Developing the MPM40

[Crow]

So I decided to start work on some old Airsoft projects I had shelved. The easiest for me to get stuck into was this an airsoft mine;

early prototype:

 

my CNC mill isn't huge but with a little patience it gets the job done:

 

 

a few design revisions later and we get this:

 

a few more design revisions later and we get this:

 

i spray painted it black but spray paint scratches off and looks kind of rubbish so i instead i spent about 6 weeks ordering different chemicals and perfecting a PVC dying process: 

 

at first it didn't gose so well: this was supposed to be black:

 

 

But with a little more effort and a few more orders and few more experiments i managed to get it just right so i went with dark green, design was also improved while i waited for chemicals:

 

i ended up switching to full stainless construction for all important components, i used stainless helicoil taps which i later upgraded to brass inserts to give a little bit of extra durability on those well used tapped holes that would secure the mounting spikes:

 

Then disaster struck my; CNC mill died, with no reason or indication, so 3 days of checking wires later i had to make a choice spend the last money i had on a new VFD (motor driver) or buy a new motor. i tested 4 other VFDs i had with no success, so i stripped the motor down could not find anything wrong with it so i took the plunge bought a new VFD wired it up mirrored over the settings and pressed "RUN" and then "pop" trapped smoke was released and things got very warm. went over the settings again turns out the manual left a few things out in its "chinglish" managed to set up the frequency to power curves correctly and it worked like a dream. 

 

we were back in business..... and then i had to go to hospital for an emergency operation because i had sepsis and was about 16 hours away from multiple organ failure.  that was fun way to spend christmas eve.

but i made a full recovery and went back to work. 

 

i dont have a propper mill yet so i have to make use of my lathe:

 

 

A few more design revisions and few more tweaks to the dying process and 2 months later we finally have this the MPM40 (Multi Purpose Mine 40mm):

 

 

 

Finally satisfied with the design i moved on to make a small batch to see how viable they are for resale production: 

 

Dyeing in bulk:

i've not built an injection mould foundry and 3D printers are not super great for their quality/cost ratio, so we stick with good old fashioned conventional removal based machining operations. Load up a billet of PVC into the CNC mill and let her rip, but first programing lots of programing:

 

So that's about 200 operations, 10 hours  for production time (inc set uptime) and 280 meters of tool path for some for just the chassis for 8 units. Definitely going to need to fill up the coolant tank for this.

once they were cut they all need to be deburred by hand and checked over. Then some of the internal threads can be added.

 

 

once the chassis is assembled i can dye them, each needs about 5x 10 minute dips for desired color quality and dye penetration, im using quite an aggressive solvent so they have to be dyed in multiple stages else they will dissolve and swell but once done i can bore the internal piston cavity out to the correct size. 

 

 

Then i needed to machine some stainless components on the lathe, the piston or plunger you could call it, the bolt handle also need to be turned and knurled and finally the disperser plate and cord reel need to done too, once those are done i need to mill the cocking handle slot which i upgraded from a 3mm slot to a 8.5mm slot which let me make the cocking handle much larger which intern makes it much easier to prime. (pictures coming soon)

 

 

 

I was feeling quite pleased with myself; then when i was testing one of the units the firing sear broke, this had not happened before during any of my previous testing, admittedly i was really giving it a hard time and firing the unit dry but nonetheless i was not pleased, now if a job is worth doing it's worth doing right, so i disassembled all of the units and replaced the firing sear with a much more robust one which; fortunately there was enough space in the unit to accommodate it:

 

Below old broken sear next to new more robust sear:

 

i think the first one breaking was largely down to the stronger springs and how i was testing them, even so i'm much more happy move to a stronger design.  this one held up under all tests, even so, if i find that it breaks after long term use ill send out replacements for free. 

 

i need to make some more in depth videos of these but for now here are just a few testing videos:

 

 

ill add more info and update this post when i get some more time.  if you've got any feedback or suggestions i'd love to hear it, i don't expect to make a lot of money on these they are time consuming and expensive to make but i enjoyed making them and it was a good learning experience particularly for the dyeing processes. 

 

if you would like to get your hands on one and support my development of more airsoft related gear you can buy one at: 

 

http://www.lhpd.co.uk/

 

update1: good lord i have bad luck, visited the girlfriend in the states, send YouTuber brainexploder one of my mines via us post, gets lost in post, i suffer gallbladder  attack 6 hours of intense pain later i finally decide to go to ER,  nothing they can do but give me painkillers, little relieve supper resistant to pain killers, pain lasts for a week, gallbladder backs up bile into my liver, eyes turn yellow with jondis, return to England, insurance refuses to cover medial bill, ~$2800. mill breaks down again (stepper motor seized). replacement parts get hold in some weird quarantine thing. 

on with the good news, mill is fixed (bearings replaced as well) and i started working on blank-firing adaptor for the MPM40: (note finish is below that of final product this was a quick and dirty prototype)

 

 

 

 

 

 

will see about getting these made on CNC lathe, not sure what the adaptor price will be hopeful it wont cost too much. (update: was quoted £28 each, might be best off making them my self)

 

okay so now its time to work on some upgrade modules: 

 

First thing to do is make an electronic actuator that can be easily added to the mine to set it off electronically, want this to be small, robust and quick/easy to add to the standard version of the MPM40 this is what i came up with: 

 

the one i made is thicker than the one modelled (i made some  tweaks post prototyping, thinned it down 17.5mm ) 

 

 

i added a breaded nylon sheath to the servo power/control cable, i used a standard 3 pole 3.5mm audio jack as the coupling: makes it easier to do replacement cables or add spliters/extenders.

Next to make was the remote control module, i re-purposed a an Emylo remote transmitter, i disabled the existing relay (its power hungry) and used the circuit as a trigger for my own programmed IC chip. This chip triggers the servo to fire the mine (twice: in-case there was a jam or miss fire (not had one yet but thought it was worth including anyway)) it triggers whenever the trigger pin experiences a state change.

For convenience i decided to use a 9V pp3 battery, they have a small form factor and high voltage compared to other battery's but low capacity 450mA for industrial grades (highest i could find) on the upside they are £1 a pop and so far ive managed to get the current consumption down to ~20mA which gives around 24 hours of standby time (active current is about 200ma but that only lasts a for a second or so). i switched to a LDO (low drop out) voltage regulator from a linear regulator. the LDO should ensure the unit remains functional even when the battery voltage drops below its normal working voltage even as low as 6V. 

 

 

i also ordered in some snazy stainless steel IP68 (waterproof) illuminated (red led) toggle switches, These have a really nice feel to them and give you some feed back that the unit i working as intended. i spent a little time making the modules a tad smaller shaved off a few mm off both the actuator and the RC control unit: 

 

 

For those that might be interested here is the code for the RC module IC chip. 

 

 

With the RC module and electronic actuator completed i moved onto the Proximity sensor version. At first a tried a PIR sensor but it was just too sensitive, it was supposed to be variable between 5-7m i tested several different ones and consistently got ranges of 7 to 14M for a human sized target. so i moved on to Ultrasonic range sensors which i assembled into an 3 directional array. When the unit is turned on it senses the proximity of the environment, when the sensors detect an object falling closer than 15mm off the original environment it triggers the actuator which triggers the mine. the ultrasonic proximity sensor is best used on flat terrain e.g indoors or suspend above any ground based foliage as these can interfere with the sensors readings and cause false positives. 

 

 

 

 

 

To minimise false positives i have programmed the IC chip to only trigger upon 5 sequential readings that are all inside the trigger zone, it only polls the sensor 5 times  IF it gets it detects something so it checks each sector for targets at about.

 

for thous that are interested here i the code for the Ultrasonic module:

 

 

With both of thous modules now complete i took a second pass at the blank firing module, someone ordered a mine but wanted a .209 primer adaptor made for it, i wasn't aware they where so popular so i now include a blank-firing module with all all adaptor orders. slightly revised the blank firing adaptor:

 

Now i understand that it looks somewhat dangerous to have the exhaust values right where your fingers will be when screwing up the unit, however it is designed in such a way that unless the firing pin is in the correct position you cannot screw the the cap on. So either the firing pin is in the bottom of the hole or its blocking the cap completely, this is the same when using the .209 adaptor its either in the correct position or you cant screw the cap on. The blank rounds tend to have a cone pressed finish at the top, this works to self centre when screwing the cap on to, so you can pop the blank into the unit then screw down and it will align itself with its own cavity. .209 primers have to be put in the adaptor first and as they are more fiddly its best to screw these in while holding both the adaptor and the cap sideways realistically this is just as easy and i have not had any issues loading the unit during my now absurd amount of tests. 

So everything was completed and i had some orders to fill, i set to work making them then when i came to test them with the recoil from the blank detonation was transferred back to the PVC firing sear which despite being reinforced from the last time still broke after a few firings. Now i could just make and sell replacement firing sears but when i make something i really really want it to last, now the only reason i hadn't made this firing sear out of steel was because i couldn't machine the shape with my machines.Fortunately a good friend of mine has a plasma cutter so (after revising the firing sear design a little bit) i went off and got some steel versions made, i did try making 8mm stainless steel version but turns out plasma cutters despise stainless steel and make a right mess of cutting it: the geometry as all over the place and by the time its cleaned up its no longer the correct size to work reliably, so i instead opted for 5mm steel versions which are indestructible anyway and while they will rust slightly over time its not something that will affect the working of the unit. i might look into chemical blacking /passivating the steel but i think it would be more trouble that it would provide benifit. anyway here are the new 5mm steel sears after they have been cleaned up and drilled to the correct size: (older green PVC version for comparison)

 

And here is a small video reel the testing videos: 

 

 

Well i think that cover just about everything, if you would like to get your hands on one of these mines and the various add on modules you can find them on my store: https://www.lhpd.co.uk/

[MILITATED]

I absolutely love the look of those! It sounds like you have had a pretty rough time but you also seem very accomplished and driven nonetheless, I believe you would do well.

I personally would love to get one if they were made available. I plan to transition my YouTube channel over to airsoft (I have to be careful as I am currently at 88k) and I think this kind of stuff would be great to see.

 

Definitely one of the coolest, if not the coolest, airsoft mine I have seen. Very happy to see the progress of this!

[Adolf Hamster]

that's definitely a well engineered product right there, maybe next you could turn your talents to making a thunder v style grenade that actually works?

[Crow]

Glad you chaps like them. @Adolf Hamster i took a look at those thunder v style grenades they seem a bit rubbish and  also seem to be a bit of a con £2 per replacement casing on top of which you have to buy a Co2 cartridge. i never muched like the idea of making something that drums up repeat business as a necessity of design.. there are grenades out there that achieve loud bangs on compressed air without needing some disposable plastic casing or an entire Co2 cartridge. all in all at about £2.50 a pop may as well buy a thunderflash or play for the long run and buy a BFG. 

[Adolf Hamster]

the thunder v's are a bit naff, a good idea poorly executed.

 

i don't mind the shells/cartridges so much, just that the constant cycle of leaking/light strikes etc is getting a bit samey.

 

maybe i should just bite the bullet and get a bfg.

[Crow]

bumped for update.

[Crow]

bumped for long over due update. lots of tasty additions.