Crazyflie 2.X Python cfclient connects but does not communicate

Update to latest cfclient

Follow this guide to update to the latest cfclient.

Update to latest firmware

Follow this guide to update firmware in the Crazyflie

Crazyflie 2.X Android client does not connect

Check compatibility

Check that your Android device supports Bluetooth smart/low energy and your Android version is equal or greater than 4.4. Also check the compatibility list .

Do not pair

Do not pair your Android device to the Crazyflie 2.X like other Bluetooth devices. Just connect directly through the app. If you have paired it already, unpair it and try again.

Crazyflie 2.X does not take off

Make sure propellers are mounted correctly

Check that the propellers are mounted on the correct motor. Check each propeller to see if it is a clock wise or a counter clock wise turning propeller and mount it according to the detailed view below.

Crazyflie 2.X propeller mounting

Make sure propellers are mounted with right side up

Check that you can see a little “ring” on every propeller’s center otherwise the propellers are mounted upside down.

Crazyflie 2.X flies badly

Check center of gravity

Check that the Crazyflie 2.X is well balanced and adjust the battery and connector until it is. Holding the Crazyflie 2.X in the small “ears” is a easy way to test it.

Balance propellers

Vibration is a normal cause for decreased flight performance. Try balancing the propellers using this guide.

Check that all propellers turn freely

Check for hair stuck in any of the propellers/motors. It can also be that one of the motors are worn out or damaged. This is a bit harder to check. It is most likely the motor towards the direction the Crazyflie 2.X takes off. Try to listen for strange sounds when blowing on the propeller attached to it.

Check for bent motor axis

Check each motor axis if it is bent as it causes vibration. This can be done by either applying a bit of thrust from a client or by blowing on the propeller and looking at the axis from above. If it is bent it might be possible to straighten it with a pair of pliers. If that doesn’t work the motor needs to be replaced.

Crazyflie is bricked

The Crazyflie hangs when started, all the LEDS stay on or fully off or does it not start at all when pressing the power button.

If the Crazyflie does not start it might be related to power, that the firmware in the flash memory is corrupt or adjusted firmware that is faulty.

Check the battery

Make sure the battery is charged. Connect the Crazyflie to a USB charger and turn it on to charge the battery.

Power via USB

Connect the Crazyflie to a USB charger and turn it on. If this works the firmware is OK.

Re-flash the firmware

Flash the latest stable release of the firmware to the Crazyflie to make sure it is good. Use the recovery mode instructions for flashing a new release of the firmware.

Force into bootloader mode

If the firmware of the NRF processor is corrupt it might not be possible to enter bootloader mode as described in the Getting started with the Crazyflie 2.X guide. In this case the procedure to enter bootloader mode is:

  1. Unplug the battery
  2. Hold the power button and plug in the battery again
  3. Release the power button after 2 seconds

It should now be possible to flash the latest stable release to the Crazyflie.

Crazyflie's blue LEDs flicker when entering bootloader

The first Crazyflie 2.1 batches (2018-2019) does not contain the correct USB power settings in the bootloader which will prevent the system to start if no battery is attached. See nRF issue #35. Workaround is to plug in a battery when bootloading.