The $29.99 all-metal desktop Stirling engine kit is one of the simplest. It can be assembled in 15 minutes and is recommended for ages 14 and up. Also for $29.99 is the Exploring Kid Steam Engine Kit.

It shouldn’t come as much of a surprise, then, that you can also still buy and build the Visible V8 model engine kit, first ...

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And if you're wishing that your old-school manual stroller had a motor … well, the Easy-Way kit is designed to give it one. Currently the subject of a Kickstarter campaign, the Easy-Way is ...