Physics Help Forum Railgun project

 May 3rd 2018, 09:21 AM #1 Junior Member   Join Date: May 2018 Posts: 3 Railgun project Hi all, I'm new here so please let me know if I am posting in the correct place and all that sort of stuff, thanks. I am a mechanical engineering college sophomore and I want to build a railgun. I have an good understanding of what railguns are and how they work and an alright understanding of the math. I can really only can find info on tiny railguns and very large ones, I want something impressive that I can build over a longer period of time but not gigantic. I have a lot of equations but I'm really just trying to start figuring out materials right now and how the equations relate to the physical properties of the materials. What are the main equations I should be looking at to find lengths and sizes of rails and other parts including caps, and if that's not the right place to start, what is? I've done a couple tiny railguns with 9v's but I think it would be fun and educational to build a bigger one with multiple caps and all that fun stuff. I have access to a machine shop that I've worked in (all manual, not cnc) so it'd be cool to fab a lot of the parts. I am contacting a couple professors that hopefully will help mentor me but I wanted to post here to get a rough idea of stuff first. If anyone has built one of any size I'd love to hear about it. Thank you!
 May 3rd 2018, 08:41 PM #2 Senior Member   Join Date: Apr 2017 Posts: 291 Great idea for a project .... I have some experience, mostly with coil guns .... It seems to me the most important and expensive part to this is the capacitor bank . This will determine the size of projectile and gun ... Decide the mass you want to accelerate , and to what speed ... and length of rail ... from this you will have an idea of the power and speed of discharge , hence the size of capacitor you ideally want ... then is it possible to get the use of such a capacitor??? This could be the limiting factor , you may have to scale down. The next most important factor must be switching such high currents ...mechanical of semiconductor ??? Some youtube videos on rifle size rail guns ...
 May 3rd 2018, 09:04 PM #3 Junior Member   Join Date: May 2018 Posts: 3 Yea the caps are most likely the most costly part, which is where I'm kinda stuck starting. Do I start with deciding my projectile and rail length and those things and then calculate the caps needed? Or do I choose the most expensive cap(s) I can afford first and then calculate all the other specs from that value? I'm assuming it's done the second way of choosing the caps first, but then I'm a bit confused on how to get to get the other specs just from that one value. I'll look at some equations and try to figure it out more but if you have an easy answer that'd be great haha. Also, what do you mean by switching high currents? Like what material I need to use that can handle the current? Thanks
 May 3rd 2018, 10:19 PM #4 Senior Member   Join Date: Apr 2017 Posts: 291 You haven't specified the sort of mass of projectile you were thinking of ... I would Guess for approximately every 100gms you ay need about 10,000 dollars of capacitors (very rough figure) ... your college may already have some .... from a given capacitor you have the energy it stores ... how much will be transferred in a discharge? perhaps half?? rail guns can be 90% efficient so you can callculate the energy in the projectile .... or your college may have some big batteries Li-ion batteries maybe a possibility.... I have over 1000's small cells , 18650, (recycled from used laptop batteries ,$100) which I use for solar electricity storage , these 1000 cells can be wired for 3.6 V and can deliver about 5,000A ...or 7.2V 2,500A ...etc When loaded with projectile you have to switch on !! fire it !!.. very high current , and needs to be switched quickly with low contact resistance .. it should be possible to do this electronically (semiconductors) but expensive .... or two copper plates separated by less than a mm and hit the two together with a hammer to make the circuit and fire the gun. Last edited by topsquark; May 4th 2018 at 03:17 PM.  May 3rd 2018, 10:45 PM #5 Senior Member Join Date: Apr 2017 Posts: 291 This may be the sort of thing you were thinking of "This is the most powerful mobile electromagnetic railgun built by a non-government." ..... Weighs 100Kg ...27KJ , cost of capacitors (manufacturers recommended price )$50,000 ...but the constructor got them much cheaper ... https://imgur.com/gallery/GrAiE Last edited by oz93666; May 4th 2018 at 12:44 AM.
 May 4th 2018, 09:26 AM #6 Junior Member   Join Date: May 2018 Posts: 3 Yea I've read all about that one, definitely not gonna be that big. I think he used something like 26 caps. I kinda of want to use capacitors instead of batteries cause that is what I've seen the most and what makes the most sense to me. Also, that guy used a paintball bun and CO2 to shoot the projectile onto the rails so he didn't need to figure out any kind of switch, he just charged the caps up then shot onto the rails which I like the idea of a lot
 May 4th 2018, 04:01 PM #7 Senior Member     Join Date: Jun 2016 Location: England Posts: 473 Safety First You mentioned that you are trying to get the support of a couple of professors. It will impress them if you are able to include within your project summary some assessment of the issues that will need to be addressed to operate this thing safely. There will be high voltages and projectiles flying about... These professors will not want to be involved with anything where someone might get hurt. A sensible safety assessment will reassure them that you are responsible enough for them to feel secure in their support of your project. topsquark likes this. __________________ ~\o/~
May 4th 2018, 08:38 PM   #8
Senior Member

Join Date: Apr 2017
Posts: 291
 Originally Posted by KCWCK55 ... CO2 to shoot the projectile onto the rails so he didn't need to figure out any kind of switch, he just charged the caps up then shot onto the rails which I like the idea of a lot
I saw that , and it certainly makes a lot of sense.....

It would be nice to incorporate some practical use in this project ....

A pree bost for rocket launch ....ameture rocketry is a big hobby , they want to get higher faster ...If it worked for small ameture rockets it could be scaled up ....

Satellites are getting smaller and smaller . According to wikipedia launch costs are " 12,000 to 18,000 dollars for sub-1 kg picosat payloads that are approximately the size of a soda can"...

The compact electronics in these small satellites should be able to handle g forces of a rail launcher ...

A soda can is very small ... it should be possible to design a relatively cheap rail launcher ... launches the rocket with payload ... when clear of the aircraft the solid propellant rocket ignites and powers the 'soda can' payload on to low earth orbit ...

I would think a long rail with a powerful compressed air injector ... length determined by the size of aircraft ... makes sense to have the rail launcher in a high flying aircraft... an old , refitted commercial jet ( these are very cheap , crowdfunding?) .... each flight could launch a hundred or more rockets with satellites

Every flight could make millions of dollars profit ....

If you do all the theory , and make a start on the practical work , I bet you could find a backer ...

This idea is not unrealistic for a practical project ... the rocket will be small .... think soda can !!!

An aircraft flying at 15km altitude is in about 12% normal atmospheric pressure .. a great help .

Last edited by oz93666; May 4th 2018 at 09:18 PM.

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