Not another university questionnaire!

[Hangtight]

You don't have to set the bar very high for efficiency. At the moment only about 20% of the energy put in emerges as kinetic energy in the form of 200mph little plastic balls. And of the energy that actually gets put into the spring, about 85% gets transferred to the BB. (Which is actually pretty damn good)

 

[Adolf Hamster]

You don't have to set the bar very high for efficiency. At the moment only about 20% of the energy put in emerges as kinetic energy in the form of 200mph little plastic balls. And of the energy that actually gets put into the spring, about 85% gets transferred to the BB. (Which is actually pretty damn good)

well for the coil idea i'd be happy if it was roughly equivalent to an AEG in terms of being able to do a day's airsofting on a single battery (well, depending on how trigger happy you are  )

do you have any references for those numbers your quoting? would be great to have a read if someone's already done some research on this topic.

 

[Hangtight]

It's simple maths. 1J/s= 1W. So 350 fps  (1.14J) × 20rps = 22.8W output.

The gun that fires those BBs draws 16A @ 7.4v = 118.4W input

In sure you can work out the percentage.

As for the spring efficiency, if you know the spring rate and the amount it's  compressed then you know the stored energy. You know the output energy contained in the BB (ignoring it's rotational energy anyway), and that's it.

 

[Adolf Hamster]

It's simple maths. 1J/s= 1W. So 350 fps  (1.14J) × 20rps = 22.8W output.

The gun that fires those BBs draws 16A @ 7.4v = 118.4W input

In sure you can work out the percentage.

As for the spring efficiency, if you know the spring rate and the amount it's  compressed then you know the stored energy. You know the output energy contained in the BB (ignoring it's rotational energy anyway), and that's it.

i see where your coming from, i did do some work before on this and got ~209n for a 1j spring theoretically, but plan is to get some proper testing done to confirm that for sure (because there's friction etc to add in as well), of course you don't need to get all of that from the coil, just to get enough kinetic energy over the length of the stroke and any left over will give you a simulated recoil.

where are you getting your 16amps from? presumably that figure's going to vary for different gearing/motor combinations.

 

[Hangtight]

The 16A is measured off one of my guns using a cheap RC power analyser. But it will vary. In this case it's a 16TPA neodynium magnet motor, 13.66:1 gears and M100 spring. Low resistance wiring, connectors and a mosfet keep parasitic losses low.

 

[Adolf Hamster]

The 16A is measured off one of my guns using a cheap RC power analyser. But it will vary. In this case it's a 16TPA neodynium magnet motor, 13.66:1 gears and M100 spring. Low resistance wiring, connectors and a mosfet keep parasitic losses low.

fair enough, it's a tricky thing to properly quantify for all cases.

tbh the only aspect of efficiency i'm concerned about is not needing to trail a power station along to power your gun

 

[Adolf Hamster]

just a wee cheeky bump in case anyone missed this thread last week.

had a great response so far, thanks to all who took part to date!

 

[ak2m4]

Filled in - I expect to see a working prototype next week

 

[Adolf Hamster]

Thanks again to all those who've filled in so far.

bit of an update for the curious, been processing some instron testing results today and found the following using a known 1j spring in an old king arms v2 box:

• the preload on the spring is ~20n
  
• the load at maximum compression is ~66n
  
• there's 2.5j of energy needed to fully compress the spring
  

so we're looking at roughly 40% efficiency in terms of spring energy being translated to bb velocity, of course this is dependant on a number of factors but i'd suggest the 3 most likely causes are lost air, compression heating of the air and leftover kinetic energy in the piston.

certainly interesting that the level of force required is much lower than i'd originally thought, of course this bodes well for getting an electromagnet to do the work.

 

[Rogerborg]

Interesting numbers.  That's more efficient than I'd have expected too.  Granted, it's only the spring energy, not losses in the motor and gears, but that's where you can make a difference.  I'm really intrigued by whether you can make this work.

 

[Adolf Hamster]

Interesting numbers.  That's more efficient than I'd have expected too.  Granted, it's only the spring energy, not losses in the motor and gears, but that's where you can make a difference.  I'm really intrigued by whether you can make this work.

indeed, the losses in the motor/gears don't worry me so much, given that with this new design they won't be a factor.

i'm still not 100% confident it'll work, not until i test the electromagnet, but certainly i intend to prove conclusively either way wether or not this idea is viable.

 

[SCAR_Jester]

Very interesting concept, you simply must let us know how it goes on, perhaps a new thread detailing the results of your project (I assume dissertation project?).

Either way good luck and I hope it goes well!!

 

[Adolf Hamster]

Very interesting concept, you simply must let us know how it goes on, perhaps a new thread detailing the results of your project (I assume dissertation project?).

Either way good luck and I hope it goes well!!

indeed, i plan to keep you guys posted, it's nice to get an external perspective.

i've got the results of the survey together, results are interesting, i've attatched the charts but the tl:dr version is thus:

about a 43:57 split indoor/outdoor airsofting

overall the AEG is the vastly popular platform, with GBB's being the second most popular, not many ebb/springer users

the features selection is interesting, aside from bb consistency being popular, there's a pretty even spread of what people want. although adjustable rate of fire didn't seem popular.

if you split it up by outdoor/indoor it's interesting. seems aeg's are less dominant (although still the majority) with more people wanting gbb's. the features spread is pretty interesting as well, both are pretty even, but there's a significant difference between indoor/outdoor as to how desirable simulated recoil is.

in other news, I have some steel and some magnets in, looking to start machining up a test set-up over the weekend. still need to order the electrical side of things, thinking initially just a large capacitor and switch, then if it works using an external power supply we can start looking at a proper control system.

View attachment 31876

 

[Adolf Hamster]

well, figure it's time for a little update on this

been having a fair bit of trouble getting the proof of concept setup done, a lot of hand winding coils and cursing the university for freaking out if you mention a circuit that's using more than 30v.

whilst i've been trying to avoid sinking money and effort into designing a firing circuit until i've at least demonstrated it's a viable idea it seems like i'm going to have to go down both routes simaltaneously, sadly it's not going to be cheap but i suppose thats just how its gonna have to be.

 

[Rogerborg]

Hang in there!  Rome wasn't burned down in a day.

 

[Adolf Hamster]

Hang in there!  Rome wasn't burned down in a day.

indeed, it must have taken at least 3 days delivery back then. with modern logistics though i reckon i'll have it burned down by monday

 

[Adolf Hamster]

well little update

still not had much luck getting this thing going, without full on designing the electrical circuit for this thing i just cant cheat my way to getting enough power into the coil to get any kind of meaningful results. although on the bright side i've yet to prove it impossible.

been doing a bit of work recently on CAD (so i have something shiny to put on a poster), given what little output from the magnetic testing i reckon it'll need to be a case of having the coil in the buffer tube of the m4 (or the gas piston/stock area of other designs)

please ignore the brain frazzled attempts at a trigger mechanism in the last one, turns out it's harder than you'd think (respect eugene, respect)

shamefully pilfered grabcad model:

first concept setup for the coil blow back:

today's slightly more developed concept:

 

[Rogerborg]

Fascinating stuff.  How is the tappet plate being actuated?  Or is that still at the "to be decided" stage?

 

[Adolf Hamster]

Fascinating stuff.  How is the tappet plate being actuated?  Or is that still at the "to be decided" stage?

in the original concept it was going to be magnetically actuated from the cylinder, that way it'd always be closed until after a shot had been fired.

in the current version the tail at the end of the tappet plate will be actuated by the last bit of travel of the piston. i'm also considering using this as part of the semi-auto disconnect system (hence the angled surface randomly placed in the middle) but i haven't got that figured out yet.

the charging handle in this version is functional, indeed if i had time i'd be looking at adding the likes of bolt hold-open to the design, i always figured the marui system was a bit clunky, i'd just have a button pushed by the follower and accept that the "last round" would actually have a couple of bb's in the hop tube that would drop free when you pull the mag (the way most aeg's are anyway), at least you wont have anything sticking out that could break.

sadly this design is going to be purely academic, for the foreseeable future i can't see the experimental side of this project bearing fruit, although i do plan on continuing it in my spare time (when i'll have enough time to learn the electrical engineering required to build a big enough charging circuit)

kind of ironic, i have ideas and plans for every aspect of this design but i still can't conclusively prove the fundamental operation would work.

 

[Adolf Hamster]

well, another day another fried circuit.

this time i fell victim to flyback, weird how there was plenty enough magnetism to cause a surge and blow out a 440v 20a rated switch but not enough to make anything even move.

fortunately there was a dark wizard electrical engineer nearby who's given me some good advice on how to make the test setup a little less explodey.

one more week, one more test, after that i'm going to have to call time for the university side of this project and get the write up done.

atm it's looking very much like i've not really made any progress, i haven't proved that this is possible but i also haven't conclusively proved that it's impossible.

fortunately i'll be staying on to do a phd, so might be able to sneak use of a few resources to try and continue this project over the next few years and see if i can get any closer to success (or at least definitive failure)