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Temple University 7/18/2011
RockSat-C 2011
RockSat-C 2011 Final Report
Team SAVSS
Our mission has been, to design, build and integrate an active vibration damping system
to alleviate vibration in the z-direction during the coast phase of the rocket flight. This
has been done utilizing piezoelectric materials.
Students: Donovan Bolger, Xuhui Liu, Greg Wells, John Zebley
Advisor: Dr. John Helferty
Temple University
7/18/2011
Temple University 7/18/2011
RockSat-C 2011
1.0 Mission Statement
Space exploration defines the current human era in anthropological terms. The
understanding of space and the uses of space for advancement on Earth have
summed up the technological advancements achieved over the last fifty years.
Besides the benefit of understanding distant galaxies and solar dynamics through
use of reconnaissance spacecrafts, space exploration has yielded an unprecedented
understanding of Earth sciences. One major factor of inhibition to the success of
scientific research performed throughout and past Earth‟s atmosphere is the
instability of the experiment‟s transporting vehicle. Sounding rockets are typical
vessels used for low earth-orbit experimentation. These rockets tend to experience
vibrations in the x, y and z-axes as well as detrimental forces of up to 25 G‟s. Due
to these vibrations and high G forces, many possibilities for useful scientific
research are prevented because they would not be able to withstand the instability
of the rocket. The stabilization of sounding rockets intended for transporting
research experimentation would offer scientists the opportunity to design and
implement fragile equipment which would otherwise be liable to fail under the
stress of serious vibrations.
2.0 Mission Requirements and Description
In order for the mission to be considered a success, the Sub-Orbital Active
Vibration Suppression System must meet stringent constraints. Listed below are
the functional and non-functional constraints. Because of the severity of the
constraints, there is little margin of error.
The five functional design constraints are shown in Table 2.1. In compliance with
the NASA RockSat user guide, the SAVSS must provide its own electrical power
for the payload. To work with the strict weight restrictions defined by the RockSat
program, two rechargeable 9V DC batteries will be utilized to supply sufficient
power to the microcontroller unit for the rocket‟s anticipated flight-time of 1000
seconds. Rechargeable lithium ion batteries will not be used as they are strictly
prohibited aboard the Terrier-Orion Sounding Rocket.
The majority of the system and its sub-systems can operated at voltages under
18V. However, the damper components will require a range of voltages from -100
to +400V. This forces the SAVSS to amplify the 18V DC to meet the proper
power requirements of the dampers so that their piezoelectric properties can
function properly.
The vibrations SAVSS aims to suppress are those that propagate randomly in the
high and low frequency range through the z-axis of the rocket. Our system must
be able to recognize and convert these vibrations from an analog to digital signal.
The vibrations will be detected by 4 accelerometers: two high range z-axis and
two low range z-axis accelerometers. Two sets of the same z-axis accelerometers
must be used in order to compare the accelerations of the non-fixed
Temple University 7/18/2011
RockSat-C 2011
to that of the fixed plate. The accelerometers will output an analog voltage signal.
To store this signal into memory, the MCU must convert the analog voltage to a
10-bit form. The data will be stored at 1MSPS to ensure that sufficient data is
recovered during the flight.
Based off of the RockSat Wallops Environment Test, SAVSS will concentrate on
a range of vibrations from 0-144Hz. This is the lower end of the vibration
frequencies the rocket will experience. The higher accelerations from the initial
thrust of each stage of the rocket are impulses. This payload will aim to dampen
vibrations with a 5 to 1 damping ratio utilizing an active-vibration suppression
system.
The entire duration of the flight is approximately 15mins. During this flight the
payload will experience many random high and low frequency vibrations. To
ensure SAVSS obtains a sampling rate fast enough to capture all vibrations, the
analog-to-digital converter must store our data at 1 MSPS. At this rate, sufficient
data storage space is required. This sampling rate requires storage capacity of 10
GB.
The non-functional design constraints can be found in Table 2. In order to
conform to the ABET handbook on accrediting engineering programs, five
separate constraints dealing with societal issues such as: economical,
environmental, health and safety, manufacturability and sustainability.
Working with an overall budget of $2,000, the piezoelectric dampers must be
affordable enough to purchase and still have enough capital for all other parts.
Name Description
Power Supply Batteries must be able to supply the system for 1000
seconds
Data Recognition
4-Channel analog-to-digital converter must switch through
all four accelerometers, convert the analog voltage to a 10-
bit form, and store into memory at 4 thousand samples-
per-second.
Vibration Damper
Active vibration suppression system must be able to
achieve at least a 5 to 1 damping ratio of frequencies under
144 Hz
Memory Memory must be vast enough to store 1.5 megabytes of
data
High Voltage DC/DC converter must convert +/- 9V to + 300V and -
300V, for the patch-driving amplification circuit
System Activation Zero currents may flow before the payload experiences 1
G of force in the positive z-axis
Table 2.1: Functional Design Constraints
Temple University 7/18/2011
RockSat-C 2011
The RockSat User Guide, designed in accordance to NASA and the RockSat
program, placed every payload under pre-existing environmental and health and
safety constraints. For instance, the use of rechargeable lithium-ion batteries is
forbidden on the rocket as to protect all payloads. SAVSS must keep the total
current in the RockSat activation line below 750mA. The system must also
conform to the values of internal pressure, temperature and spin rate set defined
by Wallops Flight Facility.
The system must be sustainable and must operate at a certain rigidity and
robustness in order for mission success. The design of the system requires that it
will survive underwater after it splashes into the ocean. The entire system must
also be rigid enough so that it can withstand periods of forces ranging up to 20
G‟s in the Z, or thrust, axis. The entire design must also conform to the RockSat
user guide in the line of its weight, size and center of gravity. The system, as well
as all others on board, must lie within a 1 x 1 x 1 inch envelope in order to
guarantee a spin-stable rocket. The system must also weigh no more than 6 lbs
and must fit in a cylindrical canister, 9.3” in diameter and 4.75” in height.
Type Name Description
Economic Cost Entire budget must be under $2000
Environmental
Saftey
May not use rechargeable or lithium-ion
batteries or wireless communications. Each
could potentially harm or create noise
interference to other payloads or the rocket
itself
Durability
Flight Survival
This system will be designed to operate over a
6-minute flight; experience up to 25 G‟s and
operate in the event of the canister becoming
wet at splashdown
Physical
Volume/Weight/CG
In accordance with RockSat constraints, the
payload canister is limited to 9.3” in diameter,
4.75” in height and 10 lbs in weight. The center
of gravity of the canister has to lie within a
1 inch envelope.
Manufacturability
Launch Date
Must have demonstrated full functionality,
passed all structural and environmental testing,
and be fully assembled and integrated by
6/23/1011
Table 2.2: Non-Functional Design Constraints
Temple University 7/18/2011
RockSat-C 2011
Figure 1: Payload Canister
3.0 Payload Design
In order to effectively explain the active vibration suppression system in its
entirety, it has been broken it down into sub-systems. A full system block diagram is
found in Figure 2 (following page.) Although each sub-system listed in the block diagram
will be explained in depth in later sections, a short overview of the entire vibration
suppression system is first given for comprehension.
The entire system must fit into a cylindrical space of 4.75” in height and 9.3” in diameter,
exactly one half of the canister shown in Figure 1. The system has been powered with 2
rechargeable 9V batteries. To meet requirements placed upon all payloads by NASA and
the RockSat program, the system was to be unpowered until time of launch. This
requirement was met by incorporating a G-switch into the system, which allows power to
flow once acceleration is experienced at the time of launch. Although power was supplied
throughout the system at the instant of launch, vibration suppression did not begin until
after the 2nd
burn of the sounding rocket. The PIC32 microprocessor began its control of
the piezoceramic DuraAct Patches after the 2nd
rocket burn to ensure that the rocket was
in its coast phase. This was done because the aim of this project was not to suppress all
vibrations experienced throughout the flight, but rather the vibrations of lower
frequencies experienced during coast phases, apogee and parachute deployment. The
frequency range in question was 0 to 144Hz, which
are the exact values used to test all payloads flying in
the RockSat program for stability prior to launch.
As the rocket experienced these vibrations,
accelerometers sitting on both the rigid and floating
plates were continuously reading and writing analog
voltages to the PIC32. The PIC32 has an internal
Analog to Digital Converter (ADC) which converted
and stored the incoming analog voltages in memory.
The ADC was 4-channel to deal with the 4
accelerometers, and sampled at forty thousand
samples per second. These values were continuously
compared and used to control the DuraAct Patches,
which fluctuated in tandem with the current vibration
frequency so as to stabilize the floating platform. The
DuraAct Patches accepted analog voltages ranging
from -100V to 400V. Analysis of the functionality of the system occurred post-flight
once the payload had been retrieved. Data from the PIC32 was loaded into a computer
which allowed for a comparison of the vibrations experienced on the rigid plates to that
of the floating plates. An official report will be written as to portray how well the active
vibration suppression system functioned during the 15 minute flight of a sounding rocket
to heights of 72 miles above sea level. A damping ratio of 5 to 1 between the floating and
damped plates was the main goal of this project.
Temple University 7/18/2011
RockSat-C 2011
Figure 4: Comparison of Rigid to Damped Plate Vibration
3.1 Control Theory Found in Figure 3 is a block diagram of the basic control theory used to control the
piezoceramic DuraAct Patches. The patches were directly controlled by the
accelerometers. The accelerometers were placed along the z-axis, faced in opposite
directions. The difference of their values was met with a proportional gain so as to meet
maximum displacement over the range of forces the canister experienced.
After the differences of the accelerometers‟ values were taken, they were sent through an
Figure 2: System Block Diagram
Figure 3: Control Theory Block Diagram
Temple University 7/18/2011
RockSat-C 2011
inverting amplifier that had a gain of 20 V/V. These inverting amplifiers had a voltage
output range of +/- 200 V. By using two of these amplifiers, the piezoelectric patches
were able to experience voltages of up to 400 V. The expected result of the rigid to
damped platform vibration can be seen in Figure 4.
3.1.1 Accelerometer Output
The accelerometers placed on both the rigid and floating plates of the payload were a
crucial part of the design of the overall system. There were two accelerometers on each
plate: one High G and one Low G. Each accelerometer gives an output of 2.5V (+ or –
1V) for every 1 G-force experienced by the rocket. For instance, if the rocket was
experiencing 0 G-forces, the accelerometers would output 2.5V. If the rocket was
experiencing a +1 or -1 G-force, the output of the accelerometers would be 3.5V or 1.5V,
respectively.
3.1.1 Amplifiers
The two differential amplifiers simply take the difference of the two accelerometers.
Since the actual blocking force of the dampers was unknown until final integration, an
adjustable potentiometer was placed so that the ratio of the resistance could enable exact
calibration prior to flight and can be seen in Figure 5Error! Reference source not
found.. Found below in Figure 6Error! Reference source not found. is the expected
blocking force capabilities versus external force that the rocket is expected to experience.
Biased at +/- 300V, the high gain amplifiers invert the output of the differential
amplifiers and give them a gain of 20 V/V. This stage of amplification uses a LF441CH
operational amplifier to control a set of five bipolar junction transistors that are rated for
+/- 300 V. The feedback resistors determined the gain of this circuit. A DC/DC
converter provided by American Power Design converts +/- 9.6 V into +/- 300 V at a
maximum current of 3.96 A. This schematic can be found in Figure 7.
Figure 6: Expected Blocking Force
Figure 5: Adjustable Gain Amplifier
Temple University 7/18/2011
RockSat-C 2011
3.1.5 DuraAct Patches
As each of the four DuraAct Patches received signals from the amplifiers, they expanded
and contracted continuously as to alleviate the
present experienced vibrations. As previously
stated, the patches were set to an initial position
of 25mm each. The patches above and below the
floating platform essentially moved up and
down, relative to each other, at the same
frequency of the present vibrations about the
payload. This allowed for stability of the center,
floating platform. In order to prevent
depolarization of the patches, diodes were
placed between their leads and the amplifiers.
The schematic of these diodes can be seen in
Figure 8.
3.2 DuraAct Patches: A Closer Look The main objective of this design was to
actively suppress a specific range of vibrations.
The problem that arose in this case was the
restriction on the payload space the vibration
suppression system had to work with and the
weight it could budget. With only about 4.75in
of height and a diameter of 9.3in, the payload
space this payload had to work with was very
small. Because of the knowledge of this small
space SAVSS was able to quickly rule out
Figure 9: DuraAct Patch Transducer
.
Figure 7: Main Amplification Circuit
Figure 8: Diode Schematic
Temple University 7/18/2011
RockSat-C 2011
many different options for a vibration damper device.
After some research, SAVSS implemented piezoelectric technology as the damper for its
design. The phrase piezo comes from the Greek word for pressure. Piezoelectronics are
used almost everywhere today; from headphones to insulin injectors for a diabetic the
uses for piezoelectric technology are endless. The particular piezoelectric device SAVSS
utilized in its design was the DuraAct Patch Transducer P-876.A12 provided by Physik
Instrumente (PI). As seen in Error! Reference source not found., the DuraAct Patch
Transducer is incredibly thin, flexible, and compact. The DuraAct has the ability to attach
to non-uniform surfaces and suppress vibration from 1Hz all the way into the kHz range.
By applying a specific voltage to the electric connectors of the DuraAct seen in , the
patch can react by changing its bending radius. The DuraAct works similar to a capacitor;
the flexible ceramic plates inside the DuraAct acts like a dielectric between its metal
surfaces. When a voltage is applied to the connectors in Error! Reference source not
found., an electric field is created inside the DuraAct. This field causes a uniform lateral
contraction of the ceramic plates perpendicular to the direction of the electric field. The
strength of the electric field determines the magnitude of lateral contraction. This
particular behavior is called the transverse piezoelectric effect and can be seen in Error!
Reference source not found. The lateral contraction property of the DuraAct is what allows us to suppress vibrations.
By utilizing the reverse analog signal outputted by our accelerometers, the DuraAct can
use this signal as its power input to effectively suppress the incoming vibration by
physically working against the vibration in the opposite manner. Because the DuraAct
will consume power within a range of -100 to +400 volts at a max current of 25mA, our
design feeds the DuraAct‟s input signal through a model F04 F Series DC to HV DC
converter before inputting that signal to the DuraAct. The F04 DC to HV DC converter
provides a voltage gain of 33.33. The electric power signal is sent to the electric
connectors of the DuraAct patches through two 18 gauge high voltage lead wires which
are insulated to withstand 5-50kV DC and a temperature range of 150-200degrees
Celsius. For SAVSS‟ design, four DuraAct Patch Transducers have been implemented.
Two DuraAct Patches lie on the bottom of the payload supporting the lower floating plate
and a duplicate pair of DuraAct Patches is then placed on the upper portion of the floating
plates. With this layout, the DurAct Patch Transducers will work almost like an active
cushion suspension on either side of our payload system we wish to suppress vibrations
within. Since the DuraAct patches are very smooth on either side, each patch was adhered
Figure 11: Transverse Piezoelectric Effect
Figure 10: Closer Look at the DuraAct Patch
Temple University 7/18/2011
RockSat-C 2011
to a thin square of plexi glass which will act as both a ridged mount to prevent the patch
from moving around to an unwanted position; also the plexi glass will act as a base for
the patch to act against. The adhesive used to mount the patches is HBM Z70
cyanoacrylate glue formulated for mounting strain gages. A model of this layout can be
seen in the mechanical section of this document. Since the correlation between voltage
and displacement is not linear, our design has be calibrated to allow the DuraAct to
receive a signal linear to the reverse of the accelerometers analog output.
3.3 Power System In accordance to the NASA RockSat user guide, no electrical
power shall flow through the payload before the Sounding
rocket has launched. This will be insured utilizing two methods;
one provided by our team and one provided by the RockSat
program. NASA RockSat will have the initial control over the
power source using their RBF (Remove Before Flight) wiring as
seen in Figure 12. The NASA RBF wire is nothing more than an
on off switch to our power source. This gives NASA RockSat
the knowledge that the payload power supplies are not supplying
power before the launch so that they can insure each payload
meets the user guide requirement. Once the RBF wire is
removed and the rocket launches, the second method provided
by our team can initiate to allow power to flow to the system.
The second method is a g-switch integrated into our design. The
g-switch will close from the force of the rocket taking off. Once
the g-switch closes, power from 9V DC rechargeable batteries
will flow into an activation circuit as shown in the diagram of
Figure 13. The 9V DC batteries will be able to provide electrical
power to the entire system for the duration of the flight which is
approximately 15 minutes.
The activation circuit displayed in Figure 13is necessary in
maintaining proper electrical power input to the main system of
the payload. The sounding rocket will not be traveling with
constant
acceleration
especially once the
parachute deploys
after apogee.
Because of this, the
design cannot
guarantee the g-
switch will continue
to stay closed. To
counter this
Figure 12: Stacked
Payloads with RBF wiring
Figure 13: Simulated Activation Schematic
Temple University 7/18/2011
RockSat-C 2011
complication, the activation circuit is comprised of a power latch that has the ability to
hold and maintain a specific voltage value to which our system demands. The output
from the activation circuit will then be regulated and sent to the specific sub-systems of
the design. Power will be provided to the PIC32 expansion board and the DuraAct
patches. Since the PIC32 expansion board can accept an input power range of +9-15V
DC to allow proper functionality of the system, the
output voltage from the activation circuit to the
expansion board was then regulated to 12V DC which
falls somewhere in the middle range. The PIC32
expansion board contains integrated power regulators to
supply the PIC32 board and Memory board with proper
electrical power. The PIC32 board, expansion board,
and memory board can all be looked at as one
component of the system since they were pre-
manufactured by MicroChip Inc.
The PIC32 subsystem not only allows us to sample and
store information, but it also acts as a voltage output for
our vibration suppression components. The output
signal from the PIC32 is a digital signal which is then
converted to a useable analog input for our vibration suppression components. All sub-
system and circuit power consumptions are listed in Table 3.
3.4 Software Design This section outlines the approach SAVSS implemented for data logging for the four
accelerometers and the piezoelectric damper control. Because the microcontroller unit
needed to complete several simultaneous tasks at speeds that met or exceeded the
aforementioned constraints, a PIC32MX360F512L Microcontroller was selected. The
PIC32, part of the PIC32 Starter Kit as seen in Figure 14, has a maximum speed of 80
Table 3: Total Power Consumption
Figure 14: PIC32
Temple University 7/18/2011
RockSat-C 2011
MHz, which was needed to complete the multitasking demanded of it. The PIC32 Starter
Kit has an internal oscillator, and 16 channels for analog-to-digital conversion. In order
to properly interface with an SD Card, the Port I/O Expansion Board was used. This
section goes into detail how the PIC32 communicated with the SD Card, and the four
accelerometers.
3.4.1 Microcontroller Unit: Accelerometers Analog to Digital ConversionAs
mentioned, four accelerometers where used in order to obtain adequate amount of thrust-
axis vibration and acceleration data the Terrier-Orion Rocket will experience during the
entire length of the flight. A high-G ADXL78 accelerometer provided by Analog was
placed on both the rigid and the damped platforms. Likewise, a low-G ADXL103 was
used on both the rigid and damped platforms. Using the internal PIC32 multiplexer, the
ADC was able to convert the accelerometers‟ analog output to 10-Bit forms at 1 MSPS,
which allowed each accelerometer‟s value to be converted at 250 KSPS. By using the
PIC32‟s Direct Memory Access (DMA) scheme, the data was stored directly into the SD
Card at that same sampling rate. Using the DMA allowed the PIC32 to spend more
operating time handling the damper control routine. At 1 MSPS, and given a maximum
flight time of 1000 seconds, the total amount of memory needed was 10 megabytes.
Because it used a 16 gigabytes memory card, the SAVSS system met this constraint. A
downside to meeting this constraint was that the memory was organized in the SD Card
serially. This meant that storing the clock time of each sample of acceleration data was
not possible, because this would require a memory buffer and time stamp appendage to
each sample. Instead, the timeline of the flight was provided by Wallops Flight Facility.
The software flow diagram can be seen in Figure 15.
Figure 15: Software Flow Diagram
Temple University 7/18/2011
RockSat-C 2011
3.5 Mechanical Design
As one of the subsystems, the mechanical design dealt with more of the stringent
constraints defined by the NASA RockSat program. The payload was integrated into the
top half of the canister shown in Figure 3.2. The other bottom half of the canister was
shared with a team from Drexel University. The biggest challenge faced was designing an
active vibration suppression system utilizing DuraAct Piezoelectric patches with the
maximum mass of 6.5 lbs, maximum height of 4.75 inches and maintaining the center of
gravity of the canister within a 1x1x1 inch envelope of canister.
The hardware system was divided into three subsystems that included the structure,
integration, and mass & center gravity. All the subsystems had to work harmoniously
with each other in order to meet the requirement. A
proper structure had to be designed in order to
make the thin piezoelectric patches suppress the
vibrations of certain damped plates and to fit both
electrical and mechanical components. The total
mass and center gravity constraints and the built
structure had to be considered when integrating
components.
3.5.1 Structure Design
Designing the structure was the primary subsystem
of hardware design. A proper structure enabled the thin Piezoelectric patches to suppress
the damped plates while meeting the height constraint. According to the RockSat-C
user‟s guide, the total usable space of the payload canister was limited to the dimension
of 9.3” in diameter and 9.5” in height. Since the
canister space was being shared with a team from
Drexel University, the usable space was half of the
total space. Ideally, the maximum height was 4.75”
without consideration of height loss after
integrating with Drexel Team‟s payload and the
canister skin.
Shown in Figure 17 is a rigid plate body with four
main standoffs connected between two Makrolon
plates. The bottom of the rigid plate body was
rigidly screwed to the top of Drexel Team‟s
payload and the top of the rigid body was mounted
to the cap of the canister skin.
In Figure 16, the damped plate body shown with 3” usable height. Most of the electrical
components were integrated on the damped plate body. The 3” plate-to-plate height was
chosen because the total height of PIC32 expansion board with the SD Card integrated
stood just below 3 inches. Compared to the rigid plates, the damped plates had four more
big holes on each plate. These four holes were created as the shaft hole for the four main
standoffs of the rigid plate body to freely move through.
Figure 17: Damped Platform
Figure 16: Rigid Platform
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The overall structure assembly is illustrated in
Figure 18. The damped plate body was damped between the two plates of rigid body.
Two Piezoelectric patches were mounted to inner surface of each rigid plate with
cushions beneath them. Rectangular Makrolon plates were used as cushion in order to
adjust the distance between rigid plates and damped plates. Since the bending height of
the patches was 0.5 mm, Makrolon cushions were used to make sure that the patches had
constant contact with the damped plates.
3.5.2 Integration
Temple University 7/18/2011
RockSat-C 2011
After the structure design had been determined, integrating all of the components was the
next crucial subsystem. The overall mechanical design is shown in Figure 18. Since 8
Nica 5A batteries and the DC/DC converter are the major weight units in our design, they
were designed to be placed on two ends of payload in order to balance overall center
gravity. Based on this idea, there was not enough space in the middle of damped plates
for Pic 32 board. Therefore, Pic 32 was mounted upside down on the top of rigid
platform.
As shown in Figure 19, only few of small components were mounted on the bottom plate
of damped body, such as 2 9V batteries and G-switch. One of two accelerometer PCB
boards with low Z and High Z was determined to be mounted upside-down on the bottom
of top rigid plate due to insufficient space on the bottom of damped plate.
Figure 18: Fully Integrated Structure
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RockSat-C 2011
The other set of accelerometer
PCB boards were designed to be
mounted on the bottom of the top
rigid plate. Due to narrow space
between the rigid body and the
damped body, rectangular hole
was cut on the top of the damped
plate so that this accelerometer
PCB board could pass through the
rigid plate and not obstruct the
experiment.
As illustrated in the Figure 3.16,
two patches were mounted to the
inner surface of each rigid plate
by 45 degrees. With this crossed arrangement, the damped body would be balanced. Any
slight unbalancing could throw the entire system off when dealing with such
environmental factors such as vibration and high G-forces.
3.5.3 Mass and Center of Gravity
According to NASA‟s requirement, the entire weight of all involved projects on board the
RockSat-C rocket must be 20±0.2 lbs. After subtracting the weight of canister, its skin
and the plate in the middle of canister from the total weight, then taking half, the
maximum allowed weight was 6.5 lbs. As shown in Table 4, the total mass of the
complete systems was currently estimated at 3.6 lbs, which is under the constraint of 6.5
lbs. Once all the masses of each payload were known, “dummy” weights were distributed
about the canister in order to meet the required weight. The locations of the weights in
the vertical axis of each payload must also be known to accurately distribute the weight
throughout the canister.
With the combination of payload‟s weight and height, the center of gravity of the canister
Figure 19: Integrated Electrical Components
Table 4: Mass Budget
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RockSat-C 2011
could be known. RockSat-C user guide requires that the center of gravity of the canister
must lie within a 1x1x1 inch envelope of the RockSat payload canister„s geometric
centroid. After carefully measurements of each component, each actual mass was
assigned to each corresponding component in SolidWorks. By running the mass property
feature in SolidWorks, the total mass and center gravity were both calculated. Simulation
of center of gravity had been completed within the Solid Works environment and the
result was shown in Figure 20. By observing the pink XYZ coordinate system, one can
estimate that the center gravity of this half payload was in the middle. As calculated by
SolidWorks, the center gravity for this payload was X 0.28”, Y -0.12”, Z 2.14”. This
center gravity coordinates are based on the origin locates at the center of bottom plane.
Z=2.14” means the Z coordinate is 2.14 inches above the origin, which is within 1 inch
envelope in the Z-axis. Therefore, the center gravity in X and Y-axis had met the NASA
requirement. The origin of the coordinate system was at the center of the bottom of rigid
plate. 2.14” above the origin met expectations and was recalculated after integrating with
the Drexel payload. Dummy weights were added to the payload to reach total weight of
20 lb as well as adjustment of center gravity.
4.0 Student Involvement (0.5 – 1 page)
Figure 20: SolidWorks COG Test on Fully Integrated System
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5.0 Testing Results
Mechanical: The mechanical systems were tested mostly utilizing SolidWorks.
Center of Mass and Center of Gravity tests were run so as to know whether or not
the entire system would comply with all NASA regulations.
Electrical: Each electrical subsystem was tested 1st individually and then all
together. We first tested each of our power supplies. We needed 2 9V batteries to
power the Pic32 microcontroller and 8 NiCa 5A batteries to power the
piezoelectric transducers. Each power supply needed to last for 6 minutes since
our project was only concerned with the first 6 minutes of the flight. We powered
on the system and verified that each of the supplies would in fact stay on for a full
10 minutes, leaving room for error.
We then tested the high voltage DC/DC converter which was needed to control
the piezoelectric transducers. We sent 9V signals into the component and
measured 300V as the output.
Software: We powered up the entire system and let it run for 10 minutes,
checking for data storage functionality. The Pic32 saved accelerometer data from
4 separate accelerometers: 2 gaining readings from the rigidly attached platforms
and the other 2 from the damped platform.
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6.0 Mission Results
Unfortunately, our payload did not return any meaningful results. The aim was to
eject the SD card from the Pic32 post-flight and analyze the accelerometer data
from both the rigid and floating plates. However, this was not completed. The SD
card had only two files saved to it from the Pic32 which had actual data in them,
both of which containing only non-sense. There were several other files saved to
the SD card, however they would not open up because of a read-write failure. It is
extremely possibly that our damping system did in fact function the way it was
designed for; however, without being able to access these files we will never
know.
This comes as a great disappointment to us, for a year of mechanical and
hardware design has gone unproven because of software problems. We can only
hope that if this project is continued next year, that actual results of accelerometer
data are retrieved from the payload so as to analyze the functionality of the
dampening system.
7.0 Conclusions
In conclusion, our design didn‟t successfully achieve expected goals since there
was no data stored on the SD card. The reasons of this cause are not yet decided.
However, it may be due to the following reasons.
1. Pic32 Microprocessor itself: according to many other Pic32 microprocessor
users, it‟s not a very user-friendlier microprocessor. It frequently goes wrong
and output wrong data. Sometimes the SD cards were burned for no reason.
2. Short circuit: Pic32 didn‟t work when we first arrived in Wallops. Later on we
found out two pins of the Pic32 daughter board were pressed, which led to
short circuit. After separating these two pins, Pic32 could store data
successfully.
3. Soldering: Pic32 could still successfully store data the night before we
soldered all the wires on the pic32. After soldering, it didn‟t work well.
8.0 Potential Follow-on Work
The SAVSS could be added to and worked upon by a future team in order to gain
better, more concrete results. It seems plausible that if the same piezoelectric
patches were used as dampers, but attached differently so as to suspend the
floating platform with more “cushion,” that a greater damping ration could be
attained. Also, a different microcontroller would absolutely have to be used. The
Pic32 gave many problems throughout the year and then again during launch.
Although the true problem still is not 100% known of why no data was saved on
the SD card, a possibility is because of the Pic32 and its incompatibility.
The actual control of the damping patches could be improved on as well. In this
design, the SAVSS eventually had to either apply 0V or 300V to the patched,
meaning an all-or-none displacement of the patches in the z-axis. If an analog
amplification circuit was designed, using power MOSFETS, the patches could
potentially be delivered an all-inclusive variable voltage from 0V to 300V. This
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RockSat-C 2011
would make the movements of the patches, and therefore of the floating platform,
much more precise and less jerky, leading to a better floating-to-rigid damping
ratio.
9.0 Benefits to the Scientific Community
If our design had worked as we expected it to (which it may have, however we
have no proof because of the foul up by the Pic32/SD card) then the scientific
community could benefit in one major way. The product, if worked on and
expanded into a larger but similar design, could allow for fragile components to
be flown on sounding rockets which would otherwise not be able to handle the
vibrations experience throughout a typical flight. This safe and steady platform
could lead to new scientific research which needs fragile components in order to
gain data.
10.0 Lessons Learned
While it is hard to deem this mission a success because of there is no data to show
for the sub-orbit experiment, this mission was a success if we look at the lessons
that we have learned from this experience. We knew the PIC32 had problems for
months ahead of time. If we had gone in a different direction for the data
retrieval, we could know more about whether the experiment actually
worked. We should have selected a user-friendlier microprocessor such as the
Adruino. Had we used a simpler board, we could have spent the time on the
piezoelectric dampers that were the focus of our experiment.
In order to focus and ensure that the piezoelectric dampers would have worked
properly, we really should have spent more time implementing the linear voltage-
to-stiffness amplifier that we could not implement due to timing constraints. With
an amplifier like this, we could have adjusted the stiffness of the dampers to
counter the mechanical vibrations that the rocket underwent. Our backup plan,
which we actually used, simply pulsed the dampers when the vibrations exceeded
a certain threshold.
We really would have preferred testing the software and hardware more
thoroughly, but that was impossible due to many factors but mostly due to our
design schedule. We would have liked to create a LabVIEW graphical user
interfaces to thoroughly test the hardware and software under every scenario
possible. This also would have allowed us to test this actively while the entire
experiment was on a vibration table.
There were a lot of things we did not have the time to accomplish. This is our
fault. We should not have selected such a difficult subject matter such as
piezoelectric dampers. We should have selected something simpler that required
less sophisticated technology than that that we did select. To adequately utilize
these piezoelectric dampers, an analog feedback circuit is typically required.
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