Integrating a Braking System and User Interface into an Automatic Belay March 24, 2016 A Major Qualifying Project Report Submitted to the faculty of WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirements for the Degree of Bachelor of Science By: Michelle Gagnon (Robotics Engineering) Submitted to: Fred Looft, Professor SE and ECE Worcester Polytechnic Institute This report represents work of WPI undergraduate students submitted to the faculty as evidence of a degree requirement. WPI routinely publishes these reports on its web site without editorial or peer review. For more information about the projects program at WPI, see http://www.wpi.edu/Academics/Project i Abstract The device discussed in this report was designed to enable a climber to have more control over their experience when using an automatic belay device. This project was broken into three parts including the device used to brake the belay webbing, a control system used to receive and manage wireless belay command signals, and a Graphical User Interface. A prototype of the braking device was created and is described. The report also discusses the design decisions behind the model and prototype, and provides suggestions for making a stronger, more robust prototype of the system. In addition, this paper discusses the programming behind the control system that is used to handle wireless signals and to host the GUI. Finally, suggestions for future work on the project are proposed that would result in a stronger, sturdier and more robust system. ii Table of Contents Abstract ......................................................................................................................................................... ii Table of Figures ............................................................................................................................................. v Table of Tables .............................................................................................................................................. v 1 Introduction .......................................................................................................................................... 1 1.1 Problem statement ....................................................................................................................... 1 2 Background ........................................................................................................................................... 3 2.1 Belay Devices ................................................................................................................................ 3 2.2 Major Stakeholders ....................................................................................................................... 5 2.3 Needs Analysis .............................................................................................................................. 7 2.4 Wireless Systems .......................................................................................................................... 8 3 Functional Design .................................................................................................................................. 9 3.1 Project Requirements ................................................................................................................... 9 3.2 Project Subsystems and Interfaces ............................................................................................. 10 3.2.1 User input device ................................................................................................................ 11 3.2.2 Braking Device ..................................................................................................................... 13 3.2.3 Wireless Communication Module....................................................................................... 15 3.2.4 Control System .................................................................................................................... 16 3.2.5 Graphical User Interfaces .................................................................................................... 16 4 Detailed Design ................................................................................................................................... 18 4.1 Braking System Electro-Mechanical Design ................................................................................ 18 4.1.1 Force Sensing with Extension Spring and Limit Switch ....................................................... 18 4.1.2 Clamping Mechanism .......................................................................................................... 20 4.2 Braking System Command Center .............................................................................................. 21 4.2.1 Reading the Limit Switch ..................................................................................................... 22 4.2.2 Reading Wireless Commands from Serial ........................................................................... 23 4.2.3 Controlling the Servo .......................................................................................................... 23 4.3 Control System Program Design ................................................................................................. 23 4.3.1 Wireless Commands for Braking Controller ........................................................................ 24 4.4 Creating a GUI using Python and Tkinter .................................................................................... 25 4.4.1 Creating and Implementing a User Log-In .......................................................................... 25 iii 5 Suggestions for Future Work .............................................................................................................. 27 5.1 Braking Device Design ................................................................................................................. 27 5.2 Working with Multiple Systems .................................................................................................. 27 5.3 GUI Implementation ................................................................................................................... 28 6 Conclusion ........................................................................................................................................... 29 References .................................................................................................................................................. 30 Appendix A: Breaking System Code ............................................................................................................ 31 Appendix B: Code to Take Inputs from Serial in Python ............................................................................. 32 Appendix C: Code to Create Sign-In GUI ..................................................................................................... 33 Appendix D: Code for Control Center ......................................................................................................... 34 iv Table of Figures Figure 2.1: From left to right Gri-Gri (Auto-lock, gear), ATC (Manual, gear), and Munter Hitch (Knot)....... 3 Figure 2.2: Auto Belay Device ....................................................................................................................... 4 Figure 2.3: Onion Diagram of Stakeholders .................................................................................................. 6 Figure 3.1: Subsystem Block Diagram ......................................................................................................... 11 Figure 3.2: SpeakUp Board by Mikroe ........................................................................................................ 12 Figure 3.3: Ratchet Strap Example .............................................................................................................. 13 Figure 3.4: Braking Device Functional Block Diagram ................................................................................. 14 Figure 3.5: Rope Tension Sensor Example .................................................................................................. 15 Figure 3.6: XBee Device and Mounting Module ......................................................................................... 16 Figure 4.1: Front View of Assembled System ............................................................................................. 19 Figure 4.2: Simple Diagram of System with Variables ................................................................................ 20 Figure 4.3: Open (left) and Closed (right) Clamping Mechanism................................................................ 21 Figure 4.4: Gear Ratio and Servo Used to Drive Clamping Mechanism ...................................................... 21 Figure 4.5: Interface Model for Braking System Controller ........................................................................ 22 Figure 4.6: Code Snippet for Reading Digital Pin ........................................................................................ 23 Figure 4.7: Control System Flow of Information for Multiple Systems ...................................................... 25 Figure 4.8: Sign In Window Made Using Tkinter ......................................................................................... 26 Figure