MeArm update – Work in progress.

Here’s an update of what we’ve been up to in the last 4 weeks of STEM club.

Team MeArm.

We initially built the excellent MeArm from a phenoptix kit, priced £29.99. It’s a nice robot with 4 degrees of freedom, that can be controlled via Arduino, Rasberry Pi, Beaglebone etc.  We managed to get it working really nicely with a Raspberry Pi and ScratchGPIO, Simon Walter’s excellent version of Scratch for the Pi.   The challenge for the group is to control the arm using Python.  It was suggested to use a Wii Nunchuk, or perhaps a Microsoft Kinect, but early experiments have suggested that keyboard input is challenging enough!

Robots building robots.  Skynet!
Progress on our MeArm build. The kit version is in the background, and our JCB yellow in the foreground.  We’re about 2 weeks away from movement control!

Once the robot is mechanically sound, and the servo positions are set, then we should be able to connect it via I2C using the Adafruit 16 channel Servo I2C board.  Once this is done, then we’ll release the python geeks, and let them run wild with their programming and imagination.


Building the Phenoptix mearm from scratch:Sourcing parts and cutting your own

Having already bought and assembled a MeArm kit from Makersify, I decided to use the open hardwire files from thingiverse to laser cut all the parts from 3mm Acrylic.

Thingiverse files.  If your DT department in school is as awesome as mine, they’ll show you how to use the cutter so you can plan and cut your own designs.


download the DXF file from thingiverse and start cutting
Laser cut parts from the DT department, hot off the cutting bed. JCB yellow is a nice touch

I had some trouble with the .dxf files running in 2D design, so I printed the design out on paper first and then did all of the measurements, comparing it to the real mearm that I built in order to make sure the scaling was perfect.  (If not, the servos won’t fit in the holes, and the bolts won’t self-tap)

I also cut a mountboard version for the students to see, and get to measure with vernier callipers to check the dimensions.  (It turned out it had scaled wrong vertically, and the test-print would never have assembled as all the circular holes were ellipses!)


Parts arrived in the post, enough for 4 robots, but we’ve only enough acrylic for one at a time. 

In order to build the robot, you’ll need a bunch of M3 bolts, and some Turnigy 9g micro servos.  I picked up a load of servos cheap on ebay , at £11.99 for 4, which seems like a good deal.   (I would get a spare set, in case you burn the servos out during a build!)

I used to get small batches of the screws, as they were by far the best deal I could find in the UK, cheaper by about £25 than all other dealers.



Once the students had done the inventory, they began to follow the assembly instructions, starting with the baseplate.  Here you can see that the longer M3 bolts are used like standoffs in the assembly.  You can also see the mounting holes to bolt on an arduino for controlling the servos.


We’ll keep you posted on the build as it happens, and then how to control it with scratch on the raspberry pi.