It can be hard enough to take a good photograph of a running kid or pet, and if we’re being honest, sometimes even stationary objects manage to elude our focus. Now imagine trying to take a picture of something moving really fast, like a bullet. Trying to capture the moment a fast moving projectile hits an object is simply not possible with a human behind the shutter button.
Enter the ballistic chronometer: a device that uses a set of sensor gates and a highly accurate timer to determine how fast an object is flying through it. Chronometers that operate up to a couple hundred meters per second are relatively common, but [td0g] had something a little faster in mind. He’s come up with an optical setup that he claims can capture objects moving as fast as Mach 2. With this chronometer tied into a high-speed flash rig, [td0g] is able to capture incredible shots such as the precise instant a bullet shatters a glass of water.
Because he couldn’t find any phototransistors with the sub-microsecond response time necessary to detect a small object moving at 1,000 m/s, [td0g] ended up using LEDs in a photoconductive configuration, where 27 VDC is applied backwards against the diode. Careful monitoring of voltage fluctuations across the diode allows for detection of changes in the received light level. To cut down on interference, [td0g] used IR LEDs as his light sources, reasoning there would be less ambient IR than if he used something in the visual range.
What really impresses with this build is the attention to detail and amount of polish [td0g] put into the design. From the slick angled bracket that holds the Arduino and LCD to the 3D printed covers over the optical gates, the final device looks like a professional piece of equipment with a price tag to rival that of a used car.
For the future, [td0g] plans on upgrading to faster comparators than he LM339’s he has installed currently, and springing for professionally done PCBs instead of protoboard. In its current state this is already a very impressive piece of kit, so we’d love to see what it looks like when it’s “finished”.
If you don’t need something quite this high end but still would like to see how fast something is going, we have covered chronometer builds to fit every budget.
Did you know the muzzle velocity of a NERF dart out of a toy gun? Neither did [MJHanagan] until he did all sorts of measurement. And now we all know: between 35 and 40 miles per hour (around 60 km/h).
First, he prototyped a single beam-break detector (shown above) and then expanded his build to two in order to get velocity info. A Propeller microcontroller took care of measuring the timing. Then came the gratuitous statistics. He took six different darts and shot them each 21 times, recording the timings. Dart #3 was the winner, but they all had similar average speeds. You’re not going to win the office NERF war by cherry-picking darts.
Anyway, [MJ] and his son had a good time testing them out, and he thinks this might make a good kids’ intro to science and statistics. We think that’s a great idea. You won’t be surprised that we’ve covered NERF chronographs before, but this implementation is definitely the scienciest!
Thanks [drudrudru] for the tip!
[Spork] over on the Netduino forums wanted to push the limits of what his little board could do. He put together a chronometer to measure the velocity of rifle rounds and Nerf darts using an Arduino-compatable CPLD shield.
The project is built around a pair of commercial CED M2 chronograph sensors; because people have the tendency to shoot through these sensors, they’re available as replacement units for much less than the cost of a complete chronograph setup. [Spork] couldn’t figure out a way for his Arduino clone to read pins with a resolution of 1 microsecond, so a Amani GTX CLPD shield was added to the build. This programmable logic chip takes the output from a chronometer sensor, starts a timer, waits for the second sensor to trigger, and stops the timer. From that, the velocity of just about any projectile can be calculated.
Of course, [Spork] needed to test his new device, so he took it out to the range and fired 25 rifle rounds through his chronometer. The result was a very nice, normal distribution centered around 2400 feet per second, exactly as would be expected. Although [Spork] didn’t test out low-velocity projectiles such as Nerf darts, we expect the same reliable results.