Steve Jackson Games - Site Navigation
Home General Info Follow Us Search Illuminator Store Forums What's New Other Games Ogre GURPS Munchkin Our Games: Home

Go Back   Steve Jackson Games Forums > Roleplaying > GURPS

Reply
 
Thread Tools Display Modes
Old 11-13-2019, 04:13 PM   #1
Varyon
 
Join Date: Jun 2013
Default Making Gyrocs Great

I had some thoughts with the 25mm Payload Rifle discussion that are best put in another thread - namely, how to make gyrocs useful. Let's start with how things stand.

Pros:
Lightweight, low ST weapon
Exceptional damage and payload capability for their small versions
Extreme 1/2D range
Incredible velocity for micromissiles

Cons:
Heavy, expensive ammo
Poor damage for their larger versions
Cannot benefit from ETC
Small Max range
Low Acc compared to conventional weapons
Micromissiles cost more than comparable "smart" bullets

These are the RAW Pros and Cons, but there should be others. First off, their flat trajectory means distance to target doesn't matter as much as for conventional weapons. This would give results comparable to having a rangefinder, but not quite as good - I'd call it +2 to hit, although this should probably be negated if the target is moving laterally quickly enough to cause a penalty and it doesn't stack with the bonus from having a rangefinder. Next, APDS and APEP don't really make sense for gyrocs, because discarding sabots aren't going to help them.

Next up, we need to resolve some of the oddities of gyrocs. This is where we're getting solidly into houserule territory. First off is the ridiculous velocity of micromissiles (1900 yards/sec, over Mach 35). If we assume a similar mass fraction of fuel to payload as Spaceships conventional weapons (which also follow the same trend as missiles), we'd expect a 1.5cm missile to be 1/10000 tons and deal around 2.5d dDamage at 1 mile per second (1760 yards/sec). Gyrocs are about half that weight and deal around 1/4 the damage. If we assume the reduced weight is due more to having less propellant than having a smaller payload, that implies a velocity of around 440 yards/sec, on the low end of rifles. Which, honestly, doesn't seem too bad. I'd probably bump it up to 500 (on par with the IML and similar).

Next up is the cost of micromissiles when compared to smart bullets. Normal gyrocs already have most of what a micromissile needs (adjustable flight surfaces, which they need to rely on for stability) and mostly just need a guidance system, while normal bullets lack any such. It may be appropriate to reverse the relationship, with smart bullets having a base cost of 10x the cost of normal bullets and gyrocs being micromissiles by default. Personally, I'm inclined to go with 10x for smart bullets, 2x for micromissiles (so base of $10 instead of $50), and make guidance systems be a flat additional cost (there's no reason a skill 14 guidance system for a 15mm projectile wouldn't work installed in a 64mm projectile, provided the software was adjusted properly); higher cost systems should also be available for a higher price, but that's a digression.

Finally, there's the oddity of lacking a 1/2D range - apparently, the bullet just stops once it runs out of fuel, rather than continuing on a natural ballistic trajectory. HT has +P give the same boost to damage and range, and UT has ETC do the same. Applying this same concept to the 15mm Magnum pistol -> 15mm gyroc -> 15mm antimateriel rifle/Heavy Chaingun, the gyroc is x1.4 to damage compared to the pistol round, x0.4 to damage compared to the rifle round. Applying the same to range, we get 329/3640 converting from the pistol, 800/3600 converting from the rifle. The gyroc's aspect ratio is probably closer to that of a rifle bullet than that of a pistol, but probably not by a lot; I'd call it 600/3600. That means the gyroc has a velocity of 500, has a flat trajectory (+2 to hit) out to 1900, has a 1/2D of 2500 (1900+600), and a Max of 5500 (1900+3600).

With all that out of the way, let's explore some potential additional options for gyrocs. Skip down to tl;dr for statistics without discussion.

Hot Gyroc: This is a gyroc designed to burn through its fuel at a greater rate, in order to achieve a higher velocity. Looking at things simplistically (which is probably wrong, as we're supersonic, but it's the best I can do), GURPS damage scales linearly with velocity, while the power required scales with the square of velocity. A 9d pi++ gyroc would have move 750, but would burn through fuel at 2.25x the normal rate, running out in 1.69 seconds instead of 3.8 seconds, so it would only travel around 1250 yards in that time (giving it Range 1850/3850). You need a more robust engine to manage the increased output - I'd say multiply CPS by the cube of the damage boost. The best you can manage is x2 speed, for move 1000, flat trajectory out to 950, Range 1550/3550, and x8 cost.

TL 10: Better propellants allow you to run "hot" by default. A baseline TL 10 gyroc is 9d pi++, move 750, has a flat trajectory out to 2850, and has Range 3450/6450. This is extrapolated from the way missile launchers work; one could continue the progression, for x2 at TL 11 and x3 at TL 12.

Long Gyroc: This is a longer gyroc, with more fuel for a longer burn. If we assume a gyroc's payload is a 15mm sphere of lead, it would weigh 20 g out of the total of 45 g of a gyroc. Sadly, nothing TL9 in Spaceships has sufficient performance to reach Move 500 within 10 yards, but if we assume roughly 50% of the remaining weight is the rocket engine and 50% is the fuel, that means around 12.5 g of fuel (a 27.8% mass fraction) gets us to 1900 yards before it runs out. Cribbing from the simplified rocket equation calculations from Spaceships - and rounding up to 30% - this implies every 5% of mass that is fuel would give around 265 yards (prior to rocket equation adjustments). A 15mm gyroc round is assumed to be able to fit in the grip of a pistol, but how long would it be? If we assume the fuel+casing and rocket are equal in density, and about half as dense as the payload, a 15mm wide cylinder weighing 25 g would be around 22.5 mm, for a total length around 37.5 mm. I think the general rule of thumb for something comfortable to grip in the hand is around 1" of width, or about 25 mm - the gyroc length is already far enough beyond this by the above simplistic calculations I think it's safe to say the grip is around the maximum one can comfortably handle. That in mind, Long Gyrocs probably have to be loaded elsewhere than the grip; a bullpup configuration may make the most sense.
A double-length gyroc is probably around the largest such a round can get. With a 20g payload and 11.5g rocket (remember, we rounded fuel up to 30%), and 1.11g/mm for case+propellant, we're looking at maximum of 55g propellant in a 86.5g rocket, or around 65%. That's good for 3445 yards before rocket equation adjustments, or around 5500 after. This would be a 0.2 lb gyroc. The rocket is probably the most expensive part of a standard gyroc, so set price to x1.5 or so.

Other sizes: Gyrocs of other sizes are fairly easy to work out - assuming the rocket scales fine with size (which admittedly may not be the case), velocity/flat range stays the same, damage scales linearly with caliber, and weight/cost scales with the cube of caliber. I'll leave it up to others to come up with the stats for launchers.

tl;dr: Note I've rounded some values to make things a bit more presentable

Standard Gyroc: 6d pi++, range 2500/5500. +2 to hit within 2000 yards if not using rangefinder. 0.1 lb, $5

Micromissile: Must have Guidance Package (see below). Range standard for gyroc; Move 500. No range penalty (Guided/Homing). x2 CPS plus cost of Guidance Package (see below).

Smart Bullet: Must have Guidance Package; unavailable for gyroc. Range standard for weapon; Move 300 for pistols, 600 for rifles (x1.5 for ETC). No range penalty (Guided/Homing). x10 CPS, plus cost of Guidance Package. Skill (6+TL).

Guidance Package: Required for Micromissiles/Smart Bullets. May be Guided, Viper, Multi-Spectral, or Multiscanner. See UT146 for the last three.
Guided: Requires user to maintain "lock" on target until impact, but uses user's skill. $50.
Viper (TL9): $150
Multi-spectral (TL10): $500
Multiscanner (TL^): $500

TL 10: At TL 10, the standard gyroc improves to 9d pi++, velocity 750, flat range 2850, range 3450/6450. Optionally, boost to 12d pi++, 1000, 3800, 4400/7400 at TL 11, 18d pi++, 1500, 5700, 6300/9300 at TL 12. No change in WPS/CPS.

Hot Gyroc: x1.5 to damage is x1.5 to velocity, x0.7 to flat range. x3 CPS.
x2 to damage is x2 to velocity, x0.5 to flat range. x8 CPS.

Flight Gyroc: Not generally available for gyroc pistols (requires loading individually, or with a bullpup configuration). Hot and Flight are often combined and offset each other. (Changed the name because Hot Long Gyroc sounded... yeah).
x1.5 flat range is x1.2 WPS and x1.1 CPS.
x2 to flat range is x1.5 WPS and x1.2 CPS.
x3 to flat range is x2 WPS and x1.5 CPS.

Reactionless (TL^): Replaces fuel with an energy bank and rocket with reactionless thruster. Standard is x5 to flat range and x2 CPS; can be combined with Hot and Flight.

Other sizes: Note, TL is just a suggestion (it assumes gyrocs are one size category less finicky than the Viper guidance package); additionally, damage is listed as for TL 9, regardless of actual TL. Largest caliber is 40mm as 64mm is an IML.
Code:
TL	Cal	Damage		WPS(lb)	CPS($)
9	40mm	15d pi++	2	100
9	25mm	10d pi++	0.5	25
9	18.5mm	7d pi++		0.2	10
9	15mm	6d pi++		0.1	$5
9	10mm	4d pi+		0.03	1.5
10	7mm	3d pi		0.01	0.5
11	5mm	2d pi		0.003	0.15
12	3mm	1d+2 pi-	0.001	0.05

So... thoughts? Does this look like it would make gyrocs a bit more usable?
__________________
GURPS Overhaul
Varyon is offline   Reply With Quote
Old 11-13-2019, 04:46 PM   #2
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Making Gyrocs Great

1900 yards per second isn't that high, with a 50% fuel fraction it requires a propellant with an iSP of about 250. It's pretty optimistic for a micro missile but not what you're making it.
__________________
My GURPS site and Blog.

Last edited by Anthony; 11-13-2019 at 04:49 PM.
Anthony is offline   Reply With Quote
Old 11-13-2019, 05:00 PM   #3
Varyon
 
Join Date: Jun 2013
Default Re: Making Gyrocs Great

Quote:
Originally Posted by Varyon View Post
Smart Bullet: Must have Guidance Package; unavailable for gyroc. Range standard for weapon; Move 300 for pistols, 600 for rifles (x1.5 for ETC). No range penalty (Guided/Homing). x10 CPS, plus cost of Guidance Package. Skill (6+TL).

Guidance Package: Required for Micromissiles/Smart Bullets. May be Guided, Viper, Multi-Spectral, or Multiscanner. See UT146 for the last three.
Guided: Requires user to maintain "lock" on target until impact, but uses user's skill. $50.
Viper (TL9): $150
Multi-spectral (TL10): $500
Multiscanner (TL^): $500
Not certain how I missed these bits. Disregard the Skill mention for Smart Bullet. For Guidance Package, add the following lines.
Skill: For all but Guided, the projectile has skill (4+TL). Optionally, higher quality guidance packages may be available, at +1 to skill for x2 cost, +2 to skill for x4 cost, or +3 to skill for x8 cost (this is based on the costs for higher-TL gear).

Quote:
Originally Posted by Anthony View Post
1900 yards per second isn't that high, with a 50% fuel fraction it requires a propellant with an iSP of about 250. It's pretty optimistic for a micro missile but not what you're making it.
I'd expect a gyroc to have comparable velocity to a firearm. Note also that the IML and MLAWS in UT move at 500 yards per second at TL 9 as well. There's also the issue that, unless their payload is tiny compared to that of a (theoretical) Spaceships missile of the same caliber, gyroc damage is simply too low for such a high velocity. Dropping velocity to 500 seems like it resolves things rather nicely.

I certainly do appreciate the feedback, however. Anything else jump out at you?
__________________
GURPS Overhaul
Varyon is offline   Reply With Quote
Old 11-13-2019, 05:26 PM   #4
Rockwolf66
 
Join Date: Jul 2013
Location: Southern oregon
Default Re: Making Gyrocs Great

Quote:
Originally Posted by Anthony View Post
1900 yards per second isn't that high, with a 50% fuel fraction it requires a propellant with an iSP of about 250. It's pretty optimistic for a micro missile but not what you're making it.
5,700 feet per second is very high velocity for a projectile weapon. It is faster than the highest muzzle velocity of current firearms. That would be the .220 Swift with a maximum muzzle velocity of 4,665 ft/s. That's over Mach 4 which is faster than a SR71 can fly.

There are currently about a half dozen known missiles that can travel over Mach 5. With improved technology I could see a Gyroc hitting those sorts of speeds.
Rockwolf66 is offline   Reply With Quote
Old 11-13-2019, 05:30 PM   #5
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Making Gyrocs Great

Quote:
Originally Posted by Varyon View Post
I'd expect a gyroc to have comparable velocity to a firearm.
Rockets can potentially go quite a bit faster than bullets, though there are several issues with UT gyrocs, including:
  • High efficiency rockets generally don't have huge thrust to weight ratios. At a reasonable chamber pressure it would take hundreds of yards to reach 1900 yards per second.
  • The kinetic damage from a gyroc is inconsistent with a 15mm projectile moving at 1900 yards per second.
__________________
My GURPS site and Blog.
Anthony is offline   Reply With Quote
Old 11-13-2019, 06:00 PM   #6
AlexanderHowl
 
Join Date: Feb 2016
Default Re: Making Gyrocs Great

Gyrocs are problematic for a number of reasons. Now, I think that giving them a 1/2 D of 950 and a Max of 3800 would be better and more realistic. It would also result in a slam damage of around 9d+2 pi++ (assuming the dry weight is an ounce). As for the cost, I would just modify the cost like they were normal ammunition of guidance systems ($20 for a viper).
AlexanderHowl is offline   Reply With Quote
Old 11-13-2019, 06:16 PM   #7
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Making Gyrocs Great

It's worth noting that 'speed = 1/2d' only applies to weapons that use the guided and homing weapons rule, and gyrocs don't. It's perfectly consistent with their stats for them to have a speed of 500 and they just retain speed and accuracy until their rocket burns out.
__________________
My GURPS site and Blog.
Anthony is offline   Reply With Quote
Old 11-13-2019, 06:41 PM   #8
Varyon
 
Join Date: Jun 2013
Default Re: Making Gyrocs Great

Quote:
Originally Posted by Anthony View Post
Rockets can potentially go quite a bit faster than bullets, though there are several issues with UT gyrocs, including:
  • High efficiency rockets generally don't have huge thrust to weight ratios. At a reasonable chamber pressure it would take hundreds of yards to reach 1900 yards per second.
  • The kinetic damage from a gyroc is inconsistent with a 15mm projectile moving at 1900 yards per second.
500 yards per second deals well with the second note, and at least helps with the first. What sort of acceleration do you feel is more likely for a gyroc? I currently have it going from 0 to 500 in 10 yards (because UT has it reach full velocity after 10 yards), which requires an incredible 1250G acceleration, if my calculations aren't off. With 25% of its mass in chemical rockets (15G), Spaceships suggests it taking around 3 seconds and 800 yards to reach 500 yards/second. That's far too slow (and far) to be useful in small arms combat. Even with its entire mass somehow in chemical rockets (with fuel magically transported to it), you're looking at around 0.75 seconds and 200 yards.

Quote:
Originally Posted by AlexanderHowl View Post
As for the cost, I would just modify the cost like they were normal ammunition of guidance systems ($20 for a viper).
I favor my approach, actually, because $20 for a viper micromissile seems too cheap to me. Honestly, I don't think the guidance system costs for micromissiles are far too expensive (although the ones for larger missiles probably are), but I do think smart bullets are far too cheap. It also seems like the bulk of the cost should be in the guidance system, not the surfaces allowing the projectile to steer, which is why I priced things that way.
__________________
GURPS Overhaul
Varyon is offline   Reply With Quote
Old 11-13-2019, 07:37 PM   #9
Fred Brackin
 
Join Date: Aug 2007
Default Re: Making Gyrocs Great

Quote:
Originally Posted by Varyon View Post
5What sort of acceleration do you feel is more likely for a gyroc? I currently have it going from 0 to 500 in 10 yards (because UT has it reach full velocity after 10 yards), which requires an incredible 1250G acceleration, if my calculations aren't off. y.
As a data point the 100mm missile in UT accelerates at 2000 yards per second at TL9 and 50% faster at TL 10. So it could meet your gyroc target but it would take a fuull second and 1000 yards to do so. Of course it accelerates like that for 5 seconds and not just 1.

I once tried to reverse engineer the 100mm missile and I got a very close match with the formulas for missiles from Ve2, specifically the ones for space missiles using 80% of the mass for the motor and 20% for payload.

If you have access to Ve2 you could try and reverse enineer gyrocs from there. I sort of remember trying to do that many years ago (probably with 3e gyrocs) and having so-so results.

Ve2 wouldn't let you build a rocket motor with a duration less than half a second and that might be a problem for your goals but even that would let you build 100mm missiles that accelerated 10x faster.
__________________
Fred Brackin
Fred Brackin is offline   Reply With Quote
Old 11-13-2019, 07:48 PM   #10
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Making Gyrocs Great

Rockets actually have a max chamber pressure, not a max acceleration, so small rockets can go faster. Gyroc ammo is 0.1 lb per shot, unclear how much of that is projectile, but if it's all projectile that's a total energy of 0.5 x 45g x 450m/s^2 = 4,556J. Accelerating to full speed in 10 yards is about 500J/m or a force of 500N, 15mm is a cross-section of 174mm^2, so that's 2.9 MPa or 420 psi, which is a believable figure.
__________________
My GURPS site and Blog.
Anthony is offline   Reply With Quote
Reply

Tags
gyroc, ultra-tech

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Fnords are Off
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 03:08 AM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.