Thursday, May 9, 2013

You Can't Stop The Signal, Feds. (Liberator 3-D Printed Pistol)

Download Liberator here.
The Feds, reportedly, have pulled the zipfile from

Two brave bloggers (Joel Huffmann and Rob Allen) have posted it. I join them.

Molon labe.

As Tech Crunch reports, “the State Department has demanded that new blueprints for a fully 3-D-printed gun be taken offline just a week after they were posted. The Office of Defense Trade Controls Compliance is forcing outspoken Second Amendment crusader Cody Wilson to remove the downloadable 3-D printer files from under expert laws known as the International Traffic in Arms Regulations (ITAR).”

"You can't stop the signal, Mal. Everything goes somewhere, and I go everywhere." --Mr. Universe, Serenity (movie)

Note: I have posted these files as an act of free speech, and I claim my 1st Amendment rights to do so.

I am not a lawyer, but this is what I understand: If you use these files, and you are not a Special Occupational Taxpayer, make these only for yourself, not for sale or trade.  And if you do, include a metal part (the firing pin) as DefCAD recommends, or you will be in violation of the (unconstitutional) Federal law against "undetectable firearms."  In fact, I recommend you paint your 3D printed guns with shiny metal paint, just so this stupid "undetectable" talking point is completely defeated.

Here is a link to the US BATFE regs on making your own firearm, 3-D-printed or otherwise.  Thousands of us have made our own firearms before.  The plans have been on the Internet for years.  Why now?  Because they're skeered, that's why.


Chris Muir gets the final word, as lovely Sam downloads the pistol files (URL in the comic!):

Tuesday, May 7, 2013

Rat, Escaping

Ol' Backwoods has been busier than a one-armed wallpaper hanger lately, doing some interviewing.  I have both evidence and a feeling that my group where I work is going to be closed, and the people let go, just like they have let go more than 100 people since last year.  Moreover, we have new management that does not appreciate what I have done for the company for the last ten years.  So, I am looking for another job.

One of the things Ol' Backwoods is trying to do is to escape the cubicle.  I want to find a job where I can work in my extensive home electronics lab, and not have to travel every day to a building in some stinking industrial park in the stinky end of some city, just to be walled up in a cubicle where I cannot see the sun all day, just to do the same thing.  Burning gasoline and money just to do something I could just as easily do in my home lab is nonsense.

Sure, I may have to travel to their facility for special-purpose equipment, like temperature chambers and whatnot.  But I can do that on an as-needed basis, and not have to have the price of being stuck in a cube.

If I can work at home, I can look out the window at my garden, and enjoy the beautiful and delicious things growing in those beds.   I can have my music as loud as I want it.  I can work any hours I want. I can leave during the day, and work late into the night if I have to, because I'm just upstairs if my family needs me.

Freedom.  That's what escaping the cubicle means to me.

And, based on how I work on my home electronic project, I believe my quality of work will go UP, not down, when I escape the cubicle.

Wednesday, May 1, 2013

Ol' Backwoods' Solar Battery System

Ol' Backwoods has a small solar/battery system that I built, used to power my ham radios, lights, a fan and miscellaneous loads in my electronics lab.

I'm storing energy in two Group 27 12V marine-type, AGM-deep-cycle, lead-acid battery, like this one, except mine is a different brand.  The two batteries in parallel have a nominal capacity of 184 Amp-Hours.  For the uninitiated, this means I could run a 1-amp load (like my LED bench light plus my ham radios in receive mode) for approximately 184 hours.

If there is no sun for several days, and the battery voltage drops, I use a 120-volt-to-12VDC power supply to charge the battery back up.

The battery is normally charged via two 20-Watt '12-Volt' solar panels, in series.

Yes, in series.  No, it doesn't 'kill' my 12-Volt battery.  Hang on, Ol' Backwoods will explain.

I have a solar charge controller than can accept up to 40V.  At full sun, my two panels in series produce 37 Volts open circuit; that is, with no load on the panels except my digital voltmeter (< 0.01 ╬╝Amps).
Data plate on solar panel #1

At full sun, with a load in the range of 1.2 Amps to 0.1 Amps, the panels in series produce between 13.6 and 14.6 Volts.   Why does the voltage drop so much?  Because the current from a silicon solar cell is a nonlinear function of the terminal voltage.  Solar cells have what the industry calls a Maximum Power Point (MPP), which is a combination of voltage and current at which the produce maximum power.  Usually, the MPP is marked on the solar panel's data plate, like mine, at the right.

At my latitude, and without adjusting
Data plate on solar panel #2
the solar panels' tilt (this is explained later in this article), I am getting about 80% of the one of the panels' maximum power, about 16 Watts.

If you are getting 80% of the rated power on only one panel, why did you connect two of them in series, Backwoods?  If you are getting 1.1 Amps at 14.6 volts, why not put the two panels in parallel, and get 2.2 Amps at 14.6 volts, or 32 Watts instead of 16?

I could do that, but it would only work efficiently when the sun is high and bright.  At lower angles, or when it is cloudy or hazy, having the 2nd panel in series boosts the voltage, so that I can still charge my battery even in non-optimum conditions.  The 2nd panel is my backup for lower-light conditions.

For calculating the optimum tilt of the panels for various times of the year, or even a fixed tilt, here is an excellent guide.

Calculating my roof angle
Ol' Backwoods happens to have a large roof surface that faces south, and is turned ever-so-slightly to the west.

As a first approximation, I wanted to know how bad it would be if I simply put the solar panels at the same tilt as the south-facing roof, what kind of efficiency figures should I expect.  Well, that let me to the need to calculate my roof angle.  Sure, I could have measured it, but I had a photo of the side of my house, and I used the inverse tangent of the rise and run of the roof (in pixels) to calculate the roof angle from the horizontal, in degrees.

The easiest installation is just to lay the solar panels at the roof angle, and leave them in the same tilt all year.  There is a calculation on the website listed above for that.  To orient you, zero tilt angle means the panel points overhead, straight up.  Positive angles points more toward the equator (south).  Negative angles point more northerly; in the northern hemisphere, where I live, all the angles are positive.

Optimum Angle, Fixed Angle All Year

My latitude: 35.9 °
lat * 0.76 + 3.1 = 30°

My south-facing roof is pitched at 32.1°; therefore, it angle is nearly optimum.

There is also an equation for optimum angles if you are adjusting the solar panel angles twice a year, on March 30 and September 12th.  In the Northern hemisphere, you go the "summer" angle on March 30 and the "winter" angle on Sept 12; in the Southern hemisphere, it's reversed.

Adjusting Twice a Year (Mar 30 & Sept 12); Optimum Angles:

Best summer angle: lat * 0.93 - 21    = 12 °
Best winter angle: lat * 0.875 + 19.2 = 51 °

Similarly, there is a small efficiency gain for adjusting the panels 4 times per year.

Adjusting Angle 4 Times a Year (April 18, Aug 24, Oct 7, March 5)
Best tilt for summer:     lat * 0.92 - 24.3 =

Best tilt for spring/fall: lat * 0.98 - 2.3 = 32.8°(nearly perfect for my roof angle!)

Best tilt for winter:       lat * 0.89 + 24 = 56°

(This post will be modified to add more information.)