Solar Can Heater Build Part 2

Last time, (Part 1) I covered the theory and plan for turning my boxes of aluminum soda cans into a solar heater.  I tested the first tube after painting it black and found that the air flow was unsatisfactory.

Testing Prototype Tube 1 in an East Facing Window

 So for the second prototype tube, I took a can opener and removed the tops as well as widened the bottom openings.

Widening Holes

Off with their heads!
(Also titled "going topless" but the wife vetoed that one)

I tried a couple of different methods to enlarge the punched holes.  Forcing them open with pliers just warped the bottom ring on the can and made for a bad fit when placed in the jig for assembly.  I settled on cutting and folding back the segments of the bottom.   I should point out that this adds a tremendous amount of labor and risk for injury to the build.

Ouchy!

This naturally got me to thinking.  Here I am, going to a lot of trouble to make what amounts to some thin metal tubes.  I could probably save myself a lot of time (of which this has already consumed a lot) if not money (band-aids ain't cheap these days!) by just buying some prefab tube or thin sheet stock and fabricating the tube myself.   With the availability of dryer vents and elbows, I've got a lot of the parts I want just at too large a diameter.

So, I've decided to take the cans to the recycling bin and start checking out my options at the local home center.  I also have thought a lot about the air flow issue.  I had previously surmised that the baffling created by the small openings would slow the air flow and allow for more heat absorption.  But as it is, Aluminum doesn't hold much heat being thin in the case of the cans.  So slow air or fast air, my temperature measurements at the top of the stack were about the same.  But with the baffles widened, and air flow increased, I at least could feel the flow of air with my fingers when testing prototype 2.  So I concluded that what I really want is not resistance but length of run.  The longer the run, the more surface area the air can exchange heat with and hopefully come out the top much warmer.

So, back to the drawing board.  Instead of columns of cans, I plan a switchback path of tubing that will allow an always upward rise for the air but will provide one long run at high volume compared to 4 or 5 narrow, comparatively short, runs at negligible volume.  Hopefully I'll have more to report later this summer as I'd like to have this done before next winter but summer activities will take precedence.

Old Plastic

I'm not a huge fan of using credit cards, but I am a fan of reusing them once they have served their purpose.  I wanted to pass along a couple of tips - before you cut your old card up and dispose of the pieces in geographically dispersed public trash cans, check out a couple of uses I found for them.

1. Shims - Seems whenever I'm working on a project, the need to fill a tiny crevice with something pretty much non-compressible comes up.  Often times cedar shims are used, but sometimes I'll have a build where that's too much or I need more material strength with less size.  I keep a stash of carefully sliced credit cards in my parts bin.

Carefully sliced to the most commonly needed sizes with a craft mat and  X-acto

2. Guitar pick!  Yeah, probably an easy one to come up with.  The trick is to smooth the picking edge.  This is my funk pick.  Yep.  You heard me.  As funky as I can get on a 5 string beat-to-death 30 year old Epiphone classical acoustic.

Master the possibilities

And just because I love it, the glorious parts bin.

When you're sure you're going to need that part... some day.

Solar Can Heater Build Part 1

Some time long ago I saw a solar can heater on the internet. I thought - that's cool.

Then I started, inexplicably, collecting soda-water cans. I found myself locating and measuring a scrap piece of ply-wood to serve as a backing. I did a math problem with my kids figuring out how many rows and columns it would take to cover the board with 12 oz. soda cans. I found some old windows which matched the size of my board. Then I started thinking... we can build one of those there thangs!

The basic idea  is that you make a thin box containing stacks of cans that are punched or drilled to let air flow through them.  The face of the box is a sheet of glass or Plexiglas.  I have some old double pain windows which I will re-purpose for the  face.

As my journal entry notes, I have a few things to figure out.  I want to have a mechanical thermostat to control the vent, so when the air temperature exiting the heater drops below a set level, the vent will close and prevent cool are from cycling into the house or the draft from reversing.  Maybe just a foot valve will do if it's light enough to open when warm are is  flowing out the top outlet and strong enough to resist a draft pulling back the other way.

I also want to incorporate an air filter on the inlet to keep dust out.  I have to also come up with a good mount, window adapter and manifold to handle routing air.  Ideally, I'll draw cold air from the basement and vent warmed air into the house, but we'll see how many holes the missus will let me put in our cottage.

Notes from my Project Journal

4 x 5 x 5 = 100 cans

So, I've got two large cardboard boxes full of clean cans now. I drink soda water a lot. Can't do beer, don't like pop. Soda water has the pleasant carbonated effect that I miss from beer, so I go through cases at a time.

Gettin' jiggy wid it.  Sorry. 

I've taken my time figuring this project out.  I don't have all the pieces in place yet, but I have plenty of ideas where I'm heading with it.  My buddy Ken suggested a jig and aluminum tape instead of glue for setting up the cans in columns.  I tend to agree - it's less messy than the build I've seen that used construction adhesive and the jig I came up with is just two conduit pipes with some 1x2 spacer held together with zip ties.

Measure, cut, repeat.

Here we have two cans butt together, lined up perfectly thanks to the jig.  Next I'll cut a length of aluminum tape.  I figured the distance the easy way.  Marked the board and a can, rolled the can, marked the board where the mark on the can was towards the board again.  I checked it a couple of times to make sure I had it right.   Worked out perfectly.  The tape is basic dryer vent tape which has pretty good heat characteristics both in terms of the material and the glue.  I chose the "made in the USA" brand on Ken's advice (He's a Dryer Vent Wizard franchise owner and knows his vents) as imported brands let loose under heat, unfortunately.

rollin' rollin' rollin'

 To apply the tape, I start on the side of the cans facing me with the tape curled to ensure a perpendicular seat at the joint.  Then, I just roll the cans on the jig to smoothly lay the tape down.

 When done, the tape mostly lines up with the other end but because it's so much wider than the joint and  the length is specific to the diameter of the cans, it's no worry and looks nice and tidy.

Air Flow

Bottom right is a shot of the bottom of the cans.  To punch them, I simply put a counter-sink bit in my drill press and didn't even turn it on, just pulled the press down into the center of the can.  I punched 200 cans in about 20 minutes I'm guessing.  Repetitive... reminds me why I'm glad to have left factory work behind me in the 1990's.  The punched hole is offset from the tab hole which will serve to slightly baffle the air flow as it rises through the cans.  This will slow it down and give it more time to soak up heat from the cans which will be warmed by the sun.

When all of the stacks are assembled, I'll give them a coat of stove-black paint, which as you might guess is hi-temperature paint that should hold up.  I will likely give them a once over with some hi-grit sand paper to etch the aluminum enough to hold the paint.

When I get further along with the build, I'll post some more pictures.  My projects tend to wind out over weeks and months in my free-time (which is scarce and sacred) so be patient.

Canon MP700 Copier Printer Fax Scanner Tear-down

Some time back I wrote about the Canon MP700 that my neighbor had given me, and my attempts to get it running.  It WOULD have made a really nice printer, but Canon's apparent policy these days is "you must take the device to a certified service center".  I guess they weren't getting enough of some sort of kickback, or too many botched DIY repair guys like me calling them for help.  In any event, I wasn't putting any more money into it after sinking $53 into a new set of ink cartridges.  (which I still have,  opened and installed but never printed from, obviously, if anyone would like to help me not eat the full cost of them - I could ship them sealed in baggies).  So, I decided to tear it down and scrap every last good part I could from it.  In the process, I scored some really nice parts and made some cool finds.  I also learned a bit about how to build cable restraints into a device and how to daisy chain smaller ground plates throughout a system so that everything, no matter how remotely tucked away, has easy access to ground.

MP700 with scanner and upper paper handler removed

My favorite find was all the stepper motors.  So far I pulled three disk style motors out and there is one large cylinder motor which is the print carriage motivator.  There's also a smaller paper handler motor yet to be pulled.  I like stepper motors due to their potential for enabling automation in small projects - something I love to ponder but haven't had the time or resources to pursue.  Now I have at least some resources!

Naughty motor on the Prt Scr button launched
a hundred Save Screen Shot applets in Linux Mint.
I plopped on the Esc key to clear them.  Took about 10 min.

Perhaps the most interesting find was an actual TUBE on the analog circuit for the phone cable pass-thru.  A tube of all things, tiny as it is.  I thought that was pretty neat.  I tried to get a picture of it but it was just to small for my cell phone to see.  It was clear, shaped like a short Christmas tree light and had two unconnected anodes inside.

One obvious bit of goodness was all the momentary contact switches provided by the control board - around 40.  These are the same kinds used in your computer mouse.  So, not only do I have a good stock of them to work into my own projects, if my favorite mouse wears out, I have a chance of being able to restore it to good working order on my own, or I might even build my own mouse or controller.

The most numerous find was all the screws.  Machine screws, screws with lock washers, and ubiquitous self-tapping screws.  I good heap of them.  My wife said, "I'm sorry, I just don't get excited about the screws."   I just left that one alone.

Results from an afternoon spent un-screwing around.

A cool item was the flat bed scanner imaging bar.  It both emits and detects light.  At first I thought it might be cool to turn it into a hand held task light, but I might see if I can turn it into a motion activated area light for under the counter.  That would be pretty neat, I think.

Last but not least, I also harvested a number of nylon or plastic gears, rollers springs and shafts.  All good parts for building things.  My goal at some point is to build my own 3D printer using many of these parts.  I have just about enough just from this tear down, and I have another HP Ink Jet printer and a very old flat-bead scanner to tear down yet.

There's something therapeutic about tearing apart a device one screw at a time. I learned some things, had an actual excuse to listen to my 80's Pandora station somewhere besides work, and just enjoyed unwrapping the present my friend gave me one piece at a time!

Weekend Project: PVC Blow Gun

I'm a firm believer that in order to teach respect, the danger of a lack of a respect must be well understood.  In polite society, crassness is the least of the problems that flow from a lack of respect for one another.  With kids, respect is paramount to their well-being, both at home in a peaceful relationship with family members, and outside the home when dealing with other kids and adults.  Respectful children are almost universally recognized and praised as worthy companions.  We would all do well to be respectful to the people around us, and of the things around us... especially the dangerous things.

Dangerous things come in all forms.  Potential kinetic energy is all around us.  A rock perched on a deck railing has the potential energy of its mass and the height at which it is perched.  As a rock falls at 9.72 m/s squared, it gains momentum and speed.  When the rock comes to a stop, its kinetic energy is transferred into whatever it lands on, whether it's a siblings head or a toy car or just the good ol' earth.  Damage will be done in some form.  A failure to respect this fact will result in injury.

Putting kinetic energy to practical use is one of man's crowning achievements in the engineering arts.  The humble blow gun is a fantastic opportunity to look into such variables as mass, air pressure, drag, mass and velocity. To make a blow gun, you're only going to need a few thing easily had at Lowe's or any other reputable hard ware store.  I made ours from 3/4 inch pipe adapters (for the mouth piece) and ordinary 1/2 inch PVC schedule 40 pipe.  I used standard two-part epoxy to weld the pieces together to ensure a good seal that would hold however much pressure we could blow through it.  We used 30" pipe sections and made four blow guns so everyone can have fun.  Maybe we'll decorate and personalize them later.

1.  Use a disposable surface to mix your epoxy, such as a cardboard box.  This stuff is pretty much permanent and you don't want to apply any of it to yourself or your fellow humans, so beware.  Also, the fumes are icky.
Here we made a good puddle, mixed for 2 minutes, and then dipped the end of our pipe in it and
swirled it to coat thoroughly.  Twist together to coat the adapter and then press firmly for 30 seconds to set up.

Once assembly is complete, the mouth piece I chose needed a little finish work for comfortable use owing to a lip in the plastic casting.

2. File or sand down lip, if any, for comfort

When blowing through the gun, the pressure tends to move your lips out a bit which can become uncomfortable after a few shots.  I used 200 grit sand paper to smooth the inner surface down and all was well.

For our projectiles, we experimented with a few things.  I first bought a bag of 3" wooden golf tees.  As we found, they lacked sufficient mass to penetrate our test target, a cardboard box.  Next I tried sling-shot marbles with some cloth wadding in front of it to keep it from falling out the other end of the pipe.  The marbles did pretty good damage owing to their mass.  The weight of the shot and it's near perfect fit in the pipe allowed most of the force of air being blown through the pipe to go into accelerating the shot.  The end result was some pretty grievous dents in the box, but no penetration.  For the purposes of our experiments, we're equating penetration of a layer of card board with "kills a rabbit" though I doubt we'd be able to achieve that in real life.  We're just killing imaginary cardboard rabbits.

With our 30" gun, the range is pretty limited with most projectiles we came up with.  The best was a 16 penny nail pushed through an inch square of cloth.

3.  Cut a 1 inch square of scrap cloth and press a 16 penny nail through the center.

The nail has sufficient mass to carry through and penetrate target (hence "kills a rabbit").  The cloth provided two functions.  One, as shown below, it provided wadding to accept the air we were blowing down the pipe.  Without it, one's breath would simply pass around the nail and it would only slide out of the pipe rather than fly from the gun.

4.  Wrap wadding around nail head to form a plug.

Carefully inserting it into the back of the pipe keeps the nail from pulling the wadding all the way down the pipe.

5.  Our "dart" is loaded into the "breech" of our "gun".  
Rabbits everywhere tremble in fear and run away to hide in their holes.

Then, just aim and BLOW!!!

6.  Keeeled a rabbit!

The gun lacks any useful accuracy, but is NONE-THE-LESS dangerous.  A 16 penny nail flying through the air for 15 feet with enough kinetic energy to poke through a single sheet of cardboard will MOST DEFINITELY BLIND someone so unfortunate as to be in the way.  This makes this a very dangerous toy and ADULT supervision should be observed at all times.

Other than that, have fun cramming stuff into the back of the pipe and seeing how far a good hard blow will send it.  It took me about 25 shots with various projectiles to grow tired of it.  Good clean and dangerous fun.  Perfect for a father on any given weekend.

Taking it further

A longer bore would give more time on acceleration before the wadding cleared the end of the pipe and your blow was no longer providing thrust. Maybe 2 meters of pipe would be better?  This would improve the accuracy, and lethality of the gun.  One could also epoxy a small brad to the end of the pipe as a front sight so that more practiced aim could be taken over time.

As for the darts, I'm sure a hat pin and cotton ball would be a better choice.  The hat pin has less mass than the nail, but greater mass relative to the size of the impact area which contributes to the resultant penetration on target.  With our nail, the surface area to mass ratio is sufficient for the nail to carry through.  With the marble, the surface area was much higher relative to the mass, so all we got were some gnarly dents.

You can probably do better than an unmarked cardboard box as your target.  My eldest minion made some nice circles with a pen, but my vintage vision couldn't see them clearly at firing range!

Tearing it Down

I've mentioned in the past my habit of collecting useful bits of hardware and sorting them so I have what I need later.  Sometimes you have to dig for useful bits, or rather, you should.  In my case, I had some old kid hauling equipment in bad shape from years of garage storage and reuse as play items.  Sitting there, dirty, housing mice and spiders, a car seat and a stroller went under the knife tonight. And the tin snips, and the cordless screw driver, wrench, and a hand small log cum impromptu mallet.

As a result of an evening of gleeful destructive disassembly, I have added approximately 20 screws of various sizes, several different gauge and size springs, lots of webbing and buckles, some wheels destined for a garden cart, and some bolts.  Left over is everything too big and too specialized to be reusable for much else but target practice.  But, not wanting odd bits of indeterminately sourced plastic all over my back woods, they will bet drawn and quartered as soon as I can find a sawsall on the cheap someplace.

Tearing down hardware is but one mode of thought though when it comes to useful destruction.  This past winter I also tore the trim off of three windows, milled and installed new trim after filling cracks and gaps in the insulation around our replacement windows.  My dad was a bit shocked to see I had torn them down to the casements and crusty drywall edges, but it was the only way the job could be done correctly.  Sometimes you have to do that.

My neighbor, Lance, gets this.  He was retained as a body man to fix a spot of rust on my car.  Lance is a Mormon.  If you know anything about Mormons, you should know that they know how to prepare for the apocalypse.  That's why it was no surprised to me that Lance hunted every trace of rust in the rocker and quarter panel, forcibly extracted it with a saw, rebuilt from stock galvanized sheet metal and welded into place a complex set of replacement parts, filled and ground the welds and repainted half the side of the van to an exact match in color.

If you're going to fix something, it's worth doing it right the first time, being thoroughly destructive of the malignant portions as much as possible.  Leaving behind any scrap of the old, defective and sometimes hazardous bits is only inviting it's return later.  Some people understand this principle, and some people are unfortunately oblivious to the reason and need for it.

So, I hope you'll take this cheery bit of advise from a plugger...  when you run up against something that is just sick with defect and you can do something about it, be thorough in your work, even if a bit more destruction than you anticipated is needed to excise all the badness.  Then, start with good materials and a raw determination to finish the project.  Otherwise, your windows will end up like mine - trimmed but not yet stained! (oops!!)

Design, Analyze and Test Circuits Online!

I have been thinking of something like this for years, but the goodly geeks at MIT Nerd Kits have created it - and let's face it, they have the skills I lack in the area of electrical engineering.  Circuit Lab is a virtual schematic designer and tester with many great tools.  Funnily enough, the day my DSONano oscilloscope arrived via FedEx, I find out about Circuit Lab from Nerd Kits.  Now you can see what putting 100v into a 555 chip does without blowing it to smithereens!

Check them both out if you want to learn how to make tiny circuit bits do their thing in useful ways.

Nerdkits

Circuit Lab

I'm already in love with the DSONano just because it looks like a cool bit of Star Trek kit right in your hands.  It is packed with functions and I can't wait to actually be able to put it to practical use!