Ground Control

1. Ground Control Jordan Hodge Jordan Lyford Wilson Schreiber

2. Contents • Background • Problem Statement • Solution • Mechanical • Azimuth • Elevation • Concepts • Static and Dynamics of System • Software • SatPC32 • Interpolation • Programming • Electrical/Controls • Position Sensing • Controller • System Diagram • Timeline • Responsibilities • Questions

3. Background • VTC developing CubeSat, transmits data • Continuing where previous groups have left off • Have to follow CubeSat to receive data • Existing 3-meter parabolic dish antenna • Low orbit satellite revolves around earth in minutes, seen for short time per orbit

4. Problem • Track a low orbit satellite such as a CubeSat from horizon to horizon in as little as 30 seconds 180°/30 seconds=6°/sec • Move a 3 meter satellite dish • 360° Azimuth (left/right) • 180° Elevation (up/down) • Interface to PC running SatPC32

5. Solution • Gears and motors, motor controllers • Freescale Coldfire 32-bit Microcontroller • Serial interface with SatPC32 simulating the functions of EGIS controls • Magnetic Encoders sense rotor/dish position • Use/Modify existing designs for elevation and azimuth control

6. Available Solution • EGIS- Current market solution • Cost: • Software $400 • Data Interface $1,100 • Hardware $2,700: EL-40°, AZ-180° • Extension $2,200: EL-90°, AZ-360° • Rotor Hardware Mount $400 • Satellite Dish Mount $400 • Total $7,200

7. Mechanical Concepts • Azimuth • A left to right angle measurement from a fixed point (north in navigation) • Elevation • Angle between the flat plane and the object in the sky (satellite).

8. Mechanical Design • Probable Azimuth/ Elevation Configurations: • Fork Mount • Same simple left-right/up/down characteristics • Allows the dish to go over backwards if it needs to.

9. Mechanical Design • Equatorial Mount: • The movement of the Azimuth (here the Declination Axis) makes an arc in the sky. • The Elevation (a) is set parallel to the earths axis of rotation. This system is much more accurate than the Fork and needs a much less complicated control system.

10. Mechanical Design Choosing a Solution: • Knowing the Satellite path ultimately determines what setup is best. • If the Satellite orbit is not a polar orbit, then the Equatorial Mount might be the best choice.

11. Mechanical Design Choosing a Solution: • If there is a polar orbit, or strange orbit all together: • The Dish with the Fork configuration may be the best choice.

12. Mechanical Concepts • Balance (RoM = Rm) • Reduce driving torque that the motor has to produce

13. Mechanical Design Statics and Dynamics: Key Points of Interest: • Dynamic Torque- The torque encountered by a system that is not only in motion, but accelerating. • Static Torque- The torque produced at constant velocity (rest or running). • Center of Mass- The mean location of all system masses. • Moment of Inertia- A measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation.

14. Mechanical Concepts • Worm Gears • Speed (Gear Ratio) • Torque • Modify existing designs

15. Mechanical Design Torque Calculations: • TStarting= KrunningTrunning Krunning = Running Torque Multiplier • To= [ 5250 x HP ] / N To = Operating or running Torque ( ft-lbs ) | • HP = Horsepower delivered by electric motor **Note: Values switch from N = Rotational velocity ( rpm)| metric to English Units 5250 = Constant converting horsepower to ft-lbs/minute and work/revolution to torque • T = [ N x WR2 ] / [ Ta x 308 ] T  = Time ( seconds )|N = Velocity at load (rpm ) Ta = Average Torque During start ( ft-lbs ) WR2 =  Rotating Inertia (lbs-ft3)|W =Weight (lbs) R = Radius of Gyration (ft2)| 308 = Constant derived converting minutes to seconds, mass from weight, and radius to circumference

16. Mechanical Design Methods of Determining and Modeling Physical System Parameters: • SolidWorks - COMSOL • Scaling system down and measure accordingly • Placement of Ballast • Forces Involved

17. SatPC32 • A free software available online for tracking satellites. Updates on screen and controls rotor to point to position satellite • Uses orbit of satellite and observer position • Many types of rotors to select for output • Uses Serial port or Parallel port on PC

18. Software- SatPC32 WinListen predicts path Screen Shot of SatPC32 in use

19. Programming Main Loop Interpolator Encoder Check Limit Check SatPC32

20. Programming • Read new position from serial • Stores values when they come in • Read actual position from encoders • Measure periodically • Decide where to turn, how fast • Always checking limit switches • If ever activated, stop motors New Serial? Read Serial Check Encoders? Read Encoders Controller (Set Outputs)

21. Interpolation 1 T 1 T G SatPC32 1 s 1 s Velocity Acceleration Data Summing Junction Operation

22. Interpolation

23. Interpolation

24. System Diagram - Electrical SatPC32 EL - Motor Controller RS232 AZ - Motor Controller Micro- controller Position Encoders Limit Switches 24

25. Electrical - Controller (Current)

26. Electrical - Position Sensing 1° step size = at least 9-bit res. 29 = 512 steps 360 deg/512 steps = .7o /step Magnetic Shaft Encoder 15,000rpm max Absolute Position Sensing Analog output from 10-bit DAQ 1024 Steps = 0.35o/step

27. System Diagram SatPC32 EL - Motor Controller RS232 AZ - Motor Controller Micro- controller Position Encoders Limit Switches 27

28. Timeline (Rev 1.0)

29. Areas of Reasonability Hodge CAD and FEA Torque Calculations/Measurements Ballast Implementation Lyford Sensors Mounting Motors Drive Mechanisms and Implementation Schreiber Project Manager Interpolation Implementation Communications Motor Controllers

30. Questions?