Date:17 December 2014
The International System of Units is in peril and science has turned to the toys left in the cot to devise a solution. Although the global effort to redefine the world’s measurement units is heavily funded on a state level, Xiang Zhang a director at the Physical Measurements Laboratory for the US National Institute of Standards and Technology wants to make this high-level process more accessible.
Zhang’s Lego Watt Balance has a target accuracy of around one milligram and is entirely constructed out of Lego parts and some easily-obtained household parts.
Zhang detailed the project on his blog:
“The full mechanical setup for the balance is fully designed from Lego, including the mass pan, knife edge, arrestment and all hinges. To actuate the balance, homemade linear actuators were used. Self-wound 200 turn coils were made from copper wire and PVC piping. Rare earth magnets were placed in opposition to generate the radial magnetic field. Position sensing was done using a shadow sensing technique made from a laser pointer and a photo-diode. To keep with the open-source theme, an arduino was used as the main controller. Once I finished the mechanical setups, I spent a large amount of time working with microelectronics and controls to actively control the balance in both force and velocity modes. Before leaving NIST in August 2013, the Lego balance was functional but needed tuning and improvement of the components before the final presentation. The project has since been taken over by other students in the lab.”
The Lego Watt Balance has since successfully determined the Planck constant and is capable of measuring a gram size mass to 1% relative uncertainty. Progress is updated on the official paper, where you can also find a parts list to build your own. The article has also been submitted to the American Journal of Physics.