Drexel RockSAT Critical Design Review • Kelly Collett • Christopher Elko • Danielle Jacobson • December 8, 2011
PDR Presentation Contents • Section 1: Mission Overview • MissionStatement • Mission Requirements • Mission Overview • Concept of Operations • Expected Results
PDR Presentation Contents • Section 2: Design Description • Off-ramps • Physical Model • Mechanical Design • Electrical and Software Design • Section 3: Prototyping and Analysis • Mechanical Subsystems • Electrical Subsystems • Mass Budget • Power Budget
PDR Presentation Contents • Section 4: Manufacturing Plan • Mechanical Elements • Electrical and Software Elements • Section 5: Testing Plan • PEA Subsystem • EPS Subsystem • VVS Subsystem • Total System Testing
PDR Presentation Contents • Section 6: Prototype Risk Assessment • PDR Risk Walk-down • Top CDR Risks • Section 7: User’s Guide Compliance • Section 8: Project Management • Organizational Chart • Schedule • Budget • Sharing Logistics
Mission Overview Drexel RockSat Team 2011-2012
Mission Statement • Develop and test a system that will use piezoelectric materials to convert mechanical vibrational energy into electrical energy to trickle charge on-board power systems.
Mission Overview • Demonstrate feasibility of power generation via piezoelectric effect under Terrier-Orion flight conditions • Determine optimal piezoelectric material for energy conversion in this application • Classify relationships between orientation of piezoelectric actuators and output voltage • Data will benefit future RockSAT and CubeSAT missions as a potential source of power • Data will be used for feasibility study
Concept of Operations • G-switch will trip upon launch, activating all onboard power systems • Batteries power Arduino microprocessor and data storage unit • Data collection begins • Vibration and g-loads on piezo arrays create electric potential registered on voltmeter • Current conditioned to DC through full-bridge rectifier and run to voltmeter • Voltmeter output recorded to internal memory • Data gathered throughout duration of flight
Concept of Operations • Data acquisition and storage will enable researchers to monitor input from multiple sources • XY-plane vibrational energy • Z-axis vibrational energy • Researchers will determine if amount of power generated is sufficient for the power demands of other satellites • Include visual verification of functionality • Use energy from piezo arrays to power small LED • Onboard digital camera will verify LED illumination
Expected Results • Piezoelectric beam array will harness enough vibrational energy to generate and store voltage sufficient to power satellite systems • Anticipate output of 130 mV per piezo strip, based on preliminary testing. • Success dependent on following factors: • Permittivity of piezoelectric material • Mechanical stress, which is related to the amplitude of vibrations • Frequency of vibrations
Design Description Christopher Elko
Subsystem Identification • EPS – Electrical Power Subsystem • Includes Arduino microprocessor, g-switch, accelerometers, voltmeter, battery power supply, and all related wiring • STR – Structural Subsystem • Includes Rocksat-C decks and support columns • PEA – Piezoelectric Array Subsystem • Includes piezoelectric bimorph actuators, cantilever strips, mounting system, rectifier, and related wiring • VVS – Visual Verification Subsystem • Includes digital camera, LED, and all related wiring
Off-Ramps VVS • Main concern: Camera activation • Relaying the camera to the g-switch for activation after launch will likely prove difficult. • If this cannot be achieved on time, the VVS will be removed from the payload. • This will drop the mass of the payload significantly, and will require additional ballast in its place.
Physical Model Accelerometer Array Power Supply Microcontroller G-Switch Bridge Rectifiers Flight Decks Camera Standoff Supports Verification LED Piezo Arrays
Canister Fitment Canister Partner’s Space Allowance 10.0” 4.313”
Mechanical Design STR Clear Acrylic Flight Decks Stainless Fasteners 8-32 threadx 3/8” long QTY = 10 ¼” thick 9.29” dia. QTY = 2 Aluminum Standoffs Fifth standoff column included to provide support for EPS electronics mountedto top deck. 5/16” hexx 2 ¼” long QTY = 5
Mechanical Design PEA Piezoelectric Strip Fasteners PZT Ceramic 40 mm x 10 mm 5 mm thick Support Block Aluminum Cantilever 2 ¼” x ½” 0.040” thick Different orientations account for vibrations in multiple planes.
PEA Design continued Mounted to Lower Deck Use 4-40 x 3/8” Screws
Electrical Design LED LED Piezoelectric Power Output Piezoelectric Power Output Rectifier Rectifier Camera Low-G Accelerometer Arduino Microcontroller High-G Accelerometer High-G Accelerometer Low-G Accelerometer G-Switch Power Supply
Electrical Design continued Piezoelectric Wire Output LED Camera EPS Power Supply
Electrical Elements To Bridge Rectifier • Powered by 4 AA batteries • Connects directly to microcontroller • Modified to incorporate G-switch Piezo Arrays (Battery) LED G-Switch To Bridge Rectifier Microcontroller Battery Pack PEA-VVS Circuit Diagram G-switch interface with EPS
Electrical Elements continued Low-G Accelerometer High-G Accelerometer
Electrical Elements continued Bridge Rectifier #1 Piezo Array 1 Bridge Rectifier #2 Piezo Array 2
Electrical Elements continued • Breadboard used for SD card and Arduino microcontroller integration http://www.electronics-lab.com/blog/?m=200806
Electrical Elements continued • Two breadboards • LED circuit • SD card integration • Allowance of 15-20 iterations to debug electronics • Limited previous exposure to programming microcontrollers and EE in general • All electrical elements have been procured • Four dual-axis accelerometers have been replaced with two three-axis accelerometers
Prototyping and Analysis Christopher Elko
Prototyping • PEA • Preliminary test setup measured voltage levels from a single strip actuator under deformation using a digital voltmeter. • Results suggest adequate voltage potential for entire system, with an average of approximately 132 mVAC generated by a single actuator. • Preliminary finite element analysis results in ABAQUS suggest aluminum is adequate for resistance to cyclic loading in this application. • Mechanical analysis, in conjunction with destructive testing of piezo actuators, will optimize dimensions of support cantilever dimensions.
Prototyping continued • STR • Preliminary FEA results suggest a fifth aluminum standoff is desirable for added support of electronic components on upper deck. • Currently finalizing design and interactions with PEA mounting methods. • EPS • SD card adapter to be integrated • Accelerometers integrated into microcontroller and tested for data output • VVS • Tested LED circuit for functional interaction with PEA
Prototyping continued Preliminary piezo strip actuator voltage testing for PEA design Preliminary piezo strip actuator LED testing for PEA-VVS interaction
Analysis cantilever deflection Point Load Distributed Load • Maximum deformation at end of beam, where x = L • Combined loadingduring flight due toG-loading and massat end of beam
Analysis FEA • PEA • Stress Analysis • Point loadto simulate mass at end • Uniform load to simulateG-loading • Maximum stress doesnot exceed 2000 psi
Analysis FEA • PEA • Deformation Analysis • Point loadto simulate mass at end • Uniform load to simulateG-loading • Maximum deformation:0.3 inches
Analysis FEA • STR • Stress Analysis • Point loadat electronic elements • Uniform load to simulateG-loading • Maximum stress doesnot exceed 649.6 psi
Analysis FEA • STR • Deformation Analysis • Point loadat electronic elements • Uniform load to simulateG-loading • Maximum deformation:0.92 inches
Manufacturing Plan Choose your weapon
Mechanical Elements • STR • Acrylic plate laser-cut to size/shape of flight decks • Flight decks among first components manufactured to ensure proper interaction with other subsystems • PEA • Cantilevers cut to size from sheet aluminum upon determining optimum • Piezo actuators to be bonded to cantilevers • Mounting blocks and deflection limiters must be custom-milled from aluminum stock
Electrical Elements • EPS • Electronic interfaces will be table-tested with breadboard and reconfigurable components • Testing will help to determine system capabilities • VVS • Testing will help to determine system capabilities and effects on other subsystems
Software Elements • Code to be finalized • Accelerometers • Voltage output from bridge rectifiers • SD card data recording • Code to be developed • Power loop for camera • G-switch • Code block dependencies • SD card code integrates all subroutines • All code dependent on “true” output from G-switch
Testing Plan Choose wisely.
PEA Subsystem Piezo Actuator Tests Non-destructive Testing • Non-destructive testing will determine voltage output from piezo actuators. • Test Plan • Connect actuators to voltmeter, LEDs; flex actuators to generate current Destructive Testing • Will determine bending deformation limits of piezo actuators. • Test Plan • Use spindle micrometer to bend piezos until fracture.
PEA Subsystem continued Cantilever Tests Unrestricted Cantilever • Unrestricted cantilever testing will determine max deformation limits of cantilevers and whether or not a block is needed to restrict deformation. • Cantilevers will be designed so that they bend freely with only slight vibration. • Test Plan • Set up cantilever assembly on vibe table • Measure deflection using high speed camera
PEA Subsystem continued Cantilever Tests continued Restricted Cantilever • Restricted cantilever testing will ensure that designed block will restrict deformation as needed such that PEA won’t deform past piezo deformation limits. • Block will be designed to restrict deformation in the + and – axis. • Test Plan • Same as unrestricted tests except for use of block.