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Old 03-25-2023, 08:42 PM   #31
Anthony
 
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Default Re: Battletech to Gurps

Part of the problem with modeling BT armor as ablative or semi-ablative is that the way GURPS does ablative armor (and hit points in general) doesn't scale well across size modifiers. In BT, a mech that's twice the weight of another mech probably has twice the armor and twice the firepower. In GURPS, doubling the size of a vehicle is typically a 25% increase in DR and damage.

That can work with non-ablative DR - if you're using 20 point attacks on a target with DR 12 and 40 hp, you need 5 hits to kill; against DR 15 and 50 hp you need 10 -- but it doesn't work with ablative DR, unless you put a layer of non-ablative DR on top of the ablative (this is not a problem unique to mecha -- if you have a battleship with a force field and it gets attacked by a squadron of fighters, its force field disappears instantly).
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Old 03-25-2023, 08:45 PM   #32
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Default Re: Battletech to Gurps

Quote:
Originally Posted by Anthony View Post
Part of the problem with modeling BT armor as ablative or semi-ablative is that the way GURPS does ablative armor (and hit points in general) doesn't scale well across size modifiers. In BT, a mech that's twice the weight of another mech probably has twice the armor and twice the firepower.
If not more.

You are not wrong. In order to fully embrace it, you have to, as I did in my example, ignore how GURPS defines HP.

Now, let's be fair--GURPS doesn't care which of its rules you use or ignore or change.
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Old 03-25-2023, 09:15 PM   #33
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Default Re: Battletech to Gurps

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Originally Posted by Fred Brackin View Post
"Middle earth" is a setting but by itself is not a game system. By itself "BattleTech" is a game system that originally had no setting much as "Traveller" (the LBBs) pre-dates the Third Imperium. BattleTech's settings came later than the basic rules.
Okay but I am not taking that trip back in time with you and I doubt the OP is either considering the entire thread subject.

Battletech now is and for many years has been a setting, not a settingless game system.
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Old 03-26-2023, 01:03 AM   #34
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Default Re: Battletech to Gurps

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Originally Posted by Anthony View Post
Part of the problem with modeling BT armor as ablative or semi-ablative is that the way GURPS does ablative armor (and hit points in general) doesn't scale well across size modifiers. In BT, a mech that's twice the weight of another mech probably has twice the armor and twice the firepower.
This isn't actually true. Unless the larger mech is also slower or using more advanced technology, it almost certainly won't. Engine tonnage grows significantly super-linearly. It's probably the case that for most mechs doubling the tonnage without reducing the speed will leave less capacity for armor and weapons.
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In GURPS, doubling the size of a vehicle is typically a 25% increase in DR and damage.
I'm very confused by this proposition. I see where the DR statement is coming from, but the claim about damage doesn't make sense at all. You can scale firepower linearly with weight. (Of course, GURPS wants to then throw it all away with the terrible RoF system.)

The thing about the DR also doesn't to some extent, because the problem is that you are thinking about mech armor as DR to penetrate. BT armor doesn't really care how thick it is. It cares how much it is. Because the attacker gets through by ablating it all, not by punching a narrow hole.

(Yes, that's pretty bizarre. Not as bizarre as heavier cannons having less range than lighter ones though!)
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Old 03-26-2023, 12:20 PM   #35
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Default Re: Battletech to Gurps

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Originally Posted by David Johnston2 View Post
I find Spaceships insufficiently granular for something like this.
I had the same reaction; so I developed some house rules for adding granularity to Spaceships. I do this by applying fractional SMs, in increments of 0.2: if SM 4 is 10 tons, then SM 4.2 is 12 tons; SM 4.4 is 15 tons; SM 4.6 is 20 tons; and SM 4.8 is 25 tons. Likewise, if SM 5 is 30 tons, then SM 5.2 is 40 tons, SM 5.4 is 50 tons, SM 5.6 is 60 tons, and SM 5.8 is 80 tons.

More generally, every table in Spaceships uses one of three standard progressions, depending on how many SMs you need to go up in order to get to ten times the quantity. The fast progression is a two-step of either 3/10 or 1.5/5; the medium progression is always 2/5/10; and the slow progression is 1.5/2/3/5/7/10. I have more granular replacements for this that let you interpolate systems that fall between these values based on whether they're ±0.2 or ±0.4. The tonnages given above are an example of applying this principle to a fast progression; but similar interpolations exist for medium and slow progressions as well. For those who want to use them, my interpolation charts follow:

Fast Progression
This is the default progression.

+0.0: 1.0, 3.0, 10, 30, 100, 300
+0.2: 1.2, 4.0, 12, 40, 120, 400
+0.4: 1.5, 5.0, 15, 50, 150, 500
+0.6: 2.0, 6.0, 20, 60, 200, 600
+0.8: 2.5, 8.0, 25, 80, 250, 800

Sometimes the progression starts at 2/6 or 5/15 instead of 1/3. To handle these, just shift the rows:

+0.0: 2.0, 06, 20, 060, 200, 0600
+0.2: 2.5, 08, 25, 080, 250, 0800
+0.4: 3.0, 10, 30, 100, 300, 1000
+0.6: 4.0, 12, 40, 120, 400, 1200
+0.8: 5.0, 15, 50, 150, 500, 1500

+0.0: 0.5, 1.5, 05, 15, 050, 150
+0.2: 0.6, 2.0, 06, 20, 060, 200
+0.4: 0.8, 2.5, 08, 25, 080, 250
+0.6: 1.0, 3.0, 10, 30, 100, 300
+0.8: 1.2, 4.0, 12, 40, 120, 400

Medium Progression
Used by Open Space, Soft Landing System, and Stasis Web

+0.0: 1.0, 2.0, 5.0, 10, 20, 50
+0.2: 1.2, 2.5, 5.5, 12, 25, 55
+0.4: 1.4, 3.0, 6.0, 14, 30, 60
+0.6: 1.6, 3.5, 7.0, 16, 35, 70
+0.8: 1.8, 4.0, 8.0, 18, 40, 80

Slow Progression
Used by Armor, Force Screens, and Weapons.

+0.0: 1.0, 1.5, 2.0, 3.0, 5.0, 7.0
+0.2: 1.1, 1.6, 2.2, 3.2, 5.2, 7.5
+0.4: 1.2, 1.7, 2.4, 3.6, 5.5, 7.8
+0.6: 1.3, 1.8, 2.6, 4.0, 5.8, 8.0
+0.8: 1.4, 1.9, 2.8, 4.5, 6.0, 9.0

Weapon systems introduce two complications which the above doesn't address: gun calibur/launchers, and D-damage. The former doubles every +4 SM; so it should be possible to build an interpolation chart. I simply haven't bothered to, as I don't know of any rules where this would matter.

The latter is more important: when you're talking about dice of damage, interpolation gets tricky; especially when you want to keep the existing damage dice in place. It's a tough nut, and the only part of the interpolation system that I haven't resolved to my liking. For now, I'm just using “round SM to nearest whole number when deciding damage”.

———

For Battletech-style Mecha, SM 4 (or rather, 4.0 to 4.4) is your Light Mechs, ranging from 10 to 15 tons; SM 5 (4.6 to 5.4) is your Medium Mechs, ranging from 20 to 50 tons; and SM 6 (5.6 to 6.0) is your Heavy Mechs, ranging from 60 to 100 tons. It actually captures much of the feel of Battletech while staying true to GURPS material.
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Old 03-27-2023, 07:16 AM   #36
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Default Re: Battletech to Gurps

Of course, if you're going to do what the OP wants to do and play Battle-Tech at the human scale, without mechs, then you can mostly just pull out Gurps and use it.
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Old 03-27-2023, 07:25 AM   #37
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Default Re: Battletech to Gurps

That goes without saying. The difficulties in doing Battletech using GURPS all lie in handling Battletech's technology; and much of that is really addressed by going with the Safetech path from Ultra-Tech.
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Old 03-27-2023, 04:37 PM   #38
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Default Re: Battletech to Gurps

Quote:
Originally Posted by dataweaver View Post
That goes without saying. The difficulties in doing Battletech using GURPS all lie in handling Battletech's technology; and much of that is really addressed by going with the Safetech path from Ultra-Tech.
Plus figuring out what handwaves to use to explain why a heavy machine gun or autocannon has a range less than a smoothbore musket.

Although that may depend on whether you're trying to simulate a particular edition of the board game, or the computer games, or the novel fiction.

(One assumes that this is the "range to penetrate armor" except it also applies when engaging infantry...)
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Old 03-31-2023, 07:24 AM   #39
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Default Re: Battletech to Gurps

As others have said UT works well enough for the non mecha game, but you will have to go through what technologies are available, starting at safetech path notes.

As for mechas if wanted: In one of my short "near future scifi" games had quie large "combat walkers", basically smallish mechaas, so I used Supers guidelines and ran them at D-scale and it worked quite well. But for Battletech C-Scale might be better fit as the mechas are more powerful than tanks in that game.
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