From DDL Wiki

First Report

We received your report on the paintball marker and are very impressed indeed. Your analysis and documentation are well executed, and your conclusions and recommendations are clear and up front. We are excited to see what you come up with in the next report. Detailed comments follow:

• We were impressed by your insightful discussion of modularity – this is an important element for our product line, and we actually spend a lot of effort pricing upgrades to avoid cannibalization (ex: loss of demand for high end gun if price difference is too great compared to low end gun)
  • We appreciate your comments
• Your executive summary is very clear
  • Thank You
• You mention the target velocity of 300 ft/s, what would be an acceptable range, and does the product fall within the range?
  • This range would be centered around 275 fps with a range of about 250-300 fps, this has been addressed in the "Product Requirements" Section
• Nice discussion of customer needs
  • Thanks
• We noticed that you did not include the user as a stakeholder. For us the user and any possible players who may be targets are our first stakeholders, and safety is a primary issue, even under conditions of misuse, since sometimes children can get hold of the marker and try to use it without proper instruction.
  • We have included players in our stakeholders
• It is interesting how many steps are involved in setting up marker. What types of failures result if the steps are not followed properly? A labeled picture would help in understanding here (ex: hopper not labeled in first figure).
  • This has been addressed in an additional notes section under Operation Procedures
• Your opportunity of firing multiple projectile is quite interesting – I’m surprised that this does not already exist.
  • It has been incorporated at larger scales for items such as gatling guns and mortars, but we are aiming more towards a design that would be marketable to the general playing population and would be used in every day use.
• Wonderful diagram – it really helped with explanation of function. A few questions: Is the striker pressed against the valve pin when at rest (before cocking) by the striker spring? The seal appears to be formed by the valve pin being held against the valve body (against an o-ring, I assume) by the valve spring. How long will the valve remain open after being struck by the striker? Is this just a function of the spring constant of the valve spring, or also the gas pressure? Also, it seems that the bolt first moves the ball forward and then the gas completes the job – is this a two-part propulsion? Why does the bolt need to contact the paintball first?
  • These items have been addressed in the Functional Operation section of our report
• Nice job highlighting conclusions from each section
  • Thanks
• You mentioned that part 10 is “milled and turned on lathe”. Do you think it is milled from an initial block stock? It seems like a large amount of material loss for each part.
  • We believe this part is machined in this fashion but probably from an "L" shaped block of aluminum, this has beena ddressed in our table. We are open to other suggestions for this particular part as we see no other obvious alternatives
• Your exploded view CAD drawing is very helpful in documenting product
  • We thought it would illustrate the internals and assembly a little bit better.
• Good thoughts on DFMA and DFE. Don’t forget that it takes energy to compress air, so if many cartridges are used in the lifetime of the marker, it’s not just the CO2 from the cartridge released, but also the CO2 from the coal burned to run the compressor to producer the cartridge, etc. How many cartridges are used per year per person, do you think? Is this negligible, or something we might want to consider?
  • This has been addressed in the DFE section and it is believed that the CO₂ released is relatively minimal, but there is also the alternative of compressed air
• You have some good ideas for FMEA; however, we typically expect use of the standard table that identifies severity, occurrence, and detection for each mode – please include in your next report. Also, what are your conclusions – should we pursue any of these issues?
  • This item has been changed to fit this format
• Can you provide a numerical analysis of the pressure in each chamber before and after triggering and estimate the force on the paintball – see if this matches the ballistics you observe.
  • We have included some numerical analysis in the "Functional Operation" section to display the actual pressure acting on the paintball

Additional Comments

Your executive summary is very well written and covers a wide number of topics.

• Thank You for the feedback

Your FMEA, while thorough, could use a more organized layout.

• This has been adjusted

Revision

We received your response to our comments on the first report, and we are happy with your responses. How dies your calculation of 24 psi in the barrel (average) compare against measurements you can take of pressure in the cartridge – does this seem like the right number? What aspects have you ignored or simplified in the analysis, and would these make the required pressure higher or lower than you calculated?