Electric training knife: “The Zapper”.

Posted: July 30, 2012 in DIY, Inexpensive, Knife, Modern, Plastic, Weapons

This training tool is not a toy, and should not be used for anything other than the stated purpose of supervised training in knife defence by qualified adults. The author assumes absolutely no liability for any injury that may result from the construction or use of this training tool. Use at your own risk.

Similar commercial products: Shocknife, H2H Trainers Cut Simulation Trainer, The Buzzard (availably unknown)

For obvious reasons, knife defence training rarely involves the use of real knives. Instead, various wooden, rubber, or plastic training knives can be used in order to increase the level of safety for both the defender and the attacker in a training drill. One disadvantage to using inert training knives is that they provide very little feedback on the effectiveness of a technique in preventing a wound. There are simple and inexpensive solutions to this, such as using a marker, a large piece of sidewalk chalk, or a foam knife with lipstick, chalk, or other marking material on the edge (for commercial examples, see here, here, here, and here). These provide an indication after the fact of where the defender came into contact with the blade. However, these also fail to provide a realistic sense of danger when training, and may be insufficient to develop a proper respect for the dangers of attempting to defend against a knife attack.

One solution is to make contact with the knife edge painful, but without doing any real damage. A mild electric shock can accomplish this, and there are a few products on the market that can add some useful pain and fear to knife defence exercises. The Shocknife, for example, looks like a real knife, has an adjustable shock intensity, and snaps and buzzes in an intimidating way. It has been put into use by many police agencies and certainly adds the important element of stress to knife defence training. However, its price tag of $500 makes it prohibitively expensive for individual use or for equipping a typical dojo for use in occasional knife defence classes.

As demonstrated at the Fight Sciences Research Institute Blog, a very inexpensive version of an electric training knife can be made by modifying an electric fly swatter. (Instructables has several examples of similar modifications to make stun guns, such as here, here, and here — use this information responsibly and at your own risk).

Electric fly swatters can generate a significant voltage (usually 1000-2000 volts) from low-voltage batteries by using a circuit board containing an oscillator, a step-up transformer, and a voltage multiplier.

This is used to electrify a set of grids in the racket, and the circuit is completed when a fly touches two of them, thereby creating a shock as the stored electricity is discharged. In principle, all that is needed to convert this into a simple stun gun is to remove the racket and replace the grids with two metal electrodes. When these come into contact with the skin, a mild (but definitely unpleasant) shock is delivered. To modify this into a training knife, we will simply be creating a “stun gun” with electrodes that run along the edge of the “blade” of the training knife.

The first step is to remove the batteries and ground the electric fly swatter so as not to receive any unexpected shocks. Then, open the handle by removing the screws. Snip the leads that connect the circuit board to the racket and discard the racket frame and grids.

Remove any screws that hold the circuit board in place and flip the circuit board over (if necessary). Solder new wires in place where the leads were originally. In this case, I used pieces of flexible, shielded wire about 2 inches long.

Then solder an unshielded, solid piece of wire to each of the flexible wires. The flexible wires can be held in place within the handle using hot glue. The desired result is a length of solid wire sticking straight out of the end, long enough to wrap down around the edge of the knife. I used hot glue and a small piece of plastic to keep the unshielded wires apart at the tip of the handle.

I also decided to fill the handle with hot glue to keep all the components and wires solidly in place and to provide a bit more weight and strength to the handle. It was also necessary to trim out some of the plastic in the top half of the handle using a rotary tool in order to get it to close properly.

Once everything is secure inside, close the handle and replace the screws. To make it more obvious which part is the blade, you can wrap it in some white tape. (Note: I originally intended to use metallic silver spray paint for realism, but this interfered with the electrical current). Then, bend the two wires down along the blade edge and secure them with tape (and/or zip ties and/or hot glue) to the handle. Wrap them well in electrical tape, and use enough tape to create a hilt for safety.

This arrangement of wires provides a complete edge to the training knife, and is suitable for practising defences against a variety of different attacks. This includes the common thrust, slash, overhand stab, and reverse-grip slash.

To operate the knife, the attacker has to push and hold a button on the handle (but note: it will remain charged even after releasing the button — always ground it when done training!). Most models will have a small LED to indicate that the button is pushed and the knife is charged.

When the button is pressed, all it takes is contact with both wires to deliver a shock. This simulates contact with the edge of the knife, and lets the practitioner know right away that they have been “cut”.

Again, it must be emphasized that although the shock is relatively mild, it does hurt and will leave a mark. This apparatus is no joke.

This is one of the simplest designs for a DIY electric training knife. This particular design does not seem to deliver a shock through clothing, so this is best used with bare arms for indicating defensive cuts. Please use it responsibly.

This training tool is not a toy, and should not be used for anything other than the stated purpose of supervised training in knife defence by qualified adults. The author assumes absolutely no liability for any injury that may result from the construction or use of this training tool. Use at your own risk.

  1. […] The truth is, I am torn on the subject of knife defence techniques. On the one hand, they’re enjoyable to practice, they provide some additional understanding of biomechanics, and they may help to keep the level of panic down if one is ever confronted with a knife-wielding assailant in a do-or-die situation. On the other hand, the attacks that we practice bear little resemblance to what real knife violence looks like, and the extreme danger of a knife assault is simply not reflected in most training environments. The latter issue is why shock knives were invented — to get the adrenaline pumping during training as it would be in a real encounter. (I can attest that the threat of even a minor shock dramatically changes the way people react to a training knife, based on the one I made). […]

  2. alex says:

    Good solid theory and practice, in Cheena-adi, we start with rubber then wood and then rarely with metal (blunted). However, having been shocked in other exercise I can fully endorse the reluctance to be shocked again. I will definitely add this to my kit.
    Whereas with the best will in the world knife training enables move practice that sometimes becomes complacent. As you’ve stated, when it’s real it’s real.
    Alex Wight (Asian Black Belt UK)

  3. CHAOS says:

    I like the concept. I’ve trained with wooden and plastic knives for years. And on special occasions, with select students, we use live blades. I’ve been cut during training, along with receiving separated joints, broken nose, injured spine and concussion. I don’t train my students this way. This little gadget will “liven” up the sessions and give students that “stress inoculation” that they need to draw from in a real encounter. But I agree that most knife training is completely inaccurate of real encounters. I’ve been trying to put more realism into the attacks, and study other means of defense with senior students and my teachers. But it usually just turns into a chaotic, mess of a nightmare for the “student” when faced with the brutality of bladed combat. We have found that the mantra we learned in the military…Speed Surprise and Violence of Action…is the best recourse. This is one of those times that the best defense is a good offense. Great article.

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