Wireless Datalink Latency Test

Tested on 3 Type of Wireless Datalink
1.HKPilot Transceiver Telemetry Radio Set V2 (915Mhz)
2.XBee 2mW Wire Antenna - Series 2 (ZigBee Mesh)
3.XBee Pro 63mW RPSMA - Series 2B (ZigBee Mesh)

Both Xbee configured in Point-to-Point Mode

Tested by sending MAVLink Message ID #70 RC_CHANNELS_OVERRIDE 26 Byte in size

Host sendding 50 message and wait for Client to replay received message

MAV_TYPE , MAV_AUTOPILOT

MAV_TYPE describe type of micro air vehicles ex. Quadrotor,Hexrotor,Fixed Wing

MAV_AUTOPILOT describe type of autopilot(Flight Controller board) 

ex. PIXHAWK,ArduPilotMega / ArduCopter

Ref:

https://pixhawk.ethz.ch/mavlink/

Arducopter Flight Mode

In HEARTBEAT( Msg id 0) consist of Flightmode stored in custom_mode field
but in MAVLink document didn't define this field because it depend on

which flight controller software was using in this case Arducopter

it was define in file "defines.h"

// Auto Pilot modes
// ----------------
#define STABILIZE 0                     // hold level position
#define ACRO 1                          // rate control
#define ALT_HOLD 2                      // Altitude Hold
#define AUTO 3                          // Waypoint
#define GUIDED 4                        // Hold a single location from command
#define LOITER 5                        // Hold a single location
#define RTL 6                           // return to launch
#define CIRCLE 7                        // orbit around a single location
#define LAND 9                          // Landing
#define OF_LOITER 10                    // Hold a single location using optical flow sensor
#define DRIFT 11                        // DRIFT mode (Note: 12 is no longer used)
#define SPORT 13                        // earth frame rate control
#define FLIP        14                  // flip the vehicle on the roll axis
#define AUTOTUNE    15                  // autotune the vehicle's roll and pitch gains
#define POSHOLD     16                  // position hold with manual override
#define NUM_MODES   17

Ref:

https://github.com/diydrones/ardupilot/blob/master/ArduCopter/defines.h

Checking MAVLink Arm/Disarm Status

In HEARTBEAT( Msg id 0) consist of arm/disarm status but it not show directly

arm/disarm these stored in base_mode field describe by MAV_MODE_FLAG

HEARTBEAT Message Structure

MAV_MODE_FLAG

As you can see MAV_MODE_FLAG_SAFETY_ARMED 0b10000000 is arm/disarm bit

so we can write simple code to check arm/disarm status from base_mode like these

base_mode & MOTORS_ARMED) >> 7

output is 1 when armed, 0 when disarm

Ref :
https://pixhawk.ethz.ch/mavlink/

MAVLink MAV_DATA_STREAM from Board Ardupilot Mega 2

in MAVLink status from flight controller pack together in MAVLink Message
ex. Msg id #30 ATTITUDE consist of roll,pitch,yaw,roll speed,pitch speed,yaw speed

but in case of requesting these msg from flight controller we need to send request to flight controller for MAV_DATA_STREAM and frequency of these stream

MAV_DATA_STREAM  is collection of different msg id group together

MAV_DATA_STREAM 

(https://pixhawk.ethz.ch/mavlink/)

for Adupilot Mega 

RAW_SENSOR
(#27) RAW_IMU
(#29) SCALED_PRESSURE

EXTENDED_STATUS
(#1) SYS_STATUS
(#24) GPS_RAW_INT
(#42) MISSION_CURRENT
(#62) NAV_CONTROLLER_OUTPUT

RC_CH
(#35) RC_CHANNELS_RAW
(#36) SERVO_OUTPUT_RAW

POSITION
(#33) GLOBAL_POSITION_INT

EXTRA 1
(#30) ATTITUDE

EXTRA 2
(#74)VFR_HUD

EXTRA 3
(#2) SYSTEM_TIME

Ref :
https://pixhawk.ethz.ch/mavlink/

Sending single precision floating point over serial

Single Precision Float (32-bit) in IEEE754 standard
consist of sign bit(1 bit),exponent(8 bits) and fraction(23 bits)

http://upload.wikimedia.org/wikipedia/commons/thumb/e/e8/IEEE_754_Single_Floating_Point_Format.svg/2000px-IEEE_754_Single_Floating_Point_Format.svg.png

using typedef union for merge float,byte array into same location

typedef union {
 float floatingPoint;
 byte binary[4];
} binaryFloat;

binaryFloat temp;
temp.floatingPoint = 3.1416;
Serial.write(temp.binary[3]);
Serial.write(temp.binary[2]);
Serial.write(temp.binary[1]);
Serial.write(temp.binary[0]);

Install PyMAVLink Tool

PyMAVLink is Tool for Bindings MAVLink with Python and also provide number tools for data analysis MAVLink stream logs

Download

git clone git://github.com/mavlink/mavlink.git

For Ubuntu

sudo apt-get install python-matplotlib

After Install Mathplot install PyMAVLink

cd ~
mkdir -p src
cd src
git clone https://github.com/mavlink/mavlink/
cd mavlink/pymavlink
python setup.py install --user

After install PyMAVLink it will show path in status message.It may vary
example : $HOME/.local/lib/python2.6/site-packages/
Edit ~/.bashrc or ~/.bash_profile and add this line:

export PYTHONPATH="$HOME/.local/lib/python2.6/site-packages/:$PYTHONPATH"
export PATH="$HOME/.local/lib/python2.6/bin/:$PATH"

Reference
1.http://qgroundcontrol.org/mavlink/pymavlink
2.http://pixhawk.org/dev/pymavlink