background problem statement solution mechanical › azimuth › elevation › static and...
Post on 19-Dec-2015
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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
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
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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