A New Method for Increasing the Efficiency of a PCP - the SSG

[shorty]

I thought this may help with the guess work. Even though I still believe a 30 cent short stiff spring will accomplish the same thing.

Guys we are getting over complicated even though I feel as if this is a think tank. Now, since we all know that negative preload (stiff spring or loaded spring) increases shot count and lowers ES, we (you all) should also consider porting since we "all" know that this helps closing the poppet (reducing dwell).

Most or all of you experimented with porting with "the old" hammer powerplant of using preload.

hopefully this spreadsheet will take the guess work out out of Bobs design when building your own.

[Motorhead]

I thought this may help with the guess work. Even though I still believe a 30 cent short stiff spring will accomplish the same thing.

Guys we are getting over complicated even though I feel as if this is a think tank. Now, since we all know that negative preload (stiff spring or loaded spring) increases shot count and lowers ES, we (you all) should also consider porting since we "all" know that this helps closing the poppet (reducing dwell).

Most or all of you experimented with porting with "the old" hammer powerplant of using preload.

hopefully this spreadsheet will take the guess work out out of Bobs design when building your own.

Personally feel your MISSING a point Bob spelled out early on .... With spring under preload it becomes for sake of hammer bounce a non yielding surface hammer simply can not rebound off of.

A heavier spring in a relaxed state as your talking, has resiliency and yield to compression motion.
It will indeed absorb some hammer motion as poppet throws hammer against it and then rebound the hammer towards poppet again.  LESS for sure than a conventional pre-loaded set up does, but no where as controlled rebound free "DEAD" as idea we're exploring within this thread.

IMO,
Scott

[SpiralGroove]

Great Work Guys, 
Bob would you mind showing some pictures of your QB SSG?
Given the efficiency of your prior set-up (1.07%) vs. the SSG (1.27%) or +18.7%, do you think it is worth the labor involved?  You got almost 80 shots previously, I guess that turns out to be about 94 shots afterwards   --------> OK, I'm sold

It's fun to watch Bob, Motorhead and lloyd's brains in action, the masses (me) find this very Cool... Happy New Year !!   Keep shooten the can down the road............. Kirk     

[shorty]

The spreadsheet is only showing what your doing and helping with the thread. That was the intention.

It was meant to help you .!"x).

Whatever....

[SpiralGroove]

Hey Shorty,
What or Who are you talking about?   Let's keep the Grinch out of this thread!! 
Kirk

[Rallyshark]

Okay guys, try not to laugh at my diagram/idea here, but...     I don't have any cad software, so this was done with paint, and it isn't to scale.  It is with an AT-44 hammer, since that is all I have any hands on with.  This is the gist of what I was talking about when I said some variation of a damped hammer.  I hope this makes sense   

[rsterne]

Yesterday and today I worked on fitting an SSG to my QB Ninja.... The gun is regulated at 1200 psi, and is modified to cock-on-open.... The best previous tune delivered 81 shots at 850 fps from a 13 CI tank filled to 3000 psi and refilled at 1100 psi.... For the preloaded spring for my "Stopped Spring Guide" modification I used two 1.75" x 0.040" wire springs on a single 7/32" guide, with 10-32 nuts both ends (the front one turned to fit inside the hammer).... The adjusting bolt is a 3/8" - 24 NF bolt drilled for the guide, and it is carried in a short piece of aluminum which is bolted inside the QB tube.... Here is the previous cock-on-open RVA, and the new SSG setup, positioned relative to each other the way they sit inside the tube....



In the uncocked position, you will notice that the end of the guide is basically flush with the end of the tube, but of course it sticks out when cocked.... I cured that later, as you will see below.... There are two screws to mount the aluminum block in the tube, a short one on the bottom and a long one on top, that goes through the breech and holds it down.... Since I didn't need the back part of the bolt that normally moves the pin for the cocking block, I cut it off flush with the back of the setscrew that holds the bolt handle, and the hole for the top screw for the SSG is immediately behind the bolt when fully back.... You can see the relative positions of the parts in the photo below....



In order to cover the back of the breech, I made a special bolt from a short metric flat-head screw by turning the head to 1/4" OD and thinning it slightly.... and then milled a recess in the breech cap to allow it to sit below flush, as below....



The bottom SSG mounting screw interfered with the trigger, so I used a low profile SHCS and counterbored a recess in the trigger as shown to miss it....



Since when cocked the guide and nuts stick out the back of the tube, and I needed something to mount the back of the trigger into, I made a cover from aluminum as shown below.... It is tapped for a 10-32 screw to attach the back of the trigger through the original hole in the back of the tube.... It does double duty to prevent the gap adjusting bolt from rotating as well.... The lip that sticks forward inside the tube has a flat milled on the top that just clears the flat on the bolt, so that once inserted the bolt can no longer rotate.... You do the adjustment with a socket wrench and then slide the cap in and bolt the trigger in place and the adjuster can no longer rotate....



When the gun is reassembled, the only change in appearance is the extended aluminum cap on the back of the tube, and the head of the upper screw on top of the breech under the scope.... It doesn't interfere with my scope rings, although something to consider if yours were in a different place....



During final tuning today I found a few more fps, and the gun now averages 851 fps (25.6 FPE) with the SSG one turn out from touching the hammer (0.042").... The ES is narrower than before (it was 12), only 8 fps over the first 86 shots of a 90 shot string down to 1100 psi.... Shot 91 was 838 fps.... This SSG gave me a gain of 9 shots over the previous arrangement (11%), increasing the efficiency to a pretty stunning 1.36 FPE/CI.... Here is the shot string....



I am now a firm believer in the SSG system as having the potential to increase the efficiency of a PCP, even a regulated one that was already pretty good.... If you can hear the telltale BUURRRPPPP of hammer bounce in you gun, and getting rid of it has been a problem for you, considering this modification could be the way to go....

Bob

[SpiralGroove]

Thanks Bob,
That's a Helll of a lot of work for 10 shots and a lower ES, but pretty darn Cool  .
Again, thanks for sharing/helping............. Kirk

Did you use a mill to help make the Extended aluminum cap?

[rsterne]

Yep, used my milling attachment on my lathe to drill the hole and mill off the side of the tab.... BTW, since when didn't it make sense to try and improve something?.... *LOL*.... Besides, nobody pays me for my time, so I can use it as I please.... *grin*.... I'm not twisting anyone's arm to do this, just showing what is possible.... and trying to figure out (and explain) why....

Bob

[rsterne]

Rallyshark.... I understand your drawing, but I remain unsure of the way this would reduce hammer bounce.... You said the oil should be "thick enough to not give on hammer acceleration but thin enough to give on valve strike".... I guess you are trying to accomplish a "dead blow" hammer?.... My thought is that expending energy at the instant the hammer strikes the valve to displace oil would, by definition I would think, require more hammer strike to open the valve to the same degree.... I don't think the hammer bounces OFF the valve stem, which is what your idea would help prevent.... It should insure that the hammer travels WITH the valve stem, but I think if does that already....

Hammer bounce, as I understand it, is the valve stem imparting energy to the hammer on the return trip (valve closing).... and then the hammer in turn causing that energy to be stored in the hammer spring.... Once the hammer stops, that stored energy accelerates the hammer forward again, with one of two results.... the valve either opens (and wastes air), or it doesn't.... Light hammers store less energy, as do stiff springs with a gap between the hammer (at rest against the valve stem).... The concept I am trying to achieve here with the SSG, is that the spring is preloaded to the point that the hammer energy imparted by the closing valve stem cannot deflect the spring, so it can't store energy to be returned to the valve and re-open it....

Bob

[SpiralGroove]

Capisce, we appreciate your efforts!!

[Motorhead]

Bit more fiddling tonight .... having not crunched efficiency numbers yet being we're still changing small details, air use is appearing to be SUBSTANTIALLY less as shot after shot gets taken & gauge does not move lower nearly as quick.

Installed the beefed up spring holder at end of limit screw adding an additional 3/16" of preload taking the 6# oem hammer spring to within 1/8" travel of coil bind.  Velocity with 18.1's now maxed out at 835 fps.

[lloyd-ss]

Rallyshark,
For just using Paint, that is a darn nice concept drawing of your damped hammer.I know that took a lot of time to do.
I am still a little fuzzy on the mechanics of the setup, though.  Please see if I have an understanding: With the initial hard hit of the hammer against the valve stem, the oil is thick enough that it can't flow fast enough and it kind of stays solid and the big hit takes place. But on the rebound, the velocity is lower, and oil flows thru an orifice, attenuating the impact such that the valve is not opened a second time.
Is that close?
Lloyd 

[Rallyshark]

Rallyshark,
For just using Paint, that is a darn nice concept drawing of your damped hammer.I know that took a lot of time to do.
I am still a little fuzzy on the mechanics of the setup, though.  Please see if I have an understanding: With the initial hard hit of the hammer against the valve stem, the oil is thick enough that it can't flow fast enough and it kind of stays solid and the big hit takes place. But on the rebound, the velocity is lower, and oil flows thru an orifice, attenuating the impact such that the valve is not opened a second time.
Is that close?
Lloyd

Lloyd,
Thanks, but it only took me about 15 or 20 minutes to do that in paint.  I did it by eye, and wasn't trying to match everything by the numbers, so it really wasn't that hard.  I tend to do better by eye, instead of exact measurements.  I'm not patient enough to do real cad, and I haven't been able to get Sketchup to work on Windows 8.  You are very close to understanding what i'm talking about, and you have the right idea.  The oil filled shock is a stolen straight from an RC car, so it is quite easily "tuned" to your needs.  The shock won't give much on the hammer acceleration prior to initial strike of the valve.  The sharp impact with the valve stem will cause it to give some, but with the light spring on the shock, it won't extend back out fast enough to cause it to bounce and reopen the valve any.  I guess it would be somewhere between a strong short spring "throwing" the hammer at the valve and a conventional setup.  Bob is sort of right about a dead blow hammer too.  The difference being that the hammer/spring will return to full length, UNLESS resting on the valve stem.  The idea being you won't have to use a really heavy spring, but maybe one only slightly heavier than a standard spring.  The hammer/spring will not extend to full length fast enough for the valve stem returning to impart any energy on the hammer spring, and thus the hammer spring cannot re-open the valve.  Essentially, the shock portion of the hammer is "slow".  Yes it is a spring, but it compresses/extends slower than a normal spring.  The very nature of a damper is to prevent bouncing, which, in this case will prevent it from bouncing after the valve returns.  I'm sorry if I'm not explaining this well.  Things always make more sense in my head than they do when I try to put it into words  

You would want it adjusted so that the shock/shock spring are slightly compressed and resting on the valve stem when not cocked.

[shorty]

Thanks Kirk, I'll keep the grinch locked up.

Since we all agree the the negative preload is the most influencing, both short spring and SSG, In my head, I am still trying to understand if the SSG rebounds the hammer (after it has struck the valve stem) with more or less force than the short stiff spring.

Based on this site of elastic collision (http://www.webassign.net/question_assets/tamucalcphysmechl1/lab_7/manual.html):

There was a nice experiment (better than me running into a wall  ). I took a steel ball and dropped the steel ball onto the back of my work bench vise , then put a 7 lb spring clamped into the vise and dropped the ball on it.

The steel ball bounced off the back of the work bench higher and with great force than when bounced on the spring.

So, it "appears" that steel hitting steel is more elastic and the spring absorbs the energy which in turn reduces the amount of rebound. But we all knew that already.

Well,
I started thinking if the SSG can be improved further. I took a small thin piece of leather (shoe tongue) and placed it on the back of the work bench vise and dropped the ball on that. The bounce back was nearly 0 to nothing.
With that being said, a small piece of dampening material placed in the hammer between the SSG and hammer may reduce that elastic/in-elastic collision to a point of nonexistence.

[Motorhead]

Glad to read many of us are dwelling on this.

I too in the last days was thinking of a K.I.S.S. damper to further stop kinetic energy transfer once shot has happened.

Tho thoughts not shared previous, was thinking a SOFT silicone 0-ring resting on the end of spring hat within hammer bore.
O-ring sits on a shoulder to hold it having say .015 . .020" of it's height above shoulder it sits on.
When action is cocked the pressure of hammer spring on the hammer simply crushes o-ring that .020" or so bottoming out the spring hat to hammer connection. as hammer is released this connection crushing o-ring remains tight.
ONLY when limiter rod bottoms out and hammer free travels forward is the small crush on o-ring relaxed.
* Now as poppet sends hammer back at the spring does this o-ring once again see compression forces ... which it promptly absorbs stopping hammer from compressing the spring again.

Very KISS ( Keep it simple stupid ) solution if rebound energy transfer is wanting / needing to be mitigated

Scott

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

OK, call me neurotic 

Went over to the lathe and made up another spring hat for end of stop rod.
* Note length is only such because i am wanting more spring preload greater than end caps adjustment can give getting OEM length spring near coil bind.


So here the part as talked about above. O-ring is UNDER the diameter of spring/hat so there is no drag by it being there, no seal made creating suction or such issue having drag.
Groove or shoulder O-ring gets Stretched over done at an angle similar to a spring guns piston holding seal.
The back wedge angle keeps the o-ring wedged in preventing the slap of rod stopping & spitting it off the end !!



Also make note of the bevels at the hats O.D.  this to counter drag as piston rocks or stop rod is off center line.
Low drag HERE is paramount if hammer it to continue independant w/o any drag created by the Spring / Hat parts.

O-ring once stretched over the wedge shaped nub on hammer end of the hat.



Next shown the COMPRESSION & DAMPING idea of o-ring compression once hammer is drawn against it while cocking.



Gap shown compresses flat with a few pound pressure, but in theory softly impacted by the rebounding hammer should stop it dead in it's tracks never coming close to getting an elastic collision bounce off end of the stop rod & spring

Theory and Testing .... what R&D is 

Even if the effect is minimal, presents of the o-ring at this location effects NOTHING else in the system 

Scott

[K.O.]

I like the damping just because anything that reduces vibration in the shot cycle is a plus in my book... the speed of sound being high in dense material means it can contribute to barrel harmonics... but it would probably have to be a dense plastic to hold up... leather would wear to quick I think.

started to write about a captive  two piece hammer and sleeve rear cocker but pulled it down...just did not have the concentration for a couple hrs. drawing and trying to explain.  I do think that it could work well but the added complexity gives it more ways to possible cause a bit of E.S. spread..? But I just like rear cockers...

Me I keep thinking of a double reg'd system and a piloted  blow open balanced valve ; small dump valve provides overpressure that bleeds off controlling  timing of the balanced valve... .

The goal being taking as much of the vibration out of the shot cycle as possible and more important the most consistent charge release you can manage.

[bstaley]

Great stuff here!

Was thinking (I know) it might make sense to integrate the whole thing into the hammer itself.  The Spring guide would run all the way through the hammer and preload the spring against the hammer body itself, with the final gap being between the back end of the guide and the rear cap. 

When cocked, the hammer would slide along the guide, compressing the spring, with the extra guide extending in front of the hammer body, so that nothing has to stick out the back of the gun.  When fired, the hammer slides along the guide until it hits the front of the guide, then carries everything with it to impact the valve stem.

No ugly parts sticking out the back of the gun, no energy wasted accelerating mass that won't be used to open the valve....just a thought.

[Motorhead]

Great stuff here!

Was thinking (I know) it might make sense to integrate the whole thing into the hammer itself.  The Spring guide would run all the way through the hammer and preload the spring against the hammer body itself, with the final gap being between the back end of the guide and the rear cap. 

When cocked, the hammer would slide along the guide, compressing the spring, with the extra guide extending in front of the hammer body, so that nothing has to stick out the back of the gun.  When fired, the hammer slides along the guide until it hits the front of the guide, then carries everything with it to impact the valve stem.

No ugly parts sticking out the back of the gun, no energy wasted accelerating mass that won't be used to open the valve....just a thought.

Only PCP that comes to mind using an Off Center poppet is Air Arms ... This would allow a guided stem & stop ideal to get played with on a pre-existing platform.

Sadly centered poppets striking hammer center are troublesome if I understand idea correctly ?

[bstaley]

Great stuff here!

Was thinking (I know) it might make sense to integrate the whole thing into the hammer itself.  The Spring guide would run all the way through the hammer and preload the spring against the hammer body itself, with the final gap being between the back end of the guide and the rear cap. 

When cocked, the hammer would slide along the guide, compressing the spring, with the extra guide extending in front of the hammer body, so that nothing has to stick out the back of the gun.  When fired, the hammer slides along the guide until it hits the front of the guide, then carries everything with it to impact the valve stem.

No ugly parts sticking out the back of the gun, no energy wasted accelerating mass that won't be used to open the valve....just a thought.

Only PCP that comes to mind using an Off Center poppet is Air Arms ... This would allow a guided stem & stop ideal to get played with on a pre-existing platform.

Sadly centered poppets striking hammer center are troublesome if I understand idea correctly ?

Not really a problem, just make the front of the spring guide similar to the mrod striker plate, just not threaded to the hammer body.