DJI Naza V2 C++ PWM Interface

A C++ interface for the Raspberry Pi to interact with the DJI Naza V2 Flight controller. The project is a diy solution for people who don't have access to dji's libraries but still need the accuracy/ advantages of the Naza V2. It allows the user to control the Naza V2 via. a Raspberry by installing this library and write their own program using the methods supplied by the library. The library does that by emulating the PWM signals which actually/ normally come from a receiver to control the Naza V2(drone). To generate the PWM signal it uses the PWM/Servo Driver - I2C interface - PCA9685. The lib consists of two different section, manual and autonomous. Manual offers standard functions to control the drone, which are immediately executed. Autonomous provides functions which require a serial connection(to decode gps, gyro/ acc information) to the Naza V2 to fly for example to differnt waypoints(is highly experimental and partly unfinished, continued here).

Demonstration video can be watched here

Webinterface

The Webinterface is built on top of this project and uses the tools/ binaries from this project to access the Naza. It's based on PHP and Js Ajax, the PHP scripts directly access the binaries compiled by this project and can be used to test the lib.

Pwm Reference

The Naza V2 can adapt to different controll interfaces PWM, PPM and S-Bus are possible. Here I will focus on PWM, since that is the one I chose to use. It is the simplest, most reliable and easiest to emulate.

PWM input signal:
Hz: 50
Pulse: 0.5-2.5 ms

To generate a proper signal you need to calculate the relative pulse length. For that you need two other values which represent the overall pulse period and the pulse length. The difference of both mustn't be greater than the period itself. The period is decomposed in 4096 values which is equivalent to a 12 Bit accuracy (2^12). So the difference of both of those values mustn't be greater than 4096. This relative pulse length can be calculated by multiplying the Hz rate, the period and the pulse length together.

50Hz:

    50Hz* 0.0005s * 4096 = 102 (relative pulse length)

    50Hz* 0.0025s * 4096 = 512 (relative pulse length)

To control the Naza V2 we need a relative pulse length that reaches from 102-512 (depends on calibration).

Setup

Installation

• git clone https://github.com/MrGrimod/dji_naza_interface_c-.git
  Clone the project

• cd dji_naza_interface_c-
  

• make
  Build the library's share object file.

• make install
  Install config and Headers to include dir

Configuration & Calibration (required)

To make the library work you need to configure the library's config file (/etc/naza/pwm_config.txt)
Each variable (left,middle,right) defines the transmitters throttle endpoint stick location. To find them you need to open your Naza Assistant and go to Rc section where you have to recalibrate the Naza for your transmitter. Next, start examples/mod_pwm/ and find the fitting values for the throttle endpoints of left, right and "middle" value for each channel and add them to pwm_config.

Usage

After successful installation you can include the header files #include "libnaza/naza_interface_manual.h"
in your own project and link libnaza by using -lnaza and -lwiringPi flag.

Wiring

Connect the PCA9685 over I2C with your raspberry pi and the Naza V2 input channels with the different output channels of the PCA9685.

Examples

Usage:

Build: ./reinstall
Start: ./<tool>

• flight_sim
  Command Line tool to test and debug the functionallity of basic functions of the project.
  

CMD commands:
forward,back,throttle,left,right,tright,tleft,flm,neutral,arm

• mod_pwm
  Command Line tool to manually set relative PWM pulse lengths for certain channels
  

• recalibrate
  Tool to calibrate the Naza V2. Start the calibration process in the Naza V2 Assistant Software, then start the recalibration tool and wait until it's done setting the endpoints for all channels.
  

• read gps
  Tool to decode Serial GPS coming from the Naza GPS module. It inputs the data in a continuous stream of data.

Dependencies

• bcm2835
  wget http://www.open.com.au/mikem/bcm2835/bcm2835-1.49.tar.gz
tar xvfz bcm2835-1.49.tar.gz
cd bcm2835-1.49
./configure
make

sudo make install
  

• WiringPi

Serial Communication with Naza GPS

Switching to AMA0 (old serial interface)

The BCM2837 on the Raspberry Pi3 , Pi3B+, PiZeroW has 2 UARTs (as did its predecessors), however to support the Bluetooth functionality the fully featured PL011 UART was moved from the header pins to the Bluetooth chip and the mini UART made available on header pins 8 & 10.

This has a number of consequences for users of the serial interface.

The /dev/ttyAMA0 previously used to access the UART now connects to Bluetooth. The miniUART is now available on /dev/ttyS0. In the latest operating system software there is a /dev/serial0 which selects the appropriate device so you can replace /dev/ttyAMA0 with /dev/serial0 and use the same software on the Pi3 and earlier models.

Unfortunately there are a number of other consequences:-

The mini UART is a secondary low throughput UART
intended to be used as a console. The mini Uart has the following features:
• 7 or 8 bit operation.
• 1 start and 1 stop bit.
• No parities.
• Break generation.
• 8 symbols deep FIFOs for receive and transmit.
• SW controlled RTS, SW readable CTS.
• Auto flow control with programmable FIFO level.
• 16550 like registers.
• Baudrate derived from system clock.
There is no support for parity and the throughput is limited, but the latter should not affect most uses.

There is one killer feature "Baudrate derived from system clock" which makes the miniUART useless as the this clock can change dynamically e.g. if the system goes into reduced power or in low power mode.

For the GPS Data input stream we need a reliable and fast serial communication interface, so we need to disable miniUART and switch back to the old ttyAMA0 interface. To do so follow these steps:

1. To disable bluethooth and set /dev/ttyAM0 to real UART (as before) Edit the file /boot/config.txt and add the following line at the end :
   

   dtoverlay=pi3-disable-bt 1 dtoverlay=pi3-disable-bt

2. Stop the bluetooth service with sudo systemctl disable hciuart and reboot.
   

3. To switch bluetooth to software UART and set /dev/ttyAM0 to real UART (as before) Keep in mind that this one will remain possible software problem on bluetooth (software UART), but not on Serial (Hardware)
   Edit the file /boot/config.txt and add the following line at the end :
   

   dtoverlay=pi3-miniuart-bt core_freq=250 1 2 dtoverlay=pi3-miniuart-bt core_freq=250

4. Edit the file /lib/systemd/system/hciuart.service and replace /dev/ttyAMA0 with /dev/ttyS0
   

5. If you have a system with udev rules that create /dev/serial0 and /dev/serial1 (look if you have these one), and if so use /dev/serial1 .

Then reboot

Library functions

Manual:

• fly_throttle:
  Sets the drone throttle for all motors.
  Corresponds to channel T

• fly_forward:
  Lets the drone fly forward
  Corresponds to channel E

• fly_back:
  Lets the drone fly backwards
  Corresponds to channel E

• fly_left:
  Lets the drone fly sideways left
  Corresponds to channel A

• fly_right:
  Lets the drone fly sideways right
  Corresponds to channel A

• fly_turn_right:
  Lets the drone turn right
  Corresponds to channel R

• fly_turn_left:
  Lets the drone turn left
  Corresponds to channel R

• set_neutral:
  Sets all stick positions to neutral.

• recalibrate:
  Moves all sticks to throttle endpoints

• set_flight_mode:
  Sets the flight mode. You can select between: gps, failsafe, selectable Corresponds to channel U

• arm_motors:
  Arms the motors

Autonomous:

• auto_liftoff
  Lets the drone take off.

• auto_landing
  Lets the drone land.

• fly_to_gps_pos
  Lets the drone fly to a certain position.

• turn_to_deg
  Lets the drone fly turn to a certain position.

• auto_hover
  Lets the drone hover.