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Zero Tilt Critical Design Review. Frostburg State University Brett Dugan, Adam Rexroad , Kaetie Combs, Michael Stevenson, Daniel Gares , Mayowa Ogundipe , Tyler Lemmert , Jared Hughes, Sean Hughes, Andrew Huntley, Subhasis Ghosh , Derek Val- Addo , 11/27/2011. Mission Overview.
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Zero TiltCritical Design Review Frostburg State University Brett Dugan, Adam Rexroad, Kaetie Combs, Michael Stevenson, Daniel Gares, MayowaOgundipe, Tyler Lemmert, Jared Hughes, Sean Hughes, Andrew Huntley, SubhasisGhosh, Derek Val-Addo, 11/27/2011
Mission Overview • Mission Statement: Zero Tilt’s goal is to provide, for the first time, a stable environment throughout the flight of a Sounding Rocket via two concurrent objectives: • Tilt correction system • Despun platform system
Mission Overview • We plan to: • Counteract the platform spin • Orient the platform parallel to the earth’s surface at all times • Confirm the altitude reading using an accelerometer on our platform • We expect to prove that it is possible to correct spin, tilt, and determine the altitude based upon a level reference. • This could benefit any scientific experiment that requires stabilization in order to collect data.
Mission Overview: Theory and Concepts • The underlying theory and concepts: • negative feedback control systems • concepts of torque and centripetal force • Micro electromechanical systems (MEMS) • Real-Time Systems Theory (for multi-tasking)
Mission Overview: Mission Requirements • Mission Objectives: • Counter the spin of the rocket during flight. • Keep a level surface to earth using our conceptual design. • Prove successful by using the stored gyroscope output and the feedback from various motors. • Minimum success criteria • Our main goals as the Zero Tilt team is to receive results indicating that we achieved zero tilt for the flight of a sounding rocket.
Organizational Chart Faculty Advisor Dr. Mohammed Eltayeb Mentors Adam Rexroad Brett Dugan Project Manager Kaetie Combs Despun Platform Daniel Gares Tyler Lemmert Kaetie Combs Zero Tilt Platform Michael Stevenson Daniel Gares Andrew Huntley Data System Jared Hughes Sean Hughes MayowaOgundipe Derek Val-Addo Sensors Kaetie Combs Tyler Lemmert Andrew Huntley Michael Stevenson
Breakdown of Sub-Systems Despun Platform Zero Tilt Platform Data Systems Sensors Design: Daniel Gares Kaetie Combs Tyler Lemmert Gears: Tyler Lemmert Everybody will be involved with programming. Processors: Jared Hughes Sean Hughes Motors: MayowaOgundipe Val-Addo SubhasisGhosh Design: Daniel Gares Mike Stevenson Andrew Huntley Accelerometers: Kaetie Combs Tyler Lemmert Gyroscope: Mike Stevenson Andrew Huntley
Zero Tilt Con-Ops t ≈ 1.7 min Altitude: 95 km t ≈ 4.0 min Altitude: 95 km t ≈ 1.3 min Altitude: 75 km Apogee t ≈ 2.8 min Altitude: ≈115 km t ≈ 4.5 min Altitude: 75 km -use the position of the zero tilt plate as initial value for the gyroscope sensor. -switch to gyro input for zero tilt system. t ≈ 5.5 min Chute Deploys -All systems on -Initialize de-spun system -Initialize zero tilt system based on low-G acceler –ometer value. -Despun system prepares for initial spin up. t = 0 min t ≈ 15 min Splash Down
Expected Results • What we expect: • Using feedback analyze whether we were successful in despinning the platform. More than a one percent error in this section would provide too much error in the tilt system. Therefore we expect this system to perform near perfection. • Determine whether we were successful in keeping our platform level. (within a plus or minus 5 degree envelope)
De-Scopes • The scope of the project has changed slightly. • We no longer require a viewport for camera due to size constraints. • There was a minor change made to the design which will be discussed in the Mechanical Design elements section. • Due to processor obligations we will not be verifying the altitude with the Low-G accelerometer. • Our method for obtaining power has changed since the 9 volt batteries we were considering do not supply the continuous current necessary. Instead we will use a combination of AA batteries and 9 volts to supply various systems with the correct power.
Off RAMPS • If we run out of time or money, or main goal would become to concentrate on the despun system. • If the tilt system does not have the time to complete the tilt correction, we may have to institute a different system. Such as running two processors and two gyros, one for each motor. • If the intuition that the priority of motors in the tilt system is wrong, then we need to consider major program changes.
Mechanical Design Elements – Main Gear • Main Gear • 75 teeth • 12 Diametral Pitch • 6.25 inch Pitch Diameter • Pitch Diameter based off design constraints
Mechanical Design Elements – Drive Gear Drive Gear 15 teeth 12 Diametral Pitch 1.25 inch Pitch Diameter Pitch Diameter based off strict design thresholds 19
Mechanical Design Elements – Gear Testing • After cutting the gears, we will utilize one of the electric motors in the campus machine shop to test the durability and precision of the • With the electric motors we can test the durability of the gears by meshing them at high speeds as well as applying a load to the gears. With such testing we can find weak points as well as any points where destructive friction is present. • By testing the gears at max conditions, we will be assured that the gears will survive the ascent and splash-down. 21
Upper Center Shaft Lower Center Shaft Top Plate Spin Servo Slip Ring Tilt Platform Tilt Servo Tilt Bearing Gimbal Drive Motor • Spin Bearing Drive Motor Housing
Slip Ring Leads Main Gear Bearing Main Gear Drive Gear Support Posts Bottom Plate Shield
Design Changes • Since the PDR there has been one crucial design change. The way the design was laid out, there was no way to get power to the spin servo located on the gear. This is shown by the blue arrows in the diagram. When the power source reached the bearing, an additional slip ring would be needed to cross the bearing. To fix this we switched the raised the drive gear and put the servo on top of the gimbal. The servo now can get power through the slip ring shown by the red arrows. The only down side to this, is the weight of the servo will have to be countered to prevent wobble in the system.
Design Changes (continued) • The support poles that we are using to hold up the weight of the capsule above us has been changed to a different material. • The old material was 7075 Aluminum. The new material is Carbon Fiber. • The reason we have made this decision is to reduce the weight of the capsule.
Electrical Design Elements • Please show finalized block diagrams, state how many PCBs/breadboards you will use and what each one will do, sensors they will have • Show the schematics for each PCB/bb • I know they will be large and difficult to see in detail but I’m looking to see that they have been completed • Any changes to this system since PDR? • How does this affect your mission requirements? • What has been finalized that wasn’t at PDR? • Will you activate with command line or gswitch/LEDEX? • If command line, state how early you want to activate and show the schematic you have derived to comply with the User’s Guide reqs
Schematics Despun and Zero tilt on following slides
Software Design Elements Accelerometer 2 Digital to Analog Converter Motor Accelerometer 1 Microcontroller Power Supply Servo φ Slip Ring Microcontroller Gyroscope Servo θ
Major Functions • Timer – From system start: counts down from start to calculated stop time, ending all programs, powering down systems at end. • Low-g accelerometer – Used at system start, before lift off, to orient tilt system with respect to gravity. Provides Initialization point. • High-g accelerometers – Major despun input, measures rocket rotational acceleration to be opposed equal and opposite to by platform. • Motor0 – Despun motor that rotates platform to cancel out rocket’s rotation.
Major Functions (Continued) • Gyroscope – Major tilt input, measures tilt platform orientation with respect to x and y axis. • Motor 1 – Tilt motor (servo) rotates tilt platform from x axis measurements to keep tilt platform level relative to initialization point. • Motor 2 – Tilt motor (servo) rotates tilt platform from y axis measurements to keep tilt platform level relative to initialization point.
Chute Deploys Latitude vs Longitude plot of past Rockonflight, anlayzed on the following slide. Altitude plot of past Rockon flight, analyzed on the following slide.
Analysis of Past Flight Data • What this data tells us about flight: • Due to the Latitude vs Longitude plot we can conclude that the motor controlling the spin in the tilt system is of a low priority. This is because the maximum angle the rocket can change in the plane of concern is 45 degrees. • The altitude plot demonstrates that the majority of the change in the tilt will occur at the apex. It must be able to rotate 180 degrees. This means that the tilt motor will have priority over the spin motor due to the greater degree in change over a shorter time period. • As will be explained in the software section we believe our processer will be able to perform both the tilt and spin tasks without falling behind due to the small variations in spin coupled with the priority placed on tilt.
Analysis of Motor Demonstration • The programming of our processor has made considerable strides with a demonstration of the PVM capabilities of the motor. • The Motor was controlled using the program provided on the following slides. • We now are assured we can control the servo motors (motors 1 and 2) and are working toward accomplishing similar goals with the despun motor (motor 0), and the sensors.
Sample Code *Created:11/13/201111:32:10PM *Author:Mayowa&Derek */ //#define F_CPU 1000000 // If processor speed (or clock) changes, redefine #include "inc.h“ #include<avr/io.h> //#include <avr/interrupt.h> // include interrupt from compiler #include<util/delay.h>// Include Delay Functions from compiler
