9KJ coilgun construction / Projects / Forums

Forums

4hv.org :: Forums :: Projects

« Previous topic | Next topic »

9KJ coilgun construction

previous 1 2 3 4 next last

Move Thread

LAN_403

KLH

Tue Feb 17 2009, 06:18PM

Registered Member #1819 Joined: Thu Nov 20 2008, 04:05PM
Location:
Posts: 137

I do highly recommend using adhesive for the coil. Super glue is probably easier to use than epoxy, since you don't have to hold the coil together for the duration of the curing time. Unfortunately, if you already have a coil without adhesive, this means winding a new coil, tacking each turn with adhesive.

Dave Marshall

Tue Feb 17 2009, 06:47PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

I've measured carbon fiber tubes of various sizes and compositions. Resistance seems to average from 20ohms to 300ohms per foot. The highest resistance I found was actually carbon arrow shafts, which can usually be had locally and relatively cheaply. The downside is you're going to be very limited in your bore size, probably to something less than .375".

Another problem is that many types of carbon fiber tubing have a very rough interior surface. I remedied that by gluing progressively finer sand paper to the outside of a lead cylinder a bit smaller than the barrel, dropping it into the barrel and shaking the bejesus out of it for about 5-10 minutes.

Dave

rp181

Tue Feb 17 2009, 09:35PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

for larger tubes, look at carbonfibertubeshop.

big5824

Wed Feb 18 2009, 10:08AM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

Iv now ordered a 10mm ID carbon fibre tube for Â£7, and im bidding on the SCRs I need, currently at $8. Iv also built a prototype optical break beam circuit, and an overclocked PIC board to control the gun. Should be able to start large scale construction in a few weeks I hope.

j.azz

Wed Feb 18 2009, 12:11PM

Registered Member #888 Joined: Tue Jul 10 2007, 06:52PM
Location: Hannover, Germany
Posts: 40

As for the roughness inside your carbon barrel... if you're lucky, then the inside is just as smooth as the outside.
Mine happened to be so smooth that a steel cylinder could be held in the tube just by closing the top thus making it airtight.

I'm really interested in how far saturation will affect perfomance with this high energy to projectile mass ratio.
keep on!

greetz, j.azz

edit: btw: has anyone yet measured the accuracy of a sensor coil driven "v-switch"? wouldn't it be easier to use static timing or the optical gate for triggering the counter-current? Or did I misunderstood the principle you want to use?

big5824

Wed Feb 18 2009, 01:24PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

Yes im going to use optics to trigger the second scr in the v switch. I will have a sensor infront of each coil, which when first triggered as the projectile moves infront of it will activate the coil, then when the projectile has moved right past it (it will now be dead center in the coil) the second scr will trigger, turning off the coil, so there should be maximum force up to when the projectile reaches the center, then no suck back once it has passed.

hotcrazyfruit

Mon Feb 23 2009, 02:11AM

banned on 5/26/2009
Registered Member #1877 Joined: Mon Dec 22 2008, 02:03AM
Location:
Posts: 147

if you've got a capacitor bank that big, you are 1) going to need a REALLLY big SCR and clamp, and 2) you should REALLY build a rail gun.
unless you are thinking of building a multistage, discharging a bank that big will just heat up the coil. you wont get much more after a certain point.
rail guns are alot more efficient anyways, although rails DO need replacing every now and then, i think you are better off with a railgun. but the bank looks good xD
EDIT: i didnt read the full post before i posted. go ahead with a coilgun if you are doign 5 or 10 stages

big5824

Mon Feb 23 2009, 04:27PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

I would have liked to make a railgun, but I dont really have the metal working skills or access to equipment to build one.

also another update, 10mm carbon fibre tube has arrived, but sadly someone outbid me in the last few seconds on a great scr deal :( so it seems il be waiting a little longer til i can begin.

big5824

Mon Mar 23 2009, 05:03PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

Im still stuck searching for SCR's.....ebay has been very dry recently, last night I lost the only good auction thats appeared over the last month or two :(
Does anybody know of any other good sources of SCR's? I need 4 rated at least 400v with 6KA surge.

big5824

Thu Apr 23 2009, 10:02PM

Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240

Finally managed to get my hands on 4x 800v 5500A Itsm SCRs

can finally resume this project.

Here's some renders of the current plan for the gun:

(album)
The barrel will be slotted intermitently, mainly so the optical sensors will function and be able to move up and down the coil, and also to reduce the small eddy currents in the graphite in the carbon fibre. However the barrel should not compress at all since the bridges are left in every 8cm.
The housing for the sensors and the coil enclosures will all be cut on a laser cutter I have access to, so they should be very high quality and hopefully a tight fit.
I have also acquired a steel rod to make projectiles out of, which is such a perfect fit in the barrel it is possible to use it like a syringe. I intend on experimenting with various sizes of cylindrical projectiles, and also more aerodynamic pointed ones, as I am currently unsure which will be more effective at these speeds.

I am currently in the process of designing the coils. I am assuming 2% efficiency for each stage, and using this to calculate how fast the pulse will need to be to dump 2kj into the projectile before it has passed the center of the coil. My current estimates are that the first stage will need a 3ms pulse, dropping to 1.2ms, 1ms, 0.8ms, and 0.7ms in subsequent stages. This equates to peak currents of around 3KA for the first stage, 6.5KA for the second, and 8-11KA for the final stages. 11KA is right on the limit of the SCRs capability, so I am hoping they will withstand this pulse. This will be achieved using coils with 4 layers of 16awg wire to start with, dropping to 1 layer on the final stage.

Currently I am stuck on a few things:
1. I need a way of cutting the accurate slots into the barrel (as shown in the pictures), im thinking of using a dremel, has anybody got any better ideas?
2. For puck SCRs, is the mounting force just required to ensure a good thermal contact, or does it ensure a better connection between the semiconducting layers in the device?
3. I need some safeguards to turn the SCRs off if the optical sensors fail, so that the entire bank isnt dumped into one SCR. I will be controling the system using a PIC, so that could provide some safety, but I have had a lot of bad experiences with PICs, I would prefer something more basic and reliable, any ideas?
4. Has anybody ever had problems with the coil inducing a current in the optical sensors and triggering them early? And if so how did you overcome it?
5. Once I get the gun operational it would be interesting to experiment with some other alloys for my projectiles, such as silicon steel or the various molydium alloys, does anybody know where it is possible to get these materials in rod form?

Also if anybody has spotted any other problems, please dont hesitate to point them out, I bet iv overlooked something important somewhere.

Thanks again for your support

Matt

previous 1 2 3 4 next last

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