Since the invention of the modern bicycle, innovators have sought to improve its efficiency, reliability, and rider experience. One area that’s long been due for disruption is bicycle gearing. At Skillion, we took on this challenge with the creation of the S-drive, a concept born in 2016 with the goal of building a better, smoother, and smarter bike gearing system.
The Innovation Behind S-drive
The S-drive was envisioned as a continuously variable transmission (CVT) for bikes—offering seamless gear shifts without the mechanical clunk of derailleurs or the bulk of internal hub gears. The core mechanism uses a flat aluminum disk and a perpendicular Drive Wheel. By moving the Drive Wheel in or out across the disk’s radius, the gear ratio is adjusted on the fly.
Our design allowed power shifting, meaning you can apply torque during a shift—something traditional systems can’t handle. This key innovation opened doors to improved rider experience and performance, especially for eBikes.
Engineering the Impossible
Great ideas are only as strong as their execution. Building S-drive meant solving complex mechanical challenges:
- Ensuring the Drive Wheel maintains grip without slipping
- Developing a dynamic pressure system that senses torque and adjusts contact pressure in real-time
- Integrating with existing eBike motors, like the Bafang system
- Designing around lightweight, compact constraints
We explored advanced materials, torque sensors, and control logic—eventually building a proof-of-concept using a Skillion eBike. A test jig was developed to simulate real-world forces using eddy current brakes and a steel disk, enabling us to refine the Drive Wheel material and friction profile.
Turning Obstacles into Opportunities
One persistent concern was Drive Wheel wear. Instead of treating it as a flaw, we embraced it as a feature—designing the S-drive for quick replacement and imagining a subscription-based model that supplies replacement Drive Wheels as part of ongoing maintenance.
Our work continued through the summer of 2020, supported by a talented team of interns and engineers. We moved from rough prototypes to CAD models in SolidWorks and planned out the bill of materials (BOM), electronics integration, and system architecture.
Why S-drive Stalled
Despite promising results and a patent pending, S-drive hit a familiar roadblock: funding. We paused development in 2021 to focus on other innovations at Skillion. Challenges like:
- Weight and complexity
- Market fit for CVT in bikes
- Difficulty scaling the design to various frames
- Cost vs benefit for riders
…made S-drive a high-risk investment, despite its clear innovation.
The Bigger Picture
S-drive might be ahead of its time—or just waiting for the right moment. Think about hybrid cars like the Prius: more complex than traditional vehicles but successful thanks to clear, user-perceived benefits. eBikes are a similar story.
Bringing a hardware invention to market isn’t about patents alone—it’s about persistence, validation, and timing. S-drive taught us that even paused projects can be valuable. They inform future work, inspire better design, and may yet rise again.
If you’re innovating in hard tech, my advice is this: keep one eye on the dream and one on the data. Innovation walks a fine line between breakthrough and breakdown. The S-drive isn’t done. It’s resting. For now.
— Pete CooperSince the invention of the modern bicycle, innovators have sought to improve its efficiency, reliability, and rider experience. One area that’s long been due for disruption is bicycle gearing. At Skillion, we took on this challenge with the creation of the S-drive, a concept born in 2016 with the goal of building a better, smoother, and smarter bike gearing system.
The Innovation Behind S-drive
The S-drive was envisioned as a continuously variable transmission (CVT) for bikes—offering seamless gear shifts without the mechanical clunk of derailleurs or the bulk of internal hub gears. The core mechanism uses a flat aluminum disk and a perpendicular Drive Wheel. By moving the Drive Wheel in or out across the disk’s radius, the gear ratio is adjusted on the fly.
Our design allowed power shifting, meaning you can apply torque during a shift—something traditional systems can’t handle. This key innovation opened doors to improved rider experience and performance, especially for eBikes.
Engineering the Impossible
Great ideas are only as strong as their execution. Building S-drive meant solving complex mechanical challenges:
- Ensuring the Drive Wheel maintains grip without slipping
- Developing a dynamic pressure system that senses torque and adjusts contact pressure in real-time
- Integrating with existing eBike motors, like the Bafang system
- Designing around lightweight, compact constraints
We explored advanced materials, torque sensors, and control logic—eventually building a proof-of-concept using a Skillion eBike. A test jig was developed to simulate real-world forces using eddy current brakes and a steel disk, enabling us to refine the Drive Wheel material and friction profile.
Turning Obstacles into Opportunities
One persistent concern was Drive Wheel wear. Instead of treating it as a flaw, we embraced it as a feature—designing the S-drive for quick replacement and imagining a subscription-based model that supplies replacement Drive Wheels as part of ongoing maintenance.
Our work continued through the summer of 2020, supported by a talented team of interns and engineers. We moved from rough prototypes to CAD models in SolidWorks and planned out the bill of materials (BOM), electronics integration, and system architecture.
Why S-drive Stalled
Despite promising results and a patent pending, S-drive hit a familiar roadblock: funding. We paused development in 2021 to focus on other innovations at Skillion. Challenges like:
- Weight and complexity
- Market fit for CVT in bikes
- Difficulty scaling the design to various frames
- Cost vs benefit for riders
…made S-drive a high-risk investment, despite its clear innovation.
The Bigger Picture
S-drive might be ahead of its time—or just waiting for the right moment. Think about hybrid cars like the Prius: more complex than traditional vehicles but successful thanks to clear, user-perceived benefits. eBikes are a similar story.
Bringing a hardware invention to market isn’t about patents alone—it’s about persistence, validation, and timing. S-drive taught us that even paused projects can be valuable. They inform future work, inspire better design, and may yet rise again.
If you’re innovating in hard tech, my advice is this: keep one eye on the dream and one on the data. Innovation walks a fine line between breakthrough and breakdown. The S-drive isn’t done. It’s resting. For now.
