Mechanical DesignTo help people with walking disabilities regain their mobility, I sought to create an omni-directional drive to give the users the same type of mobility they once had. This is a motorized drive system that can move in any direction, including side to side and pivoting. I also thought about safety, especially because people will sometime make driving mistakes, so I decided to design a collision avoidance system to keep the users safe and avoid damages around the house. I also recognized that driving a mobility system in tight spaces, going through doorways and narrow hallways is difficult, so I decided to design a system that will automatically drive in tight spaces, allowing the users to switch between the normal driving and autopilot on a push of a button.
3D Rendering of the Drive System
3D Rendering of an Omni-Directional Wheel Module
This FEA Analysis Report was performed using Autodesk Inventor Professional 2015.
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I used Autodesk Inventor Professional 2015 to design my whole project in 3D. The design phase took just under 6 months to complete. Some of the unique features of this particular drive system are:
I have created manufacturing drawings for all of the components. The drawing above is just one example of the many drawings created for this project.
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Electronics and ProgrammingFor the main robot controller, I used the BeagleBone Black because it provided sufficient processing power and was able to provide PWM outputs to 8 motors and process the analog inputs from the absolute encoders and the distance sensors. This computer-on-a-chip device runs a modified version of Linux Debian 7, providing for maximum flexibility in a compact and cost effective package.
The motor controllers used are the Talon SR’s from Cross the Road Electronics, controlled by a PWM (pulse width modulation) signal from the BeagleBone Black. For an omni-directional drive system, it is important to get an accurate feedback on the angle of the wheel. I therefore decided to use absolute encoders because they maintain the angle value of the drive module even after the robot is powered off, so they do not require calibration at startup. The functional diagram to the right shows the main components used to drive one wheel module. 
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For programming, I decided to build my own robot engine using Java 7.
The program uses 3 different threads: the robot thread, the controls thread, and the UI thread. It was important to create multiple threads to be able to keep the robot cycle time low for improved performance and a responsive user interface. This allowed me to simultaneously be able to update sensor data to my graphs while ensuring that all of the encoders and sensors were read and processed as fast as possible. A unique feature of this project is its intuitive control system driven by a 6-axis 3D mouse. The 3D mouse provides the translation and rotation feedback on the x, y, and z axis. Based on those values, the robot can intuitively change between driving modes. For example, if the user wanted to spin on a dime, all he would have to do is twist the controller in the desired direction. The control system will automatically sense that, and will change from the omni-directional driving mode to a spin around its axis mode. As soon as the user releases the twisting action, the robot automatically changes back to omni-directional driving and drives in the direction pointed by the controller proportionally to the force applied on the controller. 
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