A wooden roller bearing ? – A practical approach


Every year in Artena, since 1992, takes place a big event which puts in competition all the contradas of the town. This event is called “Palio delle contrade di Artena” and is able to entertain several thousands of people challenging the contradas in rural games that recall the origin of Artena. One of the funniest games is called “La Carettella” in which every partecipant has to drive a kart entirely made of wood, down a hill, in less time possible. A guy, who is actually the captain of the contrada in which I live, came to me asking if it was possible to improve the performance by using some wood ball bearings. The idea seemed pretty challenging to me so I started googling around to find if anyone have ever had the same insane idea. Surprisingly I couldn’t find anything that wasn’t just a toy and unsuitable for such a stressful application . I spent several weeks thinking if it was possible to make a working bearing that was also reliable for a race plus several test session and ended up with the conclusion that the only way to know it was actually doing it. So I started looking for the wood with the best properties needed to be used for the volvent parts. My research lead me to Lignum Vitaean exotic wood with an extraordinary combination of strength, thoughness and density with the exceptional property of being self-lubricating. Actually it is also the hardest and heaviest wood on the earth, according to Wikipedia. Some really useful information such as elastic modulus, modulus of ropture, etc… can be found on wood-database.com. Of course these properties can change dramatically due to so many factors ( wood is not an isotropic material at all ) that they should be used very very carefully.  Continue reading

Reviving an Ampex MM1200 – The Capstan Servo

The capstan motor is driven by a closed-loop system which is well described in the diagram below.

Capstan Servo Block Diagram

Capstan Servo Block Diagram

I started checking if the reference oscillator is feeding the board with the correct signal. A 307,2 kHz signal is generated by the A5 op-amp and the crystal Y1 which is in its feedback path. The signal is consequently divided by 32 by the 7493N (A1) mod 16 binary counter and the SN158093N dual J-K latch.

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Reviving an old Ampex MM1200


A few weeks ago I received a call from a friend who desperately needed help with an old tape recorder. I hesitated at first, because I’m not in to vintage things, but I changed my mind as soon as I realized which one this recorder was. A glorious Ampex MM1200 dated back to the late seventies, capable of recording 24 tracks on a two-inch tape

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Using Transform Matrix for PCB Drilling – Part 2

It has been a long time since last time I wrote on this blog. I finally decided to complete this project because I need to make a small bunch of pcb and I want the possibility to review the boards whenever I want, so I cannot depend on an external manufacturing company. As I described in the first part I coded a little tool in Python to achieve my goal. I also added a basilar Excellon support so it is possible to load the file generated by Eagle and it allows to compute an affine transformation in order to make an accurate drilling. I used Numpy and OpenCV libraries to get straight to te result but let’s take a look at the setup. I needed a camera to locate the pads and I went for the Logitech C270, a nice HD resolution webcam for the price. The zoom is fixed but it is easily adjustable with its own focus ring.


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Ruzzle Solving – The nerd way ..

I’ve been working on this project in my spare time for about three weeks and even though is not yet completed I decided it was time to share something. The idea was to realize a robot that could play Ruzzle versus an human player leaving him no possiblity to win. After a few days of brainstorming I decided to start writing a little of code in Python: In a few hours I managed to obtain all the right words performing a depth-first search and comparing them with a dictionary but I felt that was not enough so I asked myself: Why not use OpenCV for image processing combined to Tesseract for letter recognition ?


The image as captured by the camera

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Using Transform Matrix for PCB Drilling – Part 1

Since I started making my own PCB I always complained how boring and tricky is hand drilling all the holes in the right place. Owning a CNC router I could have the work done in a hurry neverthless I prefer etching my own boards and have the drills done by the router. The main problem is how tricky is aligning the board under the machine, furthermore there may be some scaling problem related to the master mask precision. Thus I started coding a little tool which could help me in this process allowing me to not care about all the stuff I just explained above. Continue reading