Stair-climbing trolley. 7:29 video.
https://www.youtube.com/watch?v=um8TMFvCbNw
Previously:
https://www.homemadetools.net/forum/...499#post117188
https://www.homemadetools.net/forum/...2482#post76444
https://www.homemadetools.net/forum/...184#post145724
