Architecture

In order to be able to easily work with different steps of the piloting (like detection and control) the parts are connected together using ZMQ. This gives the benefit of easily stopping, changing and restarting parts of the chain without having to restart everything.

Currently there's 5 parts:

Image processing: Find X, Y, Z and rotation
Control: Control loops
Set-points: UI for setting set-points
Client: Connection to client for sending data
Visualization: Debugging using grapghs

Parts

Image processing

The first step to controlling the Crazyflie is to detect its position and angle. For this a camera can be used, currently we are using the IR/depth sensor on the Kinect 2 together with markers. The output of this step is the X/Y/Z coordinates in meters as well as the angle in degrees and weather or not the Crazyflie is detected.

Fields in ZMQ message:

Field	Type	Unit
pos	list of floats (x, y, z)	Meters
angle	float	Degrees
detect	boolean	N/A

Example of message

{
  "pos": [0.1, -0.1, 1.0],
  "angle": 35.2,
  "detect": true
}

Control

Once the position and rotation of the Crazyflie is know the control is used to correct the positional and rotational error from the set-point. Currently the Z axis has no position control, only velocity control (set to 0 m/s by default). By default the set-points are (x, y) = (0, 0), angle = 0 and velocity. The output of the control is the roll/pitch/yaw/thrust set-points for the Crazyflie.

Fields in ZMQ message:

Field	Type	Unit
ctrl	Dictionary	N/A

The ctrl dictionary should contain:

Field	Type	Unit
roll	float	Degrees
pitch	float	Degrees
yaw	float	Degrees/s
thrust	float	PWM

Example of message

{
  "ctrl": {
    "roll": 0.1,
    "pitch": 0.1,
    "yaw": 0.0,
    "thrust": 0.0
  }
}

Set-points

In order to do something more interesting than just hovering it's possible to send set-points to the control.

Fields in ZMQ message:

Field	Type	Unit
set-points	Dictionary

The set-points dictionary should contain:

Field	Type	Unit
roll	float	Meters
pitch	float	Meters
yaw	float	Degrees
velocity	float	m/s

Example of message

{
  "set-points": {
    "roll": 0.5,
    "pitch": -0.5,
    "yaw": 10.5,
    "velocity": 0.1
  }
}

Client

When the corrections have been calculated it's time to send them to the Crazyflie. This is done using the ZMQ input in the client. This will allow to switch between manual/automatic control while also getting feedback from the Crazyflie.

Visualization

In order to debug the control algorithms there's a basic graphing tool available.

Fields in ZMQ message:

Field	Type	Unit
name	string	Name of controller for data
data	dictionary

The data dictionary should contain:

Field	Type	Comment
P	float	P contribution to PID
I	float	I contribution to PID
D	float	D contribution to PID
E	float	Error
SP	float	The set-point
OUT	float	The output of the PID (P, I, D summed)

Example of message

{
  "name": "Roll",
  "data": {
    "P": 0.1,
    "I": 0.2,
    "D": 0.3,
    "E": 0.1,
    "SP": 0.4,
    "OUT": 0.6
  }
}

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