High Speed Air-gap Flash

A bullet hitting a solid brass rod.

If you just want to buy an assembled and tested airgap flash, I have made an updated versions that can be purchased at Information Unlimited.

In my quest to capture amazing high speed photographs I notice that when photographing shooting bullets the bullets were blurred. I found that standard xenon tube, which standard flashes use, is very bright for the energy put into it because of glowing xenon gas. The book Electronic Flash Strobe by Harold Edgerton explains all the calculations, but in practice this means all the flashes from Nikon, Canon and others that use xenon flash tubes have a minimum duration of 1/40,000th of a second. That’s fast enough for most things, but not for a shooting bullet travels around 1000 feet/second. In 1/40,000th of a second that bullet can travel about 1/3rd of an inch leading to blurry photographs of bullets.

To solve this I had to make a faster flash. I’m certainly not the first to do this. I think that was Harold Edgerton. He actually created a company called EG&G to sell a product called the 549 Microflash, but that company has been dissolved and the product discontinued. Sometimes you can still find these flash units on ebay, but the ones I saw were selling for $8K+. There is also a company called Prism Science Works making a modern version of these for researchers, but you’ll need really deep pockets to afford one of those. I saw directions on how to build one in the August 1974 issue of Scientific America and emailed Alan who had already built a few. After this research I realized I could build a sub-microsecond flash for just a few hundred dollars. A sub-microsecond flash means the flash duration is less than 1/1,000,000th of a second or about 25 times faster than a xenon flash.

Here is an image showing how an air-gap flash compares to a standard flash when photographing a 1000 feet/sec pellet.

I am a strong believer in sharing knowledge so I’ll explain how I made my air-gap flash, but I am knowledgeable with high voltage safety procedures. You should not build this because this flash will kill you. It really will. This flash requires charging a 35,000 volt capacitor that will easily kill a person for a single mistake. I have a safety checklist that I use ever time I plug in this flash and it still scares me. If it didn’t scare me then I shouldn’t be using it because this thing is dangerous. The below information is for educational purposes only. Do not build one! If you go against my advice and do build one, I am not responsible for any injury, death, or any other problems it causes.

Here is a list of the main parts I used to build my air-gap flash:

Here is an overall diagram of how all the parts fit together.

This is the schematic for the custom circuit board I made. Basically it doubles the 120V AC and uses an external signal to trigger the 45 kV transformer.

And here is a picture of my custom circuit board.

Here is a picture of the air-gap flash.

This shows what is plugged into the air-gap flash. 120V to run the 45K trigger transformer, 14V to charge the big capacitor, and a 3.5mm cable to use for triggering.

Here is a side view. Notice that the reflector has a thin sheet of Plexiglas over it to make cleanup easier. The metal reflector is also grounded in case the plexiglass tubes shatter, and they do shatter sometimes. I have found they last longer if I use latex gloves so no oils from my hands get on the glass tubes.

This is a close up of the glass tubes where the spark happens. The outer glass tube is just for protection and to reduce noise. The inner tube has the wire 45 kV trigger transformer inside. When that transformer is triggered the air ionizes and that cases the big capacitor to discharge in a 1.5 inch spark that creates the flash of light. To seal the inner tube I melt one end with a torch until it is sealed.

A top down view that shows how everything is connected.

This rod is very important. It is how I discharge the big capacitor after every use so I don’t die when I’m working on the flash.

Those extra wires and circles are there so I had an easy way to discharge the capacitor.

Note about using it with the Camera Axe. The Camera Axe only allows a trigger voltage of up to 20V. This has a trigger voltage of 240V so I needed to to put a high voltage protection circuit between this and the Camera Axe. There are many examples of these circuits on the web.

Here are a few results:

Glass rods being hit by a bullet.

A balloon being hit by a bullet.

Thanks Alan for your help and letting me use some of your amazing photos.

Comments (57)

Camera Axe 4

After six months of work, the fourth version of the Camera Axe is finally ready. For those new to the Camera Axe it’s a programmable camera and flash trigger with two sensor plugs that can be used for a wide range of sensors. It can do anything from timelapse to photographing a shooting bullet. For a little background information read about versions 1 and 3 of the Camera Axe. This version is open sourced under the Creative Commons Attribution NonCommercial 3.0 License. I do sell kits, assembled versions, and various sensors at my store.

Camera Axe Video:

Here is a list of improvements from version 3 to version 4 of the Camera Axe.

  • The screen is much larger and this makes the menuing system easier to use.
  • The case is is much nicer because I had custom cases made for this project.
  • Added two LEDs to indicate when the camera or flash is being triggered.
  • Much nicer 3.5mm jacks for the sensors and camera/flash plugs.
  • Added a dedicated external power plug for those wanting to use external power.
  • The buttons feel much nicer.
  • Batteries last four times longer.
  • A new microcontroller that has two times the space for more features in the future.
  • The software is a complete rewrite and has too many improvements to list, but I’ll mention the greatly improved intervalometer mode and the new fast trigger mode.
  • The kits are easier to assemble (no wires or drilling needed).

There’s more information information about sensors, reprogramming, flash/camera cables, and much more at www.CameraAxe.com.

Here are a few images taken with the Camera Axe.

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Electric Eel Wheel 2 – An Electric Spinning Wheel

I’ve just finished the second version of my electric spinning wheel. My previous versions have more explanation of how electric spinning wheels work see here and here. I decided to use the original name of Electric Eel Wheel 2. (sarcasm)I really like this new idea I came up with of adding a “2” for the second version of a product. Good thing I open source my ideas, perhaps other products will start copying me on this great idea. (/sarcasm)

There a lot of improvements in the new version. Here’s a list:

  • Much high quality of motor with longer life
  • Lots of changes to greatly reduce noise (quiet running motor, nylon flanges, …)
  • Motor controller runs at lower temperatures
  • No soldering required so the kits easier to assemble
  • Custom enclosure to protect the electronics and create a more professional appearance
  • Larger bobbins (hold over 8 oz)

For lots of details like build guide, FAQs, and a link to a store that sells the Electric Eel Wheel visit the project’s main page.

Here is a video of the Electric Eel Wheel 2 being used:

Here are a few pics:

Don’t forget to visit www.ElectricEelWheel.com.

Comments (11)

Projectile Sensor #2

Due to a few request I decided to make some improvements over my original version of this sensor.

The major improvements are a new 3 PCB design, which makes this much more durable than the previous version. The other huge improvement is using the Honeywell SD5600 Optoschmitt Detector which has a fall time of 15 ns. Previously I was using a standard photo transistor which had a response time of 15 us. This new design is 1000x faster! This actually matters on faster bullets since sometimes the old sensor wouldn’t notice a fast small bullet. The SD5600 never misses.

The only downside to this new design is that it’s a little more expensive. Here’s the BOM.

  • Female Header
  • 2x 90 Degree Male Header
  • 2x 3.5mm Jacks
  • 2x IR Emitters
  • 2x Honeywell SD5600
  • 2x 1K Resistor
  • 2x Male/Male 3.5 mm Cable
    • This sensor has two IR sensors spaced exactly two inches apart. The user inputs the distance from the sensor to the desired position of the projectile when the picture is taken. Based on the time it takes the projectile to travel those two inches between the sensors, a velocity for the projectile can be determined. Since bullets and other projectiles basically travel at a constant velocity, it is easy for the microcontroller to calculate the delay in microseconds until the picture is taken.


      Here’s a link to the Eagle files I used to create the PCBs.

      Using the Projectile Sensor with the Camera Axe

      There are 3 PCBs and everything is labeled so it’s supper easy to plug them together. You will need the 3.0.04 or newer version of the Camera Axe software. Turn on the Camera Axe and hit menu until you get to the projectile menu. Set the distance you want the bullet to be from the second gate when the picture is taken and then push the right button until you get to the “Trigger on” menu for the projectile sensor and set this to low. Now hit the set button. If the sensor continuously displays the speed of the projectile that means the sensor boards aren’t lined up correctly. Look at it from the side and bend the boards so the emitter is pointed directly at the detectors. Once it’s sitting there waiting for a projectile put your finger through the two sensors and it will report back to you the speed of your finger. Once you get this it’s working.

      Mounting the Projectile Sensor

      I mounted a projectile sensor to my pellet gun and it is working great. The pellet’s velocity ranges from 985 feet/second to 1060 feet/second. Below are a bunch of pictures of how I did this mounting.


    Comments (10)

    A New PCB Manufacturer in Town

    Back when I started needing a way to organize my circuit designs on something more permanent than a breadboard I used wire wrapping. This was probably only 10 years ago so wire wrapping was and still is rarely used, but I liked it. It got what I needed done in an easy and fairly durable way.

    Over the past few years I’ve wanted nicer circuit boards for my personal projects. There are many ways to make your own circuit boards at home. I’m sure there are over 100 articles on hackaday explaining the various methods. I’ve never done this. It seems like a lot of work to make the circuit board and then drill it out. Plus when it’s done it’s missing the useful solder and stencil masks. The obvious advantage to doing it yourself is you don’t have to wait for it to get shipped back to you which tends to take 2-4 weeks unless you pay big $$$ to expedite the order.

    A few years ago I ordered my first few circuit boards from Batch PCB. They are probably still the cheapest place to get single boards made. The way Batch PCB works is to batch up individual orders and then send a big order to Gold Phoenix. It takes them a few days to batch up the orders. A few days to cut the boards once they get them back from Gold Phoenix and an extra week of shipping. So this means it usually took about a month from when I ordered until when I got the order. Besides the longer order time the price was expensive as soon as you started ordering more than one or two boards.

    Next I started placing orders directly to Gold Phoenix. If you start selling kits like I do they are a great supplier and I’ve been very happy with them. I always order 155 sq inches of PCBs from them. They have options for panelizing, but I never tried that since I’m usually ordering PCBs for kits. 155 sq inches of PCB usually costs $100-140 depending on the options I choose. I’ve gotten anywhere from 15 to 100 boards from this 155 sq inches depending on the PCB size. I’ve also found that if I need to order more boards they give me a decent discount. I’ve had cases when ordering more boards that they cut the cost to less than half the advertised price. I’ve gotten 1000s of PCBs from Gold Phoenix and haven’t had a bad one yet. The main thing I didn’t like about Gold Phoenix was that you sent them your Gerber files as a zip file in an email and then had to pay for it through the Paypal site. The delivery time was about 2 weeks from when I ordered which is a little faster than their website says.

    Some of the PCBs I’ve ordered from Gold Phoenix.

    About a month ago I found a new PCB manufacturer call PCBWing. I’ve only ordered one batch of PCBs from them, but they had the same great quality as Gold Phoenix. Their website was much nicer than Gold Phoenix since it had much more flexibility on order sizes and a nice a shopping cart that let you pay for your order right on the site. I feel their website cuts ordering time in half compared to Gold Phoenix. Most single boards would still be cheaper through BatchPCB, but they have the cheapest prices I’ve seen on the web for small(5) to larger(100s) quantities of PCBs. For instance I found when ordering 100 3″x4″ PCBs PCBWing’s normal advertised price is still about half the secret discounted price I could get from Gold Phoenix. After I submitted my first order, I emailed some suggestions to PCBWing on how they could streamline their online ordering even more and they implemented the ideas in 3 days. That’s amazing service and the reason I decided to write this blog post. Basically I think PCBWing is a great new PCB manufacturer and I think people who order PCBs online should consider them as an option.

    The first prototype of a new version of my Camera Axe project. Don’t mind those blue wires. I added those to work around some bugs I made in designing this prototype.

    That said there are a lot of PCB manufactures I haven’t tried and maybe some of them are great too. Ladyada has assembled a pretty good list here. Maybe she’ll add PCBWing soon.

    Comments (2)

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