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?

 

Comments

  1. zap says:

    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. marc says:

    You guys should check out http://www.pyramydair.com/blog/

    The blog is devoted to airguns in all their forms. Technically NERF guns fit tbe aorgun description. I’m sure you could pick up some tips and lots of mind blowing ballistics facts over there.

  3. Thatguy says:

    I don’t want to be That Guy, but isn’t this usually called a chronograph, not a speedometer?

    http://en.m.wikipedia.org/wiki/Gun_chronograph

  4. carbohydrates says:

    “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.

    • Ian says:

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

      Exactly. These things have been in use by Nerfers for a long time: http://www.shootingchrony.com/

      • rewolff says:

        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/

        • John says:

          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.

  5. Jope says:

    NERF dart chronograph built by Ulrike Michelsen months ago:

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