Ask HN: Largest physical open source projects?

I know rLoop right now is one. They're a really large(300+member) group with members from around the globe, which originated on Reddit to work towards creating the next hyperloop pod. (rloop.org)

Are there any other large, open source projects that you know of that are working on something physical? I know I've read about a few in the past but can seem to find those articles again. Hoping someone here has heard of some.

P.S... rLoop is also in the process of raising money if there are any kind souls out there. Their Indiegogo campaign offers some pretty sweet rewards like naming right of the pod and the boosters and being able to dress their driver (a dummy). https://www.indiegogo.com/projects/help-build-rloop-s-pod-for-spacex-hyperloop-comp#/