51 replies to this topic

[Product9]

This is something that I don't understand.

Correct me if I'm wrong, but a laser generates heat because it's taxing the reactor, correct? A Gauss gun (or coilgun) takes a lot of wattage to operate. Given that each round weighs a staggering 250 pounds (8 shots per ton, according to http://www.sarna.net/wiki/Gauss_rifle), it would take a MASSIVE amount of current to lob at a high enough speed to be dangerous.

In fact, I'll bet it would take a lot more wattage than a large laser would. Yet, no heat?

Okay, so the Gauss rifle uses a series of capacitors which presumably must be charged before the weapon can be fired. This would account for the slow rate of fire we see in game. It also means that if the Gauss rifle is destroyed it will blow up catastrophically. Anyone who's had education in electronics has seen capacitors explode, so this I can believe.

So, maybe the capacitors discharging doesn't tax the reactor because they have already been charged up slowly during the several seconds between shots? If that's the case, then why not do that with lasers, too?

Also, why is it called "Gauss Rifle" when a coilgun has no rifling in the barrel? Due to the nature of how Gauss/coil guns work, the round doesn't actually contact the barrel as it is accelerated. To do so would introduce inefficiencies and barrel wear, negating the usefulness of such a weapon.

I just know someone is going to bring up the word "railgun" so let's just prevent that before it happens. A Gauss gun is different from a railgun. The work differently and use different principals.

For your consideration:

https://en.wikipedia.org/wiki/Coilgun

https://en.wikipedia.org/wiki/Railgun

This also begs the question: why aren't there railguns?

Edited by Product9, 01 August 2013 - 07:14 AM.

[CygnusX7]

Perhaps its a high voltage, low current circuit. More efficient, less heat.

Edited by CygnusX7, 01 August 2013 - 07:56 AM.

[James The Fox Dixon]

The Gauss Rifle was introduced back in the late 80's before rail gun technology was a reality. Gauss Rifles in Battletech do generate 1 point of heat, but that's not a lot in comparison to the other weapons. Also, a Gauss Rifle in Battletech is the same a railgun. I would recommend that you keep in mind that Battletech was written at a time when many of the things we have now were just a dream back then, so use hand-wave-em to get past it.

[Product9]

Current is determined by resistance as shown in the equation I = V/R (aka Ohm's Law). So, you can have a very high voltage, and a very low current if the load resistance is high, or a very high current if the load resistance is very low.

Power, expressed in Watts (W) is determined by multiplying Voltage and Current.

James The Fox Dixon, on 01 August 2013 - 07:26 AM, said:

The Gauss Rifle was introduced back in the late 80's before rail gun technology was a reality. Gauss Rifles in Battletech do generate 1 point of heat, but that's not a lot in comparison to the other weapons. Also, a Gauss Rifle in Battletech is the same a railgun. I would recommend that you keep in mind that Battletech was written at a time when many of the things we have now were just a dream back then, so use hand-wave-em to get past it.

The first railgun was patented in 1922. Coilguns may date back to the 30s.

Still, the rules for BT get revised, right? I just want to know the logic behind the decision.


When I was in college some classmates built a coilgun for their senior project, so I'm pretty well versed in how they work.

Edited by Product9, 01 August 2013 - 07:33 AM.

[FearTheAmish]

well Gauss rifle technology is actually a real thing. Basically its using Magnets to propel a solid steel bar at high speeds. The projected future of it is having series magnets along the tuber with the "round" in the center the magnets are all positive facing inwards. Then a current goes through the "round" and makes it also positive which forces round down the tube then outwards at intense speeds. This process once refined would actually need very little energy but would be very delicate.

[James The Fox Dixon]

Product9, on 01 August 2013 - 07:31 AM, said:

Current is determined by resistance as shown in the equation I = V/R (aka Ohm's Law). So, you can have a very high voltage, and a very low current if the load resistance is high, or a very high current if the load resistance is very low.

Power, expressed in Watts (W) is determined by multiplying Voltage and Current.



The first railgun was patented in 1922. Coilguns may date back to the 30s.

Still, the rules for BT get revised, right? I just want to know the logic behind the decision.


When I was in college some classmates built a coilgun for their senior project, so I'm pretty well versed in how they work.

They may have been patented but they weren't viable for research until capacitors were able to hold higher currents and voltages starting in the 1980s. The capacitors from that time weren't like they are now. Parallel to this is the development and introduction of the transistors in the 1970s. Like capacitors of the time, transistors couldn't handle high voltages and currents. This is why it took the Navy so long to fire their first railgun in 2010. The Navy railgun is slightly bigger than the ones depicted in Battletech in my opinion.

[Lightfoot]

Super-cooling lowers the electrical impedence to near zero so the Gauss Rifle itself is cool in operation. The 1 point in heat is from the mech's reactor. The drawback is it can and does explode, alot in MWO. Not recommended for use with XL engines.

[Adridos]

The idea of the gauss rifle came from people who just wanted to prove Star League's superiority, so they took the AC, found some 'fancy' firing mechanism and created a weapon that is an AC that has better range and much better damage. They simply lacked people with knowledge of the technology and since it was ~1988-1989 when writing it, they simply didn't have access to the information about it like we do today.

[Product9]

FearTheAmish, on 01 August 2013 - 07:37 AM, said:

well Gauss rifle technology is actually a real thing. Basically its using Magnets to propel a solid steel bar at high speeds. The projected future of it is having series magnets along the tuber with the "round" in the center the magnets are all positive facing inwards. Then a current goes through the "round" and makes it also positive which forces round down the tube then outwards at intense speeds. This process once refined would actually need very little energy but would be very delicate.

So, you're saying that instead of coils it uses permanent magnets? That's... strange. I'm not certain that would actually work in practice.

At this point it's no longer technically a "Gauss" gun, though.

James The Fox Dixon, on 01 August 2013 - 07:43 AM, said:

They may have been patented but they weren't viable for research until capacitors were able to hold higher currents and voltages starting in the 1980s. The capacitors from that time weren't like they are now. Parallel to this is the development and introduction of the transistors in the 1970s. Like capacitors of the time, transistors couldn't handle high voltages and currents. This is why it took the Navy so long to fire their first railgun in 2010. The Navy railgun is slightly bigger than the ones depicted in Battletech in my opinion.

Transistors aren't needed in a railgun. In the absence of a solid-state switch (like a transistor or SCR), you can just use a hardware switch. The one my classmates built used the latter method.

Besides, they had vacuum tubes. Vacuum tubes are still used in high-power applications today, where transistors aren't practical.

Lightfoot, on 01 August 2013 - 07:44 AM, said:

Super-cooling lowers the electrical impedence to near zero so the Gauss Rifle itself is cool in operation. The 1 point in heat is from the mech's reactor. The drawback is it can and does explode, alot in MWO. Not recommended for use with XL engines.

This makes some amount of sense to me, but I ask again - why not use a similar mechanism for lasers? If they have the ability to super-cool things, then why is heat an issue at all?

Adridos, on 01 August 2013 - 07:56 AM, said:

The idea of the gauss rifle came from people who just wanted to prove Star League's superiority, so they took the AC, found some 'fancy' firing mechanism and created a weapon that is an AC that has better range and much better damage. They simply lacked people with knowledge of the technology and since it was ~1988-1989 when writing it, they simply didn't have access to the information about it like we do today.

I do believe that it is indeed due largely to ignorance. What I'm wondering is why it hasn't been changed since then.

[Lexx]

I think the better question should be why doesn't gauss have a minimum range?

Gauss should have a minimum range of 60 meters. I think it should also have a slower fire rate than it does now, since you have to charge a bank of capacitors up to massive power levels to fire it. That's the reason gauss can explode when hit since all that stored energy gets released if the capacitors take too much damage. Capacitors don't charge instantly, so I think the cooldown on gauss rifles should be increased to 6 or even 8 seconds.

[Adridos]

Product9, on 01 August 2013 - 08:08 AM, said:

I do believe that it is indeed due largely to ignorance. What I'm wondering is why it hasn't been changed since then.

It works for the game, I guess. It would just become an AC/15 if they changed that aspect of it, so it stays like it is to keep the different flavour of the thing.

[Dracol]

Gauss, added back before the ease of internet research, used to give IS a chance against the clans.

[Product9]

Lexx, on 01 August 2013 - 08:12 AM, said:

I think it should also have a slower fire rate than it does now, since you have to charge a bank of capacitors up to massive power levels to fire it. That's the reason gauss can explode when hit since all that stored energy gets released if the capacitors take too much damage. Capacitors don't charge instantly, so I think the cooldown on gauss rifles should be increased to 6 or even 8 seconds.

Yeah, capacitors have a time component which is determined by circuit resistance times the capacitance, but is also determined by the input voltage. The resistance may be low due to high-conductivity components, but we know the capacitance is going to be HUGE.

However, the voltages are also going to be huge.

Check out this calculator: http://ladyada.net/library/rccalc.html

Really, you should experience heat build-up as the thing charges up. That would make some sense. I would be cool with a mechanic that let you charge the capacitors at will, experiencing heat build-up as you did so, but once you fire the added heat would be negligible. That way you could get a higher rate of fire for less damage, and vice versa. I don't think it would jive with TT rules though...

Lexx, on 01 August 2013 - 08:12 AM, said:

I think the better question should be why doesn't gauss have a minimum range?

I don't understand why it would have a minimum range though. If you're propelling a hunk of metal at speeds exceeding the speed of sound, wouldn't it be most deadly the moment it exists the barrel?

[Tombstoner]

Personally i think it has to do with super conductivity. the energy efficiency is directly related to lost energy due to resistance in the drive systems so with zero loss all the electricity can be applied to moving the projectile. so no heat....? but very heavy.

Edited by Tombstoner, 01 August 2013 - 08:28 AM.

[Product9]

I can't really speak to that since we didn't cover super-conductivity in electronics school.

Apart from exotic materials, however, isn't the only way to achieve super-conductivity through super-cooling? I don't know about all the BT technologies, but I do know that cooling something takes energy (and produces waste heat, just look at a refrigerator), not to mention the energy required to accelerate the 250 pound projectile using only electromagnetism (did I mention that coil guns are dreadfully inefficient by nature, hence why they aren't used for much outside of hobby projects?).

I am enjoying all these different points of view

Edited by Product9, 01 August 2013 - 08:35 AM.

[orcrist86]

Im of the opinion that they use supercooled conductors to make the firing mechanism more efficient. Additionally, any heat generated is from the actual projectile launch and capacitor charge/discharge. These are relatively low heat in relation to the other weapons. Lasers aren't just the thermal heat from the reactor, but cooling the optics, and producing a beam that can melt anywhere from 150 to 1200 pounds of ablaitive armor in seconds. Do the math on that and you'll see the energy conversion differential. (PS gauss rounds are something like 100 lbs of ferrous material accelerated to mach 8 in the lore, though in game its more likely a depleted uranium sabot with HEAT arming fired at around mach 2.8)

[Skinflowers]

Superconductors turns gauss rifles into something much more viable. Admittedly i'm dredging from dusty knowledge and havn't looked up the recent stuff on these but practicla superconductivity unlocks a lot of interesting tech. Given the fusion reactor technology in Battletech lore it is likely superconductivity exists as it's probably employed to generate the 'magnetic bottle' used to contain the fusion reaction.

A note on rifling; I don't think gauss weapons use physical rifling in the traditional sense. I remember reading, again apologies as it was a loooong time agao since I last read this stuff, that a small bias in the magnetic field used to accelerate the slug could impart a spin. Would prefer it if someone who actually works with the physics involved could weigh in on this though. I get a twitchin' in my nerd zone when talking about this stuff so i'd love a relevant boffin to weigh in.

As for gauss rifles being hot. I guess it depends. I suspect superconductors solve a lot of the potential trouble because zero (or miniscule) resistance in the electrics means disspated (waste) energy is zero (or close to). The only other thing I can think of is how hysteresis operates with regards to magnets in a superconducting environment. If I remember my physics correctly, most of the heat generated in changing magnetic fields is due to hysteresis rather than simple electrical resistance.

*shrug* paging physics pro to this thread.

Edit: here's an interesting paper discussing heat dissipation in the superconducting magnets used in the LHC.

Edited by Skinflowers, 01 August 2013 - 09:32 AM.

[orcrist86]

I think your on to something, but I doubt we are talking full magnetic suspension of the projectile, the mass is just too high. Low friction sabot would be more efficient, and much cheaper in tech terms.

[Product9]

Skinflowers, on 01 August 2013 - 09:27 AM, said:

Superconductors turns gauss rifles into something much more viable. Admittedly i'm dredging from dusty knowledge and havn't looked up the recent stuff on these but practicla superconductivity unlocks a lot of interesting tech. Given the fusion reactor technology in Battletech lore it is likely superconductivity exists as it's probably employed to generate the 'magnetic bottle' used to contain the fusion reaction.

A note on rifling; I don't think gauss weapons use physical rifling in the traditional sense. I remember reading, again apologies as it was a loooong time agao since I last read this stuff, that a small bias in the magnetic field used to accelerate the slug could impart a spin. Would prefer it if someone who actually works with the physics involved could weigh in on this though. I get a twitchin' in my nerd zone when talking about this stuff so i'd love a relevant boffin to weigh in.

As for gauss rifles being hot. I guess it depends. I suspect superconductors solve a lot of the potential trouble because zero (or miniscule) resistance in the electrics means disspated (waste) energy is zero (or close to). The only other thing I can think of is how hysteresis operates with regards to magnets in a superconducting environment. If I remember my physics correctly, most of the heat generated in changing magnetic fields is due to hysteresis rather than simple electrical resistance.

*shrug* paging physics pro to this thread.

Edit: here's an interesting paper discussing heat dissipation in the superconducting magnets used in the LHC.

I only know practical (applied) electrical engineering techniques (and only the fundamentals, since I only currently hold an AS degree in the subject), so all of that you just said sounds pretty fancy to a guy like me

The idea of 'electromagnetic' rifling is interesting, and would explain why it's called a "Gauss Rifle." In fact, it kind of makes a lot of sense when you put it that way.

orcrist86, on 01 August 2013 - 09:40 AM, said:

I think your on to something, but I doubt we are talking full magnetic suspension of the projectile, the mass is just too high. Low friction sabot would be more efficient, and much cheaper in tech terms.

Coil (or Gauss) guns do suspend the projectile, but given what Skinflowers has contributed, it's possible that the "Gauss Rifle" isn't actually a Gauss gun in the traditional sense. I would be willing to accept that the weapon "Gauss Rifle" is a new concept based on the same findings of Carl Friedrich Gauss, but not actually based on the "Gauss" guns we have today.

orcrist86, on 01 August 2013 - 09:05 AM, said:

Im of the opinion that they use supercooled conductors to make the firing mechanism more efficient. Additionally, any heat generated is from the actual projectile launch and capacitor charge/discharge. These are relatively low heat in relation to the other weapons. Lasers aren't just the thermal heat from the reactor, but cooling the optics, and producing a beam that can melt anywhere from 150 to 1200 pounds of ablaitive armor in seconds. Do the math on that and you'll see the energy conversion differential. (PS gauss rounds are something like 100 lbs of ferrous material accelerated to mach 8 in the lore, though in game its more likely a depleted uranium sabot with HEAT arming fired at around mach 2.8)

It depends on the type of laser I'd imagine. I know from early research I did when I was a kid that there are several ways to make a laser, such as gas, liquid, or even semiconductors. I assume that the one's in BT use a gas or liquid medium, paired with advanced optics (probably made of artificial diamond).

As I said in the opening, I was under the impression that the heat generated when firing a laser was from the reactor being taxed. I thought that was the lore explanation, but if anyone else has another explanation I would like to know it too.

Also, I was basing the 250 pounds per projectile on the stats that say 8 shots per ton. A ton is 2000 lbs (at least here in the 'States), and if you divide that by 8 you get 250. I'm pretty sure I can do a simple division correctly! Right...?

A Gauss round (in the traditional sense) needs no sabot, no propellant, and no warhead. We know there is no warhead because a Gauss Rifle ammo explosion doesn't cause damage. So, I think it's safe to say that each shot weighs 250 lbs. As for the muzzle velocity, that I can only guess at. Maybe I'll time it sometime.


This is a fun discussion guys. Made my morning.

[PanzerFurrry]

Projectile is propelled by a magnetic field created by the coil. That field is present all around the coil, but it is far strongest inside the tube/barrel, where flux lines are condensed. Flux lines do not end at the mouth of the tube/barrel, they reach out, but get dispersed in a radius.
That means projectile will start to accelerate inside the barrel, but will still get affected by the magnetic field outside the barrel (if only slightly). If it doesn't reach max speed inside of the barrel already, it will still accelerate outside of the barrel.
Since the damage of the projectile is kinetic based only, it is heavily influenced by its speed.

E_kin=(m*v^2)/2

Therefore we can conclude that there may be a minimum range for a Gauss projectile, until it reaches its maximum speed.