I'm involved in a Taekwondo school that works with our local Parks and Recreation Department to teach martial arts to young people and families. We have use of the city's facilities, and the city helps to promote the class so that everyone can learn taekwondo if they want to. One of the classes that we teach is for younger students, and it is called Wee Warriors.

It's always a challenge to keep younger students focused on their training, so I decided to build an interactive punching and kicking dummy that would hold their interest, and Frank N. Stein was born!

Step 1: Pour the Base and Add Wheels

I started out by putting a piece of plywood inside the tub, across one lower edge. I added vinyl wheels to this piece of wood, so that when the concrete dried, I would have recessed wheels to allow me to move the (heavy!) dummy across the gym floor without scratching it. While the concrete was still wet, I also added a 4 x 4 post with metal "L" brackets screwed to it. The brackets gave the concrete something to grab on to, so that the post would not simply slide out of the dry concrete.

Step 2: Prepare Piezo Sensors

I had a handful of piezo sensors, so I decided to use four of them for this project. I used epoxy to attach each of the sensors to a six-inch steel ruler that I got at the local surplus yard. I used a piece of cat 5 cable to connect the sensors, using a single twisted pair for each sensor.

Step 3: Install Sensors and More Padding

I placed the "body" sensors over a few wraps of carpet padding, but since I had pretty thick, stiff padding for the head, I decided to simply tape the "head" sensor directly to the 4 x 4 post. After the sensors were in place, I finished wrapping the carpet padding around the body section, and added a stiff portable kicking target to the head area. I added a surplus Army duffle bag to the body area, and a padded food delivery bag to the head. I chose these things because they were just lying around the house.

Step 4: Duct Tape!

Once everything was in place, it was time for a tough outer covering, and that meant duct tape. Two full rolls, wrapped around and around, gave me a tough exterior. After the tape was in place, I hooked the sensors up to the oscilloscope, just to make sure I had a usable signal from the piezo elements. Everything looked great!

Step 5: Install Some Blinky Lights

I found a bunch of "LED Flashing Steps" (blinky lights) on closeout at Radio Shack. These are designed for runners and joggers, and are made to be threaded through the laces of the shoes. They flash brightly on impact, so I added about ten of them to the body of the dummy. I cut small cavities in the shape of the blinky lights, and embedded them so their surface was flush with the surface of the dummy. They are small enough so that, even if punched or kicked, they will sink into the padding and do no damage, but will flash brightly.

Step 6: Build the Control Box and Add the Edison

I wanted a control box that was convenient and tough, yet that could be removed and repaired at any time, so I decided to use a RJ45 ethernet jack to attach the sensors. This made it easy to unplug and remove if necessary. Because the control box is subject to some amount of shock from being mounted to a punching/kicking dummy, the Edison board is suspended from the four corners of the box on springs. I am looking forward to doing a lot more with this system, so I also mounted a self-stick membrane keypad that I got on closeout at a local electronics store for 25 cents. I intend to add routines for various games and routines to keep the kids interested, so now was a good time to add it. Down the road, I'll be wiring the keypad to the Edison, but for now it is simply attached to the box without labels. I did print a sheet showing the location of all 36 available buttons, but they have no labels as of yet.

Step 7: Bluetooth Feedback

The cool thing about the Edison is that it is able to talk to a Bluetooth speaker, cell phone or tablet. Quite honestly, I ran out of time to get past the testing stages for this part, but I was able to have the Edison talk to a small Popdrop Bluetooth speaker I have lying around. The idea is to use a large, amplified Bluetooth speaker. Using Arduino code, we read the signals from the piezo sensors that are plugged into A0, A1, A2 and A3. We've set a minimum level for the Edison to react to a signal, so background noise is ignored. When Frank N. Stein takes a punch or kick, the increased signal is picked up by the Edison, and it sends one of a number of sound files directly to the speaker via Bluetooth. The sound files say things like "OUCH!", "THAT HURTS!", "MY MOMMA CAN HIT HARDER THAN THAT!", as well as several sound clips from famous movies (think Ahh-nold!). The flashing lights on the front of the dummy, combined with the audio feedback, keeps our Wee Warriors coming back to class again and again. I brought Frank back to my lab to do some upgrades, and I was bombarded with "When are you bringing Frank back?" from all of the kids, so I'd call the project a success, even though he's got plenty of improvements scheduled.

<p>I had been thinking about a similar (and probably smaller) punching ball with a g-sensor inside. But probably the piezo is easier to handle. Great job. I should start making that for our karate kids,</p>
<p>I've got a g-sensor for future use in Frank, but the piezo sensors worked so well (just calibrate them in the Arduino code) that I am probably going to use it in another project instead. I'm also working on having Frank let them play games, like who can kick the most number of kicks in 30 seconds, or have him shout out which target to hit in real time. There's so much that can be added just in the code. I might even put a rotating red light on top of his head for the killer kicks (whoop-whoop-flash, you get the idea).</p>
<p>Yes, I get the idea :-) The main hurdle for me is to find some covering. The bag would be nice, but there's nothing around. Maybe I find someone to tailor a bag from some worn out gi.</p>
<p>If a duffle bag isn't available, try a pillow case. As long as you wrap it a lot with duct tape, it should work fine, especially for a smaller bag.</p>
<p>I have just tried with the g-sensor. My aim is to make a transportable Frank so just a slab with a hook that I can hang it somewhere (we use a public gym as dojo). But it seems that even a moderate punch will drive the sensor beyond its capabilities. I'll have to order those piezo elements...</p>
<p>I got me a couple of those piezos and they deliver a decent voltage. But now I'm a bit unsure how to connect them since depending on the force they produce a much higher voltage than the 5V which the Arduino can operate on. Did you add any protection to the circuit?</p>
<p>Mine are on a stiff piece of steel and buried deeply inside, so I simply used a 1 Meg resistor across the leads, but if you fear spikes much higher, add a 5.1v Zener diode across them as well. That should keep any voltage spikes from damaging the Arduino. So basically the resistor and diode would be in parallel across the leads of the piezo element. I was surprised at how sensitive to vibration or force these inexpensive little piezos can be.</p>
<p>I cut a piece of spring metal from an old trowel and soldered one of the piezo on it. My oscilloscope indicated a peak 40V. So I added a 10M/2.2M voltage divider (I just had these spare resistors lying around) and connected it to the Arduino. I guess the clamping diodes inside are sufficient since the current is very, very low. Alas, the reading was still at 1023 when beding by hand. Anyhow, I can play with the divider also when all is covered up. Time to wrap :-)</p>
<p>Ah, lol. One has to learn the hard way. I wrapped it up and then noticed that only one piezo sent positive voltage and the other three negative. I just tested one of them in advance. So I unwrapped it again and have to change cables/exchange piezos. I'll also add a little pcb for the voltage divider and the zener diodes. Not sure how to show the force. Probably just a few LEDs to start with. Exercising karate is easier ;-) </p>
<p>You can always just switch the leads at the other end of the cable going to each piezo, can't you?</p>
<p>Unfortunately no. I used a common ground. </p>
<p>Bummer. But thanks for telling me...when I add the remainder of the bells and whistles, I plan on expanding and updating the instructable. A reminder to keep track of polarity will be a good addition.</p>
<p>I also found that I cut the metal stripes too short so the hit point was quite small. I'll fix that along with the piezo-replacement. Below the (old) soldered piezos and the pole (which is about 1m long and has a hook to hang it on top) stuffed in the almost ready wrapped (and now again unwrapped) bag. I have used damping mats glued in a spiral on a bottom plate (finally glued up).</p>
<p>I hope you will be making an Instructable about your build!</p>
<p>I'll try to do that (I haven't documented all steps but quite some). It would be my first i'ble here. Hope I will get the missing parts this week. I'll let you know.</p>
<p>Such a fun idea! I like it a lot! </p>
<p>Thanks! These kids are worth it!</p>

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