1. Design of a Hexapod for the Phased Experimental Demonstrator MSc Mechatronic Engineering Mr. Frank Janse van Vuuren Stellenbosch University Supervisor: Dr. Y. Kim Co-Supervisor: Prof. K. Schreve

2. OBJECTIVE 2

3. Objective  Design a Hexapod mount to position a 3.69 m antennae at the PED (Phased Experimental Demonstrator). The PED is used as a testbed for the KAT project and also used to educate and train students. Project Activities :  Model  Simulation  Controller Design  Construct a scale model  Programme a Graphical User Interface  Verify the performance capabilities 3

4. Hexapod Mount (Stewart Platform)  Positioning mechanism consisting of base and platform.  Linear actuator legs.  Leg lengths change length to alter the orientation of the platform. 4 Figure 1: Stewart Platform [1]  Stewart_Platform_up_down_2.wmv Stewart_Platform_up_down_2.wmv

5. Alternative Alt-Azimuth Mount is currently widely used in telescopic positioning. Advantages of the Hexapod Mount:  High Load Carrying capacity  High Stiffness  Precise positioning Accuracy Disadvantages  Small workspace  Complex control  Singularities 5 Figure 2: Altitude- Azimuth Mount [2] (top) Figure 3: Hexapod Mount [3] (bottom)

6. Presentation Overview 1. Dynamics 2. Hexapod Model 3. Controller 4. Graphical User Interface (GUI) 5. Testing 6. PED Hexapod 6 Hexapod Model ControllerGUITesting PED Hexapod Dynamics

7. Dynamic Forces 7 f ti,z f ti,y f ti,x BiBi TiTi e2e2 e1e1 didi f bi,y f bi,x f bi,z x y z m 2 g C (piston) m 1 g C (cylinder) B1B1 B2B2 B3B3 B4B4 B5B5 B6B6 T1T1 T4T4 T2T2 T3T3 T5T5 T6T6 x y z u v w mTmT m2m2 m1m1 DynamicsControllerGUITesting PED Hexapod Hexapod Model

8. Base Joint 8 Hexapod Model ControllerGUITesting PED Hexapod Dynamics Plain Spherical Bearing Bush Housing Angular Range

9. Platform Joint 9 Hexapod Model ControllerGUITesting PED Hexapod Dynamics

10. 10 Hexapod Model ControllerGUITesting PED Hexapod Dynamics Model Design

11. Manufactured Components 11 Hexapod Model ControllerGUITesting PED Hexapod Dynamics

12. Platform Joint 12 Hexapod Model ControllerGUITesting PED Hexapod Dynamics

13. Linear Drive 13 Encoder Motor Housing Hexapod Model ControllerGUITesting PED Hexapod Dynamics

14. 14 Hexapod Model ControllerGUITesting PED Hexapod Dynamics Hexapod Model

15. 15 Hexapod Model ControllerGUITesting PED Hexapod Dynamics Controller Program Flow Controller PCB Controller Schematics

16. GUI Programme Flow 16 Initialize program Connect to Controller Send Data to Controller Controller Connected? Data Received? Display Data USER INPUTS Set Leg Lengths Read Leg Lengths Calibrate Enable Legs Stop Wait for Controller Data or User Input Controller Busy? GUI Hexapod Model ControllerTestingGui PED Hexapod Dynamics

17. Hexapod Model System 17 Controller Hexapod Power Source Computer Hexapod Model ControllerGUITesting PED Hexapod Dynamics

18. Error Radius 18 X-bus Sensor Controller Orientation Sensor Hexapod Model ControllerGUITesting PED Hexapod Dynamics Simulation ResultsTesting Apparatus

19. 19 Hexapod Model ControllerGUITesting PED Hexapod Dynamics Parameter Value Error Radius Due to Encoder Resolution>0.028° Maximum Speed3.7°/s Maximum Viewing Angle120° Cost EstimationR160 000 PED Hexapod

20. Future Work Construction of PED Hexapod PED Hexapod used as a research tool to develop singularity free tracking algorithms 20

21. References 21 1. Tsai, Lung-Wen. Robot Analysis: the mechanics of serial and parallel manipulators. NY : John Wiley & Sons, 1999. 0-471-32593-7. 2. Jangan, Manisha. Giant Metrewave Radio Telescope. [Online] January 20, 2005. [Cited: June 18, 2008.] http://www.gmrt.ncra.tifr.res.in/. 3. Kingsley, Jeffrey S., Martin, Robert N. and Gasho, Victor L. A Hexapod 12m Antenna Design Concept for the MMA. Taipei : s.n., 1997.

22. 22