I like the pep mould idea a lot! what would you suggest for the filler though? and i might fill the whole pep with a filler to help it stay together as well. i was planning on using pvc pipes for the barrel, so that could be drilled through and put into the mould as well...
Simulating Recoil
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I like the pep mould idea a lot! what would you suggest for the filler though? and i might fill the whole pep with a filler to help it stay together as well. i was planning on using pvc pipes for the barrel, so that could be drilled through and put into the mould as well...
RobTC
Member
Other than a curable casting rubber, I'm not really sure. Perhaps rubber mulch- shredded tyres- if it's available at this time of year, somehow packed in and filled with a flexible resin? Or rubber granules, if they're available, somehow. Maybe there are different grades of mulch. It seems like whatever you pick, it's going to end up at about $20-25, so it may be better just to fill it with an actual casting rubber (like SC65D or maybe something cheaper by someone other than Smooth-On). Or just Google cheap casting rubbers, there must be one for low-grade industrial purposes out there that can be picked up cheap, right? (Usually the sort of question I head to Google for to have my hopes thoroughly dashed 
)
)I've been thinking about this a lot. I've been wanting to do something to emulate the action of a HALO weapon as well.
The biggest thing you need to keep in mind is that with Newtonian physics, (as your build is fully self contained) all forces will be equal. If you want for a Sniper Rifle to "Feel" like your shoulder just got hit with the recoil from a high caliber shot, then your idea of spring forcing a weight into a rubber block against your shoulder could work. Remember that Force = Mass * Acceleration, but what you're really after is Momentum, which is Mass * Velocity. A 10lb Sniper Rifle (~10fps for average caliber) would have roughly 100Ft*Lb/sec momentum. So any internal weight would need to be accelerated to a velocity of 200fps for a 1/2lb weight.
This would give you a reasonable approximation of recoil, but it would be a double whammy. The "spring" would first pull the prop away from the shoulder, then slam it back when it hits it's stop.
I'll second this idea. I think that you would have a much easier time in the long run, if you don't try for actual recoil forces, and instead focus on the look of recoil. I'm looking at using solenoids to "piston pump" the action of a BR or such. It can be timed for a quick back to battery return, and with a small weight (a couple ounces) attached, it would give the effect without the bruising after effect of 40+lbs slamming your shoulder repeatedly.
If you want to continue with your idea, more power to you, and please use the above equations at your leisure. YMMV
The biggest thing you need to keep in mind is that with Newtonian physics, (as your build is fully self contained) all forces will be equal. If you want for a Sniper Rifle to "Feel" like your shoulder just got hit with the recoil from a high caliber shot, then your idea of spring forcing a weight into a rubber block against your shoulder could work. Remember that Force = Mass * Acceleration, but what you're really after is Momentum, which is Mass * Velocity. A 10lb Sniper Rifle (~10fps for average caliber) would have roughly 100Ft*Lb/sec momentum. So any internal weight would need to be accelerated to a velocity of 200fps for a 1/2lb weight.
This would give you a reasonable approximation of recoil, but it would be a double whammy. The "spring" would first pull the prop away from the shoulder, then slam it back when it hits it's stop.
I'll second this idea. I think that you would have a much easier time in the long run, if you don't try for actual recoil forces, and instead focus on the look of recoil. I'm looking at using solenoids to "piston pump" the action of a BR or such. It can be timed for a quick back to battery return, and with a small weight (a couple ounces) attached, it would give the effect without the bruising after effect of 40+lbs slamming your shoulder repeatedly.
If you want to continue with your idea, more power to you, and please use the above equations at your leisure. YMMV
Master Builder
Active Member
I think the best way to do it is with Co2. All you will need is a manual valve (trigger) and have a cylinder with a heavy piece of steel or something, and when you open the valve, the gas will slam the steel into the back of the cylinder. and you could have a very light weight spring to push it back.
Next idea is to have a very powerful electromagnet that when charged will slam a center rod or better yet permanent magnet into the back of whatever. These, to me, seem the simplest and least complicated ways of doing it. But I don't know if they would be powerful enough.
Next idea is to have a very powerful electromagnet that when charged will slam a center rod or better yet permanent magnet into the back of whatever. These, to me, seem the simplest and least complicated ways of doing it. But I don't know if they would be powerful enough.
Dracosfire83
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RobertShively
New Member
I didn't have time to read more than the first few posts, so I'm not entirely sure if this hasn't been mentioned already, but since you're looking for a realistic recoil, or blowback effect, maybe you could try something like what is used in electric blowback airsoft rifles. http://www.evike.com/advanced_searc...n=1&sort=3a&keywords=electric blowback&page=2
RobTC
Member
CO2 is definitely the best way of doing it, coil gun could work too, but the idea seems to be a simple mechanical solution that can be achieved with minimal tooling and expense (400V capacitors aren't that cheap).
This is thoroughly relevant. Because in a real gun the accelerated mass is actually leaving the system, it no longer needs to be accounted for in the momentum equations. But with this setup, your gun needs to be heavy enough not to be moved by the spring expanding while accelerating the mass, but light enough to be moved by the inelastic (theoretically) collision of the mass with the end of the cylinder.
This means a long, slow acceleration (relatively, anyway) followed by as hard a stop as possible with no rebound. The longer version:
F=ma (force and acceleration)
p=mv (momentum)
Through the maximum conservation of momentum by locking that mass to the end stop as hard as possible on impact to avoid elastic collision (momentum is still conserved then, of course, but in a useless fashion), and the minimisation of force at the beginning by reducing the acceleration as much as possible- since you need the same final velocity, that means a longer runup with softer springs- you can probably just about make it work, though it's unlikely to be the 50 or so ft.lb experienced from a real recoil operated damped .50 cal SR.
For realistic speed, you'll probably need capacitors rather than a battery powering that charging lever motion. It'll be more of a coil gun than a solenoid!
This is thoroughly relevant. Because in a real gun the accelerated mass is actually leaving the system, it no longer needs to be accounted for in the momentum equations. But with this setup, your gun needs to be heavy enough not to be moved by the spring expanding while accelerating the mass, but light enough to be moved by the inelastic (theoretically) collision of the mass with the end of the cylinder.
This means a long, slow acceleration (relatively, anyway) followed by as hard a stop as possible with no rebound. The longer version:
F=ma (force and acceleration)
p=mv (momentum)
Through the maximum conservation of momentum by locking that mass to the end stop as hard as possible on impact to avoid elastic collision (momentum is still conserved then, of course, but in a useless fashion), and the minimisation of force at the beginning by reducing the acceleration as much as possible- since you need the same final velocity, that means a longer runup with softer springs- you can probably just about make it work, though it's unlikely to be the 50 or so ft.lb experienced from a real recoil operated damped .50 cal SR.
For realistic speed, you'll probably need capacitors rather than a battery powering that charging lever motion. It'll be more of a coil gun than a solenoid!
Other than a curable casting rubber, I'm not really sure. Perhaps rubber mulch- shredded tyres- if it's available at this time of year, somehow packed in and filled with a flexible resin? Or rubber granules, if they're available, somehow. Maybe there are different grades of mulch. It seems like whatever you pick, it's going to end up at about $20-25, so it may be better just to fill it with an actual casting rubber (like SC65D or maybe something cheaper by someone other than Smooth-On). Or just Google cheap casting rubbers, there must be one for low-grade industrial purposes out there that can be picked up cheap, right? (Usually the sort of question I head to Google for to have my hopes thoroughly dashed
i was thinking perhaps fill the mould with some kind of fibers that could hold it, or maybe a structural cage like rebar in cement... ideas :3
i'm looking into these ideas to see what i find, but my only concern is its admittance to conventions... otherwise that would be much easier to construct, i agree
again, this might work very well, but i want it convention approved.
i like this idea too, it seems very similar to the linear actuator. again, idk how strict conventions get with that kind of thing... and i realized today i'd have to be able to disassemble it to show the closed pipes weren't explosives or anything... more problems :/
FoxtrotZero
Jr Member
Do you have any idea exactly what weapon you'd like to incorporate this in? Knowing exactly what one is working towards would help decide things like what kind of force do we have to emulate, and with what rate of fire? Because a Sniper Rifle or a Shotgun are going to have much more kick than the DMR or BR, and will have a longer period of time to afford for resetting their position. It would also let us know what sort of internal space and structure we have to work with. People (not necessarily me) could then start answering your questions with more precision. Keep in mind that because this isn't actually milled out of aluminium and isn't actually detonating explosives inside of it, this isn't going to have the same kick as the actual weapon. This is a good thing, because firing an 8ga shotgun or a 14.5mm high-velocity rifle even once would probably hurt your shoulder.
However, I'm foreseeing your weapon build into two parts, a front and a rear. The rear comprises the butt, stock, and depending on the weapon, may have to extend into the action/reciever. This should, at least in part, be made of some sort of casted rubber or similar material; This will be dense enough to take a beating and not self destruct. You can cast this inside of a pepakura model, but you're likely going to want some sort of soft material (exposed rubber or something else) on the butt. Depending on how the final design works, this may have one or two tubes buried into it. The only difficulty I can foresee is that the UNSC tends to use bullpup firearms (MA5/6 series, BR series, DMR series), and if you want a removable magazine (you do) that's going to take space, hence why knowing exactly what weapon you want is going to be critical for laying out a functional design.
The front half will be the majority of your weapon, with necessary hollow spaces. It will have any electronics you need to use, and probably the majority of the recoil-simulation system. It will have to have a hollow interface with the rear section, and the two should go together and come apart easily - either by friction or, if necessary, thumbscrews. This allows you to easily service or demonstrate the internal mechanism. Because of the way newton's third law works, you may also want to fill this, at least partially, with some sort of absorbtive rubberized compound (also keeping in mind you'll want to preserve some sort of balance of weight).
I think we can safely discard the concept of a gas-operated system, as you have your doubts about whether or not that that would be convention-approved (and if anything goes wrong, compressed gas isn't the safest thing, though the likelihood of injury is actually pretty low). This leaves us with some sort of spring/mechanical system (which would be cheap, but potentially a bit on the complicated side, and I don't see how it can be incorporated into a semi-auto system. It might work very well for a sniper rifle or shotgun) or some sort of electromagnetic/linear actuator system (which might be a bit pricier, but it would tie nicely into any existing electronics systems like ammunition counters, and would work very well for semi- or fully-automatic systems).
Hopeing some of the other people in this thread will pick at my notions of construction and operation.
However, I'm foreseeing your weapon build into two parts, a front and a rear. The rear comprises the butt, stock, and depending on the weapon, may have to extend into the action/reciever. This should, at least in part, be made of some sort of casted rubber or similar material; This will be dense enough to take a beating and not self destruct. You can cast this inside of a pepakura model, but you're likely going to want some sort of soft material (exposed rubber or something else) on the butt. Depending on how the final design works, this may have one or two tubes buried into it. The only difficulty I can foresee is that the UNSC tends to use bullpup firearms (MA5/6 series, BR series, DMR series), and if you want a removable magazine (you do) that's going to take space, hence why knowing exactly what weapon you want is going to be critical for laying out a functional design.
The front half will be the majority of your weapon, with necessary hollow spaces. It will have any electronics you need to use, and probably the majority of the recoil-simulation system. It will have to have a hollow interface with the rear section, and the two should go together and come apart easily - either by friction or, if necessary, thumbscrews. This allows you to easily service or demonstrate the internal mechanism. Because of the way newton's third law works, you may also want to fill this, at least partially, with some sort of absorbtive rubberized compound (also keeping in mind you'll want to preserve some sort of balance of weight).
I think we can safely discard the concept of a gas-operated system, as you have your doubts about whether or not that that would be convention-approved (and if anything goes wrong, compressed gas isn't the safest thing, though the likelihood of injury is actually pretty low). This leaves us with some sort of spring/mechanical system (which would be cheap, but potentially a bit on the complicated side, and I don't see how it can be incorporated into a semi-auto system. It might work very well for a sniper rifle or shotgun) or some sort of electromagnetic/linear actuator system (which might be a bit pricier, but it would tie nicely into any existing electronics systems like ammunition counters, and would work very well for semi- or fully-automatic systems).
Hopeing some of the other people in this thread will pick at my notions of construction and operation.
RobTC
Member
Disregarding the recoil forces for a second, I just measured; the BR85 charging lever has a maximum throw of around 75mm. The SRS99-S5 has a throw of around 130mm- I suppose they're directly related to the ammo used, but they're the externally visible actions. I also just checked SparkFun and the mini 5v solenoid has a throw of about 5mm. If that's a pattern, it could be a problem for solenoid actuation.
On the other hand, solenoids appear to be capable of throwing pretty heavy weights around in very short spaces, but being electromagnets they're obviously going to require a lot of juice. Maybe with some carefully controlled trigger electronics through a MOSFET you could reduce the amount of battery drain. That also doesn't eliminate the problem of "double recoil", where the recoil system is generating its own recoil upon acceleration. Perhaps a tuned LC circuit in conjunction with the MOSFET could provide a calibrated acceleration profile. That would probably need an oscilloscope and patience.
Overall, I still think the original idea is the best; KISS. You're limited to shotty and sniper, but since they're the hardest to "feel" the simulated recoil for, they're the most in need of it anyway.
For automatic weapons, a weighted rotary system is probably better, though it's not going to simulate muzzle climb because the momenta cancel out.
On the other hand, solenoids appear to be capable of throwing pretty heavy weights around in very short spaces, but being electromagnets they're obviously going to require a lot of juice. Maybe with some carefully controlled trigger electronics through a MOSFET you could reduce the amount of battery drain. That also doesn't eliminate the problem of "double recoil", where the recoil system is generating its own recoil upon acceleration. Perhaps a tuned LC circuit in conjunction with the MOSFET could provide a calibrated acceleration profile. That would probably need an oscilloscope and patience.
Overall, I still think the original idea is the best; KISS. You're limited to shotty and sniper, but since they're the hardest to "feel" the simulated recoil for, they're the most in need of it anyway.
For automatic weapons, a weighted rotary system is probably better, though it's not going to simulate muzzle climb because the momenta cancel out.
as of right now my plans for a sniper, to pep the butt and stock up through part of the main body, leaving the bolt side of the body separate so i can turn that into a removable panel, which when taken off reveals the box mounted inside containing whatever mechanism i end up using, and a battery with wires running through to LEDs that shine behind panels of colored semitransparent plastic for decals and whatnot... i'll probably make a wire cage to go into the butt before i fill it with rubber. i'm also considering doing a thick coat of bondo over the resin before the resin, and i'll do a mould for the gun butt and do rubber over the end.
![IMG_20141117_185249[1].jpg](https://405th-f28a.kxcdn.com/forums/data/attachments/4/4588-50bf6e238fadae3fb7cb58a9ad7588c6.jpg "IMG_20141117_185249[1].jpg")
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