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