Autonomous flight
The simple_offboard
module of the clover
package is intended for simplified programming of the autonomous drone flight (OFFBOARD
flight mode). It allows setting the desired flight tasks, and automatically transforms coordinates between frames.
simple_offboard
is a high level system for interacting with the flight controller. For a more low level system, see mavros.
Main services are get_telemetry
(receive telemetry data), navigate
(fly to a given point along a straight line), navigate_global
(fly to a point specified as latitude and longitude along a straight line), land
(switch to landing mode).
Python usage
You need to create proxies for services before calling them. Use the following template for your programs:
import rospy
from clover import srv
from std_srvs.srv import Trigger
rospy.init_node('flight') # 'flight' is name of your ROS node
get_telemetry = rospy.ServiceProxy('get_telemetry', srv.GetTelemetry)
navigate = rospy.ServiceProxy('navigate', srv.Navigate)
navigate_global = rospy.ServiceProxy('navigate_global', srv.NavigateGlobal)
set_position = rospy.ServiceProxy('set_position', srv.SetPosition)
set_velocity = rospy.ServiceProxy('set_velocity', srv.SetVelocity)
set_attitude = rospy.ServiceProxy('set_attitude', srv.SetAttitude)
set_rates = rospy.ServiceProxy('set_rates', srv.SetRates)
land = rospy.ServiceProxy('land', Trigger)
Unused proxy functions may be removed from the code.
API description
TIP
Omitted numeric parameters are set to 0.
get_telemetry
Obtains complete telemetry of the drone.
Parameters:
frame_id
– frame for valuesx
,y
,z
,vx
,vy
,vz
. Example:map
,body
,aruco_map
. Default value:map
.
Response format:
frame_id
— frame;connected
– whether there is a connection to FCU;armed
- drone arming state (armed if true);mode
– current flight mode;x, y, z
— local position of the drone (m);lat, lon
– drone latitude and longitude (degrees), requires GPS module;alt
– altitude in the global coordinate system (according to WGS-84 standard, not AMSL!), requires GPS module;vx, vy, vz
– drone velocity (m/s);pitch
– pitch angle (radians);roll
– roll angle (radians);yaw
— yaw angle (radians);pitch_rate
— angular pitch velocity (rad/s);roll_rate
– angular roll velocity (rad/s);yaw_rate
– angular yaw velocity (rad/s);voltage
– total battery voltage (V);cell_voltage
– battery cell voltage (V).
TIP
Fields that are unavailable for any reason will contain the NaN
value.
Displaying drone coordinates x
, y
and z
in the local system of coordinates:
telemetry = get_telemetry()
print(telemetry.x, telemetry.y, telemetry.z)
Displaying drone altitude relative to the ArUco map:
telemetry = get_telemetry(frame_id='aruco_map')
print(telemetry.z)
Checking global position availability:
import math
if not math.isnan(get_telemetry().lat):
print('Global position is available')
else:
print('No global position')
Output of current telemetry (command line):
rosservice call /get_telemetry "{frame_id: ''}"
navigate
Fly to the designated point in a straight line.
Parameters:
x
,y
,z
— coordinates (m);yaw
— yaw angle (radians);yaw_rate
– angular yaw velocity (will be used if yaw is set toNaN
) (rad/s);speed
– flight speed (setpoint speed) (m/s);auto_arm
– switch the drone toOFFBOARD
mode and arm automatically (the drone will take off);frame_id
– coordinate system for valuesx
,y
,z
,vx
,vy
,vz
. Example:map
,body
,aruco_map
. Default value:map
.
TIP
If you don't want to change your current yaw set the yaw
parameter to NaN
(angular velocity by default is 0).
Ascending to the altitude of 1.5 m with the climb rate of 0.5 m/s:
navigate(x=0, y=0, z=1.5, speed=0.5, frame_id='body', auto_arm=True)
Flying in a straight line to point 5:0 (altitude 2) in the local system of coordinates at the speed of 0.8 m/s (yaw is set to 0):
navigate(x=5, y=0, z=3, speed=0.8)
Flying to point 5:0 without changing the yaw angle (yaw
= NaN
, yaw_rate
= 0):
navigate(x=5, y=0, z=3, speed=0.8, yaw=float('nan'))
Flying 3 m to the right from the drone:
navigate(x=0, y=-3, z=0, speed=1, frame_id='body')
Flying 2 m to the left from the last navigation target:
navigate(x=0, y=2, z=0, speed=1, frame_id='navigate_target')
Turn 90 degrees clockwise:
navigate(yaw=math.radians(-90), frame_id='body')
Flying to point 3:2 (with the altitude of 2 m) in the ArUco map coordinate system with the speed of 1 m/s:
navigate(x=3, y=2, z=2, speed=1, frame_id='aruco_map')
Rotating on the spot at the speed of 0.5 rad/s (counterclockwise):
navigate(x=0, y=0, z=0, yaw=float('nan'), yaw_rate=0.5, frame_id='body')
Flying 3 meters forwards at the speed of 0.5 m/s, yaw-rotating at the speed of 0.2 rad/s:
navigate(x=3, y=0, z=0, speed=0.5, yaw=float('nan'), yaw_rate=0.2, frame_id='body')
Ascending to the altitude of 2 m (command line):
rosservice call /navigate "{x: 0.0, y: 0.0, z: 2, yaw: 0.0, yaw_rate: 0.0, speed: 0.5, frame_id: 'body', auto_arm: true}"
TIP
Consider using the navigate_target
frame instead of body
for missions that primarily use relative movements forward/back/left/right. This negates inaccuracies in relative point calculations.
navigate_global
Flying in a straight line to a point in the global coordinate system (latitude/longitude).
Parameters:
lat
,lon
— latitude and longitude (degrees);z
— altitude (m);yaw
— yaw angle (radians);yaw_rate
– angular yaw velocity (used for setting the yaw toNaN
) (rad/s);speed
– flight speed (setpoint speed) (m/s);auto_arm
– switch the drone toOFFBOARD
and arm automatically (the drone will take off);frame_id
– coordinate system forz
andyaw
(Default value:map
).
TIP
If you don't want to change your current yaw set the yaw
parameter to NaN
(angular velocity by default is 0).
Flying to a global point at the speed of 5 m/s, while maintaining current altitude (yaw
will be set to 0, the drone will face East):
navigate_global(lat=55.707033, lon=37.725010, z=0, speed=5, frame_id='body')
Flying to a global point without changing the yaw angle (yaw
= NaN
, yaw_rate
= 0):
navigate_global(lat=55.707033, lon=37.725010, z=0, speed=5, yaw=float('nan'), frame_id='body')
Flying to a global point (command line):
rosservice call /navigate_global "{lat: 55.707033, lon: 37.725010, z: 0.0, yaw: 0.0, yaw_rate: 0.0, speed: 5.0, frame_id: 'body', auto_arm: false}"
set_position
Set the setpoint for position and yaw. This service may be used to specify the continuous flow of target points, for example, for flying along complex trajectories (circular, arcuate, etc.).
TIP
Use the navigate
higher-level service to fly to a point in a straight line or to perform takeoff.
Parameters:
x
,y
,z
— point coordinates (m);yaw
— yaw angle (radians);yaw_rate
– angular yaw velocity (used for setting the yaw to NaN) (rad/s);auto_arm
– switch the drone toOFFBOARD
and arm automatically (the drone will take off);frame_id
– coordinate system forx
,y
,z
andyaw
parameters (Default value:map
).
Hovering on the spot:
set_position(frame_id='body')
Assigning the target point 3 m above the current position:
set_position(x=0, y=0, z=3, frame_id='body')
Assigning the target point 1 m ahead of the current position:
set_position(x=1, y=0, z=0, frame_id='body')
Rotating on the spot at the speed of 0.5 rad/s:
set_position(x=0, y=0, z=0, frame_id='body', yaw=float('nan'), yaw_rate=0.5)
set_velocity
Set speed and yaw setpoints.
vx
,vy
,vz
– flight speed (m/s);yaw
— yaw angle (radians);yaw_rate
– angular yaw velocity (used for setting the yaw to NaN) (rad/s);auto_arm
– switch the drone toOFFBOARD
and arm automatically (the drone will take off);frame_id
– coordinate system forvx
,vy
,vz
andyaw
(Default value:map
).
TIP
Parameter frame_id
specifies only the orientation of the resulting velocity vector, but not its length.
Flying forward (relative to the drone) at the speed of 1 m/s:
set_velocity(vx=1, vy=0.0, vz=0, frame_id='body')
set_attitude
Set pitch, roll, yaw and throttle level (similar to the STABILIZED
mode). This service may be used for lower level control of the drone behavior, or controlling the drone when no reliable data on its position is available.
Parameters:
pitch
,roll
,yaw
– requested pitch, roll, and yaw angle (radians);thrust
— throttle level, ranges from 0 (no throttle, propellers are stopped) to 1 (full throttle).auto_arm
– switch the drone toOFFBOARD
mode and arm automatically (the drone will take off);frame_id
– coordinate system foryaw
(Default value:map
).
set_rates
Set pitch, roll, and yaw rates and the throttle level (similar to the ACRO
mode). This is the lowest drone control level (excluding direct control of motor rotation speed). This service may be used to automatically perform aerobatic tricks (e.g., flips).
Parameters:
pitch_rate
,roll_rate
,yaw_rate
– pitch, roll, and yaw rates (rad/s);thrust
— throttle level, ranges from 0 (no throttle, propellers are stopped) to 1 (full throttle).auto_arm
– switch the drone toOFFBOARD
and arm automatically (the drone will take off);
The positive direction of yaw_rate
rotation (when viewed from the top) is counterclockwise,pitch_rate
rotation is forward, roll_rate
rotation is to the left.
land
Switch the drone to landing mode (AUTO.LAND
or similar).
TIP
Set the COM_DISARM_LAND
PX4 parameter to a value greater than 0 to enable automatic disarm after landing.
Landing the drone:
res = land()
if res.success:
print('drone is landing')
Landing the drone (command line):
rosservice call /land "{}"
WARNING
In recent PX4 versions, the vehicle will be switched out of LAND mode to manual mode, if the remote control sticks are moved significantly.