Brick technology (Lego)
Dr. Engine (lego)
My mechanics(restoring antiques to music, no talking )
Alex evett ( 3d size comparison of everything)
Red side (3d renders comparing the speed of things like rockets and cars and planes and Star Wars ships)
Metalballstudios ( 3d models of things like what different size asteroids would do to the Earth)
That's all I'm subscribed to that fits that criteria. I've got some star trek online ships flying around being pretty channels like Zefilms. There's a wonderful British man who builds and reviews RC cars called Tomley RC. Also a big fan of projectair, RCtestflight, And PeterSripol. All are experimental rc build and test channels for every type of RC thing.