Hacking the CP-2

[WhatUPSbox?]

George,
I'm looking forward to the 2019 explorations. You have some unique test capabilities in the airgun world.
Thanks for all your hard work

[George Schmermund]

Here are a couple of New Year's Eve photos as a last hurrah for 2018! The first image shows the gap that is between the face of the hammer and the tip of the valve stem. I'm not sure why the gap is there, but I've seen similar gaps in previous re-assemblies after a hammer treatment for whatever reason.

The second image is a DSO record of a CPHP .22 shot cycle. The yellow trace is the accelerometer that is attached to the hammer. The scope is triggered on this channel at the 50% point on the signal as indicated by the arrow at the top. I've offset the vertical so that the full signal trace can be seen.

The blue channel is the pressure sensor's signal. It's channel is triggered by the yellow channel. Any timing info will have to be divined from any numbers you can find on the screen.

The point of this exercise, besides the last minute effort to squeeze it in this year, is that the hammer-to-valve stem gap can be clearly seen in the yellow trace as valve rebounds.  It drives the hammer backwards and produces a sharp negative going signal that exists for a finite amount of time. The hammer then recovers quickly to continue its previous course.

The yellow channel gets a lot of action of all sorts during the shot cycle so I've used the DSO's digital low pass filter set at 5 kHz to make things easier to see.

This post is for Stan's amusement, but others are welcome to have a go at it.

HAPPY NEW YEAR!

[WhatUPSbox?]

the hammer-to-valve stem gap can be clearly seen in the yellow trace as valve rebounds. 

George, Thanks for posting the data, a great start to the year.
I'm not quite in seeing the gap segment on the trace . If it is free flight, it should be averaging zero acceleration for a while. Maybe between 1.5 and 2 msec?

I checked my CP-1 and it has a very slight preload on the hammer spring when uncocked.

Any idea why this hammer accel trace is so different from the 10/7/18 data (post 363)?

[George Schmermund]

I'm sure it has do with how the hammer spring is installed. There's a plug that's normally installed into one end of the spring (when I remember to look for during re-assembly) that probably has most to do with the different hammer/valve activity. This would also account for the gap I notice from time to time after a mod. It's always nice to mix up the variables to keep things interesting. The hammer mass has also been reduced after milling the new shelf for the accelerometer.

I can also do some blame-shifting on having given up beer and gin drinking. I'm now a bourbon devotee´. Good ole Jerry Brown has legalized micro-distilleries in California. Micro-breweries are now becoming passe´. I have a couple of friends who have gotten their distilling licenses and have their stills up and running. I find the distilling process much more intriguing than brewing beer.

Feeling somehow obligated to support their courageous endeavors, I've offered to experiment with an accelerated aging process. Under law bourbon requires aging in a new charred oak barrel for longer than they want to wait. There are lots of other rules and regulations that apply to making and labeling different whiskies, but I'll leave that to them. I'm just working on making a 'tunable' proxy barrel for them. Lots of sampling needs to be done so I had my liver tested recently. The results came back and they indicate that I'm fit for active duty!

This is a great way to bring in the New Year, helping friends and all, but the airgun Sirens are still calling. More than the usual allowances will probably have to be made when trying to decipher some of my postings this year. 

[George Schmermund]

It's been awhile since I've spent much time on the airgun ballistics project, but it hasn't been completely ignored. Having been seduced by the whiskey aging project along with the modal hammer/accelerometer experiments and testing sessions it's finally time to return to the ballistics bench.

The new focus has been on developing an instrument for measuring the real energy of a pellet at the target. Most of what I've seen are numbers generated at or near the muzzle of the gun using MV metrics to calculate the fpe of a projectile. The target energy seems to be based on spreadsheet calculations or ignored completely.

I've decided to raise the bar on how to arrive at the actual target energy numbers by using a force transducer that is a modified version of the modal hammer transducer. The starting mass of this device is 3 lbs, 4.5 oz. The dimensions are 2.5" dia. and 2.75" long. This should be a good match for what I'll be shooting at it.

 I'll begin with a cable connection to the scope for preliminary measurements and then, hopefully, move on to a Bluetooth or Wi-Fi arrangement along with an app to do the calculations and display the data on a smartphone.

The photos show the parts and an assembled prototype instrument that should be ready for testing within the next week.

[AmBraCol]

Welcome back, George!  Was wondering just the other day about you.  Good to see you're still cogitating on various and sundry projects.   

[WhatUPSbox?]

Yep, welcome back George....Now to go dust off my thinking cap and get ready for your posts.

[darkcharisma]

George, i was hoping you would know how to make a transducer to measure the pressure in the transfer port?

[George Schmermund]

A DIY pressure transducer isn't difficult to build. A miniature high pressure one with any accuracy, linearity, high speed response, reliability, easy to mount, etc., would be nearly impossible to make at the hobbyist level in my estimation. Your best bet would be to put Endevco and Kistler into your eBay search list and wait for a sleeper that fits your needs. Keep in mind that you'll also need the right cable along with a display of some sort that will allow you to connect a scope to the output.

I've had good luck with these transducer manufactures on eBay and there are others that make similar products. An important requirement with any of these devices when used for measuring transfer port characteristics is that they must be very fast and introduce as close to zero dead volume as possible.

[darkcharisma]

thanks for the reply. i am a complete novice and needs an "idiot's guide to build a pressure transducer" book.

looking at the suggested brands i would need a 3 to 5 ksi range. i have no idea how fast i would need. even miniature models looks pretty big to be fitted on a small power wheel. since you said it needs to be close. i can always relocate to the front of the barrel and measure the muzzle end pressure instead. but it looks like i may need a complete kit then just a transducer. and i have no idea what else i may be. wires, read out monitor and power source?

can you help me with a mini version of how to build one?

[George Schmermund]

Stay with what reliable manufactures can already supply. Go back over what I've already done.  What you'll need is detailed over the last couple of years in the CP2 and Vigilante threads. You'll just have to choose a transducer in the pressure range you want to work with.

It will take time and some money to get to where you want to go. Any DIY shortcuts will probably be dangerous!

[WhatUPSbox?]

Check out George's description on page 8 of this thread for the sensor he is using. Unfortunately they are industrial quality sensors with a price tag and also the need for supporting electronics which also have a price tag. You'll see in the thread that I tried a low cost sensor. It was low cost and easy to hook up to a readout but unfortunately not fast enough. You'll see in George's scope traces for pressure that you are looking for fractions of a milisec.

You could possibly build a DIY sensor that captures the timing of a pressure pulse. But getting a pressure amplitude would be more difficult.

[George Schmermund]

At 3-5,000 psi I'm not going to advise anything in the DIY sensor realm. At either end of the barrel.

If it's a manufactured device with that pressure range capability, then that's different.

[George Schmermund]

The preliminary testing of the new prototype 'Kill Zone' fpe transducer came out really well. The next step was to do some more machining to allow the sensor to be preloaded from the back of the of the device. This allows for easy calibration to standardize the product. There's still quit a bit of testing to do, but it's off to a good start.

The device is machined from mostly steel bar stock with the odd piece of stainless steel for the compression preload adjustment. The steel parts needed to be protected from rusting so I opted for trying my hand at making a magnetite conversion coating. Converting the iron back to a glass hard mineral at it's surface was just the challenge I was looking for.

Most everything I read about the process warned against attempting it on the DIY level at home because of the high probability of explosive boiling at some point in the procedure. Having molten lye in combination with the main constituent of gun power suddenly getting out of control while you're working with it was another one of those Sirens I find irresistible.

Ignoring my own advice about dangerous DIY projects (only a post or two ago) I proceeded forward. By good fortune I had everything needed for this doomsday project close at hand. My wife suggested that I seal my fate somewhere else than at the kitchen stove so I set up shop in the back yard. This would allow me room to run at least some distance from a disaster even though blinded and maimed. There are times when I think that her prescience transcends intuition.

Anyhow, All's well that ends well. At least that's what they told me at the ER.... just kidding. I cautiously engaged the process one beer at a time and everything worked out fine.

The photos are of the new assembly with the magnetite finish.

[WhatUPSbox?]

George, That is a work of art....now I need to search info on magnetite conversion.

Just curious, how are you going to calculate the energy at the target?

[avator]

https://www.epi.com/black-oxide/steel/

[George Schmermund]

The process of calibration for the Kill Zone Quantifier device is pretty straight forward. I'm partial to using at least two different methods to arrive at traceable calibration numbers. Therefor I'll be using the usual muzzle Velocity X Mass method using my Combro chronograph and comparing it with the Mass X Acceleration method.

I demonstrated a simple calibration of the Combro in a post somewhere in the CP-2 / Vigilante threads and found it to reliable. The F=MA measurement is more involved, but it's what I use to calibrate the modal hammers with.

The photos show the F=MA apparatus with its calibrated mass and a calibrated Bruel & Kjaer 4384 accelerometer along with one of the prototype hammers.  This hammer has the extended mass on the back. The output signals from the hammer and accelerometer are routed to a pair of B&K or Kistler charge amplifiers. The outputs of the charge amps then goes to an HP 35665A DSA and a digital scope for evaluation.

I can swap out the original mass (as shown) with the KZQ mass along with it's internal force transducer. I'll then attach a calibrated accelerometer onto the back of the KZQ. The simultaneous impact signals can then be evaluated.

 

[George Schmermund]

The KZQ project made some progress today. I moved the CP2 carbine from the bench setup out to the back patio range so that I could put more distance between the muzzle and the transducer. It was getting dark so I only had time for a quick test at 30 ft. I'll have more time to spend with the measurements tomorrow.

The image shows a basic test with a .22 CPHP. The timing window is set at 150 µS with the signal connected strait into the scope without any conditioning amplifier. The scope's digital filter is set to low pass at 14 kHz. This is all preliminary at this point so there are no comparison values yet. The next test run will be with the Combro installed.

 

[WhatUPSbox?]

Looking forward to the secret decoder ring. The 14 Khz lowpass filter, 14 Khz is around 70 µs per cycle, is that fast enough?

[George Schmermund]

Stan - The filter is to block the ~ 25 kHz transducer resonance and the ~ 200 kHz internal pedestal compression wave resonance. The signal of interest is the initial impulse which is the negative waveform in the time window. The shape of the waveform is determined by the material attached to the front platen of the KZQ. This material controls the rate of change in velocity of the pellet as the pellet's velocity goes to zero.

The active material is ballistic putty (alias duct seal). This material is attached to a disc of the same ballistic tile material that I use in my traps for bench top airgun testing. These two components are then attached to the front of the KZQ like an Oreo with one of the cookies removed, the remaining cookie being attached to the KZQ platen.

The duct seal acts as a very high viscosity isotropic Newtonian fluid when struck by the pellet as far as I've been able to measure so far. This keep the shape of the impulse waveform fairly uniform in the time window at the different impact energies being used in these early tests. The time window and thickness of the putty can be modified as needed. The tile acts as a backstop for any over penetration and protects the KZQ.

The photo shows the effects of impact on the CPHP pellets. The left one hasn't been shot. The middle one is with the duct seal. The third one is straight onto the platen. The shots were taken at a distance of 1 ft. from the muzzle. As can be seen the putty captures the pellet with little energy lost to deformation. The flattened one still retained enough energy to rebound ~ 8" to 10" and was still quite warm when it was recovered. Remarkably, to me, the flattened pellet's impact didn't phase the magnetite coating!