[John] was faced with an interesting problem: after he built his own air cannon, how could he tell exactly how fast his NERF darts were moving? Luckily he had some spare parts on hand and hacked together a fully functional projectile speedometer for less than the cost of an Arduino.
A device is essentially two detectors spaced a precise distance apart from one another. When something passes the first detector, a timer is activated which measures how long it takes the object to reach the second detector. From this, the device calculates the speed. [John] used infrared emitter/detector pairs spaced exactly three inches apart and wired them to an ATtiny2313. After a little bit of coding, he now knows just how fast he can fire those squishy ballistic missiles.
The infrared emitter/detector pairs are mounted to a PVC pipe through which the projectile travels. [John] notes that in theory this could be used to measure almost anything that could fit through the pipe, although this particular device might be damaged by muzzle flash or a pressure wave from an actual gun.
We’ve seen other NERF dart air cannons before, and we wonder if maybe there should be some sort of competition to see who can shoot a NERF dart the fastest now that there’s an easy way to measure speed?
This slick little chronograph can tell you how fast your paintballs are going, as well as what your firing rate is. In this instructible by [Klash69], you can see how to build one for yourself for less than $40. Chronographs themselves aren’t usually too interesting, but we thing he has done a great job here. You have a nice compact package with a big bright display. All it really needs now is a smooth enclosure. As far as the tech details go, he’s using IR sensors spaced 4 inches apart for detection, at the barrel. We’re not experts, but we think this might not work as well on a gun due to muzzle flash, someone who actually knows should let us know in the comments. The brains are a PIC18F13k50 and you can download a full parts list and schematic on the instructible.
You can see a video of it in use after the break.
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[Rp181] is at it again with version 2 of his rail gun project (link dead, try Internet Archive). The original did have some power with 18 400V 3900uf capacitors, but he’s ramped it up to now using 40! Reaching more than double the amount of joules of energy, 12kJ vs. the 5.6kJ! Some other changes include a new injector solenoid setup and revision 3 of his breakwire chronograph. Sadly, he doesn’t mention if this is as green as his first rail gun. Check out a video of just the injector firing and an animation explaining some new updates after the jump.
Continue reading “Making a rail gun (again!)”
All praise to [Limor] for uncovering this incredibly odd project. [magician]’s perceptual chronograph is designed to test whether time “slows down” in stressful situations. The device flashes a random number on the display very quickly so that it is impossible to perceive what is actually being displayed. If you can read the number while under stress, it means that your ability perceive time has increased. It’s hard to believe, but check out the video embedded after the break that investigates the phenomenon. We can’t help, but wonder how [magician] personally plans on testing this.
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Earlier today, we looked at DIY ballistic glass, so we decided to look into DIY ballistic gel as well. Anyone who watches Mythbusters is probably already well familiar with their extensive use of this wonderful gel. Turns out the stuff is beyond easy to create at home. With some gelatin molds (and firepower) you could have a lot of fun with it.
To get started, pick up a box of gelatin powder from your local supermarket. Using 8 oz. of the powder and 2 quarts of cold water, stir together until the consistency is thick and all powder moist. Then, place the mixture in the fridge to chill for two hours. You will then need to heat the mixture until melted; be sure the liquid does not exceed 130 degrees. Finally, apply a layer of nonstick spray to your favorite mold or tupperware, and pour the mixture in. Allow to set in the fridge for 36 hours before use.
If you want even more DIY ballistics, check out this nice guide to creating your own chronograph, for measuring bullet velocity. After the break are videos on making and, of course, shooting the final product.
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