Compact electronic hammer.
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Compact electronic hammer.
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Topic: Compact electronic hammer. (Read 11389 times))
Scotchmo
GTA Senior Contributor
Posts: 2344
Real Name: Scott Hull
Re: Compact electronic hammer.
«
Reply #20 on:
October 21, 2015, 02:38:33 AM »
Mike,
You also have to factor in the load resistance.
I'm now using a 7500uf capacitor at 25.5v. That's the voltage I'm stuck with for this design. At 25.5v, I would only need 2800uf to equal the energy of your 60v, 500uf setup. I suspect that your valve opens easier than mine.
With the .6 ohm coil, the time constant is .0045 seconds.
http://www.daycounter.com/Calculators/Capacitor-Energy-Time-Constant-Calculator.phtml
A lower resistance coil will discharge the capacitor faster. I'm thinking that the inductance factors in as well.
What stroke length were you running on your solenoid? I need to shoot the pistol for awhile with the 3/8" stroke to see if I like it that way.
If so, I might do a new solenoid with a low resistance but similar amp-turns to the existing solenoid. That might allow for a shorter time constant if I'm still wasting too much air.
I've shelved the idea of a near zero stroke valve. As Bob implied, the settings get very touchy. A slight change in stroke and it goes from 12fpe to 3fpe. The valve either opens aggressively, or, with a few thousandths less stroke, it barely opens at all. The longer stroke that relies on momentum seems more forgiving.
Mike: Another question. Did you use a reverse bias diode across the solenoid?
«
Last Edit: October 21, 2015, 02:56:39 AM by Scotchmo
»
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Los Osos, California
Morro Bay Airgunners
Scotchmo
GTA Senior Contributor
Posts: 2344
Real Name: Scott Hull
Re: Compact electronic hammer.
«
Reply #21 on:
November 08, 2015, 12:06:23 AM »
I rewound the solenoid with 2 fewer layers than shown in the pictures. It now has about 220 turns of 20awg and is .4 or .5 ohms resistance. I'm using a 7500uf capacitor at 25.5v.
I was worried that the fast acting plunger was compressing the small volume of air in front of it. So I added three flutes to the plunger in order to vent it. It also made the plunger lighter (reduced to .88 ounce or 25 gram). The downside is that there is less iron for the solenoid to act on. I was trading some "magnetic efficiency" for some mechanical efficiency.
The power now maxes out at about 12.5fpe at about .18" stroke. Reducing or increasing the stroke reduces the power.
I'm getting 11.5fpe with a .12" plunger stroke and the 25gram plunger. The maximum that the valve can open is currently .032" when the plunger bottoms out. I'm not sure if the valve is bottoming out or not. I can also get 11.5fpe with about a .25" stroke.
I'm going to run with it for awhile. I need to decide if it's better with the fast accelerating plunger at .12" (shortest lock time but more abrupt) or a slower accelerating plunger at .25" (longer lock time but smoother feeling).
«
Last Edit: July 29, 2018, 01:13:35 PM by Scotchmo
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Los Osos, California
Morro Bay Airgunners
Motorhead
Field Target Shooter .... Stand em up Shoot em down
GTA Senior Contributor
Posts: 17762
2019 GTA Hall Of Fame Recipient
Real Name: Scott
Re: Compact electronic hammer.
«
Reply #22 on:
November 08, 2015, 12:10:30 AM »
A small daub of strategic placed Prussian blue will tell ya if parts are bottoming out
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Scotchmo
GTA Senior Contributor
Posts: 2344
Real Name: Scott Hull
Re: Compact electronic hammer.
«
Reply #23 on:
November 08, 2015, 12:33:16 AM »
Quote from: Motorhead on November 08, 2015, 12:10:30 AM
A small daub of strategic placed Prussian blue will tell ya if parts are bottoming out
In this case, it's the head of the plunger that is limiting the travel, so the blue dye trick probably would not work. There is a steel bottom on the solenoid with an 1/8" hole (valve stem clearance). I did not want the plunger to contact the bottom of the solenoid as there is some residual magnetism in the plunger.
I suspect that it is not bottoming at 11.5fpe. Maybe at 12.5fpe. So it does not really matter. Just curious about it.
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Los Osos, California
Morro Bay Airgunners
Motorhead
Field Target Shooter .... Stand em up Shoot em down
GTA Senior Contributor
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Real Name: Scott
Re: Compact electronic hammer.
«
Reply #24 on:
November 08, 2015, 01:01:13 AM »
Could also place a small wrap / coil of Plastigage in there and see if it gets smashed ... and how thin
Anywho ... great project and engineering going on. Thanks for sharing
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Northern California ... Old Hangtown
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rsterne
Member 2000+fps Club
Bob and Lloyd
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Posts: 26958
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Real Name: Bob
Re: Compact electronic hammer.
«
Reply #25 on:
November 08, 2015, 01:06:03 AM »
Yes, very cool....
Bob
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michaelthomas
Expert
Posts: 1150
yes
Real Name: Mike
Re: Compact electronic hammer.
«
Reply #26 on:
November 08, 2015, 12:58:43 PM »
Scott.....the travel on mine was about .375".....and I did use a diode across the coil.
Mike
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Montrose, CO
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Scotchmo
GTA Senior Contributor
Posts: 2344
Real Name: Scott Hull
Re: Compact electronic hammer.
«
Reply #27 on:
November 11, 2015, 05:38:57 PM »
I did a little more testing before finalizing for a while.
Settings are:
25.5v
7500uf
approx 4.5 ohm solenoid
25gram plunger (hammer)
.125" stroke
The setup is very sensitive to any changes in plunger stroke.
I remade the spacers to hold the solenoid firmly in place and hold a constant plunger stroke.
With unsorted 10.3 grain pellets, I got 730fps, ES=9fps, SD=3fps.
With 16 sorted pellets, I got 731.5fps average, ES=8.5fps, SD=2.44fps.
That's the tightest spread I've ever gotten on any of my guns.
I choked down the transfer port adjuster a little to get the average down to 725fps. That's right at 12fpe.
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Los Osos, California
Morro Bay Airgunners
Scotchmo
GTA Senior Contributor
Posts: 2344
Real Name: Scott Hull
Re: Compact electronic hammer.
«
Reply #28 on:
November 18, 2015, 08:42:00 PM »
Todays results.
I did some more target practice and shot strings over the chronograph. There are some problems. Shot to shot consistency is good. But over a period of time, velocity varies considerably. I played with it some. It might be residual magnetism in the system. I made the plunger and bobbin ends out of ordinary mild steel. Soft iron might be better.
I decided to switch back to the original hammer for now. And then make a new light weight plastic hammer later. I shot it with a Delrin hammer some months ago. That worked better than the stock hammer. I'll probably use MDS nylon next time (per Motorhead suggestion) as it has better properties for this application.
The shot cycle of the electric hammer was very good, and the microswitch trigger was the best trigger I've ever felt, but it never really was any more accurate than with the plastic hammer. At some point, it's good enough and making it better does not tighten up the groups any noticeable amount.
I may work on the electronic hammer design again at some point in the future, but I already devoted more time than I planned. So back to a more conventional setup. I have some other airgun projects that I want to work on.
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Los Osos, California
Morro Bay Airgunners
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Compact electronic hammer.