Tuesday, November 29, 2011

Carbide Cannon

my giant carbide cannon

When I was little I used to see ads for Big Bang cannons in the back of Popular Mechanics magazine.  Oh how badly I wanted one.  But it was not to be.  Years later while searching Ray-Vin for some high power rifle equipment, I came across this site.  Giant carbide cannons!  The daydreams of my youth magnified twenty times!  Of course I just had to build one.  And with my daughter's birthday party being held on 4th of July weekend, I had two perfect excuses.

Big-Bang carbide cannon

Carbide cannons are the coolest noisemakers ever.  First the cannons are filled with a little water.  Calcium carbide is added next.  When the carbide mixes with the water it forms flammable acetylene gas.  Add a spark and KABOOM!  A large bang erupts from the barrel.

the business end

I built my cannon based on these plans in June 2010.  I followed the plans pretty closely with only a few minor changes.  The tee is actually a 6" x 6" x 4" tee instead of a 6" x 6" x 6" tee.  It was a little cheaper and the bottom of the tee is hidden anyway so it looks exactly the same.  Instead of pipe and a cap at the breech end, I used a 4" threaded adapter and cleanout plug.  I topped the breech plug with a wooden finial from a curtain rod.  The carriage was made out of wood left over from the mantle project.  The trunnions are made from some old electrical conduit.  The carriage was finished with whatever stain I had on hand and the cannon was painted with a gray hammered finish spray paint to give it the appearance of iron.

ready to fire

I wanted to use a lanyard to fire the cannon rather than a match or touch stick.  So I purchased a Coleman lantern igniter and inserted it through the top.  The igniter strikes a flint and makes a spark when spun.  I attached a wooden wheel with a spring to spin the igniter.  A door stop served as the lock mechanism.  The wheel is rotated about 180 degrees putting it under spring pressure.  The lock is inserted into a hole in the side of the wheel, holding the wheel in place.  When the lanyard is pulled, the lock is removed and the spring spins the wheel creating a spark which ignites the acetylene.  This setup works pretty well and the kids love to pull the lanyard from a safe distance.  However, you have to wait until just the right time to fire.  If you don't wait long enough then not enough acetylene will be generated and you get a pathetic whoomph instead of a BOOM.  Wait too long and there is too much acetylene and not enough oxygen and you get the same result.  Also, if the flint gets wet it won't spark.  That happened on one occasion and I was forced to ignite with a lighter.  The result was a much louder boom.  I think that by using a flame, the cannon won't fire until the breech is filled with acetylene, but long before it is overfilled.

breech view of igniter

I always get the same question.  "How loud is it?"  My friend came over just as I had finished the cannon body and was still working on the carriage.  He asked the proverbial question.  "I don't know", I replied.  "I haven't fired it yet."  With that we set it up on some saw horses in my garage and stuck the barrel outside.  Not knowing what to expect we loaded it, set the firing mechanism, and took refuge around the corner of my house.  I pulled the lanyard and there was an orange flash and a giant KABOOM!  Our jaws dropped in speechless amazement and I could just just barely hear my friend say "I gotta get me one of those" over the ringing in my ears.  My wife opened the window to see which house exploded on our block and just shook her head as I laughed hysterically.  With the right amount of calcium carbide, you can feel the concussion of the blast in your chest.  In short, it's LOUD!!!  Like heart attack for the elderly loud.  Ear protection is a must.  The video doesn't do it justice but check it out to see it in action.

The second question I usually get is "Will it shoot anything?"  Yes it will.  But it will also likely explode in the process sending shards of PVC into your body.  Large diameter PVC cannot hold much pressure.  The acetylene burns so quickly, pressure in the cannon never rises very high.  But if you block the barrel with something, it is very likely that you will exceed the rated pressure of the PVC and the cannon will explode.  DO NOT PUT ANYTHING IN THE BARREL!!!


inside storage

I think this one probably took me a week of evenings to finish.  The carriage took lots of planning, cutting, and gluing.  And despite the use of so many reclaimed items, it was a bit expensive for a such a frivolous item.  Total cost was probably about $100 for all the PVC.  Large PVC fittings are expensive.  But man oh man was it worth it!

small steel carbide cannon
I was so happy with the large cannon that I had to build a smaller portable cannon to take around and show off.  I used a 2" steel plumbing tee for the body.  The breech is a threaded pipe cap.  I drilled through the cap and epoxied in a piezo grill igniter for spark.  I had to solder a length of copper wire from the ground to the electrode.  The other end of the tee has a 2" to 1.5" reducer fitting.  The barrel is a length of 1.5" pipe.  I cobbled the stand together from scrap parts I had lying around.  This one is plenty loud but has a metallic ping to it when it fires.

grill igniter in breech

Sunday, November 27, 2011

Little Gem Amplifier

the completed amplifier
I needed to build an inexpensive amp to go with the Cigar Box Guitar I built for my girls for Christmas in 2010.  Once again the inspiration for this project came from Make magazine's $5 cracker box amp.  That project was based on the 1/2W Little Gem amp from RunOffGrove.  It is a great sounding little amp with separate volume and gain controls.  It is also inexpensive and easy to build.

There was no way a cardboard amplifier was going to survive in a house with a 2 and a 6 year old.  So I dug through my pile of reclaimed junk in the basement and found a wooden index card box.  (It's so satisfying to finally use something that you've been holding onto for years for no reason other than you know you are going to need it one day!)  I purchased the electronics parts that I needed from Radio Shack.  The handle, knobs, feet, and power cord were all from an old PA amplifier I rescued from the trash.  The speaker and grill were from an old Archer speaker I found in the same trash pile.  The aluminum panel for mounting the controls came from my old clipboard that I accidentally ran over.

Little Gem schematic

visual diagram of Little Gem found here

I built the amp just as laid out in the schematics with a few changes.  I swapped the battery for a 12v wall wart that I had saved from some discarded electronic device.  I housed the transformer inside the amp to make it easier to transport.  I also added a power switch and led power light.  I used this great Dremel circle cutter to cut out the speaker opening.  The controls were recessed in the side to protect them.  The LM386 power amplifier chip was mounted in an IC socket so I could easily swap it out just in case I blew it up during construction.  The final price was probably closer to $15 rather than the $5 claimed in the original article, still cheap enough.  The hardest part of this project was finding the free speaker.  The construction itself was pretty easy.  Check my video to hear the amp in action.

inside view

the finished circuit

control mount


Saturday, November 26, 2011

Cigar Box Guitar

the finished CBG and homemade amp

I first discovered this project in Make magazine.  I try to give my girls something hand made for Christmas and/or birthdays every year.  Both of my daughters love music so I thought this would be perfect for Christmas 2010.  The original inspiration was a little too rough around the edges.  I wanted to make something with a little more heirloom quality and better sound.  So I found better plans online.

I scored the cigar box from a cigar store for $3.  They have tons of empty ones.  Just ask and they'll be happy to get rid of some.  Finding a wooden one in this shape was a little tough though.  Many of them were cardboard or square.  It took a few minutes of digging to find one that was just right. 

the neck

The neck is a piece of maple from the home improvement store.  It extends all the way through the body of the guitar.  I used a wood router to thin out the neck for the headstock and the part of the neck that inserts into the body.  ***Blog lesson #1:  DON'T USE YOUR WOOD ROUTER INDOORS!!!***  It had been a long time since I used a wood router.  I forgot what a mess it makes.  It was cold out so I used it in the basement.  I'm still cleaning up the dust and shavings a year later!  I slightly rounded the back of the neck for comfort.  I glued two more pieces of maple to the neck to make the heel.   I shaped it by hand with files.  I used an online fret calculator to determine the fret spacing.  The slots for the frets were cut with a Dremel Mini Saw.  I taped some thin wood strips to the base of the Mini Saw to get the proper depth of cut.

the heel
The tuning pegs, frets, and ferrules were all from Stewart-MacDonald.  The nut is a piece of brass rod.  The saddle is a piece of aluminum angle.  The strings were from C.B. Gitty tuned to "open G" (GBD).  The "inlays" were burned in with a wood burning iron.  I cut a sound hole in the front and wired a piezo element inside between the neck and the cigar box to use as a pickup following these instructions.  I finished it with a few coats of tung oil buffed out with steel wool.

This was a big project.  Probably took a week or two of evenings to finish it.  But it was also one of my most satisfying.  My only mistake was not making two so my girls don't fight over it.  It sounds great, but it would sound even better if someone in the house actually knew how to play guitar!  If you are interested, I made the amplifier as well.  Instructions for that can be found here.

Friday, November 25, 2011

Fireplace Mantle

the completed mantle

Our house has a HUGE fireplace.  So big that we actually thought about having it removed to free up some room.  It sticks out into the room about 4.5 feet and is 5 feet wide.  To make things worse, it had a big colonial mantle that just didn't match our style.  So I tore it off and left the fireplace bare for a while.

In November 2010, we realized we had nowhere to hang our Christmas stockings.  So it was time to make a mantle.  The house came with a bunch of nice 2” x 10” x 8' pine boards.  I glued two together to get the thickness I was after and carefully cut it down to size with a circular saw.  Then I glued a thin pine slat on the front and sides to get a nice face grain.  I planed the ends of the slat even with the surfaces of the mantle.  Finally I sanded and finished with several coats of dark walnut stain and tongue oil.  There were expanding concrete anchors already in the brick from the old mantle.  I bored some large holes in front of the mantle and secured it with lag bolts to the anchors.  Holes were covered with wood plugs.

I hung it on December 20, just in time for Christmas so Santa had no problem finding our stockings. I'm not crazy about the round hole plugs. One of these days I'm going to make mission style pyramid-shaped plugs to make it just right.

Christmas 2010

November 2011

Hexapod Robot

Pololu hexapod robot

Ever since I was a little kid, I have wanted to build a robot.  My first pathetic attempt was probably 30 years ago.  My "robot" consisted of a motor ripped out of my Big Trak hooked to a wired remote and huge caster wheels, both mounted to an old piece of drywall because I didn't have to tools to cut wood.  That miserable failure likely scared me away from building robots for decades.

Older, wiser, and now with better tools, one day I came across this.  Eureka!  As an entomologist who also happens to have a passion for robots, how could I pass up the geek love offered by a robot insect!  This robot is based on the Pololu Micro Maestro programmable servo controller.  It controls 3 micro servos that make the hexapod walk.  Obstacle avoidance is achieved with two IR distance sensors.  The Maestro chooses which walking program to run (forward, backward, left or right) based on input from the sensors.  The excellent build instructions made me confident that I could successfully build it.

So I ordered all the parts and built the hexapod in April 2011.  However, it is powered by a rechargeable NiMH.  I didn't have a charger to charge that battery with until now.  So the first test runs didn't happen until two days ago.  If you are curious, I used a Turnigy Accucel 6 charger.  Very inexpensive and it worked great.

my completed hexapod

The one tricky part was programming the robot to turn left and right.  The build instructions give pretty clear guidance on how to walk forward and backward, but they leave it up to you to figure out left and right.  That was the hardest part of the build.  So here are the Maestro settings for left and right turns.  "High" and "Low" refer to servo positions, not leg positions.  If you have programmed forward and backward then this should make sense to you.

Left Turn
Right LegCenter LegLeft Leg
Frame 0highlowlow
Frame 1lowhigh
Frame 2high
Frame 3highlow

Right Turn
Right LegCenter LegLeft Leg
Frame 0lowlowhigh
Frame 1highlow
Frame 2high
Frame 3lowhigh

Easy to build, relatively easy to program, and inexpensive (especially for a hexapod).  You can see how it works in the videos below.  Look closely and you can see the IR transmitters firing.  If I get motivated, I may play with the programming a little and see what else I can get it to do.

Update:  A picture of my little hexapod was featured on Make Magazine's blog!

Thursday, November 24, 2011

School Bus Bookshelf

original photo from Pottery Barn Kids catalog

Back in September my daughter saw the picture above in a Pottery Barn Kids catalog and asked me if I could make one for her.  With her birthday around the corner, what could I say?  The original was $79.00 and looked to be made from MDF.  I figured I could do better for much less.  I used the basic dimensions from the description and extrapolated the other dimensions from the picture.

I used 3/8" birch plywood (1/2" just looked too thick).  Unfortunately the home improvement stores only carry 1/2" so I had to overpay for the plywood at Michael's Arts & Crafts.  For the wheels, I used a length of 3" diameter wooden rod.  I used whatever spray primer I had in the garage and I picked up a can of Krylon yellow spray paint.

almost ready for paint

After cutting out the parts, I could see this thing was going to be much larger than it looked from the catalog photo.  I should have known from the dimensions, but it didn't hit home until I saw the pieces cut out.  Construction was fairly easy.  To make the wheel wells, I used a 4" hole cutter and cut out 2 circles.  Then I used a 3" hole cutter to cut out the center of the circles to make 2 rings.  Cut the two rings in half and you have 4 wheel wells.

Some glue, lots of sanding, some paint and it's done.  It took me a few evenings of work and cost about $30.  (It would have cost much less if I had sourced cheaper plywood, but I didn't have much time.)  And best of all, my daughter loved it.  Not too bad if I do say so myself.

The homemade version