DIY Electric Training Knife

FSRI students are familiar with a variety of close-range weapons evasion, control and aggressive response drills. A wooden dowel or flimsy plastic knife is typically used for simulating knives and edged weapons, as well as a variety of wiffle-ball bats and foam sticks. Although these proxies provide a good margin for safety they can encourage a few counter productive habits, particularly among newer students or people new to our methods. These include:

  • grabbing at the “edge” end of the weapon
  • allowing the “edge” of the weapon to rest on their body while attempting to control the attacker’s arms
  • wielding the weapon like a 1930’s movie villain, ie, making threatening  gestures or non-threatening attacks, and not providing serious and committed attacks

A second set of problems is created by the nature of training itself. Knife attacks seldom happen in the ways that entertainment has conditioned us to expect. So training scenarios in which an attacker brandishes a knife from a body length away, and then artfully parries and ripostes his way in to the attack might be fun (or the dreadfully standard lunge-punch with knife from 6 feet out), but aren’t good preparation for the reality of concealed weapons and ambushes. Over the years I’ve developed a number of scenario based drills in which one partner carries a concealed “knife”, which may or may not be known to the other partner. During a verbal escalation scenario, randori or sparring, the weapon may be drawn at random and used. The defending partner usually ends up receiving multiple simulated stabs and slashes before he or she even knows the weapon was pulled, especially in close grappling encounters. It can be an eye-opener, but even with the random nature of these drills it is still very easy for the defender to slip into a complacent attitude towards the possibility of the concealed weapon, or to ignore the contact as they try to apply some cool technique. A few important elements are missing from such drills: fear and urgency. Fear is not an element that should be present in much of training, but it is useful to explore in affective training and for scenarios that attempt to include an element of surprise. In a training setting, fear usually manifests as apprehension.

A few companies make low-voltage training knives that can deliver a jolt to the partner on the receiving end, adding a measure of apprehension to a drill. The sting it delivers is also very, very useful feedback about where the training knife made contact with one’s body and how many times. Unfortunately, these commercially available models are prohibitively expensive, running into the hundreds of dollars. They just aren’t cost-effective for smaller groups, or for groups that may end up breaking them during intense training (this is why we can’t have anything nice). Fortunately, there are other options.

A while back someone gave me an electric fly swatter. Although it’s not very practical for actually swatting flies, it is great for jolting other people. Even when used in a playful manner the possibility of a jolt gets people moving with some urgency. They pack enough of a charge (1500-2000 volts off of D-cell batteries) to get your attention and trigger reflex actions, but not to cause any lasting injuries.  Safety concerns are low- these devices are rated to deliver a low amp charge that is below the human thresholds for serious injury or death, even if a circuit is created from arm-to-arm across the chest. And they are cheap- starting at $2. I always suspected that it would be easy to convert one into a low-voltage taser for training purposes. And boy was I right.

DIY Electric Training Knife Project

Disclaimer: these instructions are provided for educational purposes only. The author of this post and the Fight Sciences Research Institute do not advocate hacking any electrical devices for the purpose of making a low-voltage taser, or for any other reason. We also don’t advocate that you construct such a device and then use it on yourself or anyone else. Reader assumes all risk and liability. 

Materials & Tools

First, acquire an electric fly swatter, preferably a model that uses D-cell batteries. You’ll also need:

  • a drill, 1/8 inch drill bit
  • screw driver
  • wire cutters
  • router or wood chisel
  • a bit of wood at least 1×3 inches by a quarter inch thick
  • a few inches of aluminum fencing wire
  • duct tape
  • a soldering gun is handy, but not absolutely necessary


1.  Make sure any residual charge is bled off by tapping the racket into something metal and grounded, making sure that both mesh sides touch. Remove batteries. Unscrew the housing.

2. Pry apart the plastic “racket” portion and snip off the leads to the three attached wires, or simply cut them as long as possible. Discard racket.

3. Since this is supposed to simulate a knife, the leads will need to attach to something of a similar shape. The template should also be non-conductive. I found a piece of wood to be the best option, since it was easy to adjust to the desired shape. Take the overall length of the weapon into mind- how long does the training weapon need to be? With the body at 8 inches, I cut the wood template to a little under 3 inches.

4. The wood template will need to be shaped to resemble a point, as well as smoothed to remove any edges or protrusions. A channel also needs to be cut around the edge to give the fencing wire something to lay in. Either a router or small wood chisel will work.

5. The wood template will need several holes drilled in it:

  • two in the wide face for the screws that connect the housing. These will have to be recessed a bit to accommodate the plastic housing. A small chisel or a countersink bit will work for this.
  • two in the tip for the fencing wire to insert into
  • two at the bottom for the fencing wires and leads to insert into

6. Cut the fencing wire to be a half inch longer than the space between the base and tip holes on either side of the template. Insert one end into the base hole, and bend it to conform to the edge. Insert the other end into the tip hole, bend it to conform to the edge. Repeat on the other side. The wire should lay in the groove you’ve cut so that it lines the template from base to tip. Important- the two wires should not touch through the base holes or at the tip- this will cause the circuit to short, and it will not deliver a charge. Secure the wire to the template with a thin strip of duct tape or a rubber band.

7. Place the template into the screw holes so that it fits snugly into the fly swatter body. Carefully pull the leads to the base. They can be soldered to the aluminum wire, or simply pushed into the base holes so that they are snug with the aluminum wire. Important- make sure the leads do not touch through the hole, or they will short out. The ground wire may be attached to either side or simply tucked back into the handle.

8. Screw the fly swatter housing back together. The wooden tip should now be firmly mounted at the end of the training weapon. Replace batteries. Most models have a red LED charge indicator that lights up when the current is activated. The light coming on is not a positive indicator that the tip will now deliver a shock, so it will have to be tested (spouses and significant others will be all too glad to try it out on you). If no shock is delivered, remove the housing and inspect the leads and aluminum wiring for shorts, places where they touch each other or something else. If it works as intended keep in mind that it will only deliver a charge when the button is depressed, and both ends of aluminum wire are touching the other person. Also keep in mind that it may shock you too if you complete a circuit with the knife by touching the exposed batteries, wires or leads. Take the batteries out between uses or they’ll be dead after a couple days.

If it all works, the DIY stun knife can be a good cap to units devoted to weapons defense training. I personally don’t think this piece of equipment should be used in all knife defense work. If it is used too frequently, the same risks of  complacency and desensitization to the tool are possible. The goal isn’t to recreate the Milgram experiment. Instead it can offer a check on related training activities, and suggest areas of weakness that need improvement (such as grabbing at the tip). It should not be used for pranks or without a specific purpose- it’s value is in it’s ability to create some apprehension on the defender’s part, allow the attacker to model a violent or  predatory mindset, and to provide instant, non-debatable negative feedback. Also be sure that anyone using the tool realizes that it does pack a good jolt- not enough to send you flying, but enough to let you know it touched you. The person using it must be willing to cause the other partner some discomfort and attack accordingly  if it is to have any value. Although the charge is below safety thresholds, the tool should NOT be applied to the face, neck or groin, and anyone with a sensitive health condition should NOT use it. Kids should not be using it under any circumstances. Please don’t be stupid with this thing.

For some ideas, the link below might offer a good starting point:


3 responses to “DIY Electric Training Knife

  1. This has got to be one of the coolest things of all time.

    Of. All. Time.

  2. Pingback: Back in the Gi » Blog Archive » DIY training equipment collection.

  3. Pingback: » Electric training knife: “The Zapper”. Martial Makers

Leave a Reply

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

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

Google photo

You are commenting using your Google 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 )

Connecting to %s