Chris Annin Calls the Open Source AR4 Robot Arm Done with the New, Final Mark 5 Revision

Engineer Chris Annin, of Annin Robotics, has announced a fifth-generation revision to the AR4 open source six-degrees-of-freedom robot arm kit — and has declared the project complete, with no new design changes expected in the immediate future.

"The Mark 5 update isn't a huge update," Annin says of the release. "It just upgrades some of the calibration limit switches to Hall effect sensors, and that changed a few mounting points on the aluminum parts. But this update should be the last update for the arm itself for the foreseeable future. This is the last of the updates I had on my list to complete for the robot arm itself. I'll, of course, always be doing updates on the software and coming up with new stuff like that, but for the arm itself I don't have any more changes planned right now."

Annin's open source robot arm project began with the AR2, the project's first major release. The arm's open-loop control design, powered by an Arduino Mega microcontroller board, was enhanced with encoders for closed-loop operation in the AR3, which also moved to a Teensy 3.5 controller and shifted from chain-and-sprocket to belt-and-pully operation. The AR4 shifted from external encoders to motors with integrated encoders to reduce the bill of materials and simplify construction, while also upgrading to the Teensy 4.1 microcontroller board.

Since then, Annin has been iterating on the core AR4 design. The second revision moved the control electronics from an external enclosure into the base of the arm, while swapping to motors with tighter tolerances for improved performance; the Mark 4 improved this further, while also shifting to a larger base enclosure to make room for a 2×12 terminal board and the gripper control board.

"This update continues where the last one left off," Annin explains of the AR4-MK5, "and it adds Hall effect sensors for joints one, two, and three, and then joints four, five, and six still utilize the small microswitches. We've [also] got a brand new build manual here for the Mark 5. I've added the modified Denavit-Hartenberg parameters [too] — so I've got two [Microsoft] Excel spreadsheets with all the kinematics for the robot fully worked out."

The new release also brings with it new tutorials, including a course aimed at schools. "This is based on conversations I've had with a number of different professors at different schools on their curriculums," Annin explains, "and how they're using the AR4 in the classroom. So I put this together based on the feedback I've gotten from a few different professors."

All downloads to make your own AR-MK5, as well as links to purchase kits, are available on the Annin Robotics website; those who already have a Mark 4 will also find instructions on upgrading to the AR4-MK5 design.