Connection API Overview

We have a Connection class that is really just an abstract class (depending on your background, you could also just think of it as an interface). For each communication protocol our API wants to support, there needs to be a protocol specific class that subclasses the Connection class and implements all of the required functions in that protocol.

So really, when we say protocol independent, it's the Drone facing side of things that is protocol independent. All the Drone attributes and functions that you would interact with when using UdaciDrone are protocol independent. We achieve this by having our own set of attributes, etc, so each protocol needs to correctly parse messages and send information to the drone accordingly.

For example, with the mavlink protocol, things like global position and velocity are in the same message, but we have it broken out as two different attributes (and effectively two different internal messages -> from the connection class to the drone).

Currently Supported Protocols

Currently, UdaciDrone supports the following communication protocols:

• the Mavlink Protocol used in the Dronecode community.

• cflib the API used for Bitcraze's crazyflie

This means that this API currently works with the Udacity Simulator any PX4 powered drone, and the crazyflie!.

There are some limitations on functionality of different drones, so not every connection will support all of the Drone functionality. At the moment, these are the control commands that are supported:

Control Commands	Simulator	PX4	Crazyflie
cmd_attitude()	yes	yes	yes
cmd_attitude_rate()	yes	yes	no
cmd_velocity()	yes	yes	yes
cmd_position()	yes	yes	yes
takeoff() and land()	yes	yes	yes

For those interested in extending the UdaciDrone API to support other protocols (e.g. Parrot or DJI), check down below for what methods need implementation!

Messages

In order to have Drone be independent on the communication protocol, UdaciDrone uses an internal set of message names and types to pass data between a connection implementation and the Drone.

Outgoing Message Types

Here is the set of available message names and the data they should carry.

Message Name	Data Type	Description
MsgID.STATE	StateMessage	changes in either the armed state of the drone or the control state (namely whether or not the drone is configured to take external commands from a script)
MsgID.GLOBAL_POSITION	GlobalFrameMessage	new GPS position of the drone
MsgID.LOCAL_POSITION	LocalFrameMessage	new local NED position of the drone
MsgID.GLOBAL_HOME	GlobalFrameMessage	new GPS home position of the drone
MsgID.LOCAL_VELOCITY	LocalFrameMessage	new velocity vector of the drone
MsgID.CONNECTION_CLOSED	n/a	connection to the drone has been terminated. This means that attributes will no longer be updated and all drone facing commands will not be executed by the drone.
MsgID.RAW_GYROSCOPE	BodyFrameMessage	new raw gyroscope values
MsgID.RAW_ACCELEROMETER	BodyFrameMessage	new raw accelerometer information
MsgID.BAROMETER	n/a	new barometric pressured based altitude information
MsgID.DISTANCE_SENSOR	DistanceMessage	new distance measurement information (e.g. from onboard sonar or stereo vision sensors)
MsgID.ATTITUDE	BodyFrameMessage	new attitude information

Abstract Methods

Here are all the abatract methods that must be implemented. Note that while it must be implemented, not all implementations have to be functional (e.g. they can just pass). The ones that are required to have functionality are marked as required in the table below:

Function Category	Required
Connection Management	yes
Vehicle Management	no
Vehicle Commands	no

Connection Management

These are the set of commands that handle the management of the connection.

• open() and close()
• start() and stop()
• dispatch_loop()

Vehicle Management

These are the set of commands that handle managing the vehicle state.

• arm() and disarm()
• take_control() and release_control()
• set_home_position()

Vehicle Commands

These are the set of commands that actually control the drone.

• cmd_attitude()
• cmd_attitude_rate()
• cmd_velocity()
• cmd_position()
• takeoff() and land()