TIGER
Tactical Intelligent Groundbased Exploring Rover
Balrog information
General
The Balrog project started out 2009 as a collaboration between Linköping University and Saab Dynamics with the long term goal to develop an autonomous minesweeper. Over the years student groups have made different subprojects on the minesweeper. This year the purpose was to make the minesweeper capable of positioning itself and navigate in an indoor environment. poster can be found here
Positioning
The Positioning module uses dead reckoning to estimate the motion of the Balrog, and AprilTag detections to get direct position estimates. The dead reckoning estimates are fairly accurate with low noise, but they drift over time. The AprilTags do not drift, but there are certain uncertainties. Therefore, the Positioning module uses solely dead reckoning when no tag is visible. When there are tag detections, these are used to slowly compensate for drift that occurred since the last AprilTag detection. This was implemented using an Extended Kalman Filter.
Mapping
The Mapping module uses the LIDAR to implement a probabilistic obstacle map. The obstacle map is divided into grids sized 5 by 5 centimeters. Each grid has a probability that it contains of obstacles. This probability is decreased if the LIDAR beam traverses the grid without detection, and increased if there is a LIDAR detection in this grid. Eventually, most grids in the map converge to values close to 1 or 0. The mapping module also records which grids the Balrog has driven over and are considered explored.
Navigation
In order to explore the entire map, the Balrog needs to travel to new unexplored areas. The Navigation module uses the estimated position and the map in order to determine safe paths to areas that have not yet been explored. A safe path is one that never takes the Balrog closer than 35 cm to grids that exceeds a certain threshold for obstacle probability.
Control
The control module in the Balrog consists of two P-controllers, one that controls radial error and one that controls angular error. The reference is sent from the navigation module and fed to the controller via a coordinator function. Furthermore, the controller is tuned to turn first and then move straight to the reference position to avoid drift in the dead reckoning algorithm.
Documents
Our Group Members
Project leader: leading the project, is responsible for that the project's goals are reached, plan work and encourage the other team members to work eficient together.
Ingrid, Project Manager
Document manager: plan writing and verification of documents, responsible for that the different documents are available and are completed on time. Responsible for document templates and that these templates are used. also responsible for that version management takes place correctly. Note that the person is not responsible for write any of the documents by him/her-self.
Erik, Head of Documentation
Software Manager: responsible for ensuring that the code is assigned a code standard, is well structured, versioned and documented / commented.
Alfred, Head of Software
Test Manager: plans and synchronizes tests, is responsible for the test plan, test specifications and test protocols, match against requirments- specification. Also leads meetings on the tests to be performed.
Gustav, Head of Testing
Information Manager: responsible for the website, presentation, movie and so on.
Henric, Head of Information
Hardware Manager: ensuring hardware malfunctions are handled as quickly as possible.
Axel, Head of Hardware
Design manager: responsible for drawing up guidelines (coordinates, plans, etc.) for the design to be implemented for the different subsystems.
Joakim, Head of Design