My Field Target Project

[michaelthomas]

I have always loved the look of the Air Arms EV2 Mk(any), and finally got going on my own project that will try to retain the EV's good looks and implement some other features and ideas that I like.

I have finished the 250cc air tube, the valve block, valve and solenoid hammer.

I am typically bad at posting progress on any projects I do because I put it off until I have way too much done, then it seems like too much work to catch it up.

I'm starting early, and I plan to keep up this time.

I am shooting for a 16fpe .177 gun that will have at least 50 good shots per fill.  If I get 12-20fpe.....that's fine.  The gun is gonna be for target shooting at longer distances than my 753 is effective at. 

Valve is .200", throat is .140", and transfer port is .100.....stem is .078".  Concave seat with delrin valve.

I like the pellet loading into the rear of the barrel like the Mac1 guns......so that is the idea I'm going with.

I also like the idea of possibly being able to tune electronically.....so that's why I went with the solenoid.  It will be a capacitive discharge arrangement like the Daystate. 

I ran across a picture of a USFT/EV2 hybrid that somebody made, and I really liked it. http://airgundevelopment.com/custombuild/karlcaron.html

Here are some pictures of my beginning.

[michaelthomas]

I have only done some preliminary testing of the solenoid operated valve.

I had an extra spring and hammer from my Avanti 753 for comparison. 

I set up a pinball type setup that would shoot a small 55 gram cylinder with the spring and hammer.  I allowed it .5" to accelerate and compressed the spring almost fully.  It would shoot the cylinder 38 inches from a height of 33 inches.

I then set up the solenoid to do the same thing.  at 60v and 300 microfarads......I was able to get the same distance.  Increasing the capacitance lengthened the discharge time, and would shoot the cylinder further, but it was actually powering the solenoid after hitting it's fixed stop in the body.  I have up to 100volts to play with the dc to dc boost converter I currently have.  Its small and light, and will work from 2 9v batteries in series.  If 60v is all I need, I can get away with 1 9v battery and a different boost converter.  I want the solenoid to have exhausted all (or most) of the capacitors energy just before striking the valve.....so just momentum is in play.

Calculating backwards, I was able to determine that the 40gram plunger took about 5 milliseconds to strike the cylinder with the .5" approach.

One interesting thing I noted was that shortening the approach to .25" on the solenoid, made no measurable effect on the distance that the cylinder was shot.   I think this is because the solenoid becomes more powerful the deeper the plunger goes in.  I made a screw cap for the back of the solenoid housing that can be used to adjust the approach distance easily.  It may end up being an important tuning feature along with the capacitance and voltage adjustment.

Until my barrels and pump get here, I suppose that's all I can do.

I bought the Lothar Walther .177 standard rifling barrels.....I making two of these at the same time.

Mike

[Motorhead]

Very cool project !! .... love fabrication but lack advanced electronic skills 
projects like this can only sit back and watch in amazement 

[Bent]

Awesome project..

Please share some more detail of the electronics... I would really like to build my own solenoid gun in the future, but I'm more a mechanical guy than electrician..

[michaelthomas]

Thanks, Scott......you might want to hold off on any amazement until I actually get it firing some pellets.

Bent.......A simple capacitive discharge circuit is just a capacitor and a resistor in series to do the charging.  The value of the resistor sets the charging rate. 

After the cap is charged, you just have to put the load (solenoid in this case) across the cap.  The charge and discharge rates can be calculated easily......but it's easier, yet, to just use a calculator.   http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html

A micro switch that has a normally open and a normally closed set of contacts can do both operation for you.  Charge with the normally closed, and then discharge with the normally open (button press).  When you release the button the charging cycle will begin again. I'm using a SCR in conjunction with a micro switch to keep the higher current out of the micro switch for longevity.

Fool around with the discharge calculator for a bit and you will begin to see the discharge characteristics of different capacitance and voltage values.  Higher capacitance values will put more power through the circuit......but at a longer time frame.  There probably isn't much use is discharging beyond 10ms for 1 time constant, or maybe less......because the plunger has already come into contact with the valve, and can no longer supply any more forward momentum.  To get more power in a shorter amount of time (MORE KICK), the voltage will need to be increased......or the resistance of the solenoid must be reduced (meaning get a different solenoid).

I'm using photo flash capacitors that are rated at 360v......meaning they can be charged to 360v.  Photo caps are capable of very high current flow without heating up as much.  Probably doesn't really matter for this, but I had them on hand.

Don't bother with any solenoids that have high resistance......they probably won't get you where you want to go without a lot of voltage.

Don't worry too much about the rated voltage of a solenoid (mine is 12v), because for the few milliseconds that you will be pumping some amps through it.....it's not really indicative of what it can tolerate.  I can trigger mine 50 times in a row with 80 plus volts and detect zero heat from the solenoid.  I can't really tell how much a particular solenoid can tolerate.......but it's a lot more than one would think because of the tiny duty cycle.

I have scoured the net for info about the specifics needed to do what i want, but was unable to find anything definitive.  So it's trial and error, really. 

I'll just keep upping the voltage until I get what I need for starters.

Mike

[QVTom]

Beautiful work!  I'm very familiar with how much work is involved when you custom build every part of gun, then add some electronics to boot, A trying task to say the least.

I'm curious why CD and not direct drive?  A simple regulated  boost topology could give you the power you need with out the discharce curves, temp and tolerance issues associated with HV caps. You could also control the current in the winding via PWM.  Just thoughts .

Tom

[Motorhead]

Beautiful work!  I'm very familiar with how much work is involved when you custom build every part of gun, then add some electronics to boot, A trying task to say the least.

I'm curious why CD and not direct drive?  A simple regulated  boost topology could give you the power you need with out the discharce curves, temp and tolerance issues associated with HV caps. You could also control the current in the winding via PWM.  Just thoughts .

Tom

Stop speaking GREEK !!!

Lol ... had too

[QVTom]

Sorry   Just had to.  LOL

[michaelthomas]

Tom,

The main reason for CD is the ability to extract the energy needed in a few milliseconds.  The boost convertor itself would not be capable of producing the instantaneous current needed.

The simplicity of the CD arrangement is nice, too.

The discharge voltage of a cap is easily controlled by the amount of time a given voltage is applied over a given resistance......making it very easy to charge a cap to any voltage up to the max output of the boost converter just by changing the charge time.  That would be a simple task for a any micro controller.......and if I get into altering the shot string without a pressure regulator, that will be the first method I will try.

I don't expect any heat or tolerance issues with capacitive discharge.

The discharge curve is very repeatable, too.

Mike

[QVTom]

I agree with the simplicity of the CD.  A driven or hard switched circuit would still require a bulk cap to store energy, the difference is you modulate thew buss voltage in a more controlled manner allowing for programmable discharge curve.  I use this type of circuit to control the strike voltage on UVc lighting ballasts. 

I do understand keeping it simple.  Embedded systems is my bread and butter so I'm always look for way to have more control.

Tom

[michaelthomas]

Let me be the first to say that my knowledge of electronics is far from comprehensive.  I build and service cnc equipment for my living.  Most of the electronics for me is implementation......not design.

My initial plan is to put the gun on a regulator and just find a solitary discharge voltage to fire the solenoid and open the valve for the appropriate time......and when I'm off the reg, it will be time to pressure up.  I really don't have any grand plans to monitor or compensate on the fly.  I don't think valve bounce will be any issue with the solenoid, and I'm hoping that will help to find some extra efficiency.

I also like the flexibility that the solenoid can provide.  It could be adapted to a ton of different platforms with relative ease. 

That's my plan, anyway.

If it morphs into some thing more complex than this, I may have to pick your brain.

Mike

[QVTom]

A plan is a good thing   If you have any questions that I can help with just shoot me a pm.

Just curious if you don't mind.....  Are you planning on charging the cap on trigger pull or maintaining the voltage when the system is activated?  What voltage do you plan to boost to?

Sorry, can't help my self.

Tom

[michaelthomas]

I'm planning to maintain voltage while activated.  The on/off switch being the "safety".

Voltage will be the least I can get away with.

Mike

[sixshootertexan]

This a very interesting project. When you turn to switch off will the voltage be dumped ?

[jessered]

Great project you have going on here Mike! I love working with control circuits.

Starting with regulated air will make it much easier and eliminate a whole bunch of variables. If you have some success with this then I am sure others will be able to jump in and expand the knowledge base for everyone. It would also make a great foundation for the dwell experiments.

Really jonesing for the machine shop equipment I used to have access to though.

[michaelthomas]

This a very interesting project. When you turn to switch off will the voltage be dumped ?

No, I wasn't planning to dump the cap.  The SCR will be dead and not allow an accidental trigger when the "safety" is on.  I'm guessing that was why you asked......maybe not.

Jesse,

If you are CNC control repair capable.....and can be patient, you can find some great deals on broken CNC equipment.  The manual stuff always holds it's price, but a CNC with a dead control will often go for scrap value.

Here is a pic of my last summers' project.  It's a Mazak QT20n that I got for $800.00.  It was control dead and looked like a steaming $)((# when I got it......but was mechanically sound.  I originally intended to do a control retrofit, but ended up repairing the original.  It will hold a few tenths all day after its warmed up.  It's a really nice machine.  I probably have $3000.00 into it as it sits now......not including tooling.

Mike

[michaelthomas]

I've been trying all week to get a response back from Lothar Walther so I can get my barrels on the way.  I have finally found out that I now have to send them a check, as they don't take credit cards.

That seems odd for this day and age.....It's like I'm back in the 70's and ordering from the Sears catalog.  Maybe they will come by way of the Wells Fargo wagon?

Mike

[QVTom]

Yes, good luck getting what you actually ordered.  WW at LW is hit or miss with accuracy and replies.  I ordered 1 poly and one conventional, sent check with a hard copy PO and received 2 conventional   Send an email to WW at LW and never received a response.  Not a big deal, I used both anyway.   

Tom 

[michaelthomas]

I'm beginning to draw the stock while I'm waiting for the rest of my stuff to show up   I'm no wood carver, so I'm going to use a 3 axis router with a  ballnose bit.  I want to get  the basic 2d outline right.....then I'll have to work it all out in 3d to do the toolpathing.  I don't really enjoy drawing freeform stuff in 3d.

I was going to lay up a laminated stock blank......but I recently learned how inexpensive the pre-made ones are from Boyd's. ($40.00)  That's definitely not worth me messing with it.  I chose the pepper laminate.

Mike

[michaelthomas]

Got my Hill pump earlier today.

I charged the (naked) gun up to 1500psi, and tested the solenoid hammer out.  I have no barrel on the gun, so it was just an open transfer port.

I was able to get anything from a small pop to a seriously loud bang depending on the voltage the cap was charged to......which ranged from 20 to 60v.

That seems initially promising. 

Mike