Scientists Discover How To Stop Luggage From Toppling On the Race Through the Airport (theguardian.com)

An anonymous reader quotes a report from The Guardian: Scientists have worked out why suitcases tend to to rock violently from one wheel to the other until they overturn on the race through the airport. This most pressing of modern mysteries was taken on by physicists in Paris, who devised a scale model of a two-wheeled suitcase rolling on a treadmill and backed up their observations with a pile of equations and references to holonomic restraints, finite perturbations and the morphing of bifurcation diagrams. Fortunately for non-physicists, the findings can be reduced to simpler terms. For the suitcase to rock it had to hit a bump or be struck in some other manner; the faster the suitcase was being pulled, the more minor the bump needed to set it off. So far, so obvious. But Sylvain Courrech du Pont wanted to know more. Why did a rocking suitcase swerve and make such violent movements that it might eventually topple over? After more treadmill tests and more equations, the answer popped up: because a suitcase's handle pulls from the middle and the wheels are at its sides, the suitcase swerves inwards whenever it tilts up on one wheel. If the rocking overcomes the dampening effect that happens when each wheel touches the ground again, the suitcase will keep on rocking or eventually flip over. In conclusion, the researchers discovered that "when a suitcase starts to rock out of control, the correct response is not to slow down but to pull it faster." The scientists have published their findings in the journal Proceedings of the Royal Society.

Comments

This is new?

[Solandri]

People who tow trailers have known about this for decades.

Re:This is new?

[swillden]

People who tow trailers have known about this for decades.

As demonstrated in that video, trailer sway isn't caused by rocking back and forth between the wheels causing swerving but by weight distribution away from the axle creating large yaw inertia. With suitcases, while packing the weight far from the wheels does make the rocking worse, it will still happen even with the weight packed close to them (low yaw inertia). So, we're mostly talking about different effects. As evidenced by the fact that if your trailer starts rocking you should ease off the throttle, not go faster.[1]

Even if this were the same effect, there's a huge difference between merely knowing about a phenomenon and having some rules of thumb about how to handle it, derived from experience, and having a mathematical model and a computer simulation of the phenomenon. Having those opens up many more options for finding solutions.

[1] In my experience, the very best thing to do is to use the brake controller to activate the trailer brakes and slow that way, assuming a trailer that has electric brakes. I've only experienced sway on one trailer that doesn't have brakes; my flatbed (no brakes) when I have the tractor loaded too far back and not enough weight on the tongue. Easing off the throttle calms it down. None of the other trailers I've had (boat, utility, ATV) have ever swayed.

Shocking! Now add shock absorbers.

[swell]

Simple enough to design shock absorbers for the wheels. A proper shock absorber reduces harmonic effects. On vehicles these devices are remarkably affordable and effective. For luggage they could be very cost effective. A simple friction device with a compressed gas cartridge would do the trick. Feel free to design & patent- I don't need the millions it will bring.