Preliminary Detailed Design
Team Vision for Preliminary Detailed Design PhaseWhat did your team plan to do during this phase?
Our team plans for the preliminary detailed design include developing a good understanding of the product we aim to fabricate using recycled materials. By dissecting shoes, developing CAD sketches for critical technology, and making test plans, our team aims to develop a more structured approach of what to implement for our project execution plan. Additionally, our team plans to provide a list of materials along with associated characteristics such as cost, lead time, and other factors to better help plan for what the need will be in the spring.
What did your team actually accomplish during this phase?
During this phase, the Skreppa team decided to become a bit more hands-on in comparison to previous phases. The team acquired old, worn out shoes from various donors and wanted to gain a better look inside - so we sliced them in half. This launched our understanding of shoe construction which helped us move forward in our design and prototyping process. From here, we met with Chris Flemming - a Senior Industrial Design (ID) student with a similar capstone project. He educated the team on different aspects of shoe design and construction - which included a visit to the ID workspace. After this meeting, we were able to construct a shoe last - sized at a women's 8.5 foot, make test plans, and begin our prototyping with our connecting mechanism.
Feasibility: Prototyping, Analysis, Simulation
Throughout the Preliminary Detailed Design phase, the Skreppa team worked together to determine which forms of prototyping would benefit the project the most. At the conclusion of these discussions, the team decided that we will utilize 3D printing and simple modeling for the prototyping of the shoes themselves. Specifically, 3D printing will be utilized for making a shoe last and other small components that can be designed, made and redesigned quickly. This is under the assumption that the team has stable access to 3D printers, in addition to design tools like CAD software - specifically Creo. The simple modeling encompasses any Finite Element Analysis (FEA) upon completion of the final designs. Given that the overall design for the Delta shoe has changed since the last phase, this FEA analysis will help ensure that there are no specific pressure points or easily noticed points of failure.
Regarding safety, the Skreppa project has a slightly unique case to analyze. Given that our project will hopefully be used in the consumer market, we have to take a few different safety features into considerations that most projects wouldn’t need. Mostly human testing - this is to ensure comfort and that no one is harmed in the long-term use of our shoes. In partnership with FEA, the team is seeking to ensure that all potential safety hazards are eliminated before human testings.
Given our unique project, every use case scenario that we analyzed in the Problem Definition phase is applicable. For our main analysis, however, we tend to analyze the hardest case scenario. That is the scenario that will push the shoe to its absolute limits, which in this case would be any use case regarding hiking. Given that there is a wide variety of terrain, we want to make sure that the Delta can hold up anything that it crosses.
Inputs and Source
- Engineering Requirements
- Concept Selection
- Results of preliminary prototyping, analysis, and simulation
Bill of Materials (BOM) & Budget
During this phase, the team sought to evaluate all aspects of the project and worked to determine what would be physically needed to complete our task. Below, we have our working Bill of Materials (BOM) for the project’s lifetime. This is taking into consideration a multitude of factors including manufacturability, availability, resources available, and on hand experience.
With the nature of this project, many of our items will be exceptions to the MSD purchase list. Since this is the case, items will be purchased on an ad hoc basis with purchasing coming at a time slightly before need. So far, the team has identified enough material that should allow us to make at minimum one pair of shoes for the cost of $144.18 which is well under the cost of the total budget. That being said we will be creating a lot of this technology in-house so that cost will be internalized to fabrication with time and effort of the team.
Input and Source
Using our Engineering requirements we created test plans to quantitatively analyze comfort, sole switch time, cost of one pair of shoes, outsole cure time, and topsole fabrication time. Topsole fabrication time and outsole cure time will be simple estimations based on initial prototyping time. Cost of one pair of shoes will be based on the cost of materials used in one pair. Comfort will be analyzed using human volunteers rating on a visual analog scale. Sole switch time and ease of use will also be tested with these volunteers.
- Comfortable for customer
- Based on Identifying Clinically Meaningful Tools for Measuring Comfort Perception of Footwear
- Maximize comfort
- Ideal goal 3.5/5
- Marginal goal 3/5
- At least 50 test subjects
- Women between 100 and 200 lbs
- Usually wears between 8 and 9 US women
- Exclude subjects for
- Known foot problems
- Current or recent injury
- Recent surgeries
- Abnormal gait
- spastic gait- drag foot while walking, very stiff looking
- scissors gait- legs cross and hit while walking, indicated by inward bending legs
- steppage gait- toes point toward the ground while walking, often toes will scrape the ground
- waddling gait- short steps and swinging body
- propulsive gait- head and neck pushed forward, looks like a forced slouch
- Screen participants
- Ask for their name, age, weight bracket
- Ask for their usual shoe size
- Ask them to walk in their own shoes to observe gait and watch for exclusions
- Changeover time test
- Demonstrate change over technique
- Allow participants to practice changing each sole twice
- Time how long it takes the participant to changeover sole three times for each sole (9 times total)
- Comfort test (would ideally be done in two
sessions) repeated six times each top and outsole
- Familiarize subject with rating scale
they will be using
- Ask subjects to nominate the change on the horizontal 100-mm VAS that would represent a meaningful change in comfort for them
- Make sure the shoe is properly fastened and the bottom is attached properly
- Ask them to walk 200m (will be marked for
participants) at a comfortable walking speed
- Be sure to time each walk
- At the end use horizontal 100-mm VAS
- During each rating do not allow subject to see other rankings
- Ask them to fill out VAS for each of
- Overall comfort
- Arch comfort
- Heel comfort
- Familiarize subject with rating scale they will be using
- Analysis of Comfort Testing
- The minimally clinically important
difference (our error measurement)
- Subject approach- take the average of subject proposed MCID (mm)
- Take the average rating of each combination (mm)
- The minimally clinically important difference (our error measurement)
- Screen participants
- Environmental Health and Safety, Verification of
Sustainably Sourced Material
- In this stage, this will be confirmed by item descriptions
- Raw material cost <$80 on small sample run [1 pair
of insoles, 3 pairs of outsoles]
- This will just take into consideration material cost. Can be calculated with dimensions of material used and cost to purchase.
- Outsole Cure Time Length
- Can be timed during fabrication
- Long Lifetime for insole, outsole, and locking
- This will be done in part by the human testing of switch over time to be sure the joining mechanism can stand up to an inexperienced user. From this wear an initial failure point will be identified.
- Maximum expected weight of user 200lb
- Heel of shoe needs to withstand ~3X user weight= 600 lb
- Toe of shoe should withstand up to 7X user weight = 1400 lb
- Insole Fabrication Time
- This can be tested by recording fabrication time for each component fabricated
- Outsole flexibility
- To test this press the toe portion of the sole on bathroom scale at approx. a 30 degree angle => should not require more than a 5 kg (11 lb) pressure to bend the shoe
Inputs and Source
- Engineering Requirements
- Feasibility Models
Design and FlowchartsDuring this phase, the Delta changed form yet again. In the past phase, the team determined the usage of a middle mechanism unnecessary. In addition to this, we wanted to simplify our scope and the overall production of the shoe. Obviously, this was cause for a complete redesign. From the confusion caused by the last review, we decided to redefine how the team pursuing a useful design. This process can be found below:
Additionally, we wanted to double check that our process and new design still aligned with the Engineering Requirements that were defined in the Problem Definition phase. This discussion yielded the following flow-chart:
From these two considerations, the team was able to revise the current design to be a bit more user-friendly. Presently, the shoe fastening mechanism now features 3 main points of connection. First, you will have the back part of the heel slide on a small track - however, the location of this is subject to reverse. That being said, conceptually this design is to a cover of a calculator - which will serve as a hard stop for the outsole. This will be made out of a recyclable thermoplastic material, potentially covered with a 2 ply composite laminate to ensure a longer lifetime. The secondary mechanism is a wedge that will help hold the outsole in place. This will be located at the center of the outsole. Some concerns have arisen regarding the comfort of something of this nature. This will be expanded upon in the coming Detailed Design phase. Finally, the third mechanism that will ensure the stability of the Delta's structure is similar to elastic hooks. These will be located at the toe of the shoe and will hook onto a loop near the tongue of the shoe. The hook and loop mechanism will have at least 3 locations as to where to strap, which is dependent on the type of experience a user wishes. This will ensure that there is a vertical force acting on the shoes, specifically opposite of the track.
Inputs & Source
- Concept Selection
- Systems Design & Interface Definition
Output and Destination
- System Hierarchy
- Bill of Materials
- Test Plans
During the Preliminary Detailed Design phase, the Skreppa team reanalyzed the project risks and determined that for the most part - they can stay the same. We felt as if the risks that we have analyzed in the past two phases reflects the current risks that are in mind for the current and future phases. However, some small updates have been made. Those things include
- Budget risk was added due to funding being in question moving forward from the customer.
- Materials were identified that aren’t in the purchasing portal. Because of this, the purchasing process becomes more difficult because exceptions will have to be made so that material can be acquired
- Since our design changed back to a 2 piece configuration, the joining method will continuously have to be monitored so that process is robust so that topsole and outsole will not come apart.
Below, you will be able to find a downloadable PDF file of the risk assessment table as it stands currently.
Design Review Materials
Plans for next phase
- Finalized mechanism design
- Decisions regarding scope
- Shoe last created
- Testing plans finalized
- Pattern/Template drawn up for topsole
- Project plan for next semester