Talk:Car jack

From DDL Wiki

Jump to: navigation, search

First Report

We received your report on the car jack, and we are impressed with your work. You have also identified some excellent opportunities for improvement – we look forward to your research and concepts in the next report. Detailed comments follow:

  • Your diagram is very helpful in understanding operation; however, a picture of the assembly with parts numbered would be more helpful. You seemed to have missed describing the mechanical function of the jack. You have described it somewhat in your “normal use” section and your parts list, but we were expecting more detail about how the device itself works as a system. A labeled picture and some text would help, and a free body diagram would also help.

-A labeled picture was added to the disassembly section as well as a new section to better detail the mechanical function

  • Many of the aspects of the report appear to be only headings with bulleted lists. We are happy to see your bulleted lists, but we would normally expect to see a paragraph explaining each list and outlining conclusions of each section. For example, there is no introduction under the “product study” heading to let us know what aspects you are focused on, and does the heading “input” refer to the component that receives input from the user? Some explanation would be helpful.

-Introductions have been added throughout the report, flowing into the lists, to make it more in a report style.

  • Your “normal use” description of use is quite good, although you may want to consider additional issues: Many of our customers, for example, will forget to loosen lug nuts prior to taking weight off the wheel, which can make wheel removal difficult.

-The normal use section was expanded to include a tire changing section

  • You have identified some excellent opportunities, including lighting/visibility, knuckles to ground, rotation of entire jack, and improved breaker bar. We are really looking forward to what you come up with next.
  • We appreciate your documentation of the dissection process
  • Your DFMA & DFE analysis seem right, but what are your conclusions? Do you believe the jack is already fully optimized along these dimensions?

-The DFMA and DEF were updated to include conclusions and to make them clearer

  • Interesting conclusion that failures are more about the user than the product design. It looks like you have proposed prominent warning labels as the primary solution. This is okay, but from a legal standpoint, even warning labels don’t always protect us if the conditions of use are considered “reasonable” and “common” by a jury – it is best to aim for a design robust to common use/misuse. Many of our customers will find themselves in need to change a tire on moderately uneven surfaces, such as gravel, the shoulder of a road, on snow and ice or mud, etc.). Safety is very important to us, and we want to avoid any accidents, even under less than ideal conditions.
  • Also, please avoid phrases such as “user stupidity” on all documents – if any such documents found their way to the press or through an investigation, it might point to questions about our concern for our customers.

-Phrase eliminated

  • In the FMEA, it appears that the items that were most difficult to detect received the lowest numbers. This seems backward – can you comment?

-That was an error, it has been corrected

  • Your preliminary analysis is interesting. Can you comment on what this tells you about the design? Also, please include a free body diagram and the numerical analysis used to derive the plots you’ve shown. I assume the plots were constructed with simple statics equations, whereas for stress on the members you have used a FEA analysis. Please also include some details about the FEA analysis, such as boundary conditions, etc. and detail your conclusions and recommendations. Also, can you comment numerically on the output/input force ratio? Is it set properly, or could we increase the applied force to get greater lifting speed?

-The Prelimiary Analysis page has been updated to include more conclusions about what the numbers mean in terms of design. Also a free body diagram, and other calculations have been included.

Additional Comments

In your executive summary you mention that you have been able to gain a significant background in the product and see areas where improvement is possible. However, it would be very useful if you could actually list these opportunities, and present your conclusions in the executive summary, so that they could be easily and quickly be understood.

-The executive summary has been edited to include more of our conclusions.

Your disassembly page is wonderfully complete, and your pictures of the process under way is quite informative. However, when you have pictures of the pins being ground off, and the result after, it is unclear what the pins looked like before they were ground off. I realize it is impossible to take a picture now, however, if you have an old picture of these parts attached to the jack, it might be useful to post them.

Your preliminary analysis was very informative, and the movie a very unique idea. However, did the movie reveal any new information to you?

-That has been included in the revised analysis page

Your page layout is very clean, and presents many results in a small space, with easy access to more in-depth information.


We received your response to our comments on the first report, and we are satisfied. How does the calculated user input of 18lbs (a coupling) compare to observations – does it seem reasonable? A FBD of the input crank might be helpful in the design of your knuckle protector.

Personal tools