Yes autospeed is the site.
Incidentally I attached an old plastic box to my bike for prototyping purposes. After a test ride yesterday it only needs 3 changes. A quick-release attachment point, better bracing where I cut the seat hole, and a modified stand thanks to the change in cog when loaded. And silver paint.
Anyway now that you've seen the monstrosity it's time for me to ride it to work.
Catch you later.