John Michael finished grade 1 of the Splash Math app and earned this mobile crane. He built this himself, in three days. Here are some photos at various stages of build and some videos of him explaining the function.

Describing the drive gears in an early build stage
https://vimeo.com/181344890/04f051741f

Describing the rack and pinion steering
https://vimeo.com/181344895/0edbc68cf5

Describing the stabilizer operation
https://vimeo.com/181344892/27dcf75ae6

Describing the boom operation
https://vimeo.com/181344891/5015bc462c

Describing the hook operation
https://vimeo.com/181344894/d027a469d2