Airsoft Electronic Ammunition Counter Final Report

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=Conclusion and the Next Step=
=Conclusion and the Next Step=
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The current prototype is exactly that, a prototype.  There really needs to be at least one more redesign before it will be ready to be a marketable product.  From the user feedback we got from our prototype, veteran airsoft players thought it was a good idea, but the housing for it was not the ideal solution.  One user said it would be incredibly useful since it has not been effectively done before (the M41A modification kit is not an ideal solution).  For users who use high capacity magazines ("hi-caps" for short), this would not really be as useful or necessary, as the gun can be shaken and the pellets shake around in the open compartment in those particular magazines.  For people who use standard or middle capacity magazines, this would be much more useful since the pellets are held in place by a spring, rather than being loose in a compartment.  There is no way to check how much ammunition you have remaining.
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*not the final text, just thoughts*
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The current prototype is exactly that, a prototype.  There really needs to be at least one more redesign before it will be ready to be a marketable product.  From the user feedback we got from our prototpye, veteran airsofts players thought it was a good idea, but the housing for it was not the ideal solution.  One user said it was like a "holy grail" in airsoft (*I forget if those were his exact words, but somehow convey this idea*), since it is has not really been done effectively before, except in one particular product, the M41A modification kit, but would be incredibly useful.  For users who use high capacity magazines, hicaps, this would not really be as useful or necessary, as the gun can be shaken and the pellets shake around in the open compartment in those particular magazines.  For people who use standard or middle capacity magazines, this would be much more useful since the pellets are held in place by a spring, rather than being loose in a compartment.  There is no way to check how much ammunition you have remaining.
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In the future, the design could be switched from the existing design primarily composed of ten integrated circuit (IC) chips down to just one programmable chip.  The routing of the wires in the circuit is somewhat complex, especially when trying to fit it into as small a space as possible.  Cost could increase depending on how many layers each circuit board is, and more layers might be needed to get the necessary wire routing.  Another feature that could be added relatively easily when switching to a programmable chip is the ability to stop at 000 or not display digits if they are a leading 0, for  example, just displaying "55" instead of "055".  This can be done purely with existing ICs, but it adds extra complexity and circuit board space.  Currently, the prototype will loop back to 999 after it reaches 000.
In the future, the design could be switched from the existing design primarily composed of ten integrated circuit (IC) chips down to just one programmable chip.  The routing of the wires in the circuit is somewhat complex, especially when trying to fit it into as small a space as possible.  Cost could increase depending on how many layers each circuit board is, and more layers might be needed to get the necessary wire routing.  Another feature that could be added relatively easily when switching to a programmable chip is the ability to stop at 000 or not display digits if they are a leading 0, for  example, just displaying "55" instead of "055".  This can be done purely with existing ICs, but it adds extra complexity and circuit board space.  Currently, the prototype will loop back to 999 after it reaches 000.
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There is a possibility of a product family where the counter box is sold with the photogate built into a flash hider or a mock silencer.  The flash hider and silencers could also be sold iindividually with different designs, based on the varying designs of the flash hiders of different models of guns, since different guns have drastically different looking flash hiders.  Also, If the electronics are designed properly, there could also be different colored displays.  From our searching, the only displays with three digits were red, yellow, or green.  These could be made such that the front piece is replaceable with a different colored display, depending on the user's preference.  The need for this could be determined based on more user feedback.  The variety of colors could be increased also if two- or four-digit displays were able to be used.
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There is a possibility of a product family where the counter box is sold with the photogate built into a flash hider or a mock silencer.  The flash hider and silencers could also be sold individually with different designs, based on the varying designs of the flash hiders of different models of guns, since different guns have drastically different looking flash hiders.  Also, If the electronics are designed properly, there could also be different colored displays.  From our searching, the only displays with three digits were red, yellow, or green.  These could be made such that the front piece is replaceable with a different colored display, depending on the user's preference.  The need for this could be determined based on more user feedback.  The variety of colors could be increased also if two- or four-digit displays were able to be used.
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Also, if it is researched more, the possibility of putting it in a casing kind of like an EOTech holographic sight, it would be the "coolest" version, especially if the display value could be integrated into the HUD.  It would allow for a bit more space which would help the space needed for circuitry as well as a larger capacity battery, like a standard 9V battery, which is cheaper and easier to replace than a particular type of LiIon button cell battery.  Note: two people (nick and the guy who stopped by at the expo) mentioned EOTech.  It would make it very realistic, since the counter would be "camouflaged" in a realistic real steel add-on (which is what airsoft users want).
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Also, if it is researched more, the possibility of putting it in a casing kind of like an EOTech holographic sight, it would be the "coolest" version, especially if the display value could be integrated into the HUD.  It would allow for a bit more space which would help the space needed for circuitry as well as a larger capacity battery, like a standard 9V battery, which is cheaper and easier to replace than a particular type of lithium ion button cell battery.  It would make it very realistic, since the counter would be "camouflaged" in a realistic real steel add-on (which is what airsoft users want).
The possibility of having the count transmitted by and IR signal, kind of like a TV remote control, or by some sort of radio signal, like an RC car would eliminate the need for a wire connecting the flash hider or mock silencer, but it would only be possible with a mock silencer, since the front part would need to be powered by something.
The possibility of having the count transmitted by and IR signal, kind of like a TV remote control, or by some sort of radio signal, like an RC car would eliminate the need for a wire connecting the flash hider or mock silencer, but it would only be possible with a mock silencer, since the front part would need to be powered by something.
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Lat thing from me, but, the final thing that could be added, possibly, that would make it the best product that it could be would be the ability to place something into a standard magazine well for different gun variants (would theoretically only need say 4 types to cover the majority of the market, m4/m16, g36, mp5, ak, but who knows what kind of users would want to know, other types would need to include aug, famas, p90, saw/para, etc) that would automatically detect when the mag is replaced and then set it the the maximum capacity of the particular magazine, or even have a "custom" magazine that works with out product that can somehow detect how many rounds are in the magazine, and then convey that to the counter box.  This goes back to one of our earlier ideas with the counter being in the magazine.  The downside to this would be that it would add an extra component into the gun, and therefore an extra unhidden wire.  If internal modification was "allowable" then more could be hidden, but we are aiming to have it not require any disassembly of any gun to work.
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The final improvement our product could use is to have a magazine automatically tell the counter how much ammunition is in it rather than relying on the user to enter that number.  This could be accomplished through custom magazines for the most popular families of airsoft guns such as the M4, P90, G36, etc.  This goes back to one of our earlier ideas with the counter being in the magazine.  The downside to this would be that it would add an extra component into the gun, and therefore an extra unhidden wire.  If internal modification was "allowable" then more could be hidden, but we are aiming to have it not require any disassembly of any gun to work.  The alternative is that a transmitter  could be used in place of a wire and so it would not have the problem of unsightly wires.
= About the Design Team =
= About the Design Team =

Revision as of 22:44, 11 December 2007

Contents

Executive Summary

We did stuff and it worked nicely

Airsoft Background

Airsoft is a combat sport very much like paintball. The objective of the game is to eliminate other players by hitting opponents with plastic pellets fired from their airsoft guns. The guns used in airsoft games are replicas of real world guns both in a gun's shape and weight, although most airsoft guns are made of plastic rather than metal like their real world counterparts. Like real guns, airsoft guns fire their ammunition by expelling high pressure gas out the barrel. How this high pressure is created is how the gun is classified. Automatic electric guns (AEGs for short) dynamically create high pressure gas through a motorized spring piston system, while as gas guns simply releases gas stored at high pressure. The ammunition fired from airsoft guns are spherical plastic pellets that have a 6mm diameter and usually weigh anywhere from .20-.25g. These pellets have muzzle velocities between 175-500ft/s which makes them capable of hitting targets over 200ft away.

Airsoft began in Japan in the early 1980s out of necessity. At the time, there was a small market of Japanese sporting enthusiasts who wanted to own guns but could not do so because Japanese law forbids it. Consequently, the Japanese did the next best thing by creating airsoft guns. Airsoft guns allowed the Japanese to come as close as they possibly could to imitating real guns. The realism of airsoft guns is one of the appeals of airsoft. In fact, many airsoft games have been called "milsims" (short for "military simulations") since not only are players carrying realistic looking guns, but players often go to games wearing military fatigues as well as bringing two way radios and other military equipment. The appeal of airsoft's realism goes beyond civilian usage as certain police and military forces have been known to use airsoft guns for training exercises.

What typical airsoft players look likeSource: http://www.wpairsoft.com/forum/
What typical airsoft players look like
Source: http://www.wpairsoft.com/forum/

Opportunity

Ammunition is a fundamental need of an airsoft player. Without ammunition, players can neither eliminate opponents nor can they defend themselves from being eliminated by the opposing team. Airsoft players know that they should avoid running out of ammunition. However, our observations of players at an airsoft event confirmed that players do, on occasion, run out of ammunition prematurely. In fact, our team faced the same ordeal when we played in a few airsoft games. The primary cause of this problem is that it is very difficult for airsoft players to say, with reasonable certainty, how much ammunition they have remaining in their magazines. Some players shake their magazine and listen to the rattling sound made by the remaining pellets in order to get an idea of much ammunition is left in their magazine. This method is not very accurate and actually only works on certain kinds of magazines. The rest of the airsoft players simply guess their remaining ammunition count based on how many times they have fired their gun. This is also a poor way to gauge how much ammunition is left in a magazine.


The end result of the M41A Pulse Rifle KitSource: http://www.clayjohanson.com/html/M41-A(1).jpg
The end result of the M41A Pulse Rifle Kit
Source: http://www.clayjohanson.com/html/M41-A(1).jpg

To date, there are not really any airsoft products that informs the user about of their ammunition count. The only relevant airsoft product is the M41A Pulse Rifle Kit. This kit converts a Tokyo Marui M1A1 into a M41A replica. In keeping true to a M41A's functionality, the kit includes an LED display that shows a number representing how much ammunition is left in the magazine. This kit may sound like something airsoft players should embrace since the LED display solves the issue of not knowing how much ammunition is in the magazine. However, the reality of it is that this kit is worthless to the majority of airsoft players. The problem with this kit is that it is specifically designed to work only on a Tokyo Marui M1A1. What airsoft players really need is an LED ammunition counter that works on all guns. That is the opportunity we have chosen to pursue.

Design Solution

Overview

Our team has designed an electronic ammunition counter that allows airsoft players to know exactly how much ammunition is left in their magazines. The premise behind our counter is simple: when users want to know how much ammunition is in their magazine, they simply look at the number shown on our counter's LED display. This number represents the number of airsoft pellets currently in the magazine. Our counter is a very convenient product for airsoft games since it runs autonomously while the user fires their gun. The only action required on the user's part, outside of a one time installation and setup, is to hit the reset button when they reload their magazine.

How It Works

When an airsoft pellet is fired, it passes out of the gun's barrel and out through the flash hider. Hidden inside of the flash hider is a photogate sensor. Photogate sensors are electronic components that produce more or less voltage depending on whether or not something is between the light emitting diode (LED) and phototransistor. As for our counter, the photogate sensor in the flash hider is used to detect when airsoft pellets have been fired from the gun. The flash hider has wires leading to the display box. When an airsoft pellet is fired, the display box receives a lesser voltage from the photogate sensor than when no pellet is fired. The electronics inside of the display box recognizes this drop in voltage as meaning that an airsoft pellet has been fired. Consequently, the counting circuit subtracts one from the current magazine ammunition count. The updated ammunition count is then shown on the seven segment LED display.

On the top and bottom of the counter box, there are four buttons; three on one side, one on the other. The lone button is the preset button. When pressed, it will reset the value on the counter to a user defined value. The three buttons on the other side allow the user to change the preset value. Each button corresponds to one digit on the display, either the ones, tens, or hundreds place. Each digit in the presetting mode is independent from the others, meaning that when one digit overflows from 9 to 0, it will not affect adjecent digits. When the preset button is pressed and held while the individual digits' buttons are pressed, the display gives a real-time display of what the preset value is. The counter will not return to its counting mode until the preset button is released.

Engineering Drawings of Components with Assembly Process

This section presents our engineering drawings for each component as well as assembly drawings depicting how each component fits together in relation to each other.


Below is a CAD model of our a Well's L96 airsoft gun with our electronic ammunition counter attached.

Well's L96 Airsoft Gun with the Electronic Ammunition Counter
Well's L96 Airsoft Gun with the Electronic Ammunition Counter
Close-up view of the counter assembly.
Close-up view of the counter assembly.


Below is engineering drawings of all manufactured parts


Display Piece
The display houses the LED display
The display houses the LED display



Display Box
The display box houses the electronics and the LED display
The display box houses the electronics and the LED display



Display Box Clamp
The display box clamp supports the display box
The display box clamp supports the display box



Flash Hider
The flash hider hides the photogate sensor
The flash hider hides the photogate sensor



Rail Clamp Clip
The rail clamp clip is used either to hold the display box clamp to a gun rail or used to clamp the rail clamp base to a gun rail
The rail clamp clip is used either to hold the display box clamp to a gun rail or used to clamp the rail clamp base to a gun rail



Rail Clamp Base
The rail clamp base allows the display box to be mounted off a gun's top rail, rather than a side rail
The rail clamp base allows the display box to be mounted off a gun's top rail, rather than a side rail


Below is a schematic of our ammunition counter's electronics

The complete circuit
The complete circuit


Here is an exploded view of our assembly

The exploded view of the electronic counter.
The exploded view of the electronic counter.

Manufacturing and Materials

This section summarizes the materials and manufacturing processes necessary for our counter


This table lists each part's material and manufacturing process
Part Material Manufacturing Process
Display Piece Aluminum
Milling
Display Box Aluminum
Milling
Display Box Clamp Aluminum
Milling
Flash Hider Aluminum
Turning, milling
Rail Clamp Clip Aluminum
Milling
Rail Clamp Base Aluminum
Milling
Printed circuit board
varies
PCB manufacturing process



This table lists the bill of materials for the prototype counter's electronics
Part Digi-Key Part Number Equivalent SMT Part Number Qty
CMOS Presettable Up/Down Counter (CD4510)
296-2167-5-ND
296-14153-1-ND
6
CMOS BCD-to-7-Segment Latch Decoder Driver (CD4511)
296-2072-5-ND
296-3529-1-ND
3
Hex Inverting Schmitt Trigger (CD74HC14)
296-12786-5-ND
296-9179-5-ND
1
Switching Transistor (2N3904)
N/A1
N/A
1
5V Voltage Regulator
N/A1
N/A
1
10k Ohm Resistor
N/A2
N/A
5
470 Ohm Resistor
N/A2
N/A
1
.1uF Capacitor
N/A2
N/A
3
SPST Switch
N/A3
N/A
4
2k Ohm Potentiometer
T73YE-2.0-ND
N/A
1
1k Ohm Isolated Resistor Array (8)
4116R-1-102LF-ND
4816P-1-102LF-ND
3
Triple Digit 7-Segment LED Display, Red, Common Cathode
67-1425-ND
N/A
1

1 Purchased previously from RadioShack store
2 Purchased previously from www.futurlec.com
3 Purchased previously from "You-do-it" Electronics Center store

Analysis

This section details the technical aspects of our product including numerical photogate calculations, design for manufacture, design for assembly, failure mode effects analysis, and quality function deployment.

Numerical Calculations on Photogate Circuit

The airsoft pellet counter depends on a photogate to detect a pellet as it leaves the barrel of the gun in order to signal the counter to count down. As the pellet interrupts the infrared beam in the photogate, it sends one clock pulse to the counter. The electronics in the counter have measured values for various properties like rise and fall times or maximum input frequencies. Because of this, a pellet could be traveling too fast through the photogate to be detected, resulting in a miscount. Our goal is to make this product compatible with as many existing airsoft products as possible, so we need to make sure that the pellets will be detected, regardless of the speed or rate at which they are fired. Typical airsoft guns fire pellets in the range from about 300 ft/s (91.4 m/s) to 400 ft/s (121.9 m/s) at about 15 rounds per second, but highly upgraded and modified ones can reach velocities up to 800 ft/s (243.8 m/s) and rates up to 40 rounds per second. The most commonly used pellets in airsoft have a nominal diameter of 6mm, but are actually closer to 5.95mm in diameter. This slight difference in diameter will be neglected.

We are assuming that the beam that is being interrupted was sufficiently small that we could assume that when a pellet was between the LED and phototransistor, it would block the beam, rather than cause only a proportional drop relative to how much of the beam was being blocked. We are also assuming that the potentiometer in the photogate circuit is calibrated such that any decrease in the voltage output of the phototransistor will trigger the switching transistor to initiate a pulse into the counter, but not so sensitive that it will randomly switch due to slight fluctuations in ambient light.

A pellet interrupting a relatively wide infrared beam.  The beam is completely interrupted relatively slowly relative to the time the pellet takes to move a given distance.
A pellet interrupting a relatively wide infrared beam. The beam is completely interrupted relatively slowly relative to the time the pellet takes to move a given distance.
A pellet interrupting a relatively narrow infrared beam.  The beam is completely interrupted relatively quickly relative to the time the pellet takes to move a given distance.
A pellet interrupting a relatively narrow infrared beam. The beam is completely interrupted relatively quickly relative to the time the pellet takes to move a given distance.

Using the higher velocity range for a typical airsoft gun, the pellet would be traveling at about 120 m/s. This would mean that the beam would be interrupted for 5.0 x 10^-5 s, or 50,000 ns. Based on the specifications of the switching transistor being used, the switching time based on the delay, rise, and fall times should be in the range of about 25 ns to 60ns. This means the transistor should be able to switch from low to high and back to low within 100 ns, 10 MHz. This is sufficiently fast, as the counting circuit, at the voltages being used, 9 Volts, has a maximum input frequency of 8 MHz. So, with the amount of time a pellet traveling at typical speeds, interrupts the beam, the switching transistor should easily be able to create a clean clock pulse that the counter can recognize. At 120 m/s, the interrupt time of 50,000 ns is over 400 times the minimum time needed determined by the counter. Doing the same calculations for a pellet traveling at 300 m/s, which is faster than even the very high end airsoft guns can fire, the interruption time is still 20,000 ns, which is still 160 times the minimum required. Based on the assumptions, we believe the counter, if sufficiently calibrated, should be able to detect the pellets properly, regardless of velocity. With an interrupt time of over 150 times the minimum value, even if the circuit is not perfectly tuned, it should still be able to detect even the fasted airsoft pellets.

A diagram of the signal produced by the switching transistor based on the IR beam being blocked by a pellet traveling at 800 ft/s.  See image details for more information, as the image is not to scale.
A diagram of the signal produced by the switching transistor based on the IR beam being blocked by a pellet traveling at 800 ft/s. See image details for more information, as the image is not to scale.

Rate of fire must also be considered for detecting the pellets. The calculations of frequency relative to velocity are done under the assumption that immediately after the transistor has switched back to its high voltage state, another pellet is following behind it to interrupt the beam again. For a gun firing at 40 rounds per second, there will be 40 count pulses per second, meaning the pulses will spaced by 0.025 seconds, or 25,000,000 ns. This gives the circuit ample time to switch when it registers a pellet passing through (~30 ns), remain at that state while the pellet remains blocking the beam (~50,000 ns), then return to its original state (~60 ns). So, even at the highest rates of fire for airosft, the photogate should be able to register a correct count.

A diagram of the signal produced by the switching transistor based on the IR beam being blocked by a pellet at a rate of 40 rounds per second.  The vertical lines represent the signal rising to a high state, then returning back to a low state
A diagram of the signal produced by the switching transistor based on the IR beam being blocked by a pellet at a rate of 40 rounds per second. The vertical lines represent the signal rising to a high state, then returning back to a low state


Design for Manufacture

The manufactured parts of our ammunition counter are relatively simple and should not pose any manufacturing issues. For example, our rail clamp clip is an extruded shape with a hole perpendicular to the extrusion. Milling something of that complexity is very straightforward. The one part that may pose a manufacturing issue is the flash hider. The flash hider has a small section cut out of the inner diameter to house the flash hider. Creating the small section may not be possible since neither milling nor a lathe would be able to reach into the small inner diameter and cut out a rectangular area. Our team believes this can be made accessible by making the flash hider into two parts. Each half would be made as though the flash hider had been cut through the diameter of the flash hider's circular profile. The halves could be designed to fit together by a snap fit process.


The rectangular section is accessible when the flash hider is made into halves as shown
The rectangular section is accessible when the flash hider is made into halves as shown


The other issue with the flash hider is that the small section has two holes in it to allow the photogate sensor to be wired to the display box. There is not enough clearance for the hole to be drilled from either side. One solution for this would be to just drill the holes all the way through from the outside of the flash hider.

These holes cannot be created because of limited clearances
These holes cannot be created because of limited clearances
Solution: drill through the parts of the flash hider that are in the way
Solution: drill through the parts of the flash hider that are in the way

Design for Assembly

There is not much to be said about design for assembly other than it should be straightforward. Assembly of our product should be simple because it is made up of less than a dozen distinct parts. Also, the relatively simple geometry of our parts makes it impossible for any part to have trouble fitting into its larger assembly. Overall, our team sees no potential assembly problems.

Failure Mode Effects Analysis

A good way to improve the design of a product is to analyze different potential failure modes. This chart below analyzes the ways in our ammunition counter could potentially fail.


Item and Function Failure Mode Effects of Failure S Causes of Failure O Design Controls D RPN Recommended Actions Responsibility and Deadline Actions Taken S O D RPN
Display Box
  • Houses the electronics and display
Bending Potential damage to electronics 8 Excessive stress 2 Stress analysis 3 48 Not likely, so ignore Display box assembly - 8 2 3 48
Battery Cover
  • Keeps the batteries from falling out of the display box
  • Electrical contact for batteries
Bending Loss of electrical power 8 Excessive stress while back cover is removed from display box 3 Stress analysis 3 72 Not likely, so ignore Back cover assembly - 8 3 3 72
Circuit Board
  • Keeps track of the current ammunition count
  • Subtracts 1 every time gun is fired
  • Sends the right signals to LED display
Short circuit LED displays will not show the correct ammunition count 8 Water enters display box through the wire holes in the back 7 Specify wire hole tolerances 6 336 Re-design. Use headphone jack to carry electrical signal. Wire holes can be dimensioned to have a headphone jack fit snugly into it making it more difficult for water to enter the display box Circuit board assembly - 8 7 6 336
Malfunction dim LED display, circuit will not count when pellets are fired 8 low battery power 10 User testing 8 640 Include a note about low battery power into the user's manual. Circuit board assembly - 8 10 8 640


LED Display Holder
  • Holds the LED display
Bending Damage to LED display 8 Excessive stress 2 Stress Analysis 3 48 Not likely, so ignore LED display holder assembly - 8 2 3 48
LED Display
  • Shows the ammunition count
Poor electrical connection Numbers will not display correctly 8 Stress during assembly 2 Quality assurance during assembly 2 32 Not likely, so ignore Display box assembly - 8 2 2 32
Flash Hider
  • Houses the photogate sensor
Bending Photogate sensor will not detect gun fire, pellets ricochet off flash hider, barrel of user's gun breaks 8 Hit against a hard object 3 Stress Analysis 3 72 Not likely, so ignore Flash hider assembly - 8 3 3 72
Photogate sensor
  • Detects when a pellet has been fired
Poor electrical connection Sensor will not detect gun firing 8 Stress during assembly 3 Quality assurance during assembly 2 48 Not likely, so ignore Flash hider assembly - 8 3 2 48
Display Box Clamp
  • Helps hold display box to side rail
  • Helps hold display box to rail clamp base
Shearing Display box will not mount to user's gun 8 Excessive stress 3 Stress analysis 3 72 Not likely, so ignore Display box clamp assembly - 8 3 3 72
Rail Clamp Clip
  • Clamps display box box clamp to rail clamp base
  • Clamps rail clamp base to gun rail
Shearing Display box will not mount to user's gun 8 Excessive stress 3 Stress analysis 3 72 Not likely, so ignore Rail clamp clip assembly - 8 3 3 72
Rail Clamp Base
  • Allows display box to be mounted off of a gun's top rail
Bending Display box will not mount off of a gun's top rail 7 Excessive stress 3 Stress analysis 3 63 Not likely, so ignore Rail clamp base assembly - 7 3 3 63


The only major issue with our counter right now is with the wire holes in the display box. Since airsoft games are sometimes played in rainy or snowy conditions, it is possible that water will enter the display box through the wire holes at the back. If enough water fills the display box, the electronics inside will short circuit. This problem can be fixed by combining the wires that connect the flash hider and display box into a headphone jack. This jack would be made to fit snugly into the wire hole at the back of the display box much like the audio-out port on computers and MP3 players. The tight fitting between the wire hole and headphone jack would make it more difficult for water to enter the display box.

The other failure mode that scored a high RPN is the low battery power issue. There is no engineering design that can change the fact that batteries will run low on power and that they will eventually have to be replaced. The only thing that can be done is to include a note about changing the batteries when the counter is not functioning properly or when the LED display is dim in the user's manual. If the consumer really feels replacing batteries is a big issue, then the circuit could be redesigned to consume less power.

Overall, the FMEA shows that the only problem areas are those areas relating to electronics. Other failure modes such as bending or shearing are not issues because they were unlikely to occur. The reason for this is that our counter is made mainly from aluminum which is more than strong enough to handle whatever loads our counter will experience.

Quality Function Deployment

Below is an product planning matrix that compares our design with the Alien Pulse Rifle Conversion Kit, a competing airsoft product with an LED ammunition counter.

Image:AIRSOFTQFD2.JPG

From the product planning matrix, we can see that the volumetric size of the counter box and the manufacturing cost are shown to be very important to our final product design. A technical evaluation of our product shows that in both these areas the Electronic Ammunition Counter is superior to that of the Alien Pulse Rifle Conversion Kit. The Electronic Ammunition counter has a more simplistic design than the pulse rifle conversion kit, and as a result, the manufacturing cost of the Electronic Ammunition is significantly less than that of the Alien Pulse Rifle Conversion Kit.

From the competitive evaluation column, we see that we can improve the counter design by adding more realism. Although the Alien Pulse Rifle is not based on a realistic gun, it has a higher realism rating than our counter box as the Alien Pulse Rifle aims the mimic the gun from Aliens. Our ammunition counter on the other hand was meant to be placed on a military simulation gun. As a result, the counter should have been hidden in such a fashion that it resembles an accessory used for military simulations. This is one aspect of our ammunition counter that we should look into at a later time.

The product planning matrix also indicates that we can improve our design by reducing the of buttons that the user interacts with and the number of exposed wires. The competitor's product does not have any exposed wires or preset buttons as these features were integrated into the gun. The addition of exposed wires and preset button cause our counter to look less realistic and less ergonomical. Although our counter has poor ratings in these area when compared with the pulse rifle modification kit, it is a necessary evil as our electronic counter is more adaptable as a result of these trade offs. Our goal was to design an aftermarket product that can be used on nearly any airsoft gun, and to do this, a bit of convenience and realism has to be sacrificed. Whereas the Alien Pulse Rifle Conversion Kit targets players who want a gun based on a movie, the Electronic Ammunition Counter was designed for any airsoft player who wants to know the ammunition count in their magazines.

Possible ways to reduce the number of exposed wires though include adding a transmitter and receiver to the flash hider and counter. This is another area in which we can study at a further point in time.

The Prototype

Our prototype was comprised of our electronic circuit, display box, and flash hider
Our prototype was comprised of our electronic circuit, display box, and flash hider


Charles demos the prototype on a replica Steyr AUG
Charles demos the prototype on a replica Steyr AUG


What the user should see when using our product
What the user should see when using our product


The images above shows our prototype. All parts were printed on the Z-Corp 3D printer. The parts were first modeled with SolidWorks, then saved as stl files. Finally we printed loaded the stl files on the Z-Corp printer and printed our prototype. The prototype was made so as to demonstrates the overall size of the flash hider and the counter box. The prototype also serves to show the location of the preset buttons, reset button, cables, printed circuit board mounts, and photogate locations. Having a 3d model printed was useful since we got better user feedback as a result. Potential customers were able to grasp our design concept faster. Instead of having to focus on how our product might look, potential customers could instead focus on areas that they liked or disliked.

Our prototype is not complete. One way in which our prototype differs from the finished product is in the fact that the prototyped flash hider is not threaded. Due to the limitations of Z Corp printer, even if we had printed the threading, after the coating is applied, the threading dimensions would be rendered useless. Fasteners are not shown either. Ideally we would like to have snap fits to attach the front of the display cover to the electronics box. The 3 volt button cells is secured with a snap-on cover. Our finished product would most likely be made from casted or machined aluminum to give it a more solid feel.

User Testing and Feedback

Conclusion and the Next Step

The current prototype is exactly that, a prototype. There really needs to be at least one more redesign before it will be ready to be a marketable product. From the user feedback we got from our prototype, veteran airsoft players thought it was a good idea, but the housing for it was not the ideal solution. One user said it would be incredibly useful since it has not been effectively done before (the M41A modification kit is not an ideal solution). For users who use high capacity magazines ("hi-caps" for short), this would not really be as useful or necessary, as the gun can be shaken and the pellets shake around in the open compartment in those particular magazines. For people who use standard or middle capacity magazines, this would be much more useful since the pellets are held in place by a spring, rather than being loose in a compartment. There is no way to check how much ammunition you have remaining.

In the future, the design could be switched from the existing design primarily composed of ten integrated circuit (IC) chips down to just one programmable chip. The routing of the wires in the circuit is somewhat complex, especially when trying to fit it into as small a space as possible. Cost could increase depending on how many layers each circuit board is, and more layers might be needed to get the necessary wire routing. Another feature that could be added relatively easily when switching to a programmable chip is the ability to stop at 000 or not display digits if they are a leading 0, for example, just displaying "55" instead of "055". This can be done purely with existing ICs, but it adds extra complexity and circuit board space. Currently, the prototype will loop back to 999 after it reaches 000.

There is a possibility of a product family where the counter box is sold with the photogate built into a flash hider or a mock silencer. The flash hider and silencers could also be sold individually with different designs, based on the varying designs of the flash hiders of different models of guns, since different guns have drastically different looking flash hiders. Also, If the electronics are designed properly, there could also be different colored displays. From our searching, the only displays with three digits were red, yellow, or green. These could be made such that the front piece is replaceable with a different colored display, depending on the user's preference. The need for this could be determined based on more user feedback. The variety of colors could be increased also if two- or four-digit displays were able to be used.

Also, if it is researched more, the possibility of putting it in a casing kind of like an EOTech holographic sight, it would be the "coolest" version, especially if the display value could be integrated into the HUD. It would allow for a bit more space which would help the space needed for circuitry as well as a larger capacity battery, like a standard 9V battery, which is cheaper and easier to replace than a particular type of lithium ion button cell battery. It would make it very realistic, since the counter would be "camouflaged" in a realistic real steel add-on (which is what airsoft users want).

The possibility of having the count transmitted by and IR signal, kind of like a TV remote control, or by some sort of radio signal, like an RC car would eliminate the need for a wire connecting the flash hider or mock silencer, but it would only be possible with a mock silencer, since the front part would need to be powered by something.

The final improvement our product could use is to have a magazine automatically tell the counter how much ammunition is in it rather than relying on the user to enter that number. This could be accomplished through custom magazines for the most popular families of airsoft guns such as the M4, P90, G36, etc. This goes back to one of our earlier ideas with the counter being in the magazine. The downside to this would be that it would add an extra component into the gun, and therefore an extra unhidden wire. If internal modification was "allowable" then more could be hidden, but we are aiming to have it not require any disassembly of any gun to work. The alternative is that a transmitter could be used in place of a wire and so it would not have the problem of unsightly wires.

About the Design Team

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