BlueROV-8: Functions to Drive the Vehicle

Some functions like goto function or speed setting function are limited because they are GPS dependent. GPS is not available for an underwater robot. If I change the vehicle mode to "ALT_HOLD", the arm_and_takeoff function will work:

from dronekit import connect, VehicleMode, LocationGlobal, LocationGlobalRelative
from pymavlink importmavutil # Needed for command message definitions
import time
import math
vehicle =connect('/dev/ttyACM0', wait_ready=True)
 
defarm_and_takeoff(aTargetAltitude):
    print"Arming motors"
    # Coptershould arm in GUIDED mode
   vehicle.mode = VehicleMode("ALT_HOLD")
   vehicle.armed = True
    print"Taking off!"
   vehicle.simple_takeoff(aTargetAltitude) # Take off to target altitude
    whileTrue:
       print " Altitude: ",vehicle.location.global_relative_frame.alt      
       if vehicle.location.global_relative_frame.alt>=aTargetAltitude*0.95:
           print "Reached target altitude"
           break
       time.sleep(1)
 
arm_and_takeoff(5)
print("Completed")

Battery: Voltage=0.0,current=None, level=None.

Building ArduPilot for Pixhawk/PX4 on Mac with Make (Download the ArduCopter in the BlueROV)http://ardupilot.org/dev/docs/building-px4-with-make-on-mac.html

In the terminal:

brew tap PX4/homebrew-px4
brew update
brew install genromfs
brew install gcc-arm-none-eabi
brew install gawk
sudo easy_install pip
sudo pip installpyserial
mkdir -p px4
cd px4
git clone --recursive https://github.com/ArduPilot/ardupilot.git

Set the current path to:/Users/apple/px4/ardupilot/ArduCopter

make clean
make pix-v2

https://www.bluerobotics.com/forums/topic/autonomous-operation/

Commands to change a value are not guaranteed to succeed (oreven to be received) and code should be written with this in mind. For example, the code snippet below polls the attribute values to confirm they have changed before proceeding.

vehicle.mode = VehicleMode("GUIDED")
while not vehicle.mode.name=='GUIDED' and not vehicle.armed and not api.exit:
    time.sleep(1)
vehicle
    print " Getting ready to take off ..."

vehicle.armed =True

Observing attribute changes:

Callbacks are added using Vehicle.add_attribute_listener() ortheVehicle.on_attribute()decorator method. The main difference between these methods is that onlyattribute callbacks added with Vehicle.add_attribute_listener() canbe removed (see remove_attribute_listener())

• The observer callback function is invoked with thefollowing arguments:
• self - the associated Vehicle. This may be compared to a global vehicle handle to implement vehicle-specific callback handling (if needed).
• attr_name - the attribute name. This can be used to infer which attribute has triggered if the same callback is used for watching several attributes.
• value - the attribute value (so you don’t need to re-query the vehicle object)

The code snippet below shows how to add (and remove) a callback function to observe changes in Vehicle.location.global_frame using Vehicle.add_attribute_listener(). The two second sleep() is required because otherwise the observer might be removed before the the callback is first run.

 #Callback to print the location in globalframes. 'value' is the updated value
 def location_callback(self,attr_name, value):
    
     print "Location (Global): ", value
# Add a callback `location_callback` for the `global_frame`attribute.

 vehicle.add_attribute_listener('location.global_frame', location_callback)

# Wait 2s so callback can be notified before the observer is removed

 time.sleep(2)

# Remove observer - specifying the attribute and previouslyregistered callback function
 vehicle.remove_message_listener('location.global_frame', location_callback)

Note: The example above adds a listener on Vehicle to for attribute name 'location.global_frame'You can alternatively add (and remove) alistenerVehicle.locationfor the attribute name 'global_frame'. Both alternatives are shown below:

vehicle.add_attribute_listener('location.global_frame', location_callback)
vehicle.location.add_attribute_listener('global_frame', location_callback)

The example below shows how you can declare an attribute callback using the Vehicle.on_attribute() decorator function.

 last_rangefinder_distance = 0
@vehicle.on_attribute('rangefinder')
 def rangefinder_callback(self, attr_name):
     #attr_name not used here.
     globallast_rangefinder_distance
     if last_rangefinder_distance == round(self.rangefinder.distance, 1):  
         return
     last_rangefinder_distance = round(self.rangefinder.distance, 1)
     print " Rangefinder(metres): %s" % last_rangefinder_distance

The examples above show how you can monitor a single attribute. You can pass the special name (‘*‘) to specify a callback that will be called for any/all attribute changes:

# Demonstrate getting callback on any attribute change
def wildcard_callback(self, attr_name, value):
    print " CALLBACK: (%s): %s" % (attr_name,value)
print "nAdd attribute callback detecting any attribute change"
vehicle.add_attribute_listener('*', wildcard_callback)
print " Wait 1s so callback invoked before observer removed"
time.sleep(1)
print " Remove Vehicle attribute observer"
#Remove observer added with `add_attribute_listener()`
vehicle.remove_attribute_listener('*', wildcard_callback)

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