Options for GURPS Mecha

GURPS Mecha is probably one of the most flexible mecha-design systems on the market. However, there's still room for improvement; following are some ideas for making GURPS Mecha even more versatile.

This is very much a work in progress; comments and criticism are strongly encouraged; send them to traveler@io.com.

Table of Contents

  1. Miscellaneous
  2. Battlesuits
  3. Transformable Mecha
  4. Combining Mecha

Miscellaneous

Hybrid Subassemblies

Following are a couple of ideas for making a mecha's subassemblies more versatile.

Arm motor options:

Motive Arm
A motive arm can double as a leg, providing an additional ST/300 kW of Motive Power. Compute ground performance for the various combinations of motive arms and legs, noting that there must always be at least two walking limbs in use, or none at all. Double the cost of the Arm Motor. This option is incompatable with the Striker Arm option.
Ornithopter Arm
Ornithopter arm motors must be placed in Wing subassemblies, and must be purchased in pairs. The pair can act as an ornithopter drivetrain with a motive power equal to their combined ST/300. Double the cost of the arm motor. This option can be combined with Motive Arm to define a wing that can be walked on and which has a manipulator on the end. This option is incompatable with the Striker Arm option.

Ornithopter leg drivetrains:

An ornithopter leg drivetrain is placed in wings, just like a regular ornithopter drivetrain; however, it allows the wings to double as legs; compute ground performance for the various combinations of wings and legs, noting that there must always be at least two walking limbs in use, or none at all. An Ornithopter leg drivetrain weighs the same as a leg drivetrain for the same TL, but costs twice as much.

Postures

The traditional mecha design has an upright posture, just like humans; however, there are a few designs out there that are built comparatively low-to-the-ground, more in line with a traditional vehicle. This rule is rated X because it changes the performance of numerous existing Mecha designs that are fine as is.

A mecha can be designed with one of two postures:

Horizontal:
This is actually something of a misnomer; the craft does not neccessarily travel along the ground on four legs and with no arms; however, it is built very low to the ground, making it fairly stable and difficult to hit; attempts to target or scan it from the front or back are at a -1 penalty. The biggest drawback to it is that, unless the pilot is likewise built hunched over, there is no species-compatability bonus available for this design. This is the default for most vehicles.
Upright:
The mecha's body towers into the air. The higher center of balance gives the craft a +0.25 MR and a -1 SR; in addition, attacks from above or below the mecha are at a further -1 penalty. Note that, in order to be species-compatable with a human, a mecha must have an upright posture. This is the default for most mecha.

There is no additional cost or weight for selecting any given posture; although human battlesuits, being species-compatable automatically, must have an Upright Posture. Transforming Mecha can (and usually do) have different Postures in each configuration; in general, the legged mode will be Upright, while the vehicle mode will be Horizontal.

Example 1
The Kuonichi 5's "humanoid" configuration has an Upright Posture, while its "van" configuration has a Horizontal Posture.
Example 2
The Stormhawk's "humanoid" configuration has an Upright Posture, while its "raptor" and "plane" configurations have Horizontal Postures.
Example 3
The Kamen Panzer's "humanoid" configuration has an Upright Posture, while its "cycle" configuration has a Horizontal Posture.

Superpowered Mecha

Some of the stunts pulled by mecha in some anime belong more in the realm of superheroes than in giant robots; there are mecha that absorb incoming attacks to recharge their power cells, mecha that are capable of creating duplicates of themselves at a moment's notice; mecha that reflect attacks back at the attacker... Instead of trying to convert each of these into components or surface features, I would suggest simply purchasing the appropriate Advantages for the mecha with appropriate gadget modifiers, which can be found in GURPS Supers.

Alternatively, you could check out J.C.Connor's Super Robots article, an expansion of an old Roleplayer article concerning the design of robots using GURPS Supers.

Battlesuits

Non-human battlesuits

The battlesuit system as currently described works fine for humanoids, but fails to account for non-human species. The following are guidelines for how to design a battlesuit for other species.

  1. Start by determining a battlesuit's proportions: Find each location that the subject has on the table below, and make a note of the Proportion Rating of each as well as the total Proportion Rating:
    Location Proportion Rating
    Body 10
    Flexibody 16
    Head 2
    Arm 1
    short -0.5
    long +0.5 per hex
    Striker 0.5
    extra reach +0.5 per hex
    Leg 6/(number of legs)
    Ornithopter Wing 6/(number of wings)
    Example 1:
    A 150-lb human has a body (10), a head (2), two arms (1 each), and two legs (3 each). The total proportion rating is 10+2+1+1+3+3=20.
    Example 2:
    A 50-lb winged snake has a snake-like body (16), a head (2), and two wings which double as two-hex strikers (higher of 3 each or 1.5 each). The total proportion rating is 16+2+3+3=24.
    Example 3:
    A 300-lb octopoid has a body (10) and 10 arm/legs - each with an extra hex of Reach (higher of 0.6 or 1.5). the total proportion rating is 10+1.5+1.5+1.5+1.5+1.5+1.5+1.5+1.5+1.5+1.5=25.
  2. For each location in the battlesuit, install an appropriate Battlesuit Control Component:
    Weight:
    1.2 × Pilot Weight × (location's proportion rating/total proportion rating).
    Volume:
    Pilot Weight × (location's proportion rating/total proportion rating) / 50.
    Cost:
    ($3000 + $20 × Pilot Weight) × (location's proportion rating/total proportion rating); halve it at TL9, and again at TL10+.
    Power:
    Negligible.
    Example 1:
    The various battlesuit control components for the human's battlesuit are:
    • Body Control Component: Weighs 1.2 × 150 × (10/20)=90 lbs; volume = 150 × (10/20)/50=1.5 cf; price = ($3000 + $20 × 150) × (10/20) = $3000.
    • Head Control Component: Weighs 1.2 × 150 × (2/20)=18 lbs; volume = 150 × (2/20)/50=0.3 cf; price = ($3000 + $20 × 150) × (2/20) = $600.
    • Arm Control Component (per arm): Weighs 1.2 × 150 × (1/20)=9 lbs; volume = 150 × (1/20)/50=0.15 cf; price = ($3000 + $20 × 150) × (1/20) = $300.
    • Leg Control Component (per leg): Weighs 1.2 × 150 × (3/20)=27 lbs; volume = 150 × (3/20)/50=0.45 cf; price = ($3000 + $20 × 150) × (3/20) = $900.
    Example 2:
    The various battlesuit control components for the winged snake's battlesuit are:
    • Body Control Component: Weighs 1.2 × 50 × (16/24)=40 lbs; volume = 50 × (16/24)/50=0.67 cf; price = ($3000 + $20 times; 150) × (16/24) = $2666.67.
    • Head Control Component: Weighs 1.2 × 50 × (2/24)=5 lbs; volume = 50 × (2/24)/50=0.08 cf; price = ($3000 + $20 × 50) × (2/24) = $333.33.
    • Wing Control Component (per wing): Weighs 1.2 × 50 × (3/24)=7.5 lbs; volume = 50 × (3/24)/50=0.125 cf; price = ($3000 + $20 × 50) × (3/24) × $500.
    Example 3:
    The various battlesuit control components for the octopoid's battlesuit are:
    • Body Control Component: Weighs 1.2 × 300 × (10/25)=144 lbs; volume = 300 × (10/25)/50=2.4 cf; price = ($3000 + $20 × 300) × (10/25) = $3600.
    • Arm/Leg Control Component (per tentacle): Weighs 1.2 × 300 × (1.5/25)=21.6 lbs; volume = 300 × (1.5/25)/50=0.36 cf; price = ($3000 + $20 × 300) × (1.5/25) = $540.

    If one or more of the pilot's head and/or limbs is placed in the battlesuit's body, the appropriate control component must also be placed in the body. Note that when the volume of the battlesuit's body exceeds 10 × the Body Control System's volume, this must be done with every location, turning the suit into a Master-Slave model.

    Also note that part of the pilot need not be inside the battlesuit; for instance, the battlesuit might leave the pilot's head exposed. When this is done, the appropriate control component is not used. Note: if any of the pilot's legs are thus exposed, all of them must be, and the pilot must rely on his own movement capabilities, counting the battlesuit's weight as encumbrance; likewise for wings.

Cheesecake Armor

Cheesecake Armor is unlikely to be used by anyone as is; Open-Frame Armor weighs 20% as much, and is superior in many ways (i.e., it protects fully against collisions, falls, rolls, or swinging melee attacks); and similar in concept. rewrite Cheesecake Armor as a compromise between Open-Frame Armor and normal armor (say, has a 4-in-6 chance to protect against thrusting attacks/beams/arrows/bullets/etc, and protects as 1/2 DR vs. Flamers, Explosions, and Wave Projectors.)

Innerwear

The battlesuit is designed to attach to a specially-modified suit of body armor. Include the weight of the pilot's armor when determining the pilot weight. The pilot must now be wearing the specially-modified body armor before he can don the battlesuit.

Lightweight Battlesuit Systems

Allow the designer to reduce the weight of a battlesuit system to a base of 1.1 × pilot weight at TL11, or reduce the weight to 1.05 × pilot weight at TL12.

Adjustable Battlesuit Systems

At TL11, lower the minimum weight that a pilot can have to one-third of the pilot weight.

Pilot-Augmented Battlesuits

Any battlesuit with total volume no greater than (pilot weight/25) cf can be designed so that rather than the motors moving everything, the motors merely match the wearer's movements; the result is a suit of armor which seems to be weightless. The advantage of this is that the pilot weight is not counted into the loaded weight of the armor, and that half the pilot's ST is added to the ST of the vehicle. The disadvantage of this is that the battlesuit's speed cannot exceed the running speed of the pilot.

Compact Lifesystems

The statistics for the Full Lifesystem given under battlesuits are identical to the ones given for cockpits; this is not a good thing, because a mecha's lifesystem needs to handle a much larger volume than the battlesuit version does. Reduce the stats to 10 lbs, 0.2 cf, and $100 for battlesuits only.

Justification: This modification was based off of MA Lloyd's Vehicles Additions for Chapter 6. At one gallon per day, the water-recycling aspect of a battlesuit's full lifesystem is only a small fraction of the entire unit: At TL7, 1.2 gallons per day translates to 0.05 gallons per hour; the equipment would weigh 0.1 lb, take up 0.002 cf, and cost $5. Add a quart of water for a further 2.5 lbs, 0.0375 cf and, $0.50 and an Environmental Control for another 5 lbs, 0.1 cf, and $50. If we assume that TL11 full water recycling and environmental control are no better than their TL7 equivelents (an arguably pessimistic assumption), these systems account for, at most, 38% of the weight, 14% of the volume, and one-ninth of the cost of a TL11 full lifesystem. What's left is the air system. Apply the air mask option to it, and you can effectively halve the full lifesystem's weight, quarter its volume, and divide its price by five without being in any danger of violating these (probably overly severe) limits.

Transformable Mecha

Speed of Transformation

It's difficult to believe that a 1-cf mecha and a 1,000,000-cf Mecha can complete a transformation in the same amount of time. Thus, I would like to propose the following rules-change: for every 500 cf of total volume (round to nearest), a mecha requires one second to transform, with a minimum transformation time of two seconds.

Transformable Subassemblies

A Transforming Mecha can be designed so that their subassemblies transform when they do - for example, one configuration's arm becomes another configuration's leg. Following is a summary of possible subassembly transformations:

arm to leg
Build as an arm. In any configuration where it acts as a leg, it adds arm ST/300 to ground motive power.
arm to wing
Build as a wing, but place an arm motor in it. The arm motor can be modified to act as an ornithopter drivetrain in configurations using wings; multiply arm motor cost by 1.5. When doing so, the arm motor adds its ST/300 to ornithopter motive power.
arm, leg, wing, or turret to pod
build as an arm, leg, wing, or turret as appropriate.
arm, leg, or wing to turret
build as an arm, leg, or wing as appropriate, and include the correct amount of turret rotation space in the body (5% for limited-traverse, 10% for full-traverse).
leg to wing
build as a wing, but place a leg drivetrain in it. The leg drivetrain can be modified to act as an ornithopter drivetrain in the appropriate configurations; multiply its cost by 1.5.
motive arms to arms or legs, ornithopter arms to arms or wings, ornithopter legs to legs or wings
build normally, then include the component restricted by configuration bug (below) to eliminate the appropriate capabilities.

Combining Subassemblies

A subassembly doesn't have to fold against the body; any other subassembly will do quite nicely. A few complications occur when you do this, however:

Restricting Components by Configuration

This bug is only available to a mecha with a transforming structure. In one or more configurations, one of the mecha's components is either rendered useless or has its performance seriously downgraded. Note that the Kamen Panzer has this bug, and is unable to use its thrusters while in cycle mode.

Transformable Crew Stations

Transformable mecha can be designed with cockpits that reconfigure when they do. This feature is most often used by battlesuits to transform into motorcycles...

Transforming Convertibles
A mecha with a transformable structure can be designed so that the cockpit is exposed in certain configurations. There is no additional cost for this feature.
Transforming Cycles
Mecha can transform into a mode where the cockpit or battlesuit system opens up to form a cycle seat (note that this is the only way that a mecha with a standard battlesuit system can transform); in the configuration with the cycle seat, subtract half of the "area" of the cockpit or battlesuit system from the body's surface area for performance calculations. Note also that this could radically change the statistics and performance of existing transforming battlesuits (the Kamen Panzer, for instance, will reduce its surface area by a further 7.5 for performance purposes).

GURPS Vehicles

GURPS Vehicles allows for the creation of a much broader range of designs than GURPS Mecha does; following are some notes for how to adapt the Transformable Mecha rules for vehicle types other than wheeled and winged.

Vehicle Subassemblies: Motive and Flight subassemblies can be folded away just like arms, legs, pods, turrets, and wings; superstructures, masts, and gasbags pose much more of a problem, and should only be introduced to a transforming mecha with extreme care. No more than one motive subassembly can be unfolded at any time (note that all of a mecha's legs are considered a single subassembly for this purpose).

Propulsion and Lift Systems: Sails and drivetrains can only be used while the appropriate subassemblies are unfolded (flexibody drivetrains can only be used when all motive subassemblies are folded). Other propulsion systems can be used in all modes unless specifically prohibited by the Component Restricted by Configuration bug.

Performance: Calculate each mode's performance as per GURPS Vehicles, subtracting half the area of all folded subassemblies when computing Aerodynamic and Hydrodynamic Drag.

Nanotach-based Transforming Systems

GURPS Robots provides a great system for designing some of the more outlandish transformable mecha out there. Optional: At TL15, it becomes possible to store large portions of the item's mass as energy, allowing the size and weight of the item to vary with the configuration in use; compute everything as for TL11-14, except that weight and volume are now based on the configuration in use.

Combining Mecha

Core/Shell Mecha

There is a lot of similarity between a Core/Shell Mecha design and a battlesuit design; the Shell Mecha is effectively a Master-Slave Battlesuit design with the Core Mecha as its pilot, and the "core system" is a master/slave battlesuit system in all but name.

Design the Shell Mecha of a Core/Shell Mecha pair exactly as you would design a master/slave battlesuit, substituting Core Mecha Loaded Weight for Pilot Weight, and setting the core system's volume equal to the Core Mecha Total Volume.

Alternately, you could design a "wrap-around" Core/Shell Mecha in the same manner as you would design a standard Battlesuit, except that it requires a volume in each of its subassemblies equal to the volume of the equivelent Core Mecha subassembly's volume.

Also note that, if the Core Mecha is a Battlesuit, the combined Core/Shell mecha should also be considered a battlesuit for such rules as the Handling Modifier listed on p.ME97; base the final Handling Modifier on the difference between the Shell Mecha's Size Modifier and the Core Battlesuit pilot's Size Modifier.

Revised rules for Super Combining Mecha

The following rules are a hybrid of the rules from the first playtest draft and the ones from the finished product; they are what I wish I had proposed during the final proof playtest, and are far superior to what finally made it into the book.

Sub-Mecha

First, design the "sub-unit" mecha. These are mecha that make up the big machine. Each sub-mecha is built as a transforming mecha, with one of its modes being set aside for each combined mecha that it is a part of; battlesuits are generally not allowed, although an exception might be made for a master-slave battlesuit.

The Combination Mecha

To design the combined mecha, start by deciding what subassemblies the combined mecha will have. Next, mate the various bodies and subassemblies ("locations") of the submecha to locations in the combined mecha: every location in each of the sub-mecha must be designated as "mated" with a single specific location in the combined mecha, and every location in the combined mecha must have at least one sub-mecha location mated with it. There are a few restrictions:

  1. A combined-mecha wheel subassembly can only have sub-mecha wheels mated to it, and the combined volume of the mated subassemblies must equal at least 10% of the combined-mecha body volume.
  2. A combined-mecha wing subassembly can only have sub-mecha wings mated to it, and the combined volume of the mated wings must equal at least 60% of the combined-mecha body volume.
  3. A combined-mecha arm or leg should have at least one sub-mecha arm or leg mated to it; failing that, it must have at least one sub-mecha body with a wheeled drivetrain mated to it.

Statistics and Performance

Statistics
To find the combined mecha's loaded weight, empty weight, loaded mass in tons, and volume, simply add up the appropriate statistics from the various sub-mecha. Calculate the Size Modifier and dimensions from the combined mecha's volume.
Motive Power
If the Combined mecha has legs, the combined mecha has a motive power equal to the combined motive power of every sub-mecha drivetrain in a location mated to a leg + (the combined ST of every arm motor in a location mated to a leg)/300. If it has wheels, the Combined Motive Power is equal to the combined motive power of every sub-mecha drivetrain in a location mated to the body + (the combined ST of every arm motor in a location mated to the body)/300.
Body ST and HT
The combined mecha's Body HP, for the purposes of calculating HT and Body ST only, is equal to the HPs of the largest location mated to the body plus half of the total of the HPs from every other location.
Body ST is equal to (combined Motive Power - combined loaded tonnage) × 80, with a minimum of half Combined Body HP and a maximum of twice Combined Body HP.
The Combined Mecha's Structural HT = (200 × Combined Body HP/Combined Loaded Weight) + 5.
Arm ST
Arm ST is the combined ST of every arm motor in a location mated to the arm + 80 × (the combined motive power of every sub-mecha drivetrain in a location mated to the arm).
Performance
Calculate the Combined Ground Performance off of the Combined Motive Power.
Calculate the Combined Aerial Performance off of the total thrust of every available thruster and the sum of every sub-mecha's drag.
Calculate the Combined Space Performance off of the total thrust of every available thruster and the combined weight of the mecha. The combined mecha is space-capable if every sub-mecha is space-capable.
Stealth, IR Cloaking, and Chameleon Systems
Use the lowest available levels of Stealth, IR Cloaking, and Chameleon Systems.
Transforming
Sub-mecha cannot transform while forming part of the combined mecha.

Variant rules for Super Combining Mecha

The following was rescued from the first-draft GURPS Mecha playtest files; in an over-the-top style game, it is superior to the rules that made it into the final book. Many thanks to David Pulver for his fine work!

Sub-Mecha

First, design the "sub-unit" mecha. These are mecha that make up the big machine. Each must be drivable mecha with at least one cockpit; battlesuits are generally not allowed, although an exception might be made for a master-slave battlesuit.

Combination Mecha

Second, design a "Combined Mecha." While building it, make sure of the following:

Third, after all of the mecha have been designed, it's time for the difficult bit. Every body or subassembly ("location") in each of the sub-mecha must be designated as "mated" with a single specific location in the combined mecha. The sub-mecha location containing the cockpit can only mate with the location on the combined mecha that contains the equivelent cockpit. Finally, every location in the combined mecha must have one or more sub-mecha locations mated to it.

Finally, the cost of each sub-mecha equals 2 × (it's figured cost + the cost of the combined mecha/the number of sub-mecha). In rare cases, a mecha might be a sub-mecha in more than one combining mecha; if this is the case, the cost of a given sub-mecha is (number of combined mecha it can participate in) × (its base price + (first combined mecha's price/number of submecha) + (second combined mecha's price/number of submecha) + ...).

Credits

Thanks to the following people for their contributions:

Barbarian <brbarian@tezcat.com>
For his insights on Motive Arms
Anthony Jackson <ajackson@iii.com>
For ideas concerning pilot-augmentation battlesuits
MA Lloyd <malloy00@io.com>
For his Vehicles Second Edition Additions
Lizard <lizard@dnai.com>
For ideas concerning cinematic transformers
Dataweaver <traveler@io.com>