Boxing Trainer Uses DIY Force Sensors

Boxing Trainer

A team of Cornell students have designed and built their own electronic boxing trainer system. The product of their work is a game similar to Whack-A-Mole. There are five square pads organized roughly into the shape of a human torso and head. Each pad will light up based on a pre-programmed pattern. When the pad lights up, it’s the player’s job to punch it! The game keeps track of the player’s accuracy as well as their reaction time.

The team was trying to keep their budget under $100, which meant that off the shelf components would be too costly. To remedy this, they designed their own force sensors. The sensors are basically a sandwich of a few different materials. In the center is a 10″ by 10″ square of ESD foam. Pressed against it is a 1/2″ thick sheet of insulating foam rubber. This foam rubber sheet has 1/4″ slits cut into it, resulting in something that looks like jail bars. Sandwiching these two pieces of foam is fine aluminum window screen. Copper wire is fixed the screen using conductive glue. Finally, the whole thing is sandwiched between flattened pieces of corrugated cardboard to protect the screen.

The sensors are mounted flat against a wall. When a user punches a sensor, it compresses. This compression causes the resistance between the two pieces of aluminum screen to change. The resistance can be measured to detect a hit. The students found that if the sensor is hit harder, more surface area becomes compressed. This results in a greater change in resistance and can then be measured as a more powerful hit. Unfortunately it would need to be calibrated depending on what is hitting the sensor, since the size of the hitter can throw off calibration.

Each sensor pad is surrounded by a strip of LEDs. The LEDs light up to indicate which pad the user is supposed to hit. Everything is controlled by an ATMEGA 1284p microcontroller. This is the latest in a string of student projects to come out of Cornell. Make sure to watch the demonstration video below.

[Thanks Bruce]

18 thoughts on “Boxing Trainer Uses DIY Force Sensors

  1. Another class project that’s “under $100” if you have access to multiple university research and engineering labs.

    These have been some very cool projects that have that one stupid, distracting line. Doesn’t Cornell have an intro accounting class?

    1. What advanced tools/machines did they use to make this that the rest of us wouldn’t have/ have access too? I think its commonly understood that when a project is listed as a “budget build”, the dollar amounts are primarily that of the BOM, not BOM + every tool used. Otherwise, even the simplest of woodshop spice racks would “cost” hundreds if not thousands of dollars to make after adding up the cost of every power saw, drill, etc. If one really wanted to nitpick, one could argue that the door everything is mounted to is a necessary component, therefore it should be on the BOM, and probably costs several hundred dollars, making it the most expensive item on the BOM.

      But lets not nitpick over this kind of stuff. Instead lets support these kids and their projects – they accepted a challenge, made a project in true hacker fashion, learned a thing or two in the process, and shared their project and findings with the hacker community. I was under the impression that was sorta the point of this website & community…

      Unless I’m missing something, I don’t think they used any fancy tools that wouldn’t be commonly found in a tinkerer’s garage.

      1. “Otherwise, even the simplest of woodshop spice racks would “cost” hundreds if not thousands of dollars to make after adding up the cost of every power saw, drill, etc”

        Hence the need for a 101 Accounting class that you yourself might find illuminating. Casting aside the intellectual capital and skills necessary for a moment — not inconsiderable in the real world — the context of ‘cheap parts’ must also include access to tooling outside the means of most. It has to be considered a valid criticism if the means to employ the ‘cheap parts’ is still beyond what most can do in a typical maker garage.

        Knowing > guessing.

        1. Your distasteful verbiage leads me to arbitrarily assume an opposing stance. Logic seems to dictate the same approach.

          Logically, you do articulate a valid point. Tooling costs can represent a significant component of cost… However, The typical “blacksmith’s garage” is assumed to contain a forge, enough coal to fire it, an anvil or other hammering surface, as well as a hammer, tongs, blower… etc…
          the typical “maker garage” (probably) contains solder, a soldering iron, a breadboard, enough wires to do anything you need, power supply… etc…

          In addition, there are no unreasonable tooling costs associated with this specific build. If YOU require “access to multiple university research and engineering labs” to accomplish cutting slits in foam rubber sheets and using conductive glue… I suspect you’re doing it wrong…

          Lastly, there is technical skill and hand/leg work to be done to accomplish this project, and it is impressive that, from raw parts which presumably had not been associated together, something creative and useful appeared. This project is awesome, and cost effective due to the lack of extensive tooling. I like it!

    1. Reading capacitive sensors is quite a bit more difficult then resistive ones, so that’s probably why they didn’t do that. I’d think the antistatic foam will crumble quickly, if it’s anything like the antistatic foam I’m used to seeing. They could have avoided this potential problem (and make the mechanical construction easier) if they had just lined some compressible foam rubber with a conductor on each side, and measured the capacitance instead.

      This measurement doesn’t actually need to be very difficult; it you would charge the capacitor through a rather high valued resistor up to a voltage within the range of your ADC, you should be able to read the impacts. The way this works is that the capacitance of the capacitor rises if the plates are moved closer together by the impact, and on the short term, the stored energy has to remain almost the same (because of the high value of the resistor, limiting the current to a very small value). This means the voltage has to drop, and when the capacitor is restored to it’s original state, the voltage would briefly increase a little beyond the supply voltage. This way, you could only measure impulses, and not static pressure, but that wouldn’t be needed anyway.

      I think this would work, but I’ve never tried. One possible problem would be the rather small initial capacitance, but the relative change in capacitance should be quite significant.The sample-and-hold capacitance of the microcontroller should be very small to be able to measure this way, but I’d think any controller that is suitable for capacitive sensing would work, like the MSP430, and various controllers from Cypress, Microchip, Atmel, etc.

    2. Here is a general observation without reading the article:
      Reading capacitance sensor would not work well unless the *percentage* change in capacitance is large enough to be detected. So if you have long dangling wires, breadboards etc all that can contribute to have a large base capacitance reducing the sensitivity. Further more if your dangling wire or breadboard etc move around would cause a change in measurement too.

      So to make it work, the sensing circuit have to be at or integrated with the sensor. A resistance based sensor would be a bit easier for prototyping as your extra wires wouldn’t affect the sensitivity too much.

  2. Apart from boxing being dumb, shouldn’t any sports simulation hardware at least try to be able to measure the performance of the random advanced practitioner? I mean, even if scrawny kid had a couple of lessons, he’d be no jard-stick to calibrate sensitivity levels with surely.
    Perhaps, before building a system that maxed out at “Hey Bro” back slap levels, one should look now to build a sensor that can detect at least novice to semi-pro levels of energy, otherwise it’s just a kids toy.

    1. Boxing is not dumb you slack-jawed wussy. That being said you are correct this wall game has nothing to do with boxing. Boxing is learned by being coached and sparring with a partner preferably one that is better than you. There are multitudes of things besides punching, punching is probably the least important part of boxing. If you don’t have your footwork, headmovement, and conditioning down pat being able to punch doesn’t help you. This silly wall game won’t even teach you how to do anything except break your wrist.

      1. It’s a final project completed in a couple weeks and the students had loads of other work to do, calm down. I’d say its pretty impressive given the time constraints. These guys weren’t building this to help boxers, they’re just trying to get a good grade. But if you were looking for someone to build a system to revolutionize boxing training, I’d call up a Cornell engineer. #LetsGoRed #BestEngineeringIvy #HarvardSucks

      2. There are only 2 things that boxing is exclusively good for. Grow collie flowers for ears and brain damage. Any other possible benefits are easily to be had in various other less moronic activities.
        The whole concept that you must, in your mind, project weakness on somebody who’s honest opinion of boxing is that it is a violent simpletons sport supports my loathing of it.

        1. How do you feel about English? Cauliflowers, whose, simpleton’s…

          The whole concept that you used this forum to express an opinion about the time-honored sport of boxing is a bit self-absorbed. Why do you imagine anyone cares what you do/don’t consider moronic? Why take THIS opportunity to express a very negative thought? Ever consider that this isn’t about you?

        2. Voxnulla -> I hate it when people like yourself take away from an achievement such as progressing technology into new fields. Boxing is also referred to as the “sweet science” the combination of body movement, reaction time and forward thinking are obvious lost on some one like yourself.

          Every technology or piece of equipment starts somewhere. A proof of concept that provides positive feedback and data even at “hey Bro” back slap levels is a necessary first step. The individual components can always be upgraded in the future.

  3. This is a pretty standard method of making DIY force sensors, dating back decades. Even the Miracle Piano foot pedal was basically a piece of ESD foam sandwiched between aluminum foil pads.

    1. I think perhaps the first mention of using conductive foam for DIY pressure sensors with from Forrest Mims in one of his electronics scrapbook or robotics builder articles, back in about 1987 or so. That is why it has been a persistent theme in the hacker community, ever since. Conductive film ESD bags are also popular for flex sensors, and non-conductive foam may be used for capacitive pressure sensors (in an oscillator circuit).

  4. I would like to point out a few things. If anyone who could actually throw a good punch tried this they would very quickly either break their hand or the door there needs to be some distance for decelerating all the body parts moving during a punch. Also, and this is just me being a nerd and fan of boxing but comparing this to actual boxing training is like comparing the movie “Hackers” with actual hacking.

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