Common, But Strange, Product Design Terms

Lately I have been pondering over some of the common product design terms we use in our industry. If you really think about some of these terms, you may find like me that in reality they actually make no sense at all. Perhaps they can tell us much about how software vendors have changed our world.

Here are just a few that I think about. There are many others, but I'm going to pick on these three for now.

Top-Down Design

When humans first designed ships that crossed the oceans, do you think they used top-down design or bottom-up design? I really want to know. How did they do it?

I understand what top-down design actually refers to, but does the contrary, bottom-up, ever yield good design? is there really another choice? Is this term simply used due to the nature of our CAD tools we use today? Are we forced to use this term due to some awkward deficiency in our CAD tool? Try to forget about your favorite CAD tool for just a moment. How would you REALLY approach the design?

In-Context Design

What is the contrary to in-context design? Out-of-context design? What is that? Is real product design ever done out of context? No, never has, never will. So why do we need this term? When the rocket scientists designed the rockets that sent men to the moon, did they design them in context or out of context?

Do you suppose they went to the rocket parts bin, and started bolting parts together to make the rocket? I guess that would be an example of out-of-context design (and bottom-up design), and I bet it wouldn’t work. Do we really need special tools and training to keep our designers from designing out-of-context? Again, why does this term exist? Ignore your CAD tool again for a moment. How would you REALLY design a product; in context or out of context? Is there another choice I missed somewhere along my education or career. Does the use of the term have something to do with our CAD tools?

Design Intent

Is there a difference between "design" and "design intent"? I once heard this response from someone after seeing a demonstration of direct modeling: “No, we could never use direct modeling with our products. Our products demand firm design intent”. (Or something close to that). Wow, many thoughts crossed my mind. Thoughts I couldn't repeat in front of them, but will share here: “Are you telling me that your products are so sophisticated that they couldn't be designed without history-based modeling?” Or worse yet: “Are you saying that you can’t design without history-based modeling?” Another crazy thought: “So you think that this rigid design intent will keep you from making mistakes? Oh, right.” Hopefully they are just telling me that it would be more difficult to design their product without it. I’ll think positive and assume the latter.

It’s almost as if humans were never before able to design, and convey the intent of the design, until we had CAD with history trees. History trees certainly provide a useful method of documenting your design "intent". Do they provide the best method of conveying your design "intent"? (And do we really need to use the word "intent" after the word "design"?)

How do you suppose the caveman above was ever able to document and convey the intent that the center hole had to be concentric, at a specific tolerance, to the outer diameter of his new round wheel? Eventually it had to be done. How’d he do it? By the way, how do you REALLY define design intent? What defines it? If your answer has anything to do with CAD - you are wrong. There are certainly many ways to “document” and "convey" your design intent - with history trees, with 3D models, with 2D CAD, even with paper and pencil. What do you suppose is the easiest and most universally understood method of documenting and conveying your design - intent?

Bottom line: Do our tools fit the process of design, or are we forced to adjust the process to fit the tool?

Paul

Some Fun Direct Modeling with Chain and Sprocket

I hear the term "direct modeling" being used and abuse to describe many different things. To me direct modeling refers to a CAD systems ability to interact with edges, faces, features, parts and assemblies directly during the design process. It means that the CAD system is intelligent, not necessarily the geometry. It means that the CAD system can intelligently interact with geometry regardless of how or where the geometry was created – basically; “what you see is what you get”. There is already a lot of useful information in a solid body. A direct modeling system should be able to recognize this and take advantage of it. Here's an example.

Below is a video I created after doing some direct modeling with some drive chain and a sprocket using Creo Elements/Direct Modeling. As I mentioned in the video I am not sure how useful this is in the real world, but I found it interesting and wanted to share it. I personally have not done much design with drive chain since my brother and I designed and built a go-cart, about a thousand years ago. The chain kept falling off on those tight corners, (and I lost part of my eyebrow on another tight corner. "Wear a helmet, stupid" - Whatever!).

Chain is interesting simply due to the relationship from one link to the other. By recognizing the physical properties of the solid bodies that make up the chain, you can visualize some of these interesting behaviors, especially as it interacts with the sprocket.

For this example I started out by downloading the sprocket and chain in STEP format from a 3D content web site. I then created the simple shaft in the center of the sprocket. All parts are dumb solids, and there are no assembly relationships to begin with. In the “Position” function of Modeling there is an option called “Physical”. If you turn this option on, the system will recognize the physical properties of the 3D solid models, and recognize the relationships between models in real time (or very close to it). You will notice that I do eventually put a fixed relationship onto the shaft, but I apply no other relationships to the models or assembly. There are no “user defined” relationships defined between the chain and the sprocket, and there are no assembly references. What you see is what you get. Watch:

What I find interesting is the various ways of using the “Relations” capability together with the “Physical” option when moving parts. The system doesn't recognize gravity, acceleration or anything like that so it’s not doing kinematics. It simply knows moments of inertia, CG and the fact that these models are solid. And best of all – it makes no difference how the models were created or assembled, and on what CAD system they were created or assembled, (just had to throw that in).

Paul