The Challenge of Bicycle Stability Modeling

With all that we have been able to model about cycling, it would seem that it is a well understood process with no major gaps. But that is not the case. Physicists may have developed models for Electromagnetic Waves, Quantum Mechanics, Quantum Field Theory, and Chaotic Phenomena. But one of the Classical Mechanical results that has remained a challenge is what makes a moving cycle stable.

Quantum physicist Michael Brooks summed it up nicely in a 2013 article in the New Statesman, when he wrote: “Forget mysterious dark matter and the inexplicable accelerating expansion of the universe; the bicycle represents a far more embarrassing hole in the accomplishments of physics.”

The Traditional Explanation

For decades, the explanation for stability was that the spinning wheels created a gyroscopic effect which kept the cycle upright. However, that explanation has been showed to be either not the whole story, or not even a factor.

This has been demonstrated in the lab where cycles have been constructed with added gyros that counterbalance the effect of the spinning wheels.

 

Self Steering Cycles

This may sound like some futuristic prototype along the lines of driverless cars. However, it is actually a property of any cycle you may own. In the video below from Andy Ruina of Cornell University, he demonstrates two riderless scenarios.

In the first, a cycle is given sufficient speed and travels just fine making adjustments on its own. In the second part of the video, the handlebars are locked in so they cannot move and the cycle falls over almost immediately.

http://bicycle.tudelft.nl/yellowbicycle/stringtie53b.mov

Stability and Steering

What is clear is that stability and steering are connected. We have discussed countersteering earlier how small turning actions can be used to correct for small imbalances which are experienced continually when riding.

When a riderless cycle turns in the wrong direction, the bike countersteers itself in the opposite direction which returns it to a vertical position. Add a cyclist, and the cyclist must instinctively be able to do the same.

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