When I was a kid, I used to make cranes, bridges, and other devices with Erector Sets. Alas, my childhood Erector company is long gone, but a French company called Meccano produces their products in the US under the Erector name. It’s not quite the same stuff, and actually is better in my opinion, but not quite compatible. Exacto out of Argentina makes some tougher pieces that conform to the Meccano Standard.
These pieces are great for constructing Arduino projects. You can mount servo’s, stepper motors, Arduino boards, and displays, Load cells, or any other adaptation you can think of. You can make Arduino controlled vehicles or robotic arms.
Here’s an older document that explains some of the differences, and gives some of the history of the competing standards:
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http://www.arrickrobotics.com/erector.txt
Metallus – Meccano compatible http://www.metallus.de/index.php?&page=einzelteile
Exacto – Meccano compatible http://www.exactosystem.com/
Meccano / Erector http://www.meccano.com/ / http://www.erector.us/