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SRAM And Autodesk Reimagine The Bicycle Crankarm

In the decades that I’ve been an avid bicyclist, there have been too many design breakthroughs in the sport to even count. Cogsets have gone from five gears to twelve (yes, I’m old enough to remember people bragging about getting a new ten-speed bike). Frames, once offered in a great variety of materials so long as you loved only steel, are now also made of aluminum, titanium, and carbon fiber. Brakes were calipers then cantilevers then V-brakes then discs. Mountain bikes appeared, got suspension forks, then became full-suspension wonders. And so on…

But the humble crankarm—that bar your pedal threads into, which your pedaling motion rotates to turn the crank and its chainring and transmit your pedaling power to the rear wheel through the chain—has looked pretty much the same all that time. Sure, its shape has changed a bit over time, and it’s had its own evolution of materials of construction just like your frame, as well as various changes in how it mounts to the crank spindle. But there have been no revolutionary changes to its basic appearance or its design as a monolithic “beam.”

That is, until now. Chicago-based component-maker SRAM teamed up with Autodesk and made use of the generative design feature of its Fusion 360 design program to come up with several iterations for revolutionary new designs for these small but critical bicycle parts.

How they got to that point is a tale unto itself. “It’s what we call an ‘epic story,’” explained Sean Manzanares, Senior Industry Manager, Manufacturing at Autodesk, a die-hard cyclist who’s been involved in the project since its inception. Autodesk had become a member of MxD in Chicago, one of 14 federally-sponsored institutes across the country that make up Manufacturing USA, created to secure U.S. leadership in advanced manufacturing technologies. “We got 1,000 square feet on the MxD Factory Floor, which opened in February 2019,” he said. “We needed flagship customers for emerging tech—people ready to think differently. We got with the SRAM folks through some internal contacts, and met and kicked around different ideas.”

Will King, Senior Design Engineer at SRAM, was one of the people pulled in to work with the new design team. “I’ve been a lifelong cyclist, so I was super-excited to combine that passion with my work,” he said. “I dove right into being an expert in crankset design. Generative design is made so you think differently about basic design. We chose to focus on crankarms because they’re a structural component that has to be safe, but we thought they offered us the opportunity to cut weight if we looked at them this new way.”

The fundamental difference in using generative design is that, rather than starting with a drawing, the designer starts with the parameters required for the end product. For the crankarm, that includes the forces it must withstand, as well as specific critical dimensions. “It has to be shaped so that it keeps out of the way of the bicycle frame and the rider’s heel,” King said. “You can also specify fabrication method, whether it’s cast, forged or 3D printed.” Once the parameters are entered, the system generates thousands of potential solutions in just a few hours, and identifies the top few options that best fit the requirements.

“You’re going to see outcomes no human ever would have thought of,” Manzanares said. “That’s the secret sauce. We were able to cut out whole pockets of materials.”

“The old way, we certainly couldn’t do things overnight,” said King. “And we might have had 100 different ideas. Generative design helped us understand design aspects we’ve been teetering on, like removing all the material that’s not needed. It also helps remove barriers to the design process, allowing the engineer to get to the final product more quickly, optimizing for weight, cost and stiffness. It speeds up the design time, and time savings is cost savings.”

The end results from the design team employ differing materials of construction, and vary from something that still looks quite a bit like any other crankarm, but with significant portions of material removed, to a futuristic design that resembles a structural truss. These aren’t finished products yet, but they’re being tested in real-world conditions. “I have the titanium cranks on my bike,” said Manzanares. “They can handle 10 g’s [or ten times the force of gravity]. They’re all prototypes, but what we got out of it is tribal knowledge. So now it’s about, what lessons have we learned to take forward? I’m so excited to see this at the one-yard line.”

The prototype crankarms being tested out on the trails. Image courtesy of Autodesk

At SRAM, it’s a great fit with their business model. “We design products to get to the podium in the Tour de France, or to hope for medals in the Olympics,” King explained. “This helps us get to the finish line faster and more educated—to see where material needs to be, and where it can be removed. Generative design has a great app for our traditional construction materials, helps us understand loads and constraints, and pushes ideas we can evaluate.”

There’s one central feature of Autodesk’s program that became an unforeseen critical advantage during the project. “We got together last January and decided to work on crankarms,” said Manzanares. “Then the world shut down. The benefit of Fusion 360 being cloud-based was that it allowed us to work effectively together between California and Chicago.”

For both companies, it’s about looking to the future. SRAM recently acquired Time Pedals to add to their lengthy list of component brands, and they also recently unveiled a line of electric shifting components priced for the middle market consumer. So while they start with products for pro racers and Olympians, in the end it’s all about bringing those breakthroughs to weekend warriors like me.

Autodesk, meanwhile, sees similar movement in the application of generative design. “It’s moving toward real-world applications, not just the Airbus and VW proof-of-concept experimental products,” said Scott Reese, Autodesk’s EVP of Product Development and Manufacturing Solutions. “Mainstream manufacturing is adopting the cloud and adopting the computer as a collaborator, not just a place to store things. We think you’re going to see a lot more like this in the future.”

For a cycling aficionado, mechanical engineer and manufacturing zealot like me, that’s marvelous to hear in any number of ways. I’m not going to lie: the geek factor of all this is off the charts. And meanwhile, I’ve gotten to benefit personally from all the many technological advances folks like these have brought to my favorite sport over the years, so I’m eagerly awaiting the commercial offering of the new crankarm design, along with whatever else the application of these new design software tools brings to the table.

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