A six-axis robot arm sitting on your desk used to mean five figures and a service contract. Chris Annin’s AR4 quietly tore that idea up — and with the brand-new Mark 5 revision, he’s calling the hardware officially finished.
The AR4 is an open-source, six-degrees-of-freedom robot arm you build yourself from CNC-cut aluminum, 3D-printed parts, and off-the-shelf motors and electronics. It’s the latest in a lineage that started with the AR2 and has been refined release after release. The Mark 5 isn’t a dramatic redesign so much as a final polish: Annin says it’s the last item on his hardware to-do list, with future effort going into software and tutorials instead.
What changed in the Mark 5
The headline tweak is sensing. Joints one, two, and three now use Hall effect sensors for their calibration limit switches instead of mechanical microswitches, which meant reworking a few mounting points on the aluminum parts. Joints four, five, and six keep the small microswitches. Annin has also shipped a fresh build manual and published the arm’s modified Denavit-Hartenberg parameters — the math that describes how each joint moves — as fully worked-out spreadsheets, so the kinematics aren’t a mystery you have to reverse-engineer.
I really want to build one of these. Gonna have to find blueprints for a CNC machine and a 3D printer first I guess.
If we can keep the internet from getting corporatized and segmented, we could have build guides for everything from basic hand tools, to metal foundries, to robotic equipment, just… on the internet for anyone to pick up and use to build their own tools. Starting from scratch, if they so desired. That would be cool.