Pocket Sized Robot Arm - MeArm V3.0 - Small, Hackable, Open Source

The MeArm is a Pocket Sized Robot Arm. It is a project started in February 2014, and the long journey to its present state is thanks to it being an open source product. Version 0.3 was featured on Instructables back in April 2014 and snagged second place in the Robotics Contest. I'm wearing the t-shirt I won as I type this!

Since then we've seen it built all over the world, for fun and profit (as is allowed by the licence). There are some very professional clones and variants of the MeArm out there and there are probably 10s if not 100s of thousands of these things out there!

Before you start with this instructable please check your version!

This tutorial is for the v3.0, where the build time has come down from two hours, to around 30 minutes. It is the current version and there are few people who are cloning it. Although this is for the "official" build an image is included here to show how you can use it for your own creations.

All of the previous versions and this can be found on thingiverse.

This guide covers how to build the v3.0. Currently there is code available for the Arduino, Raspberry Pi, Beaglebone Black and Espruino.

We also have a build along video on youtube that compliments these instructions.

Let us know any feedback you have, and what more you'd like to see. Huge thanks to everyone who takes part in instructables for making this site the amazing community that it is!

Acrylic or wood, around a letter size (300 x 200mm)

M2.5 metric machine screws

Hobby Servo Motors x 4 - metal gear are best

Baseboard PCB

Your own controller

First calibrate your servo motors. The ones we use have a 180 degree range of motion, and you put a little plastic part called a horn on them. You have to put the horn in the right place when the gears inside are in the right place to get the correct range of motion in your arm.

Using the calibrated servo with the "double" horn. Place it through the base PCB or custom cut base, then place the central part over it and hold it together (this is advice for this build but you can apply that to your life too). Have a close look at which way round I've wrapped the cable. Plug the servo in so that the orange cable lines up with the little o on the circuit board.

Next we add the end parts over that central part, then slide through the hockey stick looking parts. These will hold it all together, so you can take a break now. I know its been stressful, but we can get through this together.

Now we push on the sides and secure them with 2 x 10mm screws each side. The screws self tap into the acrylic of those hockey stick parts we just used.

Find the parts shown in the first picture and rearrange them to look like the second one! You'll have to hold them together while you screw in the 10mm screws from each side, and I find it easier to put the whole part together and hold the sides.

This bit can be a bit confusing. Lets take it slowly. Find one of the many 6mm screws in your kit and lets first attach the longest lever to the central strut then one of the smaller levers to that. There three of the smaller levers that look very similar, one has a triangle cut out of it. Don't use that one. Pick your favourite of the remaining two, they should be exactly the same but one of them will call out to you to be first picked. Trust your instinct!

This bit uses different length screws and you can built it backwards. Squint at this images until you've worked out which way around they should go then join the two parts together with the 6mm screw. Use the 10mm screw to attach it to the part you made in the last step. Feel free to squint at this part again to see if you can work out how it's going to work, or just carry on and enjoy the surprise a few steps later.

Building the other side requires a bit more looking at images and squinting! Add the triangle part and the lever with the rounded end first, with the triangle cut out pointing towards where the robot head will go.

Add your second favourite identical lever to the back of the triangle with a 6mm screw.

Now add the lever with the triangle cut out, keeping the triangle cut out near the triangle cut out on the triangle part.

Now we attach the parts we've made together. Using just a 6mm screw. Push it through the bottom hole on your lever assembly, then screw it into that central part.

There's a little washer that needs to be put between the second favourite lever and the back of the right hand side plate. Screw them together with a 10mm screw. Now is is good time to just see if all your joints move. As you've attached them together you should have realised that as they are pivot points, you want to be able to move them. If you didn't realise this you're not alone. Hundreds of people have screwed these parts together to make a solid unmovable structure, only to find when they try to move the joint with a weak servo motor that it's solid and unmovable.

You want it to be like a puppet that you control with the servo motors.

Now lets fit that right hand servo. It's the one where the horn sticks out at the side angle. Thread it through the collar, put the horn in the horn shaped hole and secure with two 10mm screws. Wrap the cable around the servo to keep it neat and tidy and line up the orange wire with little o on the circuit build.

Just like the last time, only with one of your calibrated servos where the horn points forwards. Screw together, wrap cable, plug in with orange cable near the o on the circuit board.

This part is a bit fiddly and you can build it the wrong way around. Have a look through these images and see if you can follow along. The part that goes over the horn goes over then is rotated. Here the pictures are worth a thousand words. Secure the whole thing with the 20mm screws!

Simple but maybe fiddly, law one jaw over the servo horn, mesh the gears with the other jaw, place the base plate on, line up the holes and screw in that 10mm screw.

Attach the head to the levers using three 6mm screws. This bit should be easy and satisfying

The final step of the physical build. Slide the small base plate over the double servo horn, then put the big base plate over the double servo horn and screw the two base plates together. Stick four sticky feet to the base.

Probably the most important step is adding some googly eyes. It makes the whole thing look and feel professional.

We have a bunch of kits for this bit, but you can use any controller you like. We'll do a bunch more instructables coving DIY electronics builds. There are some on here already but they could do with some additions. Step back and enjoy your work.