52 replies to this topic

[Kartr]

trycksh0t, on 10 February 2012 - 11:32 PM, said:

Unfortunately, there is quite a bit of canon and 'Fluff' available that supports AC's being of several different calibers, specifically ranging from 30mm to 203mm, and are grouped by damage, not calibre. http://www.sarna.net/wiki/Autocannon

Also - http://www.sarna.net...i/Autocannon/20 .

There are 3 seperate AC/20's listed on these pages, each a different calibre (150mm, 185mm, 203mm).

Ok didn't know that, most of my BT knowledge comes from reading through the Master Rules Revised and the only fluff about AC's in there that I remember is that they range from 30mm to 120mm and fire in bursts. Now I know and it totally busts my common ammo theory.

trycksh0t, on 10 February 2012 - 11:32 PM, said:

Now, with that out of the way, I'm not sure how recoil would really play a role in combat. We'll keep with AC/20's for this, specifically the Crusher Super Heavy150mm sited from Sarna. The Crusher is a 150mm weapon that weighs 14 tons (as do all AC/20s). By comparison, the heaviest weapon I could find in a similar calibre is the U.S. M198 155mm Howitzer, weighing 15,772 lbs (7.886 tons). Since the AC's in the BT universe seem universally designed to put all shells on target, my assumption is all that the majority of that extra weight is used to reduce recoil. Also, modern 150mm shells weigh about 50kg, and I doubt that 150mm shells in the BT universe weigh much more than that. A 50kg shell, even a burst of 50kg shells, would have little noticeable effect on a multi-ton 'Mech designed to implement said weapon system.

Recoil would affect the grouping of the rounds, the larger the recoil the faster your group disperses which would decrease your maximum effective range. This would explain why the smaller the gun the further range it has. Smaller callibers fired the same number of rounds in a burst would have a larger effective range than a larger caliber firing the same number of rounds because there would be less recoil. Even if the larger guns fired smaller bursts they would most likely have a larger group since the larger caliber would have more recoil per shot.

@Chuckie: Don't forget the M1A2 could aim at and hit the cockpit on the Summoner from 4km away. Summoner can't return fire until roughly 600m. Wonder how many 120mm rounds the M1A2 could put on the cockpit as the Summoner closes that 3.4km? If the M1A2 can land 5 rounds on that cockpit as the Summoner closes the 3.4km distance, bye-bye Clanner.

[Pht]

Zerik, on 09 February 2012 - 08:07 AM, said:

Makes sense. Bigger cannon = rocks you, and your enemy even harder than you.

Actually, you've got it exactly backwards. If 'mechs took knock from incoming enemy fire, the 'mechs that fired those shots would have to absorb more recoil energy than their targets would absorb in knock. The shots lose KE as they go down range.

Nasty McBadman, on 09 February 2012 - 09:02 AM, said:

The mass of the mech firing the weapon should also be used in determining recoil effects for ballistic weapons.

That's not the only factor - 'mechs also can compensate for recoil (and knock) via not just their gyroscopes, but also by altering their stance, tension in the various myomer muscles, limb and torso placement, and "leaning into" incoming fire.

'Mechs in the BTU simply do not suffer from recoil or knock at a level that warrants them being pushed around or having their aim thrown off.

Yes, 'mechs do fall over - when they lose a lot of weight nearly instantly from weapons fire. They don't get "knocked over" by this weapons fire - they lose their balance due to weight loss in armor and structure.

I don't see why people want to have recoil and knock factor into this game.

[Azalie]

Pht, on 11 February 2012 - 01:51 PM, said:

I don't see why people want to have recoil and knock factor into this game.

Because it is cannon.

[Pht]

Azalie, on 11 February 2012 - 04:21 PM, said:

Because it is cannon.

Source?

Because everything I've seen in the lore says otherwise.

[FACEman Peck]

Common sense dictates that higher caliber requires higher charger to send it down range, thus higher kick... But that's just me.

[NotNewHere]

1. PPC's have less recoil than a pea shooter because they fire a trail of ionized atoms that have a total weight of the less than a gram. So you do have recoil but its the kind that wouldn't bother an ant.

2. I wonder if you fired a HGauss in mid jump could it topple your mech over backwards?

[EDMW CSN]

Kartr, on 11 February 2012 - 12:06 PM, said:

@Chuckie: Don't forget the M1A2 could aim at and hit the cockpit on the Summoner from 4km away. Summoner can't return fire until roughly 600m. Wonder how many 120mm rounds the M1A2 could put on the cockpit as the Summoner closes that 3.4km? If the M1A2 can land 5 rounds on that cockpit as the Summoner closes the 3.4km distance, bye-bye Clanner.

If you played Battlemechs with Aerotech fighters in atmosphere, ya know that an AC-20 can hit over 4km. Or 4.5km (9 hex) to be exact. A LB-10x has 18 hex range or 9km range. Hence coupled with cluster shots, that is why they are the preferred anti-air artillery against VTOLS and Aerospace Fighters.


Ranges have being truncated to make sense for mech melee combat. Because 500m rocket punches and an Urban mech leaping 1km in a single bound is silly. A Summoner would be able to "fly" 2.5km during the course of 10 seconds !! In Mechwarrior games, range was once against truncated to make combat more "intense". Same for novels. Unless you prefer the whole battle which boils down to basically people sniping each other, which coincidentally explains why mech accuracy blows. Because ranges are too far out !

So against a "real" Summoner (which has 2 weapons that hit further and harder than the LB-10x btw), a modern day M1A1 company best recourse is to call for artillery and airstrikes.


P.S. I know it has no bearing to the current discussion but just throwing this out.
But yes if there is an autocannon, I want to notice the recoil when i am firing a huge arse cannon.

Edited by [EDMW]CSN, 11 February 2012 - 06:42 PM.

[Strum Wealh]

Nightwish, on 11 February 2012 - 04:48 PM, said:

1. PPC's have less recoil than a pea shooter because they fire a trail of ionized atoms that have a total weight of the less than a gram. So you do have recoil but its the kind that wouldn't bother an ant.

Recoil is a function of momentum and energy conservation.
(momentum, p) = (mass, m) * (velocity, v)
(Kinetic Energy, E) = 0.5 * (mass, m) * (velocity, v)^2 = (p^2)/(2*m)

For a PPC, let's say m = 0.5 grams (0.0005 or 5x10^(-4) kg) and v = 0.01c (1% of the speed of light, or 3x10^6 m/s)
p = (5x10^(-4)) * (3x10^6) = 1500 N-s, or 1.5x10^3 N-s
E = 0.5 * (5x10^(-4)) * (3x10^6)^2 = 2.25x10^9 joules, or 2.25 gigajoules

For comparison:
-- The recoil force of the GAU-8/A (pretty much the real-life equivalent of a RAC-2) is 10,000 pounds-force (45,000 N), which is slightly more than the output of one of the A-10's two TF34 engines (9,065 lbf / 40.3 kN each).
-- One megajoule (1x10^6 joules) is approximately the kinetic energy of a 1-ton (1000 kg, or 2204 lbs) vehicle with a velocity of ~160 kph (44.44 m/s, or 100 mph).

2.25 gigajoules = 2250 megajoules

Based on that, it would seem that a PPC would have some kick to it (more than a non-Them! ant could handle ) - but still enough that most 'Mechs could handle it.
(Also, a fair bit of that energy is being delivered to the target - remember that a single salvo from a single PPC is able to destroy slightly more than half-a-ton of BattleMech-grade armor...)

Nightwish, on 11 February 2012 - 04:48 PM, said:

2. I wonder if you fired a HGauss in mid jump could it topple your mech over backwards?

There are 4 HGR slugs per ton (1000 kg), indicating a mass of ~250 kg (~551 lbs) per slug.
We know (from various descriptions in several of the novels) that standard Gauss Rifles fire their slugs (0.5x the mass of a HGR slug) at hypersonic velocities - at least Mach 5.0 (1,710 m/s), thought to be closer to Mach 10 (~3,420 m/s).

(We do have a statement from the TRO entry for the Yellow Jacket VTOL gunship of Gauss Rifles having muzzle velocities as low as Mach 2.2 (~749 m/s) - either a continuity error or an indication that the power of the weapon can be dialed down to allow the VTOL to be able to handle the recoil of its sole weapon.)

So, let's say that out HGR has a muzzle velocity similar to that of a standard Gauss Rifle (v = Mach 10, or 3,420 m/s).
p = (551 kg) * (3,420 m/s) = 1.88x10^6 N-s
E = 0.5 * (551 kg) * (3,420 m/s)^2 = 3.22x10^9 joules, or 3.22 gigajoules

Note that the momentum value for the HGR (1.88x10^6 N-s) is several orders of magnitude greater than that for a PPC (1.5x10^3 N-s), and is described as "so great that the rifle cannot be mounted in a vehicle's turret or 'Mech's arms, as firing the rifle would essentially rip it off".

As such, I would imagine that attempting to fire a HGR in mid-jump would be a rather bad idea...

[Okie135]

F = ma

Kinetic Energy = mass x velocity².

Force (recoil) = mass x acceleration.

Sorry, been doing physics II homework today. And this is way more interesting than flux and Gauss's Law.

I think Strum Wealh summed it up nicely.

Only thing to add is that damage causes stability problems for a target even without imparting kinetic energy. ie. A group of large lasers burn off a section of armor from a mech. The beam destroys the armor it hits and the connections for a plate of armor. The armor section that just had it's connections burned away falls off. That mech is now off-balance and will be jostled around a bit even though the photons aren't imparting as much E_k ​as an auto-cannon.

In Battletech this was handled by a pilot check for every 20 points of damage taken that round.


Edit: Fun fact: The first A-10 to crash did so in a test flight. The GAU-8 was fired and the smoke from the sustained burst choked the engines which died from oxygen starvation. The design of the A-10 was modified shortly there after.

Edited by Clark, 11 February 2012 - 07:17 PM.

[Kartr]

[EDMW]CSN, on 11 February 2012 - 06:40 PM, said:

If you played Battlemechs with Aerotech fighters in atmosphere, ya know that an AC-20 can hit over 4km. Or 4.5km (9 hex) to be exact. A LB-10x has 18 hex range or 9km range. Hence coupled with cluster shots, that is why they are the preferred anti-air artillery against VTOLS and Aerospace Fighters.


Ranges have being truncated to make sense for mech melee combat. Because 500m rocket punches and an Urban mech leaping 1km in a single bound is silly. A Summoner would be able to "fly" 2.5km during the course of 10 seconds !! In Mechwarrior games, range was once against truncated to make combat more "intense". Same for novels. Unless you prefer the whole battle which boils down to basically people sniping each other, which coincidentally explains why mech accuracy blows. Because ranges are too far out !

So against a "real" Summoner (which has 2 weapons that hit further and harder than the LB-10x btw), a modern day M1A1 company best recourse is to call for artillery and airstrikes.


P.S. I know it has no bearing to the current discussion but just throwing this out.
But yes if there is an autocannon, I want to notice the recoil when i am firing a huge arse cannon.

Ah see I didn't know that, my BT experience started with MW3 and some of the novels and only over this last Christmas did I actually get to read the Master Rules and try my hand at a couple of games. So up until now everything I've experienced in the BTech universe pointed to really short ranges.

[Azalie]

Pht, on 11 February 2012 - 04:30 PM, said:

Source?

Because everything I've seen in the lore says otherwise.

How about the entire collection of battletech books? Examples of recoil are few and far between and it would take me days to find a decent example but knockback is present and described in just about every fight in every battletech book I have read. It is particularly evident in fights where a medium or light mech goes up against a heavy or assault. In the thread about aim distribution and knockback also in general discussion I even quoted a passage about the forces involved when energy weapons impact a 'mech.

[MaddMaxx]

Thoughts? Will there be a Test?

If an object arrive to target with mass and stored kinetic energy, those energies have to be absorbed and or released. How the Dev decide to visually indicate that release will determine how a Mech, or Mech of differing masses react. Beyond that, knowing the real world physics is cool but has to be mitigated with the understanding they are designing a game.

A very cool game that needs to have the best possible physics possible, but game physics...

Edited by MaddMaxx, 12 February 2012 - 10:36 AM.

[Yeach]

So is this the trade-off for using high damage projectile weapons.
Higher recoil PLUS higher knock to target?