Ovidiu Predescu's Weblog

Make your own hardware parts

Some time ago I was looking at a way to build some hardware parts for a small project I want to do at home. I found the emachineshop solution to be fairly expensive and with huge lead times, sometimes in the order of months.

I did some more research into how can one like me, with only software experience and a limited understanding of mechanics, build his own parts. Learning to use an old fashioned mill to make your own parts doesn't sound too enticing: you cannot install such a machine in your garage as they tend to be really huge, heavy and noisy.

The manufacturing industry is using the so-called CNC machines - Computer Numeric Control. Using relatively simple instructions in a custom programming language called RS274 (or G-code), you can tell a machine what to do. You can design a part using a CAD application, and have the application generate instructions for a specific machine in the RS274 language.

The RS274 language is interpreted by a computer which then drives stepper motors on the CNC controlled machine (mill, lathe, router etc.). Usually these programs and specialized computers cost thousands of dollars. However the Linux CNC project maintains EMC, a free-software implementation of the RS274 language, that runs on a Linux system and can drive motors through a special driver attached to the parallel port. I found one company, Sherline Products, that builds and sells CNC mills and lathes driven by EMC. You can buy such a mill for less than $2,000. For the ultimate system, their 8620 package gets you a mill and a lathe for some $4000 (if you don't buy their computer).

As far as software is concerned, it would be really cool to be able to draw your part in an application and see it in 3D, then tell it to generate the G-code for the machine to build it. SolidWorks appears to be one such application, although very expensive. I'm still looking for such an application, especially one running on MacOS X rather than Windows.

Sun Fire X2100 server

I bought a Sun Fire X2100 server to act as a back-up for the current dual AMD server I use for hosting this site.

If you decide to buy such a machine, get the basic configuration and buy the rest of the components yourself. Sun charges a lot of money for upgrades. The slim DVD internal drive is $95, but you can get one for as low as $50 (see this drive here).

The default configuration ships with a 512Mb of RAM. To upgrade from 512Mb RAM to 1Gb Sun charges $270. I used the 512Mb memory DIMM which I took out of my Mac mini after I upgraded its internal memory to 1Gb. I bought two additional DIMMs to further upgrade the memory to 2Gb (2 x Kingston 512MB PC3200 400MHz 184-pin ECC Unbuffered CL3 DDR SDRAM DIMM, ~ $78 each). Upgrading to 2Gb cost me $156 instead of the hefty $590 Sun would have charged me.

As for the hard drives, I got two Western Digital 160Gb SATA drives, which cost $95 each. Sun charges $150 for an 80Gb drive and $300 for a 250Gb disk!

As for the operating system, don't bother getting Solaris or one of the Linux systems they offer. I downloaded and installed the AMD 64 versions of both OpenBSD and Debian, and they both work just fine.

To conclude, from the savings described above, you can buy another X2100 machine! I wonder how many people are doing just this.

Remote controlled projection screen

After spending two months researching, designing and implementing, I finally finished my home project: a remote controlled projection screen system. Here are some pictures of the whole system, as well as two videos, of the system extending and retracting.

What was interesting in this project is that it required a lot of mechanics, electronics and programming to be implemented. Since I've never studied mechanics or electronics (OK, I actually took some basic classes in high school and university), these have been the most challenging and fun parts of the project.

The basic requirement was to have the screen sit on top of the multimedia cabinet, slightly retracted. When I want to make a slide film projection, the system would extend the screen about 10" in front of the cabinet, and allow the screen to drop. The whole system would need to be remote controlled through a regular IR remote, as the cabinet is pretty tall.

The basic design started by choosing the projection screen. I chose a Draper Salara matte white 84" x 84". This was the only projector I found that had the screen attachments flexible, all others had them on either side of the screen. I got the screen from projectorzone.com, the only company that allowed me to get the very basic package (screen only, no remote controls whatsoever).

The next step was to design the system to perform the horizontal movement. After investigating linear actuators, I decided to go with a much simpler, home-made rack and pinion mechanism. This needs to move the projection screen horizontally about 15" (~38cm), and is powered by a small DC motor. Here is a small program in bc that I used to size the motor. The actual mathematics used in the program comes from here (look for motor selection and sizing). I bought the parts from mcmaster.com, an excellent source for mechanical parts. The DC motor, as well as most of the wires, electronic components and others I bought from jameco.com.

To control the movement of the whole system, I chose to use a BasicStamp system. This component receives inputs from an IR sensor from the remote control, two limit switches to indicate when a horizontal movement should stop, and an IR emitter/receiver to limit the movement of the vertical screen. Here is the program to control the whole system.

Custom hardware parts on demand

If you want to design your own parts, and have them machine-made for you, this is very interesting: emachineshop.com. You design the part using a program they provide, upload the design to their site and have the part shipped to you later. Really cool!