Subsystem Description
Planning Subsystem
Path planning subsystem is essential for generating the desired trajectory for the drone to carry the package around the apartment. The subsystem takes the package location and platform location as input, and outputs the desired trajectory for navigation subsystem to follow. The components of the subsystem will be detailed further in the subsection below. Noted that our planning algorithm is based on the pre-built static map of the test location since we assume we have prior knowledge to the environment and there is no dynamic obstacles.
Navigation Subsystem
Navigation subsystem is responsible for maintaining reliable state estimation of the drone at all times, and following the path provided by planning subsystem. Navigation subsystem takes input from planning subsystem and creates control signals to track the desired waypoint or trajectory. First, navigation subsystem will take the IMU and GPS data from sensing subsystem and fuse them in DJI flight controller to get the accurate localization. Then the control command will be generated by a cascaded PID control loop, and sent to the flight controller through a DJI interface.
Manipulation Subsystem
Actuation mechanism – Electro-permanent-magnets
The manipulation subsystem is necessary for grasping the package which is to be transported. The end-effector to be used is an electro permanent-magnet for easy grasping and release of the block. The actuation of the electromagnet is carried out by our grasping algorithm which will communicate with the required sensors and send out the necessary signal for grasping and releasing the package. The electromagnets will be mounted at the base of the drone by means of a designed mechanical frame.
Package design
In order to facilitate the grasping of the package by the electromagnet, the package will be designed with a ferrous material on the surface of the package.
Control PCB
The self-designed PCB is used for efficient power distribution of the system.
Sensing Subsystem
The sensing subsystem consists of several sensors responsible for the operation of the drone. The sensors include:
Inertial Measurement Unit (IMU)
An IMU is used for determining the acceleration and attitude of the drone which is used as a feed-back for pose estimation and tracking.
Proximity sensor
The proximity sensor is used as feedback while picking and dropping the package.We will be using a “Miniature DC Metallic-Object Proximity Switch”. It senses the distance between a metal surface and the sensor itself, and since the package will have a metal surface for the magnetic gripper to be effective, this is the most suitable proximity sensor for us.
Camera
The camera is used for AprilTag and platform detection. We are using the Intel RealSense D435i camera.
Perception Algorithm
The perception algorithm is employed to detect the presence of the AprilTag on a package or platform, and return the drone’s pose transformation relative to the AprilTag, to perform visual servo.
Visual Servoing
To accurately grasp the block, the system depends on the visual servo to approach the package or platform while maintaining a steady pose. In the package servo case, the drone will end up right on top of the package and in range for the gripper to activate and grasp the package. In the platform servo case, the drone will fly to a safe distance from the platform and drop the package.
Software & Simulation
The software subsystem involves the simulation and server that receive and manage the delivery requests and communicate with the drone.
The Platform
The platform is where the package is dropped. It consists of a self-designed mechanical frame bounding a net which is used to prevent damage to the package while dropping. The platform is attached to the balcony where the delivery has to take place. It has a positional beacon attached to it which serves the system with positional location for delivery.