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V3 Coil Carbine

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DerAlbi

Wed Sept 16 2015, 06:09PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Cool! Do you have an oscilloscope?
1) I would be interested in the battery voltage waveform during shot (AC coupled is ok)
2) how many working stages?
3) Fresh charged LiPo means 12*4.2V, right? ~50V That should give some pretty high current. Do you know how much (estimated)
4) how do you stop the projectile?

ben5017

Thu Sept 17 2015, 03:42AM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

Here is a bit more data on the test firing.

Note: data point 5 on the charts are ESTIMATED values for a 5th stage.

I am encouraged by the linear nature of the performance data to consider squeezing a 5th stage on the V3.
Although it will be a considerable amount more work on a project that never ends.

ALBI:

-No scope. sorry. any recommendations?
-4 working stages, with no injector. I havnt had time to adjust the pulse length in the software so it blows its fuse with the higher volt batteries.

The coils used are the same ones I made and tuned for a 6s pack (82 ft/s).

Hopefully i can squeeze some more power out of her by winding new ones in the future

Maby a new goal of 25J muzzle energy could be possible...

DerAlbi

Thu Sept 17 2015, 07:35AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Recommendations for an Oscilloscope? Uhhm. Rigol DS1000Z-Series. but it costs 400$. (if that kind of money is too much, please tell me)
Its interesting how your kinetic energy rises linear while in my design the velocity rises linear - i dont know hoewever how long that trend will hold in my design due to current limitations. Your graph should break down too due to the same reason soon. The faster the projectrile get, the higher the acceleration power. So with the increasingly higher current the LiPos should draw a natural boundary somewhere.
5J per stage is impressive. I mean.. maybe not, because you cheat by having a heavy projectile...

still double of my design with way lower voltages and much lower costs.

How long are your Coils and your projectile?

ben5017

Thu Sept 17 2015, 12:28PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

Thanks for the tip on the scope, I will give that one a look. I don't mind paying for a nice one.

Attached is a picture of the slug. they are modified solenoid cores. I ordered 50 of them (from Germany no less)
Only modification made was to cut of the back portion off.

Slugs are 68mm Lg.

Coil geometry:
12 ga. magnet wire, 75mm Lg.

Stage 1: 5 layers
Stage 2: 4 layers
Stage 3: 3 layers
Stage 4: 3 layers

ben5017

Fri Sept 18 2015, 01:58AM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

Some photos of my slug catcher. made from the 1.17mm stainless steel shell of a broken meat grinder.

Inside is lined with 1/2" thick rubber.

I had to start using a 3/4" thick mdf wear-plate on inside once i noticed the stainless was still denting even with the rubber.

ben5017

Fri Sept 18 2015, 02:03AM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

Since im in the posting mood, Here are some more recent photos of the V3

DerAlbi

Fri Sept 18 2015, 04:28AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Quite some build

how heavy?
Your energy density (Joules per acceleration length) is also interesting. You get 19.3J / (4*6.8cm)=0.71J/cm while in my design i achieve 1.43J/cm. So all my optimizations make it only twice as compact.

Not bad considering the coil geometry and beeing battery driven and so on.. nice!

Are those fuses for the coils?

What is for coil behind the magazine or?

ben5017

Fri Sept 18 2015, 02:03PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

I cant remember the exact weight, will weigh it next time i get a chance to take it off its stand. (breadboard is attached to the stand for development so the V3 has not been off it for months) It was pretty heavy before upgrading the batteries (+400ish grams) & possibly adding a 5th stage... However the weight is well balanced & the front grip give additional stability, so its not to awkward to hold at all.

You are correct, the fuses (60 amp) are for the coils. Trying to protect from catastrophic failure.. After many f-ups in the development of the V3, they proved their worth already (have a box full of burnt ones... the 60 amp fuses will get your attention when they go...).

The coil behind the drum mag is the "injector" it is a homemade spring return solenoid that pushes the slug out of the drum.
I am planing on redesigning it to be much more compact, allowing me to move the drum towards the rear and should give me enough room to add a 5th stage.

DerAlbi

Sat Sept 19 2015, 03:24AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Do you have any schematic on how you switch and what did you actually decide for? I hope you use mosfets at this voltage

The fuses surely blow spectacular if they do. They are not made for the high voltage.. if they melt they can sustain a spark that dissipates quite a lot of bang.

ben5017

Thu Sept 24 2015, 01:14PM

Registered Member #3315 Joined: Thu Oct 14 2010, 04:23PM
Location:
Posts: 156

Even after the success of recent upgrades, I am still not satisfied with the power of the V3. I am debating more radical changes to increase performance.

I have two options that would keep overall dimensions of the V3 the same but increase performance.

#1) stay with 12s (50 volts) and add 2 additional stages (cheaper/safer route)
#2) increase to 18s (75 volts) and add 1 additional stage (would need to buy different mosfets & tvs diodes and an additional 6s lipo)

Interested in hearing feedback from my fellow coil gunners on what option i should take. I believe #2 will give me biggest boost in KE, But not sure it will be worth extra expense/weight

Additional changes that will be made

Change 1) gear motor/encoder drum mag is replaced with a direct drive stepper motor. this configuration is more compact and should be easier to program and integrate on the arduino.

Change 2) Injector is removed and replaced by a full stage coil (one of the additional stages mentioned above) directly in front of the drum mag. this coil will be pulse length controlled by the arduino to pull the projectile out of the drum and will act as the first accelerator stage.

-Albi no schematic to post right now sorry. 100v 420 amp mosfets were used. driven by 12V 1.2A gate drivers tc422 series (mouser# off top of my head). Gate driver gets 5 volt signal directly from arduino mega.

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