# As Fast As A Speeding Bullet

[Electronoobs] built a coil gun and the obvious question is: how fast is the projectile? To answer it, he built a chronograph suitable for timing a bullet. The principle is straightforward. A laser and a light sensor would mark the entry and exit of the projectile over a known distance. As it turns out, there are some issues to resolve.

For one thing, a laser is too narrow and might miss the projectile. The first attempt to rectify this used mirrors, but the loss was too great — we suspect he was using a second surface mirror. The final answer was to use an array of detectors and removed the laser’s collimation lens to cover a wider area.

# Measure The Speed Of A Speeding Bullet

In the study of ballistics, you can do very little without knowing the velocity of a projectile. Whether you need to hit a target at over a mile, check if a paintball gun is safe for opposing players, or photograph high-velocity objects, you need a way to measure that velocity. [td0g] enjoys the challenge of photographing bullets impacts, and has created an open-source ballistic chronograph to help achieve this.

[td0g]’s design makes use of two light gates spaced some distance apart, and the time that an object takes to travel between the two is measured and used to calculate velocity. Most commercial ballistic chronographs also work in this way. [td0g] created the light gates using pairs of infrared photodiodes and LEDs. When there is a sudden dip in the amount of light received by the photodiode, the Arduino control circuit knows that an object has passed between the photodiode and LEDs and triggers the timer. An LCD shield on the Arduino is used to control the software and display velocity. As you probably guessed, clock accuracy is very important for such time measurements, and [td0g] demonstrates a simple technique using a smartphone metronome app to manually calibrate the clock to acceptable accuracy for his purposes. Continue reading “Measure The Speed Of A Speeding Bullet”

# Supersonic NERF Dart Speedometer

[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?

# Paintball Chronograph

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.

# Making A Rail Gun (again!)

[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.

# Perceptual Chronograph

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.

# DIY Ballistic Gel

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.