GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: Bent on September 20, 2013, 03:36:00 PM
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Couldn't help...... needed to share... 8)
Woow, haven't worked much in Solidworks before... It's amazing what you can make... to make it look goooood.. ;)
The gun will be made as a semi auto.
Right now I'm working on how to lock the probe when firing. One solution is to have an arm locking it, but I'm worried about problems and wear..
The power to make the probe go back comes from a piston inside the shroud.
The simple solution is having the probe so heavy and the returnspring so strong that the probe stays in place during the shot. Heavy spring won't do it alone, then the shroudpiston can't give enough force to cycle the probe.
Anyone know how to calculate that?
Data:
2200 psi (max-regulateded)
.25 kaliber
Maximum energy 890fps / 48 grains >> 84FPE
Barrellength 600mm
Don't think I'll get that high, but just to play it safe
Very nice design work! The force is significant at 83 lbs. It's simply the bolt face area * the peak operating pressure, SW will give the area easily or use pi*r^2. Keep us posted.
Rotating bolts are easier designed than executed, they are great if you can create the geometry and finishes needed to operate smoothly. Other options are over center and falling block mechanisms. Also consider a pneumatic pin type lock that can be operated by the same source as your bolt, orifice and piston size can be used as timing control.
Tom
Thank you Tom, I've only been working about 10 hours with Solidworks, but it has some really nice tutorials... So everything is coming along nice...
I know how to calculate the force pressure/area. What I'm looking for is how much inertia (isn't it called that in english?) is needed in the probe and spring to withstand the pressure until the pellet has left the barrel.
Solidworks can make all those calculations.... but for now I don't have a clue on how to put them in there.. :-[
Ex.
Pellets exits barrel in 20 milliseconds >> I need the probe to have a maximum movement of 2mm in those 20milliseconds to keep the O-ring sealed.
And your thoughts of rotating bolt and similar solutions are the same as mine.. They would need refinement to work properly...
Sidenote: The stock is only close to finish at the rear, grip and everything in front of that are just roughly drawn as for now.
I'm considering making the stock in 2 shelled out aluminum halfs welded or bolted. And then having parts of it covered with skatertape... where I place hands and cheek... so I don't end up like "Dumb and dumber". I have access to getting it anodized as well 8)
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The solution I will try to put in the construction is a small plunger lock, then it's locked the same way as most PCP airguns. Because there's no force needed to load the hammerspring, it can be made much smaller... Just taking into account the movement necasary to feed in a pellet.
http://youtu.be/aW9rGaZnyg4 (http://youtu.be/aW9rGaZnyg4)
But it also have to be in a way so it's machineable... :P
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Bent, I kind of thought you didn't need the force calc for the HPA on the bolt face but threw it out there just in case. Are you looking for the inertia for a blow back design? IMO there just isn't enough pressure and volume to spare for that purpose. Dependent on valve timing, barrel length, pellet weight, etc expect anywhere from 400 to 1000 psi when the pellet reaches the end of the barrel. If you had a delayed bolt opening I't may be possible to blow back the bolt but I'd opt for a more positive approach.
Tom
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I have been wracking my brain for a rotating locking mechanism the right size you can "steal" ready made :-).
Bill
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Bent, I kind of thought you didn't need the force calc for the HPA on the bolt face but threw it out there just in case. Are you looking for the inertia for a blow back design? IMO there just isn't enough pressure and volume to spare for that purpose. Dependent on valve timing, barrel length, pellet weight, etc expect anywhere from 400 to 1000 psi when the pellet reaches the end of the barrel. If you had a delayed bolt opening I't may be possible to blow back the bolt but I'd opt for a more positive approach.
Tom
Yes, a blow back design..! But only partially..! Not like on a PB. I just need the inertia to keep the probe sealed until pellet has exited.
The force to move the probe comes from a piston inside the shroud. Similar to how the FX guns work, but I just need force/pressure enough to cycle the probe, there's no hammerspring in my gun.
But I think I'll go down the lockingmechanism road.. ;)
Anyone know how the FX Revolution semiauto locks the probe?
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Wondering if you can use a "knee" mechanism like the Luger uses ??
(http://images.drillspot.com/pimages/7585/758583_300.jpg)
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Been thinking about different solution for locking the probe. Making a locking knee like on most PCP's gave me some worries on how to have room enough.
Knee, links and measures needs to be adjusted a bit... But I think it could work...
http://www.youtube.com/watch?v=E-1Vhqa8_y0# (http://www.youtube.com/watch?v=E-1Vhqa8_y0#)
The two connectingrods go all the way through the reciever to a piston in the shroud... Giving the blowback for pelletcycling... 8)
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Refine it a bit, I think this is close to how I'm gonna do it.
http://www.youtube.com/watch?v=jAwAqK_rzYM# (http://www.youtube.com/watch?v=jAwAqK_rzYM#)
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I have been wracking my brain for a rotating locking mechanism the right size you can "steal" ready made :-).
Bill
You and a guy on a danish forum got me thinking....
Why not do the lock using spheres like a Fosterfitting..... Here shown as a quick sketch with:
- Probebody
- Tophat
- Probe
Instead of using rods to deliver the force to the probe, I'm making channels for the airpressure from the shroud, leading it in front of the Tophat. The small "penspring" keeps the probe locked until pressure hits the front of the tophat. It relaeses the spheres, and the probe can move backwards.
http://youtu.be/RV_7Sca1d6Y (http://youtu.be/RV_7Sca1d6Y)
The first picture shows the round groove for locking the spheres, and just left of it you can see one of the two holes leading in pressure from the shroud.
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That is interesting :-).
I wonder how much pressure is present in the shroud ?
Bill
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Don't you love mechanical design? Every detail is a compromise of some sort. With the ball style lock you trade diameter length. Good work! Keep it coming.
Tom
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Don't you love mechanical design? Every detail is a compromise of some sort. With the ball style lock you trade diameter length. Good work! Keep it coming.
Tom
Thx Tom, Always loved it.. ;) And most of all I like when people comes up with "crazy" ideas, even if they are totally worthless as ideas, they still make you think "out of the box"..
So all, please keep the "crazy" ideas coming... ;D
I wonder how much pressure is present in the shroud ?
Bill
My questimate is about 2 bar (??psi) on the Tophat... could be up to 4 bar in the shroud, but thats one of the things I'll test on my Cometa before making chips.. not the amount, but whether I can make the probe cycle. I'm in the progress of making af testsetup connecting a 3mm pipe to the shroud of the Cometa.
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After measuring my .25 and .22.
Reading rsterne's informative threads on airgundesigns.
Some advice from a fellow danish airgunner (He has build 8 guns from scratch.. 8) from .22 to .458 )
Testing the probecycle on the Cometa.. it works but needs a returnspring instead of the "closed room air"
And the parts for the solenoid circuit finally arrived... Dont have time for testing this weekend :( going for FT pistol competition. PB though .22, 9mm and .357 revolver both saturday and sunday... ;)
I've almost settled for the construction... Comments appriciated..!
Concerns: How fast can the plenum refill? Probecycle to work flawless. Drawing errors fx. making something that works but unable to asemble..
- Bulpup (decided before the first line was made)
- Regulated
- Optimized for Cal.25 using 25-32 grain pellets.
- Priority is precision and shotcount.
- Power from 55-75 Joule.
- Semiauto... cycletime maximum 0,5 second but going for 0,1... charging of the capacitors.
- Magazine will be FX magazines. But theres is space for a 30 round magazine without compromising line of sight..
Cylindervolume: 400cc (max 200 bar with a safetyfactor of 4)
Plenumvolume: 60cc @130bar (max 200 bar with a safetyfactor of 8 )
Valvesize: 6.8mm (exchangeable maximum is 12mm)
Throatsize: 5.5mm (exchangeable maximum is 10mm)
Port in valvepart: 5mm
Port in reciever: 9mm (shrunk to 5mm for Cal. .25)
Max OD of barrel:20mm
Max lenght of a singleloaded pellet/solid is 18mm.
The gun is intended for rooks, crows, magpies and of course some FUN shooting and plinking.. ;)
By exchanging parts in the reciever it should be able to shoot up to 9mm pellets. And if the regulator is removed it should be able to shoot bigbore solids... but that is going to be at a later...