How-to Forge a Skull Crushing Robotic Arm to Do Your Dirty Work.

I recently was given 10 servos as a birthday present, so the question really was what to do with all of them? I started looking around at robotic websites that offered robotic arm kits. One of the sites Lynxmotion.com sells robotic arms that are very cool, but they are also very expensive at prices upwards of $300. Then I came across a miracle on Lynxmotion's website, an older robotic arm known as the L6AC-KT. The whole construction was of lexan, so I thought to myself, hey, I have lexan as a resource. Now that the build is completed I hope to spread my ideas and hopefully inspire someone to build something equvilent.

Also, if you could please vote for this instructalbe in the Microcontroller contest , the Toy contest , and the Make it Move contest it would be highly appreciated ;D

Step 1: Design and Fab

For this project I used the lynxmotion arm as a large point of reference, but because the site does not actually give any CAD files or any dimensions of the older arm I was forced to make those decisions for myself. I used SolidWorks for the design of the whole arm assembly, this made everything go by so smooth since I could save the files as .STL or .Dxf and have a laser-cutter and FDM machine make the parts for me. Besides that the Items I used are:

1x 24x24 sheet of neon green lexan.
5x Hitec HS-422 servos
2x Hitec HS-645MG servos
1x box of 4-20 x 3/8 self tapping screws
1x box of 2-28 x 1/4 self tapping screws
some 8/32 x 1/4 socket cap screws

Check the next step to see what all the parts are used for...

Step 2: What Goes Where?

The picture here shows where all the materials are used on the arm.

Step 3: More on Fabrication

I never touched any tool on this project except a simple hand-drill, and yet the quality of this project is very high. My secret, I used a combination of laser-cutting, and 3D part printing. To print my 3D plastic parts I did work in SolidWorks creating the dimensions of the part which I saved in a .STL file and sent to an FDM machine which would drip plastic in a pattern in layers to construct a full plastic part. I mainly used this method to create supports between pieces of lexan that were not held by much other than servos. As far as using the laser cutter I used a similar process, but instead of saving the file in SolidWorks as a .STL, I saved it as a .Dxf which the laser-cutter could use as a path for cutting on flat sheets of material (i.e. lexan). One thing to highly note is that the base servos that lift the arm up, (the ones on the desk in the picture) will fight each other for position. In order to stop those servos from over heating and causing failure you have two options. The first option is to slot the holes in the lexan where they are mounted to the servo horn, this will allow for adjustment of the structure against the servo horn so that both servos will both be in the same position at the same time. Another method is to program both servos to go to 90 degrees, but take the horn off one of them. When both servos reach the correct position, screw the horn back on and it should be all set. Also note that I added a spring in the final design to assist the forearm in lifting.

Step 4: All Your Base Are Belong to Us!

The base for this project was an old project box I found in my basement, nothing special, but it makes a great space for placing all the electronics I plan on using for this project. The base also has a Hitec HS-645MG to act as the whole arms rotation, not much more here, except an added switch and led to turn on the servos with external power.

Step 5: THE CLAW! and More...

I did not really feel like making the claw for this project, but i still may in the future. Right now I'm using a claw from lynxmotion, which in turn is okay, but the quality of the claw can really be improved on. I recommend designing your own claw if you wish to grasp larger objects, because the claw I have only opens to a width of 1.5inches, not that big at all. Also note that I used large HS-422 servos on the claw for rotation and the open/close function, please, if you have the money, purchase small servos that don't weigh as much as these, it will improve the movement of your whole robot.

Step 6: Electronics

UPDATE (6/20/11): The arm has been mounted to the base, only things left to do are the electronics and programming. Also, the controller I'm deciding to use is an Arduino Duemilanove. It has just enough PWM outputs to control all of the arms movements. Hopefully in the next update I can upload a sketch of my code for others. I will add a video when the project is 100% completed.

Now that the arm is completed I have decided to make it into a modular arm for a larger robot, but that is for another day.