Embedded Motion Control 2017 Group 3 / Maze Design

This page is part of the Embedded Motion Control Group 3 of 2017.

Changes after Corridor challenge

This page is about the design for the Maze challenge. After the corridor challenge we were left with a number of issues:

1.) The turning was not very robust outside of the simulation and would fail often

2.) During the last few days of testing and coding before the corridor challenge we made rapid changes to the codebase without properly refactoring so we had incurred some technical debt.

3.) Keeping the PICO aligned to the wall during navigation was a problem

To solve there problems we decided to go with a new approach for the motion control. We discarded a big part of the code and refactored the rest to make the code easyier to change and maintain.

World Interpreter

We removed the wall/path detection and replaced it with what we call the "world interpreter" whose function it is to take all the sensor data and do all the processing required for the rest of the code. For example dead end detection for the door supervisor and calculating the angle to the nearest obstacle pint for the wallfollowing function in the motion supoervisor. All the processed data is stored in the world model which is a struct that gets distributed to the supervisors in the main loop. This is clearly visible in the short (82 lines) and well documented main.cpp[1].

Virtual Circle

The pledge algorithm that we use require the motion controller to define 2 states where PICO either has to follow a wall on either the left or right side (the user can decide and we chose for right) or where PICO has to drive straight ahead in a direction until it meets an obstacle.

For following the wall we designed a method that we call the virtual circle following. The method looks if the nearest obstacle point is in an outer "sensing circle", if this it true it will attempt to allign the detected point to a set distance r at PICOs right hand side (-90 deg. from the front facing direction). It does this by applying 2 PID controllers. One for the distance r and one for the angle theta (shown in picture)

This method does not require any additional code for taking turns when following an obstacle (wall) because it will keep the nearest point on the right side while moving forward (shown in images)