Phase Planning
Shared Phase Vision
Our vision for this phase is to finalize critical subsystems and test non-critical subsystems. Key related technical questions related to our subsystems include:- Distance and heel strike sensor
- How do we integrate distance and heel strike sensing?
- How do we receive real time response based on heal strike and distance?
- Electrical control of air muscles
- How to control the solenoid from the Arduino?
- How to supply different voltage levels?
- Specify the right solenoid
- Secure foot – Lower
- How to apply torque?
- What possible materials to use?
- Does the brace remain comfortable when force is applied?
- Secure foot – Upper
- How will the muscle be attached to the brace?
- Does the brace remain comfortable when force is applied?
- Are additional components needed for support?
- Lower and Upper base attachment
- What possible materials to use? permanent elastic?
- Is it abrasion safe?
- Is it user friendly?
- Air muscle lift / operating pressure
- What are the muscle dimensions?
- Air Tank for a full day
- How much air does the muscle need?
- Do we need a bigger tank?
- Low battery alert
- Is a hardware approach better than a software approach?
- Is an audio alert or visual alert better?
- Air tank sensor
- Is using an air tank sensor feasible?
- Can it be connected to Arduino?
- Air tank tubing
- How will it feed to the air tank?
- What is an appropriate dimension range?
Some additional plans for this phase for our group are as follows:
- Identify vendors and review budget
- Develop an assembly build and test plan
- Review MSDII plan
- Review Risks
- Update post prototype test plan; make sure that requirements can be tested.
- Update and iterate the Risk Table
- Update action items from last review
- Review and update project timeline
Prioritized Tasks
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Week 15 Plan
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Bill of Materials
System Design
Mechanical System Concept
Lower Attachment
During this phase, new attachment/lift methods were analyzed. Modifications were made to the ankle brace and a stage 2 test was completed. The modifications that were made addressed issues that were identified in the previous phase, phase 3.Pugh Charts
The following charts were generated to analyze the proposed attachment and lift methods.
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Stage 2 Test
Questions to be Answered by Test-
a) How much force does it take to lift the foot, using
the chosen attachment method?
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b) Is there any apparent slippage of the brace when a
force is applied?
- c) Does the foot lift as soon as the force is applied? If not, how much force is needed before movement is observed?
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d) Does the brace remain comfortable when a force is
applied? Are there any specific ways that the force is
applied that causes the brace to be uncomfortable or
constrict blood flow?
Procedure
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1. Have volunteer sit on table top with their right
foot hanging freely
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2. Place modified ankle brace on volunteer’s
foot
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3. Strap the volunteer’s leg to the table using
two Velcro straps, to ensure that the leg remains still
when the force is applied
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4. Hook the ribbon loop onto the spring force gage
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5. Using a spring force gage, a second volunteer will
lift the volunteer’s foot
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6. Have another volunteer read off the force
measurements and the test volunteer record the measured
forces.
Setup
Results
Comfort Survey
Conclusions
- a) It takes approximately 8lbs of force to lift the foot
- b) The brace does not slip when a force is applied
- c) No movement occurs until at least 2lbs of force is applied
- d) The brace remains comfortable during the lift. The volunteer indicated that no discomfort was experienced during the test. The feeling of the brace during the lift can be compared to that of wearing a thick sock.
Next Steps
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1) Discuss ways to address the issue of a delayed lift
(i.e. foot does not raise as soon as a force is
applied)
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2) Complete same test with enhanced attachment
method
Upper Attachment
During this phase, the additional strap that was found to be needed in stage 1 of the process was tested to determine its functionality. The strap was added to our assembly, and the test completed in the subsystem design phase was iterated.Stage 2 Test
Questions to be Answered by Test-
a) Does the attachment point about 2 inches below the
top of the brace still provide the support needed to
counteract the force from the McKibbon muscle?
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b) Does the new non-elastic, Velcro strap provide
enough support to support the McKibbon muscle
function?
- c) Is there any apparent slippage of the brace when a force is applied?
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d) Does the brace remain comfortable when a force is
applied? Are there any specific ways that the force is
applied that causes the brace to be uncomfortable or
constrict blood flow?
Procedure
Very similar testing procedure completed as compared with
Stage 1 of testing.
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1. Have volunteer sit on table top with their right
foot hanging freely
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2. Place modified leg brace on volunteer’s
foot
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3. Strap the volunteer’s leg to the table using
existing two Velcro straps, as well as new strap sewn
to the top of the brace
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4. Hook safety pin 2 inches below the top of the brace
to simulate attachment point
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5. Using a spring force gage, a second volunteer will
pull down on the attachment point
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6. Record force measurements when slippage occurs, as
well as document the distance the brace slipped, if at
all.
Setup
Results
Results of phase 2 of this test showed the no significant
slippage occurred on the brace when about 7 pounds of
force was applied. The attachment point broke at this
point, so no additional force could be added, but after
an anticipated initial slippage to have the brace settle
on the leg, subsequent pulls did not significantly alter
the position of the brace.
Conclusions
- a) The attachment point will still need to be about 2 inches below the top of the brace
- b) The new non elastic Velcro strap should be sufficient enough to counteract the force from the muscle
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c) There will be an initial slippage, but the strap
prevents any major slippage after the initial slip
The foot lift calculation model was compared to 7 foot
lift tests (including the two conducted in this phase,
DDR) in order gauge the accuracy of the model:
Next Steps
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1) Iterate test again once prototype muscle attachment
piece machined and added to brace (see design below).
This will allow us to use an actual air muscle with the
forces that we will see in our system, as well as
closely simulate the function of our final
prototype
Full Report with additional plots:
P15001_Feasibility_Testing_Report_Upper_Muscle_Attachment_2
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Muscle Optimization Stage II
Motivation - The purpose of this test was to design and construct an optimized muscle for the integrated system. This was achieved largely through iterative testing and by researching past muscle optimization studies.Procedure and Results - These tests were conducted following the same general procedure and data processing methods as in Muscle Optimization Stage I. A series of 11 formal, distinct, tests were conducted during this phase consisting of at least 5 different muscles with various dimensions. The table below describes the deflection, dimensions, and estimated steps for each muscle:
The figure below depicts the raw results of all 11 tests color coded by muscle design.
In order to make the data more transparent, the following plot was created using only M4, M5, & M7 with the estimated number of steps shown in the legend:
Conclusions - The optimal muscle should have the smallest diameter possible while still allowing for >1 inch of deflection. This was most closely achieved by M7 (L0=6", Inflated-Dia=1/2", Silicon tubing). It demonstrated the potential to achieve 1 inch deflection at 55psi. The expected life of this optimized muscle is shown in the table below by varying the tank dimensions:
Full Report with additional plots:
P15001_Muscle_Optimization_Stage_II
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Muscle Optimization Stage II Addition (Single Weave Sleeve)
Motivation - This sub-test was added on later in the phase in order to test the performance of a single weave muscle sleeve as opposed to a triple weave sleeve as previously tested. The sleeve appeared to have a small diameter and a comparably large strain rate.Procedure and Results - These tests were conducted following the same general procedure and data processing methods as in Muscle Optimization Stage I and II. Two muscles were tested (M8=latex and M9=silicon) under 2 weight loadings (7.51 and 10.1lb). The initial lengths were: M8=7.5in and M9=4.8in. These muscles performed best under high pressure and the charts below illustrate the estimated number steps and the recorded deflection for three pressures:
Conclusions - The single weave sleeving appears to hold potential benefits for the optimal muscle design. M8 performed exceptionally well but the tubing was latex (allergen) and the initial length exceeded our constraints. With thinner silicon tubing and proper length adjustment single weave sleeving appears to be an optimal design.
Next Steps -
1.Purchase thin silicon tubing.
2.Construct an optimized single weave sleeve muscle with
an initial length of approximately 6in (subject to
change).
Full workbook with data tables:
P15001_Muscle_Optimization_II-Single_Weave_Sleeve
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Number of Steps Research
Motivation - The purpose of this research was to find a reasonable and practical number of steps that our average user will take in a typical day.Procedure and Results - Original findings were based on a New York Times article claiming that average American adults take around 5,000 steps per day. However since “Nearly three-quarters of all strokes occur in people over the age of 65” it seemed that the majority of our target market would fall under the category of 60 years old or more. Research from two different sources both agreed that 4,000 steps is the approximately average daily steps for people above the age of 60.
Conclusions - Based on these findings we conclude that it is safe to assume the majority of our end users will not average more than 4,000 steps/day. Furthermore, based on our observations from the Nazareth clinic we conclude that it is reasonable to reduce the target number of steps by 25% since most of our clients are not likely to be as physically active as their peers. Thus the target number of steps is 1,500 steps per leg.
Full Report with additional information and citations: P15001_Number_Of_Steps_Research
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Tank Selection
Motivation - The purpose of this research was twofold:a.) To research the cost of 4,500 Psi compressed air tanks and the corresponding estimated number of steps.
b.) To perform a sense check on the CAIR calculation model and the assumption that a larger tank will provide the addition volume as estimated.
Procedure and Results
The budget research was conducted by researching paintball tank prices online at at least two different suppliers. If available, the tank's weight, length, and diameter were recorded.
The tank life research was conducted by finding a third party paintball tech website with tables estimating the number of shots from a paintball gun with a give tank. The number of shots data from four tanks were selected and the corresponding number of steps was calculated using the CAIR Capacity model. As shown in the tables below, there is a consistent 20% difference between the estimated number of shots and the calculated number of steps:
Conclusions - Based on these findings we conclude that:
a.) A 90ci 4,500 Psi carbon fiber paintball tank is currently available for $160.95. Manufacturer specs: 2 inches long x 4 1/2 inches diameter - 1 3/8 inches bottle to ASA.
b.) The calculation method used in the CAIR capacity model is the same method used by a third party paintball tech. This is reassuring to know because it indicates that even if the muscle volume calculations are off, the estimated life of a particular muscle with a larger tank can still be determined using a tank exhaustion test.
Detailed Tank Selection Information:
PDFa
Paintball Shots Information:
PDFb
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Fishing Line Deflection Test
Motivation - The purpose for this test is to find:a) What grade or fishing wire should be used?
b) How much deflection is absorbed by the elasticity of fishing wire?
Test Setup
Two different grades of fishing line were tested in this experiment: 8lb transparent line and 60lb green line. The test was performed in the BAD Lab by suspending weights from an overhang as shown in the figure below:
Procedure and Results - The 8lb transparent fishing line broke under 7.5 and 5.6lbs of force before any accurate strain readings could be recorded. The green 60lb line was tested in four steps: 1. The wire was loaded incrementally and corresponding length readings were taken, 2. The wire was subjected to additional human body weight in an effort to test the upper limit but no failure was observed, 3. Measurements were taken as the loads were removed, 4. The data seemed to indicate a post-loading permanent deformation so incremental loads were added again to acquire additional data as shown in the figure below:
Conclusions
a) The green 60lb fishing wire far outperformed the transparent 8lb line which broke under less than 5.6lbs of weight. The 60lb line did not even break under 20lb of weights plus downward bodyweight force.
b) The deflection absorbed by the elasticity of the fishing line was found to vary with loading and fishing wire length. For approximately 10.5” of fishing line at 10.1lbs, the deflection was measured to be less than 1% strain or 0.09” It is recommended that the fishing wire be pre-stretched in order to reduce initial deformation if strain is a serious concern in later phases.
Full Report with additional plots and tables: P15001_Feasibility_Testing_Report_Fishing_Line_Deflection
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Muscle Attachment Design
Purpose - An assembly to attach the muscle to the brace needed to be designed that fit the following criteria:a) The assembly must be small and lightweight
b) The assembly must be safe without dangerous abrasive protrusions
c) The assembly must allow the muscle to be easily attached and removed so the AFO can be washed
d) The assembly must be feasible to design during MSD and not overly complex
Pugh Analysis
During the course of this phase, a brainstorming session was conducted and the following Pugh chart was made according to the selection criteria listed above:
Design
A preliminary design was completed for the muscle attachment piece. The design consists of 2 parts:
1. Integrated plug for the McKibbon muscle
2. Attachment base to be attached to brace
The first piece, the integrated plug, combines the plug on the McKibbon muscle with an attachment piece. The plug portion of the design serves as the air inlet to the muscle. It was designed to have the same functionality as existing plugs for McKibbon muscles, with similar dimensions. The plug was then combined with the attachment piece to easily slide into the base, with 2 screw holes to easily secure the muscle to the base.
The second piece, the attachment base, was designed to easily mate to the integrated plug. The plug easily slides into the cavity on the base, and the 2 screws holes should align to easily connect the piece together. Holes were drilled around the outside to easily sew the base to the brace.
Annotated photos of the 2 pieces are shown below:
Next Steps
This was a very preliminary design for the piece. Once
the prototype is made, the design can be iterated and
optimized.
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1) Note positives and negatives from completed
prototype
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2) Complete stress and fatigue analysis on current
design
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2) Refine design with changes needed in mind
Electrical System Concept
System Architecture
Schematic
Critical Systems
- Power Input: Power connection and 5V regulator
- System Clock: 16 MHz microcontroller clock
- TO_AFO: FlexiForce (heelstrike) input, IR Sensor (distance sensor), 5V and ground connections
- TO_SOLENOID: Two drive circuits for the Solenoid control as well as a ground connection
- TO_SWITCH: This connects the manual switch on the board to a digital input on the microcontroller.
Optional Systems
- SD Card: Level shifter and MicroSD card shield as well as the 3.3V regulator
- TO_FLOW_SENSOR: Power and ground connections as well as an ADC input to read the flow control as needed.
- SERIAL_I2C: Debug connections to the I2C communication as well as the Serial line.
Top Level Pseudocode
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Subsystem: New Heelstrike Sensor
Motivation - The motivation of this test
was use the new distance sensor that has the higher
pressure limit and make sure that the functionality of
the system remained.
Procedure - The nice part about this
testing was that in the previous testing, a header was
created that allows for the sensor to be easily swapped
out. Therefore, the test included swaping the new sensor,
raising the threshold that the code was measuring
heelstrike at, and to preform more tests on the system.
There were no major code changes
Results - It is clear that the heelstike
and distance sensors are working together. It is also
clear that the new sensor works the same as the old
sensor which was a desired outcome.
The output was also monitored and is seen below.
Next Steps - The next step would be to test the system on different terrains.
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Subsystem: Heelstrike and Distance Sensing (Part 1: Levelground)
Motivation - This test was to combine
the two working subsystems that we had for gait sensing.
These two subsystems were the heelstrike and the distance
sensing.
Procedure - The first part of this
testing was to find a way to attach the Heelstike sensor.
This was done by creating a header that would allow the
sensor itself to not be sodered and make it so they
sensor was easy to remove. After this was done, a class
function was written for the distance sensing and the SD
card logging. This was used during the test to verify
that the system was working.
Code - The rest of the test was to
create a function that will test the value of the ADC
input for the distance sensing and to create log, and
close files for the SD card.
- Distance - The code will set the ADC that is monitoring the sensor. the function will return a float value of the distance sensor at that time. The function does not require any inputs.
- SD Card- This function will set up the SD card and make sure that it is accessible. The next function will create a new file by not overwriting any file that already exists. The next function will write new lines in the file that will contain distance sensing information and also the heelstrike sensor. The last function will close the file.
Results - It is clear that the heelstike
and distance sensors are working together. This testing
was also done with the lower threshold sensor, which
explains why there is almost clipping at the bottom of
the heelstrike curve.
The output was also monitored and is seen below.
Next Steps - The next step would be to test the system on different terrains.
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Subsystem: Heelstrike and Distance Sensing (Part 2: Stairs)
Motivation - With a working subsystem
that combines heelstrike and distance sensing, the next
portion of this test was to test the two sensors on
stairs.
Procedure - The same procedure as above
applies to testing the device on stairs.
Results - Although the distance and
heelstrike sensors can work really when walking on
levelground, this does not appear to be the case when
walking on stairs. This is mostly due to the fact that
all the weight was applied near the toes when walking on
stairs. As a result, the heelstrike sensors could not
pick up enough force to set off the system as shown on
the two plots for upstairs and downstairs.
Next Steps - If the force sensor could not pick up enough force when walking on stairs, a second sensor could be necessary for varying terrain. Or even an automatic timer which could sense when heelstrike could occur based on additional calibration tests.
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Subsystem: Heelstrike and Distance Sensing (Part 3: Levelground with Toestrike)
Motivation - After the stair testing was
done, it was clear that to accurately adapt to terrain,
an additional sensor would be needed. This sensor would
be placed on the ball of the foot.
Procedure - The sensor that was used was
of the same type that was used by the heelstrike. This
means that the same type of header could be created for
the sensor and that it could be wired in the same way. It
also means that the class function that was created could
be used for toestrike as it was for heelstrike.
Results - It is clear that all three
sensors now work. The difficult with these sensors is
going to be placing them in the right location in order
to ensure that there is consistent readings coming from
them.
Next Steps - The next test would be to see how the system works while on stairs
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Subsystem: Heelstrike and Distance Sensing (Part 4: Stairs with Toestrike)
Motivation - Since it was verified that
an addition sensor placed under the ball of the foot
resulting in all three sensors working in synchronicity,
it was then necessary to see how the system works on
stairs.
Procedure - The same procedure as above
applies to stairs.
Results - Since walking on stairs does
not produce enough force on the heel and a lot of the
force is shifted to below the toe, the force sensor by
the toe was picking up most of the force for triggering.
In addition, the distance and heelstrike sensor were
working properly as was tested earlier.
Next Steps - The next test would be using all three sensors and the coding to predict and ultimately, detect what terrain a test subject is walking on.
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Subsystem: Gait Articulation
Motivation - This test was to test the
time it took to dorsiflex and plantiflex the foot in
order to ensure the McKibben muscle and solenoid would
actuate the foot at a natural rate of speed.
Procedure and Results - Multiple slow
motion videos were taken of an individual. The videos
were used to determine roughly how long it took an
individual to plantifex their foot and to dorsiflex it.
In addition the video was analyzed to determine which
period of the gait cycle needed to be plantiflexed. A
video was taken at the same frame rate of an unloaded
McKibben muscle to determine how quickly. The test
yielded that it took about one eighth of a second to both
plantiflex and dorsiflex the foot. The video of the
muscle showed that it was constricting and releasing
slightly faster than one eighth of a second. The arduino
code was modified to reflect this information. Then the
functionality of the heal strike sensor, arduino,
solenoid and muscle was tested and confirmed, as seen in
the video.
Conclusions - The foot can be
articulated at the same rate as an individual's natural
motion and it can be articulated at the desired time of a
person's gate cycle using the heal strike sensor and
arduino.
Next Steps - Build and test a prototype
to test on an individual to determine if plantiflexion
and dorsiflexion feel natural and are occurring at the
desired time during a gait cycle.
Video 1 -Gait
Time Analysis
Video 2 -Muscle
Articulation Time Analysis
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Subsystem: Solenoid Hold State
Motivation - This test was to develop
away to have an unpowered hold state so that when the
orthotic has diminished its pressurized air supply it
will become a passive orthotic, holding the foot in a
dorsiflexed state.
Procedure and Results - The first step
was to conduct research and contact a subject matter
expert. Richard Bullers was contacted from SMC, a company
that specialized in solenoids. Rich suggested a five port
two position double acting solenoid to achieve an
unpowered hold state. This type of solenoid does not have
a returning spring but a separate solenoid to move the
pin in order to open and close ports, using this solenoid
with one of its ports sealed would yield an unpowered
hold state. The arduino code was modified to reflect the
need to output a signal to contract the muscle and a
separate signal to vent the muscle . A five port two way
solenoid valve was acquired from the bad lab and tested
in the same configuration as in the gait articulation
test. The functionality of the hold state was verified as
seen in the video.
Conclusions - An unpowered hold state
can be achieved.
Next Steps - We need to block the second
port along with refining the air muscle design to ensure
there are no leaks. We also need to find a way to exhaust
the vented air.
Video - Muscle
Articulation with Old State
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Subsystem: Data Storage
Motivation - This test was performed to
help determine how much much of memory capacity will be
necessary for a micro SD card to hold through typical
usage of the device.
Procedure and Results - A five minute
walk was performed with the device and current SD card.
After five minutes of walking, the SD card had used
approximately 2.95 MB of data storage. A screenshot of
the properties is shown below.
Conclusions - A typical day's worth of this device does not use up much space on a micro SD card.
Next Steps - The most we'll need for memory capacity on a micro SD card is 4 GB.
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Subsystem: System Housing
In order to hold the PCB board that contains the distance sensor and force sensor, PCB housing.
Next Steps
1) Research various assembly options for attaching the IR
sensor
2) Look for various adhesives for waterproofing the
system
3) Add the thru hole types and screws
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MSDII Test Plan
Build, Assembly, and Debug Plan
During this phase, progress was made on the Build, Assembly and Debug Plan. The additions on the mechanical side consist of Upper Muscle Attachment Base and Integrated Plug build plans as well as preliminary assembly and integration instructions. We plan on updating this document much more in the next phase.Build, Assembly, and Debug Plan
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Risk Assessment
Resources
- Plastic Strap Adjusters
- Paintball Shots Per Tank
- Air Muscle Orthotic and Exoskeleton Benchmarking
- Paintball Tech Shots Website
- ATmega328 Microcontroller Datasheet
- GP2Y0A0YK IR Long Distance Measuring Sensor
- Aurduino solenoid control
- Watertight Box
Past Projects
- P12029 - Robo-Ant: Untethered Air McKibben Muscles
- P13001 - Active Ankle-Foot Orthotic: Tethered Air Muscle
- P13002 - Ankle-Foot Orthotic Un-Tethered, Mechanical
- P14029 - Robotic Fish Powered by Hydraulic McKibben Muscles
Detailed Design Review
The Previous Action Items taken during the last review have been updated.
The following Agenda was used during the technical review on November 18.
The following Notes and Action Items were taken during the phase 4 Detailed Design Review.
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- Node updated 2015-05-11 16:04 by mde5019