Modeling PCP Valve Lift and Dwell

[joel w]

What about instead of trying to alter the way the gun shoots with lift and dwell changes. What if we changed the weight of the pellets during the string. Lighter pellets at start and finish with heavier pellets in the middle? Hmm..

[willbird]

Yes, the added weight would change the dwell by the square root of the change in weight.... a 10% change in weight would cause about a 5% change in dwell.... The lift would NOT change....

Bob

So, it would to a degree accomplish what I had in mind ?? Would it increase velocity on either side of the high point somewhat ?? Flatten the curve ?

[willbird]

What about instead of trying to alter the way the gun shoots with lift and dwell changes. What if we changed the weight of the pellets during the string. Lighter pellets at start and finish with heavier pellets in the middle? Hmm..

I was thinking about that one on the way to work today :-). But at longer yardage will the lighter pellets shoot higher or lower ?

Bill

[joel w]

In my mind anyways, I would think there would not need to be that much of a weight change to offset the pressure difference?  How much and how it effects the flight path at longer ranges, I can't answer but it should not be too hard to test.

[Motorhead]

Regulation is SO MUCH EASIER .... K.I.S.S. so comes to mind 

[Bill G]

Absolutely Scot

Bill

[willbird]

Regulation is SO MUCH EASIER .... K.I.S.S. so comes to mind 

For me it is an exercise in thinking :-). I have come up with a lot of elegant solutions to problems which only allowed limited types of solutions. Adding and removing weight to the hammer of an unregulated pcp during the shot string would be an interesting experiment.

Bill

[Bill G]

Regulation is SO MUCH EASIER .... K.I.S.S. so comes to mind 

For me it is an exercise in thinking :-). I have come up with a lot of elegant solutions to problems which only allowed limited types of solutions. Adding and removing weight to the hammer of an unregulated pcp during the shot string would be an interesting experiment.

Bill

Agreed, but very laborious.  Ask Scot how laboriuos it is just experimenting with a reg and various hammer weights.  That 's using the Kiss principel.  I too enjoy the exercise in thinking.  My thinking tends to lean toward what Scot says though.  I believe the thought is best spent understanding what the least amount of air (psi and volume) can be used to provide a desired output.  Also, How to dispence that air through mechanical manipulation.  By this I mean, Least air used with the least mass in motion for the shortest distance.  although, I have found that low mass and long travle renders great performance with lighter springs.  This all is dictated by the ability of the porting to flow the max possible with the least expenditure of mechanical force.  Basicly, squeezing all the variables to the least deviation of a series of shot.  I have found that the reg is probably the best method for achieving this with the least amount of mechanical things to add more variables.  More links in a chain, the weaker the chain.

Bill

[rsterne]

I agree with the premise that using a regulator avoids the problem.... However, it also prevents one from tuning the gun to take advantage of the tiny sips of high pressure air at the beginning of a shot string which provide the best efficiency.... With a regulator, set at let's say 2000 psi, the best you can do for efficiency is what you can acheive at that pressure.... If you are shooting between 3000 psi and 2000 unregulated, and can achieve a shot string within, say, 1%ES at the same velocity.... you have achieved what you can do with a regulator, and I can almost guarantee the overall air use will be less.... That should translate into more shots above 2000 psi, right?....

I still haven't seen a usable and yet simple idea (for I'm convinced in the KISS principle as well) that can accomplish this.... but if we don't think about it, it will never happen....

Bob

[jessered]

How about what Daystate is doing with their Air Wolf MCT and MVT? Electronic solenoid, variable regulator and you take the hammer out of the equation.

Now of course I do not have a Rogue or Daystate gun to check against. From the little I have read here, the Rogue did not get the variable regulator exactly right and the speed varies. From what I can see from the hype it looks like Daystate is reading the pressure both on the upstream and downstream sides of the regulator and making micro adjustments before the valve opens. Has anyone actually seen a chrony string on a map compensated technology gun and does it make it truly consistent?

[jessered]

Ignore the previous post. Just saw a youtube chrony string and there was a 30 fps variation in a 16 shot string. And this would clearly not be a KISS route to go anyways.

[rsterne]

While in theory it should be possible to do this with electronics, in practice it seems to be much more difficult than the theory predicts.... For the most part, it also removes it from the abilities of the home airgun mechanic....

Bob

[willbird]

But within the "basic" footprint of say a Disco, adding a regulator (without adding a bottle, or disco double kit) takes away tank volume ?? Does it break even if you can run 3000 psi on the other side of the regulator ??

With the disco too there might be a mechanical way to change the effective orifice size through the pressure gauge block ?? That orifice seems to help reduce velocity change as the tank pressure drops ??

[Motorhead]

But within the "basic" footprint of say a Disco, adding a regulator (without adding a bottle, or disco double kit) takes away tank volume ?? Does it break even if you can run 3000 psi on the other side of the regulator ??

With the disco too there might be a mechanical way to change the effective orifice size through the pressure gauge block ?? That orifice seems to help reduce velocity change as the tank pressure drops ??

Don't have a DISCO, but can offer some insight to what happens efficiency wise in spite of air tank volume loss by a regulator being installed.

*M-rod in .22 cal when stock was pushing 18.1 pellets @ 850 fps ( @ 29# energy ) on a 3k fill was good for 30 shots with a relatively decent ES, then fell off pretty sharply past that.
 
** Same rifle with a Regulator set at 1850#, 3k fill , modified valve and a lighter hammer get 52 Shots !! at just a tad higher velocity ( @ 875 at 30# ) Gun makes 40 shots under regulation and another 12 off because gun is set up so the 1850# pressure is right before peak of the tunes bell curve.  It self regulates off the curve accurate enough to get those extra 12 shots.

So in spite less tank volume, efficiency takes a MAJOR jump when you can control valve dwell and eliminate near all the bounce with a lighter mass hammer.

Shot string looked like this BTW 



Yup, am sold on K.I.S.S and use of TUNED regulated PCP's 

[willbird]

But within the "basic" footprint of say a Disco, adding a regulator (without adding a bottle, or disco double kit) takes away tank volume ?? Does it break even if you can run 3000 psi on the other side of the regulator ??

With the disco too there might be a mechanical way to change the effective orifice size through the pressure gauge block ?? That orifice seems to help reduce velocity change as the tank pressure drops ??

Don't have a DISCO, but can offer some insight to what happens efficiency wise in spite of air tank volume loss by a regulator being installed.

*M-rod in .22 cal when stock was pushing 18.1 pellets @ 850 fps ( @ 29# energy ) on a 3k fill was good for 30 shots with a relatively decent ES, then fell off pretty sharply past that.
 
** Same rifle with a Regulator set at 1850#, 3k fill , modified valve and a lighter hammer get 52 Shots !! at just a tad higher velocity ( @ 875 at 30# ) Gun makes 40 shots under regulation and another 12 off because gun is set up so the 1850# pressure is right before peak of the tunes bell curve.  It self regulates off the curve accurate enough to get those extra 12 shots.

So in spite less tank volume, efficiency takes a MAJOR jump when you can control valve dwell and eliminate near all the bounce with a lighter mass hammer.

Shot string looked like this BTW 



Yup, am sold on K.I.S.S and use of TUNED regulated PCP's 

What does the regulator look like ??

Bill

[Motorhead]

Like this, these shown being the Dutch Huub regs ... old style on right, newest on left 

[michaelthomas]

I'm gonna give the solenoid hammer a try......but it will be on a regulator.

With the right capacitance, I believe I can get the solenoid to have exhausted all of the capacitors electrical energy before it hits the valve.  I think that would eliminate any bounce.

I believe it will have to be a very high voltage system, though.

I'm not looking to control dwell or lift with anything but voltage and hammer weight......meaning it's not going to be a "on the fly" adjustable thing. 

Rest of my parts won't be here for a bit.....but I'll post about it when I have some data.

The rest of my system is yet untested, so that's a giant variable, too.

I'm looking forward to messing with it.

Mike

[jessered]

Sounds interesting Mike.

The only thing I have come up with that seems feasible would be using a stepper motor to turn a screw and adjust the hammer spring preload. Mount it on the gun and shoot a string across a chrony for a baseline. Then you should be able to play around and program the stepper to adjust the preload in a reverse bell curve?

[willbird]

Well I think being able to model things and their effect opens up all the possibilities.

Mechanically I feel adding and subtracting weight to the hammer is one possible solution. But every factor of the equation is honestly open to manipulation. The hammer at present normally free falls, but the field is open to altering that behavior too.....there have been rate reducers made and used on fa pb guns that used a variety of means to delay or alter the behavior of moving parts :-).

The o ring ideas on the valve stem illustrate how changing behavior at the end of the hammer stroke is also open to discussion....

[joel w]

For something to do today, I drilled out the back of some JSB 25.4g pellets for a testing.  Since I only have a scale that weighs grams, I put 8 unaltered pellets on the scale and they weighed 11.2 grams combined.  After drilling out 8 pellets, they then weighed 10.4 grams combined. Not much lead removed. 

I set my target at 40 yards and shot a sting of unaltered pellets from 2800-2000 psi and the arc was clear.

For the next string I took 9 shots with unaltered pellets and then shot the 8 lighter drilled pellets and then finished the string with the stock pellets. 

Several of the drilled out pellets shot a noticeably flatter arc but I think that the pointed angle of the drill might be effect the flight of the pellet as they were not as accurate/stable. 

I need to try this with a small end mill so the inside bell of the pellet has a flat surface..

edit:  This had the opposite effect that I thought it would have BTW.