DR copter.

Motors Don’t Arm (Double-Flashing Yellow Status

LED)

The double-flashing yellow status LED indicates that the drone is failing one of the pre-arming safety checks. 

The autopilot performs these checks before each flight to ensure that all systems are operating correctly. To 

see the specific error, connect to a ground station and view the primary flight data display.

GPS Error:

The most common pre-arm safety check error is due to insufficient GPS signal. Your drone requires a strong 

GPS signal to fly accurately. There are two important measurements of GPS signal required to pass the prearm check: the GPS lock (the strength of the signal) and the HDOP (the accuracy of the signal).

A lock is obtained when the GPS receives positioning data from multiple satellites. You can see the status of 

the lock and the number of communicating satellites on the controller’s flight data display. (For IRIS+ and X8+ 

only, press and hold the controller’s DN button to view the flight data display.)

IRIS+ and X8+ Controller Flight Data

Five or more active satellites will produce a strong GPS lock. It is possible for the GPS to acquire a lock with 

less than five satellites, but there is a greater chance of losing the lock during flight with fewer satellites. 

Generally, a clear of the sky will produce the highest satellite count, but it can also depend on your specific 

location and the time of day. Use this tool to see how many satellites are predicted for your flying location.
Horizontal dilution of precision (HDOP) is a measure of the accuracy of the GPS signal, as opposed to the 

strength of the signal as measured by the lock. To pass the pre-arm check, HDOP must be below a specified 

value to ensure accurate GPS measurements. A high HDOP can result from the positions of the satellites, 

obstructions such as buildings and mountains, atmospheric effects, electromagnetic interference from radio 

towers or onboard radio transmission equipment, or the time of day. You can receive an HDOP error even with 

a high number of satellites and an active lock.

To improve GPS signal, move to a more open space with a clear view of the sky and wait for the GPS to 

acquire an active lock or a lower HDOP.

RC Calibration Error:

If the pre-arm check failure specifies an RC calibration error, use Mission Planner to re-perform RC calibration.

If you do not see any response in the calibration screen from moving the controller sticks, ensure that both the 

controller and the copter are powered and the copter is connected to the Mission Planner. If you still do not

see any response, follow the instructions in Reference 1. (Ardupilot.com tutorial) to rebind the controller with

its receiver. Do not perform this process unless you see an RC calibration error and no response from the 

controller when attempting to re-calibrate using Mission Planner.

Turn on the controller, and power the copter normally. Now check the RC receiver (pictured below); if you don’t

see a green LED, follow these steps to re-bind the receiver to the transmitter.

1. Disconnect the battery from the copter, and turn off the controller. Ensure that both the on/off switches on 

the back of the controller are set in the down position. Now hold down the F/S button on the back of the 

controller, and turn the controller on while holding down the button.

Controller
2. Hold down the F/S button on the receiver, and connect the battery while holding down the button.

Receiver

3. Disconnect the battery, and turn off the controller. Then turn on the controller and re-connect the battery. 

You should see a green light on the receiver indicating that it is connected to the controller. If so, reattempt

the preflight steps.

Motors Spin at Different Rates

If the motors spin at different rates, you will need to re-calibrate the ESC by following this video tutorial

(http://youtu.be/sKBVadRDcEw).
Unexpected or Inconsistent Flight Behavior

Step 1: Examine your copter to ensure that the components are undamaged. Verify that the propellers are in 

the correct order of SF and SFP as shown below. Check that all propellers are attached with the writing on the 

propellers facing the sky.

X8+ Propeller Order

Step 2: Press the safety button until blinking red, and connect the copter to Mission Planner or APM Planner

on your ground station computer, and connect the copter to MavLink by selecting Connect. Select Initial Setup 

and Mandatory Hardware, and perform an accelerometer calibration as shown in the video tutorial 

(http://youtu.be/M-gJK_hefkI). Next, perform a compass calibration as shown in the video tutorial

(https://www.youtube.com/watch?v=oD9Z9IR2TNU&feature=youtu.be).
Reference 1

Radio Calibration

Autopilot calibration: calibrate your autopilot to work with your RC transmitter and receiver.

• 1 Prerequisites

• 2 Prepare transmitter

• 3 Calibrate

1 Prerequisites

Before performing setup, ensure that:

• The vehicle is completely built to flight condition.

• Firmware has been loaded onto the autopilot.

• Autopilot is connected to APM Planner and connected to Mavlink.

• RC transmitter and receiver are bound and powered.

• Propellers are removed.

2 Prepare transmitter

Turn on the transmitter, and verify that it is in airplane mode (APM needs airplane mode regardless of the platform type being 

piloted) and all trims are centered.

For Mode 1 transmitters, the left stick will control pitch and yaw, the right stick will control throttle and roll. For Mode 2 

transmitters, the left stick will control throttle and yaw; the right stick will control pitch and roll. For either type of transmitter, the 

transmitter’s three-position switch should be attached to channel 5 and will control flight modes.

3 Calibrate

Select Radio Calibration to teach your autopilot to work with your RC transmitter and receiver. Select Start Calibration to begin. 

Read the instructions in the following prompt and select OK.
Select Start Calibration to begin. Move both sticks in the largest circle possible so that they reach their complete range of motion. 

Move the Ch 5 and 6 toggle switches through their range of positions.

Your transmitter should cause the following control changes:

Channel 1: low = roll left, high = roll right.

Channel 2: low = pitch forward, high=pitch back.

Channel 3: low = throttle down (off), high = throttle up.

Channel 4: low = yaw left, high = yaw right.

Watch the red bars on the screen to ensure that the correct controls activate for each stick movement. If the red bars move in the 

opposite direction that you’re moving the sticks, you will need to reverse the channel on your transmitter. Select End Calibration

when complete. Resulting normal values are around 1100 for minimums and 1900 for maximums.