Supersonic NERF Dart Speedometer

ATtiny Chronograph

[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?

 

8 thoughts on “Supersonic NERF Dart Speedometer

  1. Did that guy from a while back ever figure out how fast his rail gun worked? I recall the EMP from it firing seemed to mess up the commercial unit he was using to measure with.

  2. “A device is essentially two detectors spaced a precise distance apart from one another.”

    *This* device.

    “now that there’s an easy way to measure speed”

    There have been many ways to do this for a long, long time.

      1. If I make a speed measurement device and it reports the speed in “factors of two”: “between 5 and 10mph” or “between 10 and 20mph” and so on. And if it does this correctly in 99.5% of the cases, does it have 99.5% accuracy? Now read the chrony page again…. http://www.shootingchrony.com/

        1. I mainly made this because its price is an order of magnitude lower, and still accurate to a few ft/sec at speeds below regular guns. A hundred dollars may be reasonable for people whose jobs involve measuring speeds, but then its probably too inaccurate, or really high end air soft/bb/paintball guns. I’m neither, so I made this instead.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s