- Creating resistance with eddy currents
- Measuring power directly
- Smart trainer control
- Virtual Inertia
Creating resistance with eddy currents
When an electrically conductive material, such as your aluminium alloy wheel rim, passes through a changing magnetic field, it creates small electrical currents called eddy currents. These eddy currents have their own magnetic fields, which interact with the original magnetic field to resist the motion of the conductor, your wheel.
This ability to resist your wheel's motion without touching it eliminates noise, vibrations, and wear on both your wheel and the trainer.
Fun fact: Eddy currents also provide the fail-safe braking systems on drop tower thrill rides.
Measuring power directly
Force: Newton's law says for every action there is an equal and opposite reaction. When the magnet array applies force to your wheel to slow it down, the wheel produces an opposing force on the magnet array. The magnet array is mounted directly on a load cell, which measures that force.
Speed: The optical speed sensor detects wheel speed in high resolution, updating with every single spoke that passes the sensor- not just once per wheel revolution.
Force x Speed = Power.
With no extra variables such as mechanical wear and tear or changing tire pressure and rolling resistance influencing its power calculation, the Fliiiight has unparalleled consistency and doesn't require regular recalibration.
Smart trainer control
Fliiiight and your training app communicate with each other wirelessly, over one of two communication protocols: ANT+ or Bluetooth. While the trainer sends the app its power readings, the app sends back a series of commands to create a specific level of resistance (SIM mode) or a power (ERG mode). Fliiiight then moves the magnets in or out to meet its power or resistance target at your current wheel speed.
Learn More: A Beginner's guide to smart trainers
Inertia is the tendency of your wheel to maintain its speed, and it's the most important factor in achieving a realistic road feel. Without enough inertia, you'll notice your wheel slow during the less powerful parts of your pedal stroke, a sensation that's often described as "riding through sand."
Outdoors, the forward momentum of the bike and rider keeps that wheel speed consistent. Indoors, the conventional solution is to add a heavy flywheel. That makes conventional trainers heavy and awkward to transport or store, and adds to their cost.
Instead, virtual inertia varies the resistance slightly in time with the power variation in your pedal stroke, so your wheel maintains its speed. In order to achieve this, Fliiiight samples speed over a hundred times per second, and uses machine learning to build a model of your predicted wheel speed.
That's right. We decided to predict the future to build you a better trainer.
Virtual Inertia in action