coilguns...accuracy? / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

coilguns...accuracy?

1 2 3 next

Move Thread

LAN_403

Quantum Singularity

Tue Feb 14 2006, 03:47AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Hello, I am new to this forum. A few might remember me from the Tesla List during the late 90's (aka The Mad Coiler). All my HV stuff has sat idle the last 5 years, but I am hoping to soon get back into things.

My first project, slotted for this summer if I can get my 'lab' cleaned up, will be a coil gun. I have been studying the web with vigor on this topic, and I am sure to have lots of questions here. But first I thought I would ask this. After days of reading websites, one thing I have not ever seen results of is a coilguns accuracy. Do we have any coil gunners here? Or has anyone heard of any reports on accuracy?

I have seen barrels that were loose fitting with the projectile, and guns with no barrels at all?!? And have read that the magnetic field will 'center' the projectile in the barrel anyhow, so I wasnt sure if more tight fitting or loose fitting would be better and what effect on accuracy they would have.

In any case I am curious to see if there are many gunners on this forum yet!

Self Defenestrate

Tue Feb 14 2006, 05:45AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I'll take a step forward. Coilguns have plenty of accuracy if built carefully. The coil will pick up the projectile and center it within itself during the acceleration. Barrels are nice to keep the projectile from tumbling at low powers, or to align multiple stages properly, but also introduce friction on the projectile. As for aiming, I would often shine a laser pointer down through the coil to align it with a target. My coil at 200j was acurate to about a half inch around the dot at 26 feet. Not too scientific, but close enough.

...

Tue Feb 14 2006, 06:37AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I an not sure how accurate coilguns are, but I would not expect it to be very high because the bullet has no stabilisation...
Most (it not all) guns today have a rifled barrel with spins the bullet with in turn makes it go strait; coilguns do not.

That said, with my 10j coilgun (using a 1/2" by 1/4" ferrite slug as the projectile) with a 4" barrel from a ball point pen would shot strait across the room, but I never did any tests on accuracy...

Wilson

Tue Feb 14 2006, 06:57AM

Registered Member #78 Joined: Thu Feb 09 2006, 11:27AM
Location: Sydney, Australia
Posts: 133

Using a long barrel would improve the accuracy i guess. At around 10m, the projectile from my ball point coil never hits point first.
Keep in mind that although the deviation of the projectile left or right will not be high, the vertical displacement will be much greater, especially over long distances.

TheMerovingian

Tue Feb 14 2006, 10:54AM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Since the final kinetic energy of the projectile is scarce (1-10J) we cannot waste it in friction with the barrel, even if it would improve accuracy but will lower efficiency.
Also the gravity works against us making the projectile fly in a parabolic trajectory (this happens alfo to gunpowder firearms).

Also the projectile thumbling can be cool and dectructive on the target (coke cans cut in half and so no)

Quantum Singularity

Tue Feb 14 2006, 04:26PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Hey thanks for the feedback here... I am already learning new stuff. Didnt consider the bullet may tumble, but a lot of force + poor aerodynamics = tumble. However the accuracy Self_Def mentioned sounds good to me. Half inch around the dot - guess that dpends on how big the dot is?

Vertical deflection is expected, thats a function of speed vs gravity and can be roughly calculated/measured. Its the consistency I am looking for... One of my goals is to build something that is 'usefull'. With a CG I think of usefull as maybe being able to shoot the squirrels of my birdfeeder in the back yard.

Since riffling a barrel of a CG is probably not something that is practable or even possible, I guess the only way to improve accuracy would be by having as perfect of coils as possible and focusing on the projectile. I think with a lot of machining a good projectile could be made, perhaps with fins (helical?) formed at the rear, but their stabalizing effect might be minimal at relatively low velocities.

tecNik

Tue Feb 14 2006, 07:33PM

Registered Member #77 Joined: Thu Feb 09 2006, 10:24AM
Location: Leicestershire, England
Posts: 26

Maybe you could spin the projectile before it is accelerated by the coil/s. Anyone else with any ideas to improve accuracy?

...

Wed Feb 15 2006, 12:21AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I remember someone adding a 'tail' on the back made of feathers or something... I am not sure how much it improved the accuracy but it did make sure it the target point first...

I wounder if you could make a pair of fins the diameter of the bullet, trailing behind it... Would there be enough airflow there to make it stable like a rocket? I would run a rocksim simulation, but it is not installed right now...

Quantum Singularity

Wed Feb 15 2006, 02:45AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Hmm, small fins on the back might work especially on a longer projectile. I wonder if you used a square barrel instead of round and put 4 fins on then the 'corners' of the square barrel would give the fins a little extra room. Plus if you used the right type of feathers they can compress real well and then spring out once the projectile is free from the barrel. Lots of things to try. Wish I had me garage cleaned out so I can start building.

Dr. Shark

Wed Feb 15 2006, 02:21PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

there is a fundamental difference between normal firearms and coilguns: with firearms, you want a big bore so there is some volume for the gas to burn, so you end up having relatively short and fat projectiles. With a coilgun, you want your projectile as long as the coil, so and you can make it fairly thin. Thus the idea with the fins is a very good, if not the only way to stabilize the projectile.

But should you not figure out how to give your coilgun enough power before you worry about accuracy? Normal coilguns with a few 10s of m/s muzzle velocity do not need to be accurate as the projecile just drops to the ground after a few meters :P

1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob