Meet the maker of the MeArm robot arm

Great for Raspberry Pi and Arduino

The current v0.4 MeArm kit, which Ben sells for £24.99 [3], is made of acrylic and is sold with everything you need to build it – four servos, pre-cut acrylic, and all the associated fixings. The acrylic is prepared on a laser cutter Ben houses at his office. "The full kit is really for people who are already into Raspberry Pi or Arduino, because you need something to drive the servos," he explained. "It's also possible to buy the fixings alone for £4.99, allowing anyone with access to cutting equipment to build their MeArm at minimal expense."

Like the Plotclock, which Ben credits as a source in the documentation, the MeArm is completely open and the designs are readily available on Thingiverse [4]. This openness has led to more than a few "wild" MeArms (as Ben puts it), popping up all over the world.

"It really helps with our development that anyone can just pick it up, cut it out and make it. I met a lad from Switzerland who has a homemade CNC mill, and he had milled out all the parts from balsa wood and built his own." There are others too – a few in the UK, America, and Mexico. Ben sent us a picture of the Mexican MeArm, who he's dubbed the "amigo," because the builder sent him an email that simply read: "Greetings from Mexico Amigo!"

The MeArm has also been discovered for sale on an open hardware site in Peru.

Taking Control of the MeArm

One UK maker who has played a pivotal role in the MeArm is Bob Stone from the York Hackspace. Not only did Stone make a couple of version of the MeArm himself, but he also worked extensively on Python code to help drive the MeArm with the Raspberry Pi [5]. He's created a script that uses Adafruit's excellent 16-channel servo driver [6], effectively allowing him to control four MeArms at the same time. The board is compatible with both Raspberry Pi and Arduino, and it is widely available from maker stores all over the world.

Because it's far from optimal to control the MeArm programmatically with just angle data for all four servos, Bob has written an excellent inverse kinematics control library for both the Raspberry Pi and Arduino, which lets you control the arm in your scripts and sketches by specifying the position of the gripper based on an easy-to-use Cartesian coordinate system (x, y, z). The library does all the heavy lifting (and ultimately translates the servo angles), leaving the user with the simple task of specifying the coordinates in millimeters from the base rotation center. When initialized, the MeArm starts in its initial home position of (0, 100, 50), which translates to a gripper position 100mm in front of and 50mm above the center of the MeArm's base.

The Python library is incredibly easy to use and gives plenty of scope for users to control the MeArm with simple pre-defined Python scripts. The library also supports control using any number of input devices, including thumb sticks and accelerometers.

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