Bortolo - how to build a robotic arm

I was fascinated by robots since I was kid. I was always dreaming about to have one or, better, to buil one by myself.

On the other side I was always conscious about what a hard work it could be especially for the mechanical part, the motors, the gears and the sensor that every jont needs to have to give positioning feedback.

Two years ago I was surfing on the web and I saw the very nice robotic arm from Lynxmotion. I was very interested because it is a very compact arm with full 6 D.O.F (degree of freedom) capabilities. It is using servo motors to move the joints, this way with a single component (the servo) the computer may move the arm and have an idea about the arm position. Anyway at that time I decided that it was too expensive for me as I thought I would use it for a very short time like every funny new toy.

Some months later I found an hobby shop that was offering non-branded decent servos for just €9 each! It was the right chance that I was waiting for!

I immediately bought 6 of them and started to design my arm using the Lynxmotion arm as example. That's how it looks now that, after 2 years I finally found time to complete it with the gripper:

And here you can find a very short video that I shooted two years ago, when I completed the arm but not yet the gripper:


When I made the gripper I took some photos so I will explain the realization using those pictures.

Basically I build my robotic arm using a very cheap and easy to find material: the PVC. I got it from standard sewer pipes, of course new pipes and not used one!

I got some spare pieces of them for free in a construction site but if you can't find any you will surely find them in brico shops. The one I used is about 2-3 mm thick, you will also easily find the grey ones that are thinner (about 1 mm) but they can be used just for few parts of the gripper (the three layer structure) as it is too weak and probably will bend if used for other parts like the finger and the gears.

I cut a small piece of the pipe and then cut it on one side, the I placed it in the home owen! Yes, the one that resides in your kitchen!

After about 10 minutes at about 100 degrees Celsius (but it is better to make some test before as probably it will change from different pipes and owens) the PVC was so soft that I was able to get it out an press it beetween two flat wooden boards. This way I got free plastic board ;-)

The second step was drawing the parts you need to cut.  The most annoying part of work like this is to copy the drawing on the PVC board in order to cut it.

 I easily solved printing the pieces drawing with a laser printer and then using the toner properties to transfer it on the PVC board.

I mean that I simply placed the drawing on the PVC board, with the printed side facing the PVC itself, I firmly blocked the paper sheet with some adhesive tape then I ironed it at the higher temperature and.....voilà! The toner melted transfering to the PVC!

If you don't have a laser printer don't worry! It will work also if you print it out with an ink-jet or whathever other technology and then make a photocopy of it! So, if you would like to try it follow this link to download the drawing that I used for the gripper.

The third step, probably the longest one, was to drill and cut the PVC board. I used one of the most useful tool that I ever had: the dremel with the cutting disc!

If you will try this please consider that it will make a lot of dust, PVC powder during the cut, so protect your eyes with pool glasses and your mouth and nose with a good breathing mask.

Last step was round down all the pieces in order to have them as precise as possible with a special attention for the gears. This part infact is the most difficult one and I proceeded in very small steps in cutting them.

There's one detail that probably needs some attention: when you transfer the drawing on the PVC board the heat of the iron will probably warp the board. I had this problem on one side of the board itself, and I simply ignored it and cut the PVC anyway, lately I placed the warped pieces on the iron and powered it up again. Then I took the soften pieces and flattened them like I did with the original pipe in the owen. I thought this way was more easy than try to flatten again the whole PVC board instead.

So, after some hours of work (half of a day more or less) I finally assembled my robotic arm gripper!

As of today, my robotic arm needs some improvement. On one side the PVC is not so efficient as material because it is quite heavy, in addition the is the weight of the metal bolt and screws that I used. On the other side the cheap servos that I used are not powerful enough. So, at the end of the game now that there's also the gripper, the arm needs a little help to raise up.

For this reason I'm thinking about to buy better and more powerful servos at least for the two DOF of the shoulder.
But this may be the topic of other posts.....stay tuned!

Thanks for reading,
enjoy!