What Smells Like Blog?

Science (Railgun)

This page was originally dedicated to documenting the development of my mini-Railgun that I was making as a fun project. I haven’t had time to do any work on it for at least two years now, but I’m leaving this page available just in case my notes might be helpful to someone else.

07.02.2010

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22.10.05

Read the initial blog entry about my Railgun by clicking here.

29.10.05

Been on holiday for most of the week, but still found time to work on the Railgun. The rails themselves are finally secured in place, and equal distance apart along the whole length. I tried making the projectile the same width as the distance between the inside edges of the rails. This was intended to improve the accuracy of the projectile, but it just resulted in several jams on firing!

So the projectile now has a few millimetres clearance on either side, so it moves along the U shaped rails comfortably. I’ve decided that the next modification should be a system that allows the rails to be replace easily, since they are having chunks blown out of them with every test firing. Currently they are soldered into the rest of the firing circuit, but this is going to be a pain in the long term… Haven’t decided on the best solution for this yet.

Some better images of the Railgun can be seen by clicking on the thumbnails below. The first two images show the Railgun from the side and front respectively, while the third images shows all the capacitors I have crammed in the black box at the rear of the gun.

I’ve also taken two videos of various test firings; click on the links below to view them. You’ll have to excuse the poor resolution, but they weren’t taken on a dedicated digital video camera. Unfortunately the resolution was not sufficient to take a long range shot of the entire projectile flight path (since the projectile is so small), so that’s why the videos are close-ups of the firing process. However, this does mean you can see the damage done to the rails. Just to make it absolutely clear where the projectile is on the rails, a ‘before’, ‘during’ and ‘after’ images have been added, with the projectile circled on the ‘before’ image.

Test Firing Video 01 –

Test Firing Video 02 –

That’s it for the moment. Will post further developments as they happen.

10.01.06

Preparations are underway for a second Railgun prototype. I’m hoping to get a 1.5 Farad (!) capacitor from eBay some time next week. This high-spec capacitor is intended for car audio systems, and will charge/discharge (effectively) instantainiously, which is just what I require. More news on this next week.

23.01.06

I managed to get the 1.5 Farad capacitor from eBay and spent my lunchtimes last week carrying out some tests and browsing the RS electrical components catalogues for cable, switches, etc, that are able to handle high currents.

While it was possible to work on the first prototype under the guise of doing my normal job, unfortunately this new cap is rather large (30cm tall), and has a built in voltmeter and flashing blue LEDs (God knows why, probably because it’s designed to appeal to the “boy racer” market as an addition to their car audio systems), making it somewhat more conspicuous. Hence I have to work on it at lunchtimes when there is nobody around.

Anyway, I’m very pleased with the inital tests. I connected it to the original prototype using some suitable large copper wires, effectively by-passing the capacitor bank, and was able to get the same effects as normal with only a few seconds of charging, rather than the normal 4+ minutes. Now I’m able to get several firings in a short period of time, two facts have come to light:

1. The rail damage from each shot with the new caps is both increased and significant. There’s no doubt that the portable ‘rifle-style’ prototype will need to have easily replaceable rails.

2. While I was able to get a reasonable range with the small projectile, it becomes too prone to misfirings – such as being blown off the rails by the sparks, rather than propelled forward. To eleviate this I created a larger projectile that fits snugly inside the rails, making it less likely to deviate. Of course, this has reduced the range somewhat, but made firing much more reliable.

Now I have suitable magnets and capacitors, the railgun is starting to become and engineering project. My next step will to be build another prototype that will mainly consist of the rails and little else. This will allow me to experiment with new types of projectiles without causing further damage to the original prototype, among other things. Pictures of the new cap and new prototype will follow in due course.

07.02.06

What with one thing an another, work on the Railgun has currently slowed to a crawl. I keep getting side-tracked with great ideas for other projects and doing bits to them (with mixed results). However, I do plan to do more work on the Railgun itself this afternoon. Photos of the new prototype (v1.5 I guess) that I mentioned in the previous entry and the capacitor (with 15cm ruler for scale) can be seen by clicking the thumbnails below. The photos were taken on my new Nokia 1.3 Megapixel camera phone. Note that the rails are now held in place with bolts, rather than glue. This will allow cables to be attached without the need for solder and to allow the rails to be more easily replaced.

31.03.06

At last, I’m finally going to get some free time to work on the Railgun next week, which frankly has been going nowhere of late. Check back in a week if you’re interested in updates – any successes (or failures) will be reported, with pictures obviously.

14.04.06

Ok ok, I’m a bad man. Instead of working on the Railgun I got side-tracked by my Leyden Jar project. Still, it’s almost as interesting as the Railgun, and I got some good pictures out of it. I’ll be adding a seperate Leyden Jar page very soon.

22.06.06

Hah, I bet you all thought this project was dead? Well this is clearly not the case as I finally managed to get the chance to work on it yesterday, and made some very good progress. Essentially I built a whole new system, incorporating the v1.5 prototype and large capacitor (shown in previous entries), which I shall call the v2 prototype. Photos can be seen by clicking on the thumbnails below. The photo on the right shows some of the different projectiles I’ve been experimenting with, but more on that later.

You’ll notice that the work bench is a bit untidy in the first photo, you can see the v1 prototype in the background. :s Anyway, I’m slowling moving towards portability; this version draws power from two heavy duty batteries rather than a power pack plugged into the main. If you’re wondering about the two switches, the first one operates the charging of the capacitor, and the second is the firing switch.

If any of you feel compelled to contact me to let me know how lame the capacitor looks being held on with string, then I’ll save the the trouble and acknowledge that here and now. Rest assured, I have now got my hands on some decent mountings – adding these will be the first job for today.

The rail components of the v1.5 prototype are clearly visible in the middle image. You can see the magnet is currently balancing on a pile of metal weights – this is the only thing stopping this design from being fully mobile. This current magnet is £150 worth of ‘Major’ magnet, made from the Alcomax alloy. We have a milliTesla probe here, but I’m unable to get a reading for field strength, as it takes it off the scale. However I’m starting to suspect I could get a similar field from several of the infinitely more portable ‘Magnadur’ magnets. This is something else I’ll look into today.

Now the essential matter of how well v2 works. Well thankfully in some ways it is better than v1, although I’m still having trouble with projectile design. Various attempts can be seen by clicking on the thrid thumbnail. When fired, all of these projectiles move – scooting along the rails quite impressively – but the flaw is that they are too light to be held on the rails by their own weight. This leads to the problem that when they start moving they loose contact with the rails before the capacitor can fully discharge through them, and esentially skip down the rails, re-establishing contact each time they land, but still not discharging fully. This current design flaw results in virtually zero range, a pretty serious flaw by anyones standards. But work on v2 is not complete, so my third job for today will be to sort out the projectile design. I’ll post more information tomorrow.

23.06.06

Ok, so I got some more work done on the Railgun yesterday after writing the above post. As can be seen from the thumbnails below, I completed the first task of fixing the capacitor securely. It looks a lot better now I think, but that’s not the point really. The image on the left is without the magnet in place, the one on the right is with the magnet. As you can see, I’m yet to decide on the best way to secure the magnet.

I also completed the task of investigating which had the stronger field, the Alcomax or the Magnadur. I must have been high on solder fumes when I decided that this needed to be investigated – the Alcomax is a professional research grade magnet, for goodness sakes. Actually, it was probably intense desire to find a more portable solution to my magnetic field needs, but needless to say, it wasn’t to be!

As stated previously, our milli-Tesla probe could shed no light on the field strength between the two arms of the Alcomax, and it proved similarly useless when four Magnadurs were mounted on an armature. I really must persuade the powers that be to invest in a Tesla probe with a wider range. Anyway, I pondered the best test for relative field strength, then remembered we had a few search coils. While these are intended for use with a moving magnetic field, I reasoned that if I moved the coil through the fields of the competing magnets at the same steady rate, I may be able to observe relative differences on the resulting oscilloscope traces. This test was rendered redundant however, as on moving the Alcomax near to the oscilloscope, the almost the entire trace was displaced off the screen! Comparatively there was only a minimal effect from the Magnadurs. Case closed.

My third task was to investigate different projectile designs, and this didn’t go as well. I tried a more solid, heavy projectile. My thinking was that lightness, to enable further range, counts for nothing if it’s too light to maintain contact with the rails during the discharging. But even this heavier projectile – essentially a solid rectangle of aluminium 26 x 5 x 3 mm – wasn’t maintaining contact well enough to allow any significant discharge. I could tell this was the case by the way the capacitor read-out only dropped by a marginable amount. I guess I’ll have a think about this problem over the weekend – including Sven’s suggestion of a H-on-its-side shaped projectile to grip the rails – but I’m starting to suspect I’ll have to bite the bullet, so to speak, and replace the rails for better quality alternatives. More when I get some spare time.

13.09.07

Wow, has it really been a year since I last worked on the railgun? If I’m going to offer an excuse, I guess it’s that I was a bit put-off when construction became more about engineering than physics…

Anyway, today I picked up exactly where I left off last time, by replacing the rails with a higher quality alternative. As you’ll clearly see, I’ve now opted for circular rails and projectile, which I hope will prove the better choice.

The image on the left shows the full railgun, and the image on the right is a close-up of the new rails, projectile and magnetic armature. These look nicer than the previous set-up (not that it matters), and were salvaged from a spare bit of physics demonstration equipment. Actually, it was the acquisition of these materials that inspired me to restart the project. Oh, and yes I acknowledge the poor hacksaw work on the wood at the end of the rails, but it was nearing the end of the day and I was in a hurry to get things working. I’ll sort this out tomorrow.

So does it work now? Well, yes. I’ve run a few tests (note the damage to the rails in the close-up already) and jams are quite clearly a thing of the past, but the range is quite poor. However I only ran three or four tests with the Magnadur magnets (see previous post for data on the magnets), and the projectile needs to be made smaller and lighter. More test results very soon, probably with the Alcomax magnet reinstated.

03.12.07

At the end of last week I decided to try an interesting “overcharging” experiment with the railgun. I’ve had an old 4700 micro Farad capacitor sitting around for a while, and although this is a smaller capacitance than the newer 1.5 Farad cap currently attached to the railgun, this older capacitor can be charged with 250 volts.  Since the energy stored by a capacitor is the product of 0.5 * capacitance * (charging voltage)^2, then the older capacitor can store quite a bit more energy than the new one.

So why isn’t the old one permanently incorporated into the railgun, you might ask? Simply because I don’t have a portable 250V DC power source. Anyway, just out of interest I thought I’d connect this old capacitor into the railgun to see what would happen. I connected it with jumper leads attached to the rear of the rails.

The results were spectacular to say the least. I really wish I’d caught it on video. The instant I connected the charged capacitor, there was a massive bang and a blinding flash that left a searing after-image on my retina for about half a minute. It was like some sort of ‘flashbang’ grenade going off right next to me – it was that loud.

Anyway, the projectile was thrown off to one side, as was one of the connectors at the back of the rails. The rails themselves were quite badly damage, loosing a large chunk in the process. That doesn’t matter though, since the current versions can just be rotated. There’s an image of the aftermath below.

You can clearly see the damage to the projectile, and a little further back the damage to the rails. I won’t be doing this again, due to the both the quite dangerous nature of this experiment and also the damage it does to the rails. I’ve satisfied my curiosity now anyway, so I’ll go back to trying to improve the range using the batteries and 1.5 Farad capacitor.

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