1. HOW BIG DOES IT NEED TO BE?
GURPS: Robots notes on p. 39 that the average human arm is 0.05
to 0.2cf in volume. It notes that legs must be 30% of the body
volume. But how do you know what volume you need for your character?
You could use the volume calculations as for battlesuits but what
about a cyberhand?
Note that this contradicts some parts of Robots, specifically the values given for head volumes (0.1 to 0.4). You would have to be HUGE to have a .4cf head. As in like 400 pounds. I think the head values are a bit overstated (he seemed to use weight/400 as a guide). Feel free to use those values in Robots but note they don't match what anthropometric data I have seen.
To get the characters limb volumes multiply the characters weight by the appropriate Volume Multiplier (see Chart 1).
For example, Buz got his arm lopped off in a vicious Nerfball accident. He weighs 160 pounds so his original arm had a volume of (160 x0.0007=) .112. Or rounded to just .11 cf.
2. HOW MUCH DOES IT WEIGH?
To determine the original limbs weight use the following multipliers.
All multipliers are listed as percentage of total body weight
and the sublocations are percentages of that.
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| Full Arm |
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| ->Upper Arm |
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| ->Lower Arm |
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| ->Hand |
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| Full Leg |
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| ->Upper Leg |
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| ->Lower Leg |
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| ->Foot |
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| Head |
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| Torso |
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For example, Buz from the previous example would have had an original arm weigh (160 x0.051=) 8.16 pounds. Rounded to 8.2 pounds.
3. HOW STRONG IS THE NEW LIMB?
Arm motors are bought pretty much as for robot arms, but leg motors
are done a bit differently. To find the weight of an arm motor
for partial limbs multiply the weight of the motor by the Volume
Multiplier (not the Weight Multiplier in this case) of the location.
For example, an TL8 arm motor for an upper arm weighs (.2 x .0004=) .00008 x ST
The leg motors for the character should be equal to the original ST value. It can be higher, but the increased strength will only affect kicking damage, and cannot exceed twice the original value without causing physical damage during the kick!
(ST/80)+ Weight in tons = Desired motive output in kW.
4. HOW DEXTROUS IS THE LIMB?
GURPS assumes that the limb is as good as the unit controlling
it can make it, with a few restrictions (typically involving design
options).
To get a somewhat more realistic accounting of cyberlimbs add
the following option:
| Modifier |
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| Dexterity |
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For example, an limb with a DX of 15 will have a weight multiple of x1.5 and a cost multiple of x1.5.
Typically the limb will equal the users own DX. If the limbs DX is lower then use the lower rating for tasks using that arm. A higher DX will typically only apply for tasks involving precise control and precision for standard tasks. Options such as Bad Grip apply theit penalties to the DX of the limb they are attached to.
If you wish to apply this design option to conventional robot arm motors then the multipliers are based on the base DX of the robot in question. Reduce/Increase Cost by 10% for each level greater or less then the base value.
For example, Synthia is a robot with a base DX of 12. If Synthia had a DX 11 arm then the price for the arm would be reduced by 10%.
5. INTERFACE GEAR
In order to interface with the human body the limb must have various
equipment that allows it to mimic the behaviour of the original
limb.
This interface is treated as are the arm motors for purposes of determining their size when used with partial cyberlimbs.
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| TL | Weight | Cost |
| 7 | .01 | $1,000 |
| 8 | .075 | $600 |
| 9 | .05 | $300 |
| 10+ | .025 | $100 |
6. STRUCTURE AND SURFACE AREA
The limb needs a structural framework, and this is determined
as noted on pp. 39-41, RO.
7. QUICK AND DIRTY ECU CALCULATIONS (Shadowrun)
If you only want to get more realistic ECU capacity for SR cyberlimbs
without the fuzz and bother of making the limb from scratch then
figure the volume of the limb and multiply by 100. That will give
you the ECU for the limb as if it was a obvious limb. Divide by
2, rounded down, for concealed limbs.
For example, an 1100 pound troll has an arm volume of (1100 x.0007=) .77. Multiplied by 100 that gives the troll 77 ECU! Remember that according to M&M he still has to buy up his Strength to match his natural Rating if he does not want to suffer penalties.
An 98 pound dwarf on the other hand will only have (98 x.0007=).07cf arms. Thus a dwarf only has 7 spaces in a cyberarm. 3 if its synthetic.
CONVERTING ECU TO CUBIC FEET
Multiply ECU cost by .002
ROUGH ECU TO WEIGHT
Multiply ECU by 50. For example, an stock cyberdeck (4 ECU) comes
to .008 cf and .4 pounds (.18kg)
8. EXAMPLE (Shadowrun Oriented)
Bob the ork is about 280 pounds and has a Strength
of 8 and a Quickness of 2. He loses his arm during an winner-take-all
super-soaker match and now hes out shopping for a replacement.
His original arm was about (280 x.0007) .196cf and (280 x.051) 14.28 pounds. He wants a limb that matches his original values.
Arm Motor: He will need a ST 15/DX 9 arm motor to match his Shadowrun Strength. This is a full arm and he won't be using a modular design so the motor will weigh (.2 x 15) 3 pounds and costs $6000 (I'm thinking of using GURPS $ as DP). However, its a bit cheaper because it only needs to be DX 9. The multiple is x.9 for Weight and x.9 for cost. Thus the final weight and cost for the arm motors is actually (15 x .2 x .9) 2.7 pounds and (15 x 400 x .9) $5400. The arm motors consume (2.7/50) .054cf. The arm requires (15/200) .075KW of power to operate.
Interface Gear: He then needs to add the necessary components so he can actually make use of the limb. This is based on DX so it will weigh (9 x.075) .675 pounds and cost (9 x600) $5400. The interface gear takes up (.675/50) .0135cf.
The arm motor and interface gear take up .0675cf. Leaving .1285cf. But we still need to add a structure for the limb and possibly a covering.
Surface Area: Consulting p. 40, RO we see that at .196cf the limb has a surface area of about 2.
Structure: Consulting structure table we see that using standard materials the arm structure will consume 8 pounds and cost $200. The structure does not consume space (its already factored in).Thus the arm comes to 11.375 pounds and $11,000. Before surface features of course...
Hit Points: The arm has a standard structure so it has (2 x3) 6 hit points. In Shadowrun this value should be considered the arms Body for purposes of resisting damage.
Surface Features: We decide the limb does not really need armor (although Bob does look at the nonrigid coverings closely). However, we do decide to Seal the limb (2 x 20) $40. We want to get some biomorphic coverings so it does not look like an mechanical arm. We give it a Realistic Flesh coating. This costs $800 and weighs 1 pound. The final limb weighs 12.375 pounds and has .1285cf remaining for other options.
Power: Ahh, but remember that power requirement? Without some batteries its an 12 pound paper weight hanging from your shoulder.
Looking at the options we decide that the limb will be powered by two rechargable C cells. The cells weigh 2 pounds and consume .02cf. Costing $200. Each stores 1,800KWS of power, giving the limb an active span of over 13 hours. Thus the limbs final weight is 14.375 pounds and has .1085cf of space remaining. The weight is close enough to the original to have no noticable effect.
Total cost of the arm is $12,040. using that as a DP total
we can determine that x5 seems to give close results to established
prices. The final SR price for the arm is 60,200 nuyen.