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New ideas for railguns.

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LAN_403

rp181

Sat May 24 2008, 07:24PM

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

So, i was thinking, With railguns, errosion is a major issue, due to the fact that the contact isn't perfect. Would it help any if i Covered the rails with silver conductive grease? it would make better contact, shield from errosion, and make the projectile easier to move.

I saw some designs utilizing 4 rails, the sereis agumentation, and the parrallel one. Has anyone tried these? does it increse effeciancy?

ea6b607

Mon May 26 2008, 02:54AM

Registered Member #1320 Joined: Sat Feb 16 2008, 01:31AM
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Well, the problem with the erosion is that you have to service the rails every few shots. Doesn't really help if you have to grease the rails every shot. The goal is to find a way to shoot multiple times without messing around with the contacts. Both series and parrelle augmentation are both going to make you have lower efficiencies. Their goal is to input more power with out more contact damage. In your case with a relatively low power supply you want to get the most efficiency possible. At least I assume you do.

rp181

Mon May 26 2008, 03:08AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Well, its not like the grease is just all going to disapear, only a little will stick to the projectile.

badastronaut

Mon May 26 2008, 03:41PM

Registered Member #222 Joined: Mon Feb 20 2006, 05:49PM
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Serial and parallel augmentation can improve efficiency by increasing the inductance gradient if done right. There have been many papers on this issue. Serial augmentation is better than parallel for small scale railguns. They are not the same and they are used for different reasons.

There has also been at least one paper where silver grease was used as lubrication. I don't think it turned out to be useful. Another paper was done on using indium metal as a lubricant. Nothing groundbreaking came from it. You could try graphite powder without any hydrocarbon binders. You could also try to fashion some brush contacts.

Basically, if you can load the projectile by hand, then it will loose contact with the rails when it fires and the plasma that forms between the armature and the rails will cause severe erosion.

Friction isn't much of a big deal in large scale railguns. They have to use hydraulic rams to load the projectile in that case. The most damaging erosion happens when the armature looses contact with the rails, something that should be avoided but is often not feasible for small scale railguns. Another phenomenon is known as gouging and is mechanical in nature and will happen regardless of the flow of current.

Barry

Mon May 26 2008, 04:16PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

The usual mind-set here seems to be a solid sliding block of conductive material. What about roller bearings?

How would it work to use two smooth cylinders which roll along the rails on the outside, and roll against each other in the middle? They could be enclosed in some light plastic framework to keep them in alignment.

Each of these touch points have solid metal-to-metal contacts and no sliding occurs. There should be very little friction as they roll along. The main drawback I notice is the reduced contact area along the line where the cylinder meets the flat rail.

Just a wild idea!
Barry

rp181

Mon May 26 2008, 04:56PM

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

thats what my problem was, the low contact area. If that does work, you could use 2 alu cylinders, which are tensioned with springs.

ea6b607

Mon May 26 2008, 10:55PM

Registered Member #1320 Joined: Sat Feb 16 2008, 01:31AM
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bad astronaut wouldn't it be more effective to reduce inductance by just making the rails thicker, that way the resistance is still reduced, but you still keep the better magnetic coupling between projectile and rail since they are still next to each other.

badastronaut

Tue May 27 2008, 12:35AM

Registered Member #222 Joined: Mon Feb 20 2006, 05:49PM
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Or you could use permanent magnets to augment the field while having the hollow metal cylinder just sit on top of the rails. That way you can make that thing roll off there with under 15 amps. It is quite an amuzing toy. You cannot use steel or other magnetic rods since it gets attracted to the magnets and will not accelerate with the normal amount of current. Since the resistance is so low, you could probably use a couple of AA batteries in parallel. It would make a great and very safe science fair experiement. A digital storage oscilloscope would be ideal for taking measurements.

Why would you want to reduce the inductance gradient of the rails? If that is your goal, then thicker rails will work, but it is counter productive.

Parallel augmentation is two sets of independently powered rails. The augmenting rails are used to increase the magnetic field in the railgun while the rails carrying the armature can use a smaller current. The point of this is to reduce the current flowing through the sliding metal contact. To use parallel augmentation you generally would need to have two separate power supplies. Using the same power supply would just be equivalent to thicker rails as you say.

Serial augmentation is where you have an extra "winding". The extra turn provides an increased magnetic field. The price you pay for this is increased resistance, but this resistance is very very small compared to the other resistances found in amateur railguns. It has been used with success in small and large scale railguns.

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