From DDL Wiki

Client Comments on Report

We received your report. Your summary suggests that weight reduction and functional improvements are the two primary areas you have identified for improvement. What do you mean by "functional improvement"? Your findings that the primary failure modes are material wear and spring fatigue are interesting.

Detailed comments follow

• We appreciate the clear and well written overview

• You mention that the industry standard prevents alternative boot designs. Is it possible to design a boot with two configurations - one that meets the standard and one that is better for walking?

• Your descriptions of product use are nice. How/where does the user typically carry the device while skiing?

• Please include product function descriptions to explain how the product works mechanically.

• Please label the components from your BOM in your assembly picture. Any overall findings from the BOM?
  • Please see the BOM section. The picture of the entire product has been updated such that each subassembly is listed.
  • Also, major findings from BOM are reflected mostly in the DFX (Design For X) sections.

• Parts 1-2 list "adhesives". Are there multiple parts here? How is the truss structure molded?

• Please be sure any subassemblies in the BOM are labeled as such
  • Please see the BOM section. The picture of the entire product has been updated such that each subassembly is listed.

• Interesting thoughts in the DFMA - the line balancing rationale for including two rotating hooks is interesting. If the plates on the bottom of the ski boot are secured without screws, why are the screws needed?
  • The plates and the bottom of the ski boots have series of plastic channels so that the assembly of the parts (lining up the plates to the bottom of the boots) can be accomplished with ease. Although these components can be secured without use of screws, the connections between the plates and the boots' bottom need to be little more rigid than plastic pins holding them. When the ski boots are under the operation, great deal of stress is applied to the bottom of the boots both in normal and tangential directions. As a result, having plastic pins as only means of connections between the plates and the boots would pose a high probability of failure. In addition, using screws for the joint allows the end-users to replace the plates when they are worn out. Thus, the structures on the ski boots' bottom are designed primarily to make the assembly process more efficient rather than to secure the plates to the boots.

• Your LCA concludes that EOL dominates production based on $1M activity in each of the sectors, but $1M worth of equipment will not produce $1M worth of waste management at EOL. Please reconsider. Also, please comment on how representative the categories you identified are.
  • According to "THE PRICE OF SOLID WASTE MANAGEMENT SERVICES IN VERMONT" a study conducted by DSM Environmental Services, Inc. for the Vermont Department of Environmental Conservation (2005), managing 1 ton (1,000kg) of waste costs approximately $100. As the product analyzed in this DFE (WalkEZ) weighs about 1kg per unit, the waste management cost per unit is calculated to be around $0.10. The market price of the product is approximately $20 (200 times greater than the cost of waste management). Therefore, the simulated environmental impact per $1M from the EOL sector needs to be divided by a factor of 200 before being compared against the environmental impact per $1M from the manufacturing sector. (Please see DFE section of the original report)
  • Combining the cost per unit of product from the manufacturing and the EOL sectors and EIOLCA results based on $1M input yields the following. The manufacturing sector contributes approximately 0.602g of toxic release, 26.0g of conventional pollutants, and 0.0144 MTCO2E of GHG to the environment from producing one unit of the product. On the other hand, the EOL sector is responsible for 0.00151g of toxic release, 0.25g of conventional pollutants, and 0.00076MTCO2E of GHG per unit of product. Thus, it is apparent that the manufacturing sector is far more responsible for all the environmental impacts discussed here. (Please see DFE section of the original report)
  • The manufacturing sector of the walking attachment is best represented by "Sporting and athletic goods manufacturing" sector. The example of the industries included in the sector include but are not limited to manufacturing of ski boots and various plastic athletic equipments. Given that the product is made of rubber materials (commonly used in several athletic equipments) and that the product's primary operation is for athletic/leisure purposes, "Sporting and athletic goods manufacturing" sector best describes the manufacturers of ski boot walking attachment - a very unique product. (Please see EIOLCA section of the original report)

• Good findings on FMEA. What scale are you using? What do you mean by "use hydraulic/piston system instead of springs"?

• Your modeling and analysis results look quite interesting, but you do not document enough about how your model works for us to understand the assumptions behind it, so we can't know how to interpret the results. Did you build the model from scratch, or is it built on models from another source? What are the basic kinematic and kinesiological assumptions that generate the results you report? Why don't you plot GRF directly? Please explain the even step / tilted step cases and your contact width assumptions.

• Nice explanation of your wear tests.

We are looking forward to seeing your market research findings and new ideas in the next report.

Client comments on the Mechanical Analysis

The mechanical analysis is interesting and well-performed. The comparison of curves in the normalized height graph is nicely presented. The durability test shows the team’s additional effort, which is and useful and appreciated. My few comments:

• The Matlab analysis begins with very little information. Please state your assumptions clearly and explain how you carry out the simulation.
• There should be many ergonomic settings in your analysis. Please explain them clearly. If any reference is used, please indicate them in your analysis.
• A picture should be included in the beginning of step simulation to indicate the location of hip point, hip flex angle, knee flex angle, and ankle flex angle in the three-bar linkage representation. That will be a great help for a client reading this report.
• The GRF equation seems not correct because force should be calculated from mass and acceleration (d²y/dt²), not velocity (dy/dt). Please verify it.