Cheerson CX10 (RED) rate mode firmware employing integrated RF controller and stock TX

1. About

The Cheerson CX10 (RED) is a specific version of a quadcopter incorporating an ARM Cortex M0 MCU, Invensense MPU-6050 and Beken BK2423 (Nordic NRF24 clone). In 2014, Felix Niessen released alternative firmware for the device which allows it to be flown in rate mode using a standard PPM receiver. See the following page for details: http://www.rcgroups.com/forums/showpost.php?p=30045580&postcount=1.

This code builds upon Felix's work by enabling the device to be flown using the onboard radio, using the original controller (or even better, any device implementing the appropriate protocol). The radio driver was mostly derived from the Crazyflie project (see bitcraze.se), and the protocol implementation from the DevtiationTX project (http://www.deviationtx.com).

In making these changes I have attempted to change as little as possible in Felix's original code.

2. Building

Current binaries are provided in the /builds subdirectory, produced from both the Keil MDK-ARM toolchain, and the GNU ARM toolchain. The former is flight-tested, the latter is not.

A Keil uVision v5 project file is included to build/debug using MDK-ARM on Windows platforms (note that the code-size is such that the 32Kb-limited evaluation version may be used). A modification of the original Makefile is also included, which will build the firmware using a suitable GNU ARM toolchain under OS X, and presumably, Linux.

3. Programming

To program the firmware will require that you connect to the SWD pads on the CX-10 (RED) PCB, before using an appropriate programming tool. Note that the device is level-1 protected by default, and these option bytes must be cleared before programming. Alternatively, the embedded UART boot-loader may be used to program the device. See the original firmware thread for more details.

4. Operation

• Upon power-up the CX-10 will try to bind to a suitable TX, during this phase the LEDs will light alternately, flashing at a slow rate.
• When bound to a transmitter, but waiting for valid data, the LEDs will flash rapidly.
• Once valid data is received, the LEDs on one side of the device will illuminate, this indicates that the device is bound and disarmed
• Use a 'forward-flip' command on the stock TX to arm (internally setting Aux 1 high). On a Mode 2 transmitter this involves pressing the right stick then pushing full forwards. This must be performed at zero-throttle. All lights will illuminate when armed.
• Disarm using a 'backwards-flip' command on the stock TX. If multiple RF packets are lost, the device will disarm automatically.
• Under low battery conditions, the LEDs will blink.

5. Credits

• Felix Niessen's original work: http://www.rcgroups.com/forums/showpost.php?p=30045580&postcount=1.
• Bitcraze (for nrf24 driver): http://www.bitcraze.se
• DeviationTX (for their reverse engineering of the YD717 SkyWalker protocol): http://www.deviationtx.com

6. Porting/future development

• With little modification this code should also run on the Cheerson CX-11, which I believe also uses the Beken BK2423 RF chip.
• The CX-10 (BLUE/GREEN) PCBs also exist which use the XN297 RF chip and an alternative protocol. This firmware is not compatible with these versions, support could be added if the XN297 is air-compatible with the nrf24/Beken BK2423. Contact me if you have any information.