New Blowgun Video

Regular readers of my blog will remember my doing a post or two about blowguns. The "native blowgun" has fascinated me since I was a boy. As an adult I have played with both manufactured as well as home made ones off and on over the years. Within the last couple years, not only have I made improvements to my home made ones, but have also found a new use for them as a teaching aid.

Each semester, I do a graphic demonstration of pneumatics principles for my students in Hydraulics and Pneumatics lab. I shoot darts into a board from across the room using a home made blowgun. It's quite amusing to see the "yeah, right - whatever" looks on students' faces as I take the blowgun out and load it with a dart. It's even more entertaining to see the looks on their faces and hear a few of them gasp when they see and hear the darts slam into the board. Most are left with no further doubts regarding the power even a few PSI of air pressure can deliver.

To follow is a link to my latest YouTube video. This was shot at a high frame rate and slowed down so the flight and impact of the dart can be observed.

InKarlsLab - Blowgun Video

Enjoy :)

P.S. One of the most memorable remarks a student made to me in class early on one semester was "I wanna know when the darts come out." He had obviously heard about it from the prior semester's students.

More on Blowguns

A while back, I wrote a post about making and shooting a homemade blowgun. Shooting blowguns is becoming quite a popular sport - both in the United States as well as in Japan. And it's inexpensive and thus affordable by nearly anybody. It's also one of the safest of the shooting sports if one uses some common sense.

My previous blowgun post may be found here:

http://inkarlslab.blogspot.com/2011/10/pvc-blowgun.html

Recently, I have found some other web sites on blowgunning that I think are well worthwhile to check out. A couple general interest ones are here:

This one is a great discussion group that covers all aspects of making and using blowguns.
http://blowgunforum.com

The guy who did this site has an engineering background, and offers some interesting analysis as well as some construction ideas of his own.
http://www.polar-electric.com/Blowgun/Darts/index.html#TableTop

Here is an organization devoted to furthering blowgun shooting as a sport.
http://usblowgun.com/

Measuring Performance
Anyone seriously pursuing the shooting sports will at some point want to measure the velocity of their projectiles. Velocity has a direct impact (no pun intended) on both accuracy as well as, in the case of hunting, how effective it is at killing the intended game. Relating to blowguns, velocity measurements also give a quantitative measure of how one's lung power is developing over time.

Regular readers of this blog have also seen my "Poor Man's Ballistic Chronometer" plans. This definitely follows the old adage that "necessity is the notherhood of invention." I did not have the money in the family budget to buy a ballastic chronometer for measuring dart and arrow velocities, so I did some research and built my own out of about $15 in electronic parts. The article, done in two posts, starts here:

http://inkarlslab.blogspot.com/2012/01/poor-mans-ballistic-chronometer-part-1.html

The engineer I mentioned above had a somewhat similar idea, though he did things a bit differently. He has written some cool looking software that is free for downloading. Looks like a viable idea, though I doubt it would work well outdoors or in environments with a lot of background noise. Here's his setup:
http://www.polar-electric.com/Blowgun/Software/Dartspeed.html



A Word of Caution:

This should be common sense, but in view of how rare a commodity it is in this world today, the following bears mentioning:

NEVER aim a blowgun at, or shoot at, another person or any animal you don't intend to kill and eat!
There have been some news stories about people who have shot at ducks and geese in municipal parks with blowguns, resulting in darts still being lodged in their bodies. Do NOT do a stupid stunt like that! This gives ALL of us who engage in blowgunning as a sport a bad name and could result in blowguns being made illegal EVERYWHERE - as they already have in Kalifornia and Massachusetts.

If you want to hunt small game with a blowgun, as some folks successfully do, make sure you have the right type of equipment and comply with all local laws!

Children and teenagers should be well supervised when using this or any other weapon.


Sport blowgun shooting can be a fun and safe activity for people of all ages and from all walks of life. Blowguns, darts, or the makings for doing your own, are available just about anywhere and are quite inexpensive. I did mine and the darts for about $10 worth of supplies found at the hardware store and/or around the house.

Poor Man's Ballistic Chronometer - Part 1

Many people who participate in paintball, archery, or other shooting sports have a desire to ascertain the velocities of their arrows, bullets, ... Usually this is done with a chronometer. Such devices can be rather pricy, and they are not something you can just walk into any hardware store or Wal-Mart and buy. Readers of this blog might recall that I enjoy archery and also have recently been shooting a primitive blowgun. See my post -
http://inkarlslab.blogspot.com/2011/10/pvc-blowgun.html

After shooting the blowgun a bit, I wanted to have at least a 'ballpark' idea of how fast the darts were flying. This information helps in comparing the performance of various dart designs, as well as giving an idea of how one's lung power is developing. I did NOT want to spend a lot of money on a chronometer, though. Some Google-searching turned up several pages suggesting the use of a computer's sound card as a data acquisition unit for ballistics measurements.

By far the best article I found on this was James Sluka's site at
http://www.inpharmix.com/jps/Jims_chrono.html. He apparently is a spudgun and BB gun enthusiast who, like me, decided to build his own chronometer.

How It's Done
From the basic concept he outlined, I designed a circuit using a photodetector to trigger when the dart leaves the blowgun and a microphone attached to the target to record the dart's impact. I use the sound card in my computer to record the signals, and some free audio editing software - Audacity - to measure the time from when the dart exits the muzzle to when it hits the target. With this time of flight data, and the distance from muzzle to target, one can calculate the average velocity of the dart. Here is the formula: distance = velocity x time, or

velocity = distance / time

While this formula gives the average velocity, a pretty good approximation of muzzle velocity can be had by simply shooting with the muzzle close (in this case, within 2 or 3 feet) to the target. Using such a short distance effectively minimizes the slow-down of the dart due to air friction. Comparing these approximate muzzle velocity measurements with 'time of flight' data at the distances you normally shoot from could yield some good insights into the darts' performance.

The Hardware
The circuit I designed, shown above (REVISED 02/04/2012), uses Mr. Sluka's basic idea with some modifications. I redesigned the "optical gate" to better suit a blowdart's geometry. I wanted to use the dart's airseal cone to start the time measurement just as the dart leaves the muzzle of the blowgun. So I oriented the photodetector setup somewhat off-center with respect to the tube so the shaft of the dart wouldn't prematurely trigger it. The detector is made from a 2" piece of 3/4" PVC schedule 40 pipe. I cut 1/2 way through the tube at the 1" mark, then split one of the sections lengthwise. This provides a spring-loaded 'expando' ring for clipping the device to the blowgun's muzzle. You can see the design and use in the photos below.








NOTE: These dimensions are for a blowgun made from 1/2" PVC schedule 40 pipe. If you are using a different size or type of tubing for your blowgun, you will need to use a different diameter tube for the detector housing, and quite possibly modify the mounting of it to the blowgun. The detector LED and phototransistor leads are 22 gauge stranded, twisted pair wire, approximately 10' in length. The same kind of wire can be used for the mic as well, since the mic impedance is fairly low.












The actual circuit consists of an Op Amp coupled to both a microphone and the phototransistor trigger circuit. When the light from the sensor LED to the phototransistor is interrupted, the 1 uf capacitor produces a pulse that is sent to the Op amp. Note that the phototransistor trigger circuit is coupled to pin2 of the OP amp through a 330K resistor - the same value as the feedback resistor on the amp. This provides essentially a voltage gain of 1. A voltage divider consisting of a 100K and a 15K resistor is used to provide about a 1.6 volt supply to the phototransistor trigger circuit. The mic, actually a noise maker out of an old PC modem, is also coupled to pin 2 of the OP amp through a 4.7K resistor. This provides the gain needed for the mic to work properly. Note that the 330K and 4.7K resistors, coupled to pin 2 of the OP amp, form a crude audio mixer. Power and ground are provided to the OP amp via a voltage divider comprised of a pair of 10K resistors. These are bypassed by capacitors to keep everything at AC ground and help prevent oscillation. The voltage divider is powered by a 12 volt battery. A diode protects everything from getting zapped if the battery is ever connected backward. I also provided a red LED to indicate when the power is 'on'.

The output of the OP amp is connected to the PC's sound card via a 0.1 uf capacitor followed by a voltage divider. The voltage divider, comprised of a 22K and a 2.2 K resistor, was determined by experimentation to work with my sound card's microphone input. If you have a 'line level' input on your sound card, you could probably eliminate these two resistors. Depending on your sound card, you may need to slightly adjust the ratio of these values, but the total resistance value should NOT be made significantly smaller, or circuit performance could be hindered.

The completed circuit assembly, built on a piece of experimenter's perf board measuring 1.75" x 3", is shown in the photo below:




Operation
With the detector, the mic, and the battery connected, use an audio amplifier or your PC to monitor the output. A tap on the mic should produce a clear sound; inserting your finger into the detector and pulling it back out should produce a click or pop sound. If these tests pass, the unit is ready to be used.

My follow-up post, "Poor Man's Ballistic Chronometer - Part 2", will explain how to use Audacity to record and interpret the data.

PVC Blowgun

Regular visitors to this blog know already that, besides high-tech pursuits, I have a few of what some folks would consider rather anachronistic interests. Topics covered here have ranged from the latest Free Open Source Software, computers and networking, electronics, shortwave and amateur (ham) radio, to pre-1982 telephones and archery. Off and on during the past few weeks I have enjoyed shooting an unusual and primitive weapon: the blowgun.

A (very) Brief History:
Blowguns have been used by indigenous peoples all over the world, including those in the Americas. They originally were made from 7-10 foot lengths of cane or wood which had been bored out into a hollow tube. The darts ranged in length from six inches to over a foot in length and consisted of narrow splints made from bamboo, cane or other stiff material. The person shooting it would wind cotton or some other fibrous material on one end to serve as an air seal in the tube. These darts in some cases were tipped with plant or animal-derived poison; in other cases they were used "as is" to shoot small game. Some people took birds with a short, relatively heavy "blunt" cylindrical or marble shaped dart designed to stun, rather than penetrate the prey.

As an aside, one book I read a few years ago indicated that the native blowguns and darts brought back by European explorers may have inspired the invention of the reciprocating steam engine. Indeed, the operating principles of both ARE strikingly similar - both involve a compressed gas acting upon a movable piston.

Modern-day blowgun use:
Even today, some peoples inhabiting the Amazon River Basin and other remote areas of the world still use blowguns for hunting. Some native American tribes hold contests and give shooting demonstrations as part of keeping their cultural traditions alive. During the past couple decades in America, many people have enjoyed them as an outdoor sport. There are even organizations that promote blowgun shooting as a sport:

In the US, The United States Blowgun Association
http://usblowgun.com/

and internationally, The International Fukiyado Association (IFA)
http://www.echigo.ne.jp/~dhiguchi/index_e.html
Parts of this site are written in Japanese.

Now, for the details of my blowgun:
The blowgun is 50 calibre, consisting of a 5 foot piece of 1/2" ID schedule 40 PVC water pipe. A 1/2" to 1.25" pipe bushing serves as the mouthpiece. The larger end was heated with a heat gun until pliable and flared slightly - this gives a more comfortable surface to seal against one's mouth.




















The darts are made from bamboo kabob skewers purchased at the grocery store. The air seal cones were made from 1.5" square pieces of printer paper folded to the cone shape, then glued to the skewers. When dry, the whole dart assembly was coated with spray paint for moisture resistance.

I haven't gone into any more detail because nothing here is unique - there are many sites on the Internet where one can find details on constructing just about any kind of blowdart imaginable.

In the picture of the darts, a shorter dart made from a roofing nail is shown next to the bamboo skewer dart. The paper cone air seal is identical to that on the skewer dart. Though the roofing nail is shorter and heavier, it flies more reliably and carries a much greater impact with the target. The foam archery target cannot be used with these because, even at a 50 foot range, the nail darts bury themselves beyond retrieval into the target's surface. A thin sheet of plywood would be most appropriate for stopping these projectiles.

The "range" shown in the top picture is a parking spot in a municipal park. From the 'near' end of the white line to the wood fence where the target is positioned measures approximately 25 feet using a measuring tape. All of the targets shown in the pictures were shot by me standing as this distance, unless otherwise noted.

In one of the close-up shots, one can see that a dart pierced the air seal (cone) of another one already in the target. Almost the blowgun equivalent of "splitting the arrow" in archery.

The green circle in the photo shows where two of the roofing nail darts buried themselves into the target face. One was shot at 25 feet; the other was at approximately 45 feet. The skewers penetrate between 2 and 2.5 inches into the target.