Automotive and 3D Design Knowledge
Inside Digital Design and Product Development
Explore practical insights into automotive and product design, digital surfacing, visualization and modern 3D workflows.
From Autodesk Alias and VRED to real-world design processes, events and customer perspectives, this is where we share the ideas, tools and experiences shaping digital product development.
Hybrid Modeling
with Autodesk Alias
How creative can you be without losing precision in 3D modeling?
The power of a hybrid SubD-NURBS workflow.
A good product doesn’t just materialize at the push of a button; it tends to start with a thought, a jumble of ideas, and a rough vision. But when designing products, two worlds always collide: free-form design and technical engineering.
While aiming to create a concept design for an aerodynamic time trial bike, this very problem became apparent - one that often slows down the design process.
So how do you find the perfect balance between free-form design and precise engineering in the process? What workflow can facilitate the smoothest and most dynamic implementation possible to ultimately produce a fully developed 3D model?
The project began with rough brainstorming, form studies, and the development of a concept. The blend of various influences - from clear, geometric structures to organic natural forms - inspired a dual approach to the bicycle’s design language. This also involved rethinking the classic frame geometry.
From the initial thoughts and inspirations, a concrete design direction gradually emerged. Digital sketches were created, followed by AI renderings, to make different ideas visible and comparable as quickly as possible.
The early transition to 3D modeling software was crucial in this case, as it allowed for the import of numerous technical specifications and components that guide the design through constraints, and the focus was clearly on a high-quality surface model.
Hybrid Workflow
Autodesk Alias is well-known as an established program in the automotive sector for Class-A surfaces of complex vehicle shapes, but the tools offer just as much potential for other industries as well. Particularly exciting is the ability to combine SubD modeling and classic NURBS surfaces in a single workflow.
Both options offer the best of both worlds. NURBS is ideal for technical reference geometries and precise surface control. SubD offers enormous advantages in the concept phase: geometries can be created and modified quickly, and dynamic adjustments are possible without the need for time-consuming surface reconstruction. This allows for a greater focus on proportions and overall impact without getting bogged down in specific surface details.
Especially for a bicycle, whose design is heavily influenced by technical components, this flexible workflow is extremely promising during the concept phase. NURBS offers seamless integration of technical data and important reference points, while SubD provides a dynamic, creative workflow.
Challenges in the Process
Good key sketches do not automatically lead to good 3D models. One example of this was connecting the head tube directly to the bottom bracket. In the side view, the idea looked convincing; however, in the 3D model, the down tube ended up significantly wider than intended. The bicycle lost its elegance and appeared clunky.
However, this is precisely where SubD polygonal modeling in Alias can demonstrate its strengths. Thanks to the flexible control points (vertices), proportions can be adjusted quickly until a balanced compromise is found between the original design concept and the technical model implementation.
While NURBS has its advantages in surface control and precision, SubD offers a significant speed advantage and creative freedom without having to think in terms of construction. This allows early shape adjustments to be made much faster without having to reconstruct the existing surface structures.
Nevertheless, in Alias you are not limited to either of these two modeling techniques. Creating the cable cutouts in the bicycle frame using SubD would make the model unnecessarily complex due to the large number of vertices. In combination with NURBS surfaces, cutouts within the SubD surface structure can be implemented much more easily.
Best Practices
Just as there are some important tips and tricks in classic NURBS modeling to make the process more enjoyable and efficient, there are also helpful tools available for SubD modeling:
1) Symmetric Modeling
Like most modes of transportation, bicycles have a symmetrical basic structure. There are two tools in Alias for achieving symmetry, each serving a different purpose during the design process. Subdiv Symmetry Align is particularly useful in the concept and creative phase of modelling. It previews the limit surface shape across the center line as if the model is a single welded subdivision object. Since it does not create actual geometry across the symmetry plane, the model remains lightweight.
Symmetric Modelling, on the other hand, enables true symmetrical editing. Every modification made, is automatically synchronized to the mirrored geometry in real time, ensuring consistent geometry throughout the modeling process.
2) Proportional Modeling and Transformation
The combination of Rotate and Non-Proportional Scale can be applied to vertices in SubD modeling just as it is in NURBS. First, a pivot is defined, and then the vertices can be proportionally transformed using the tools without having to select each individual vertex.
3) Combination of NURBS and SubD
In certain situations, it makes sense not to unnecessarily complicate the shape geometry of SubD surfaces with many additional vertices and instead continue working with NURBS surfaces.
Intersection surfaces are a good example where vertices can be saved, resulting in a cleaner outcome. This hybrid approach offers particular advantages when dealing with technical reference surfaces and specifications, helping to keep the SubD topology as simple as possible.
Conclusion and Outlook
The basic concept was now in place after several rounds of iteration. Harmonious proportions had been defined, technical specifications incorporated, and the original design idea translated into a 3D model.
The advantages of SubD modeling were particularly evident in the early development phase. There, quick adjustments could be made with immediate feedback, resulting in a dynamic workflow between design and technical specifications.
The project is now at another exciting stage. To prepare it for potential future production, surfaces must be further refined so that highlights and transitions flow perfectly, and aerodynamic aspects must be taken into account more precisely.
This will be covered in detail in the next part.
