DIY 3D Printed Ballistic Chronograph

Ballistic Chronograph MK2 #DIY

A 3D Printed Ballistic Chronograph for $70 – $100 USD!

This ballistic chronograph is based on my original design, the MK1 (which can be viewed at https://td0g.ca/2016/07/28/ballistic-chronograph/). I’ve used the MK1 to take many high-speed photos, including a shot of a mach-2 bullet hitting a nice wine glass!  The new MK2 has the same performance as the original, but is much easier to construct.  It can be used for measuring high-powered rifles, paintball guns, and everything between!

3D Printed Ballistic Chronograph

What’s New Since MK1?

My original ballistic chronograph has been very reliable in my high-speed photography hobby.  The biggest problem with the original was that it was hand-built and couldn’t be easily reproduced.  The MK2 uses the same working principals as the MK1, but has been redesigned for easy construction:

  • All components are off-the-shelf or 3D printed
  • The Light Gate sensors are (soon!) available on tindie.com
  • Multiple sensor configurations are available (single/double  sensor height, 3 mm / 2 mm slit width)
  • Only simple tools are required for assembly

How To Build It?

Collect all the materials in the Bill Of Materials. Download and follow the assembly manual instructions.  The total cost at the time of this writing was $95 CAD ($70 USD) for a single-height sensor or $140 CAD ($100 USD) for a double-height sensor. You will need the following tools:

  • 3D printer (200 mm x 200 mm bed)
  • Soldering iron
  • Hacksaw
  • Side cutters
  • Allen wrenches

If you have any questions, feel free to leave a comment!

Light Gate Boards

2020-05-06 – I’ve ordered a batch of sensors from JLCPCB.  They are currently being shipped and will need to be tested before they are listed on tindie.com.  The price per board will be $12.50 USD.

On the original ballistic chronograph, I soldered the entire photodiode circuitry onto perfboard.  It was a big job and isn’t really ideal as the boards were large and ugly.  Soldering a circuit on perfboard requires just a bit of skill as well, so it increases the difficulty to manufacture a ballistic chronograph.  Finally, there was also the issue of the bias power supply, which I had purchased from eBay and had to mount separately from the sensors.

Ballistic Chronograph Sensors

The new Light Gate boards I designed are smaller and much better looking.  They include an onboard boost converter which supply the bias voltage and use a meager 25 mA @ 5 V.  The Gerber files are available on Github and I have started manufacturing them for sale on tindie.com.

Mounting the boards in parellel result in an 85 mm sensing height.  The maximum width of the sensing area (distance from sensor to emitter) is 125 mm.

Testing

I fired several different projectiles through the MK2 alongside the original ballistic chronograph.  The projectile speeds ranged from 100 m/s (330 fps) to 875 m/s (2,800 fps, or mach 2.5).  The raw test data is available on Github.

Both chronographs reported speeds quite consistently, although the MK2 measured about 1.5% slower than the MK1.  This is probably due to a calibration issue which I need to investigate.  I will update this post when I have more information. Edit 2020-05-06: I finally found the cause of the reporting error in the firmware.  It was caused by a firmware issue which affected the calibration factor (actually doubling the error…  The calibration factor was inverted).  The original MK1 was reading 1.8% fast (0.9% * 0.9%).  Correcting for this error brings the readings into fairly close agreement.

The chronographs also failed to detect a small number of projectiles.  Since the number of missed shots wasn’t correlated with the projectile speed, I believe this was due to marksmanship issues (I had difficulty aiming for the sensor area).  The firearms were equipped with scopes and I couldn’t use the iron sights.  I also forgot to bring a rest and had to rely on my own skill (or lack thereof).

Now I’m not out to challenge commercially available chronographs.  Cheap ballistic chronographs can claim an accuracy of 0.25%.  If this is true (and I’ve heard a few people say that it isn’t, but lets not go there without actual test data!) then that’s better performance than this chronograph.  This is a hackable, open-source design which has its own benefits.

~RABBIT TRAIL AHEAD~ While I was making the pellet rifle portion of this video, something very unusual happened.  You’ll note that I fired 11 rounds into the cardboard box, which contained a small piece of plywood to stop the projectiles.  I wasn’t aiming at a particular area of the box, but instead focused on the sensing areas of the ballistic chronographs.  Here’s what I found inside the box: several (maybe 6?) Robin-Hooded pellets! Never tell me the odds…

Photos

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18 thoughts on “Ballistic Chronograph MK2 #DIY”

  1. This thing is great and i am really looking forward building this! And fortunately it’s also reeaaally up2date (like yesterday ^^)
    Just curious about your sensor boards and Tindie (never used before). How much will shipping be.. as i am located in germany.

    Reply
  2. Really interesting project, thanks. I have built a chrono also, and I’m interested in the sensor arrays that you use. The main drawback with mine is that you need to make a barrel adaptor to fit the gun, the advantage is that it doesn’t miss a shot. It would be great to combine the two ideas. https://youtu.be/1Kd4M1qzbcQ
    regards, john

    Reply
    • Thanks John! I like your kit. The barrel adapter is a good idea for air-powered guns, it would be cool if it used a universal clamp that could fit various barrel sizes.

      Reply
      • As aif-rifles don’t have flashhiders/muzzle brakes and also different barrel diameters i think its difficult to do a universal clamp.

        Reply
      • Thanks, did you experiment with fewer sensors (further apart) to cover the area? I use OP254A emitters and OPL550 sensors that incorporate a schmitt trigger, to drive the Arduino directly. I have not tried making an array with them yet.

        Reply
        • I calculated the greatest distance between the sensors / emitters for a given projectile size (0.177 caliber), and was happy with the coverage and performance. I should update the drawing and add it to the repository… Someone could actually test larger sensor-sensor distances, but I doubt that the loss of reliability would be worthwhile.

          Reply

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