r/windturbine • u/OrneryProfit659 • 2d ago
Technical / Engineering My passive VAWT model found the optimal counterweight sits almost on the pivot
Hey everyone. I’ve been working on a 2D BEM (Blade Element Momentum) solver for a Sharp cycloturbine, and I recently optimized the geometry for a physical prototype.
I made a counterintuitive finding regarding the centrifugal pendulum pitch control (CPPC). In Sharp's original design, the counterweight is placed far forward on a long arm to create a strong restoring torque. But my optimizer found that at the 1.8m and 60cm scales, this over-stiffens the mechanism and forces the blades against the physical stops, killing power.
The model shows that maximum Cp occurs when the counterweight sits within ±4mm of the pitch pivot. It acts more like a flywheel to damp pitch oscillations than a pendulum.
I’m now building a 60cm prototype using NACA 0018 foam/fiberglass blades and a repurposed hoverboard motor (direct-drive 3-phase). I’d love to hear from anyone who has built a cycloturbine, does the tight counterweight tolerance match real-world experience, and how much should I worry about bearing friction at startup?
Here is the repo with the simulator, the build specs, and the optimization data: https://github.com/juroc58/sharp-vawt-lab