Ground ControlJordan HodgeJordan Lyford

Wilson Schreiber

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Contents Background Problem Statement Solution Mechanical

› Azimuth› Elevation› Static and Dynamics of System

Software› SatPC32› Interpolation› Programming

Electrical/Controls› RS232› Controller

Timeline Responsibilities

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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

Existing solutions› EGIS Bi-axial antenna positioning system

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Problem

Track a low orbit satellite such as a CubeSat from horizon to horizon in as little as 30 seconds180°/30 seconds=6°/sec

Move a 3 meter satellite dish› 360° Azimuth (left/right) › 180° Elevation (up/down)

Interface to PC running SatPC32

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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

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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

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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.

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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.

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Mechanical Concepts

Azimuth› A left to right angle

measurement from a fixed point (north in navigation)

Worm Gears› Speed (Gear Ratio)› Torque› Modify existing designs

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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.

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Mechanical Design

Choosing a Solution:

If there is a polar orbit, or strange orbit all together:

The Dish with the Fork configuration may bethe best choice.

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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.

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Mechanical Design

Physical Dimensions:

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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

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Mechanical Design

Alternatives to Predict Key Points of Interest:

SolidWorks- Flow Works Scaling system down and measure accordingly

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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

Software- SatPC32

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Screen Shot of SatPC32 in use

WinListen predicts path

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System Diagram

Micro-controller

EL - Motor

ControllerAZ -

Motor Controlle

r

Limit Switches

RS232

SatPC32

PositionEncoders

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Programming

Read new position from serial port› 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

Controller(Set

Outputs)

New Serial

?

Check Encoder

s?

ReadSerial

Read Encoders

Questions?