Link share

NIST Researchers Link Cutting-Edge Gravity Research to Safer Construction Crane Operation

At first, all Stephan Schlamminger wanted to do was write an equation that would help him get a more accurate value for G, the gravitational constant that determines the strength of attraction between massive objects. To assess this attraction, Schlamminger, a physicist at the National Institute of Standards and Technology (NIST) and his colleagues, studied the motion of a so-called torsion pendulum – in this case, a set of masses suspended by a thin wire. which periodically twists and untwists instead of periodically rocking back and forth.

Schlamminger’s Derived Equation provides guidance on how to quickly minimize or alleviate the amount of yarn twist back and forth. If the quantity is small, it is easier to locate and measure the position of the wire, which results in a more precise measurement of G. Schlamminger was eager to publish the result immediately. But then he got to thinking: the discovery would interest only a small number of people, those who measure G using the torsion pendulum method.

Could the equation be applied to other devices?

Turns out he didn’t have to travel very far to find a connection.

Crane load movement control

The animation shows the carefully timed maneuvers a crane operator must use to safely deliver a heavy load to the desired destination.

In a paper published online Feb. 17 in the American Journal of Physics, he and his colleagues describe a surprising connection between their equation for G and the maneuvers required for crane operators on a construction site to quickly and safely transport heavy loads.

Schlamminger, of course, was not initially thinking of construction cranes. But he remembers a conversation he had when he was a postdoc about 15 years ago, when he was working on a similar project to measure G at the University of Washington in Seattle. Schlamminger’s adviser had asked him if he knew the tricks of the crane operator.

Driving a crane is not for the faint hearted. Swing a thousand pound piece of steel too fast or too far and someone can be killed. But in just two carefully choreographed maneuvers, a skilled crane operator can lift a heavy load and bring it to a complete stop, without any dangerous swinging, exactly to the right destination. Additionally, a crane’s cable and load can be modeled as a vertical pendulum that moves back and forth in a manner similar to how a torsion pendulum twists and untwists. The time it takes for the pendulum to complete one cycle of this motion is called the period.

By applying the equation he had derived for the torsion pendulum, Schlamminger found he could predict the force and timing of gear changes that crane operators must apply to the trolley – the wheeled mechanism that moves loads horizontally along a rail.

If a crane operator is carrying a load at rest and moving it a relatively short distance, the equation suggests this prescription for stopping the load in the right place: the operator must first apply a speed opposite to the movement of the crane trolley, then apply exactly the same speed in the opposite direction exactly one pendulum period later.

If the operator needs to lift a load initially at rest and move it a relatively large distance, tens of meters, the equation provides different guidance to account for the greater swinging motion of the crane in this scenario: the Operator must first apply a force that accelerates the crane trolley from rest to a certain speed, then apply a second shift of the trolley, doubling that speed, half a period later.

Things get more complicated if the load has its own initial rocking motion, independent of the crane. In such cases, the two instants at which the operator applies a force to control the load are no longer exactly half a period or a period apart, but the equation still provides the appropriate action times.

“I think well-trained operators can perform these maneuvers,” to more safely transport construction loads, said NIST engineer Nicholas Dagalakis, who developed the mathematical models and optimized the design of NIST’s RoboCrane. Dagalakis was not a co-author of the new study.

Although experienced crane operators instinctively know the strategies developed by NIST researchers and the computerized control of the trolley incorporates these movements, this appears to be the first time that crane maneuvers have been described by a mathematical formalism, Schlamminger said.

“It really is a rich application worth sharing with the world,” he added.

Satisfied that the book would reach a wider audience, he and his collaborators, including Newell, Leon Chao and Vincent Lee of NIST, as well as Clive Speake of the University of Birmingham in England, were finally ready to publish.


Article: Stephan Schlamminger, Leon Chao, Vincent Lee, David B. Newell and Clive. C. Speak. The crane operator trick and other shenanigans with a pendulum. American Journal of Physics, vol. 90, 169 (2022). DOI: 10.1119/10.0006965. Published online February 17, 2022.

/Public release. This material from the original organization/authors may be ad hoc in nature, edited for clarity, style and length. The views and opinions expressed are those of the author or authors. See in full here.