Here I am back in 2008 digging eight 5 ft deep holes for some 24" x 24" "bigfoot" post base and 10" sono tubes that will become the foundation for a new 20' x 30' workshop. The Micro Hoe plans currently include the original size 350 lb backhoe that can dig up to 5.5 ft deep for garden tractors, and I am also including a page that shows how the crowd arm can be lengthened 12" for a digging depth of 6.5 ft. this includes increased leverage required for the longer arm and a 2" longer crowd arm cylinder.
The extend-a-hoe prototype you see in this video is able to dig about 7 to 7.5 ft. deep or so (for compact tractors) and weighs about 425 lbs. The extend cylinder runs off a foot controlled single spool valve (under my right foot) via the power beyond port on the main backhoe controls. The extend-a-hoe option requires a fair amount of work (and cost) to add the additional 20" reach above stock, which is why most folks end up simply creating a 12" longer single piece crowd arm with thicker wall than the stock unit for larger tractors that can take the additional weight.