Big Daddy A Cyborg

* See also Big Daddy
* See also Alphas
* See also CityMaintenance
 "Flesh Fused To The Machinery" 
Such A Cyborg cannot be Mindless ( ie- BDs have their own 'internal world' )
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A Big Daddy is a Cyborg - Part Human, Part Machine, Joined (Grafted) :
Assume they can use the genetic tech or other medical tech that their genius created to solve several problems :
For the grafting - tissue/foreign body rejection issues for attached mechanisms - The treatment/whatever that keeps their tissue from reacting significantly ( rejecting the foreign matter ... ). Not sure to what extent the 'grafting' is done. Structural reinforcements, control mechanisms. ( Note - cosmetic appearance is not so much an issue. )
For the Diving Suit problems ( we've seen them out in the Ocean ) - Those suits Big Daddies wear are not Diving Hardsuits ( which are built to keep the water pressure out ). They are like the conventional flexible Diving Suit ( real ones are made of rubberized canvas ) for which you maintain the pressure inside ( by pumping in air from the surface ) to just over the outside water pressure ( around 19 atmospheres of pressure at only 600 feet -- This is well beyond safe/survivable prolonged diving for humans of 150-200 feet ). "The Bends" (google it) when the Daddy comes back inside and the pressure is lowered to the 1 atmosphere inside Rapture. You also get the pressure change effect simply moving between different depths. I would not put Rapture too deep (too much beyond 600 feet), or the resulting materials/technical problems will increase geometrically, eliminating any practicality.
So the Daddy needs some Tonic/Plasmid to sweep gases out of its blood rapidly for that transition ( or to mitigate the effects some other way ) to prevent the bubbles shutting down its vascular system.
Then there is the strength to move in that very heavy suit when out of water ( Suit plus tanks and tools and their power systems/weapons and those weights to keep it from floating away because of the displacement buoyancy ) that may weigh MANY hundreds of pounds ( 600 - 800 lb total weight from what the displacement volume looks like. That would require Strength Tonics ( we've seen ) to super grow muscles and bones ( ie- as per Brute Splicer ) to support/move that weight.
To power that physiology, the digestive system/vascular/etc would also have to be enlarged/made more efficient - A bulky/bigger size means squeezing into the Suit ( closely or the Suit gets bigger/heavier and the body needs to carry that, requiring even more weight, then more strength, etc ... )
Add whatever mental conditioning ( possibly reinforced via Plasmids/Tonics/other ) needed for the Big Daddy to operate/behave as it does ( still capable of recognizing problems and working solutions, handling tools to make repairs -- Which all takes coordinated actions and planning, etc ... ), and to take direction for tasks OR act independently and recognize problems to fix ( with a mental compulsion to do so ).
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The technical part of the Suit has to hold enough Oxygen for a normal work cycle ( time to get outside/walk to work location/do some work/get back to wherever to recharge - Preferably more than 30 minutes of work each cycle ) - With that larger more energy burning physiology - perhaps some Tonic/Plasmid (or other) helps with that to make the respiration more efficient. Inside it can renew its air directly for whatever inside work they do ( and babysitting Little Sisters ... ).
I haven't figured out if there is any 'power assist' for the main body actions ( combustion based power source - I'm not sure can work in that water pressure -- It has to exhaust to the outside of the suit, so batteries and electrics might be the only workable solution - possible so limited that it is really only viable for the tools/comm ). We already have a physiologically upgraded 'engine', so just mostly use that.
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A (deep diving) Hardsuit with a normal human in it has alot of problems - weighs alot and you generally need a crane to put you/take you out of the water ( an expensive facilities/technicians to maintain ).
Movement with that mass is quite tiring - even just the water resistance of the larger non-streamlined surface/volume requires significant exertion.
With ADAM to simplify ( by making the 'Divers' immune to the water depth effects ), there was a great savings of expenses and limitations.
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Big Daddies - Originally External Repairmen/Maintenance :
"A Stitch in Time Saves Nine" isn't about Sewing Cats, It is about doing preventive maintenance to keep something from eventually falling apart ( and wreaking havoc ). Big Daddies thus would best fix things BEFORE they become a problem - plugging/patching minor leaks before they grew into major ones, treating/stopping corrosion, unclogging blockages, reinforcing things to a point it is no longer a risk ( welding more metal in place, bolstering a concrete wall to strengthen it ... )
How do the individual units sense problems before the problem develops ?
* Constantly inspecting things helps catch problems before they get worse ( naming BD as mindless brutes is just stupid ).
* Sound travels better through water and BDs can hear the sounds structures make (They can FEEL Rapture in distress...)
* The sounds they make can cause materials to vibrate which can indicate defects ( cracks make dull reflections of sound )
* Sometimes they get reports/orders from a central computer that has its own sensors/monitors, gets reports form Citizens ("Dial 555 to report a Leak"), and correlates/tracks/coordinates developing situations.
The Big Daddy Central controller can keep track of inspection coverage and increase attentions to problem areas ( and predict problems based on the histories of similar situations ). "The Thinker's" Predictive capabilities were developed for such an operation. Even without supervision/external guidance Big Daddies would continue their crucial work.
It would be interesting to see more of the training facilities used to condition and train the Cities Maintenance Cyborgs ( which predated the 'Protectors' by many years ). Even more interesting would be a role-playing ramp of the Player playing a Maintenance Cyborg Big Daddy and working your way up the levels of abilities/skills and experiencing their life/work and those places you might not see otherwise.
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Maintenance Daddies THE BD Predecessor
What were their official name ? "Maintenance Cyborgs" ? 
"Cy" The Cyborg used in City Explanatory Public Service Shows/Commercials ( 'Just stay out of Cy's way so he can get on with his work KEEPING YOU SAFE' ).
* What do they eat ? Fish is a primary component and they operate several semi-automated fishing facilities to meet that need ( They also burn alot of calories moving those heavy suits ).
* Standard diver service stations are located all over Rapture to recharge their systems as needed ( compressed gas/air ).
* Do they consume EVE ? ( Better not or they would have shutdown and Rapture fallen apart long ago )
* How do they get around ? ( Can use the Metro cableways as transport - have a cable clamp like the Bathyspheres do )
* Where do they go - do they ever sleep ? They should have bases where they can store tools/materials.
* How do they know what to do ? The Thinker coordinated their activities. A simpler system of repair markers was also used. And they have been known to coordinate more complicated repair jobs.
* How many were/are there ? At least 300 were created ( exclusive of Big Daddies ). Most of them survived and continue to function ( They weren't attacked the way the Big Daddies guarding Lil Sisters were )
* Is there any hope for them ? Tenenbaum thinks maybe in time - to rehabilitate them.
* Has anyone ever proposed that everyone in Rapture be turned into these Cyborgs who seem to be the only ones truly adapted to the depths ??? Yes, and they were then hustled off to the Sanitarium for renewed treatment.
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A Big Daddy is a Cyborg - Part Human, Part Machine, joined (grafted together) :
We assume they did use the ADAM-based genetic and medical tech ( which their genius and circumstances created ) to solve several significant problems.
For the grafting - tissue/foreign body rejection issues for attached mechanisms - the treatment/whatever that keeps their tissue from reacting significantly. Not sure to what extent the 'grafting' is done. Structural reinforcements, control mechanisms. Plasmid/Tonics could manage this - preferably long lasting and 'stable'.
For the Diving Suit problems ( we've seen the Big Daddies out in the ocean ) - those are not "Hardsuits" Diving Suit that keep the pressure out, they are the conventional flexible diving suit ( real ones are rubber sandwiched between cotton twill canvas ). Other stronger 'clothish' materials might be used, but can't be too stiff, and needs to resist salt-water corrosion.
In Real Diving Suits of that type the air pumped from the surface was kept slightly higher pressure than the depth's water pressure ( so the air wasn't squeezed out of the helmet and the body gets pushed/squeezed into it ). The interior of the suit always is at a slightly higher pressure than the water's depth. SO you pressurize to the suit interior to just over the outside water pressure - it is around 19 Atmospheres of Pressure at only 600 feet -- something well beyond safe/survivable diving ( which is 150 - 200 ft max for human safety -- where Nitrogen narcolepsy, nitrogen narcosis as well as rapid decompression "the bends" were the hazards ). You have to manually keep adjusting the pressure as the depth changes ( Most divers of tnbhis type did not change depth that frequently - most being on descent and ascent to the water surface ). "The Bends" ( google it ) could happen when the Daddy comes back inside and the pressure is quickly lowered to the 1 atmosphere inside Rapture - re-entering Rapture ( via an airlock ). You also get the pressure change effect simply moving between different depths. I would not put Rapture too deep, or the materials/technical problem increase geometrically, beyond any practicality.
So the Daddy needs some Tonics/Plasmids to sweep gases out of its blood rapidly for that frequent pressure transition ( or to mitigate the effects some other way ) to prevent the bubbles shutting down its vascular system. A Big Daddy could potentially work at much greater depths.
Then there is the strength to move in that very heavy suit. The BD suits are heavy and the oversized helmets and devices on the back which real human divers didn't have ( air supply/pressure pumps was thru air tube from surface/elsewhere ... ) and add even more weight from adding tools/weapons, plus tanks and their power systems and those heavy weights ( that keep it from floating by displacement buoyancy ). It all would weigh MANY hundreds of pounds - 600-800 total weight from what the displacement (volume) looks to be. That would require Strength tonics ( we've seen 'Brute' Tonics exist ... ) to super grow muscles and bones to support/move that weight. They would require even more strength to carry all that outside of the water.
To power that physiology, their digestive/vascular/etc ... systems would also have to be enlarged/made more efficient - bulky/bigger size means squeezing into the suit ( closely or the suit gets bigger/heavier and the body needs to in turn carry that, requiring even more weight then more strength, etc ... )
Add whatever mental conditioning ( possibly reinforced via Plasmid/Tonic/other ) needed for the Big Daddy to operate/behave as it does ( still capable of recognizing problems and solutions, handling tools to make repairs that all takes coordinated actions and planning etc ) and to take direction for tasks or act independently to a limited extent.
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The technical part of the suit has to hold enough oxygen for a normal work cycle ( time to get outside/walk to work location/do some work/get back to wherever to recharge - preferably more than 30 minutes of work each cycle ). With a larger more energy burning physiology, perhaps some Tonic/Plasmid (or other) helps with that to make the respiration more efficient.
I haven't figured out if there is any 'power assist' for the main body actions. Combustion - I'm not sure can work at that pressure - 20 + atmospheres ( and it would require oxidizer be carried to function ), so batteries and electrics might be the only workable solution - possible too limited so that it would be only for the tools.
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The Big Daddy's damage resistance might be similar to the Brute's, but with the thicker covering and some projectiles bouncing off the various metal bits ( covering 1/3 the surface ? ) it can absorb more damage. Fortunately patching the suit is easy, as it doesn't have to hold more pressure than a few PSI ( pounds per square inch ).
It is possible that the Big Daddies suits are liquid filled ( And they breath an oxygenated liquid - ?? That yellow stuff in the big daddy factory in [[[BS1]]] ??? ). That kind of mechanism lowers compression/decompression effects somewhat, but having fatal bubbles form in your blood/tissues is still there with the kinds of depths involved. SO the Plasmid to take care of that would still be a needed solution - possibly to work to very great depths ( water depths OFF Raptures's underwater volcano may go to 10,000 feet deep, and more - - - that is 300+ atmospheres of pressure ).
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What routine repairs/replenishment do Big Daddies get (and from where) ? All of such details will probably be explained in the MMORPG.
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The Protector Programs Roots :
A Brainstorm : What to do with a growing number of criminally-insane and self-destructive Splicers whose ADAM addiction had damaged their brains beyond repair. Even with tonic therapies which stabilized the patients and more conventional (non-ADAM) techniques, left large numbers in various damaged/impaired states, with most of their humanity gone. They started to fill up all the mental facilities in Rapture, to the point of them being chained in the hallways. Instead of simply killing them, it was thought that some usefulness might remain for these permanent inmates ( with future hope of technical developments to 'fix'/reconstitute them ). Research showed that they were capable of being trained/conditioned to do basic work tasks for the City ( to earn their keep and be productive in the interim ). 
Many were hideously deformed and were found to need mechanical reinforcement/moderation of their bodily functions, which lead to the support suits being employed. Many tonics/Plasmids were available that would let them adapt to the suits and accommodate varying severe environments ( including pressure differentials of the ocean depths ).
Ryan gave the go-ahead as long as there was hope that individuals might eventually be restored, and instituted additional research to that end, as well as for a general cure to the 'ADAM disease' afflicting an ever larger number of his City's citizens ( which did result in at least better stabilization of existing ADAM users ).
This was the origin of the Cyborgs (machine enhanced humans) which came to inhabit the City and become a living component of Rapture, particularly as time went on and more significant repairs were needed to maintain it. A whole infrastructure was developed to facilitate/maintain their existence ( largely out of sight of the public ), including extensive repair and supply systems. Most operated largely out of sight of the Citizenry.
Many 'Cyborg' skills were actually accumulative for individuals, the same as ordinary humans, and rankings and skill achievements were systemized. A wide range of capabilities/uses were developed for them, extending their usefulness as more were deployed. ( The MMORPG has a 'BE a Big Daddy' Roleplaying mode with achievement ramps, etc ... ). Some operated with more than a little coordination by the AI system known as 'The Thinker' to organize and solve City maintenance problems. 
The Protector program was an extension of this Cyborg system ( which converted these ADAM-wrecked humans into something useful ) and and utilizing of the various degrees of their sentience ( required for more complex city maintenance tasks and activities ) and was used to solve the 'Vulnerable Little Sister's' problem. 
A better engineered solution might have been having Big Daddies serve as 'The Ferryman' and drag ADAM laden corpses to well-protected/fortified Little Sisters, but apparently nobody thought of that. (( Actually, even just regularly cleaning up corpses instead of leaving them lying about might have helped the City's ambiance a bit )).
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Big Daddy Recruitment in Persephone :
This would be something interesting to have shown in detail ( subject for Flashbacks and such in the MMORPG ) -- more of how prisoners were convinced to volunteer ( no proof they were forced for similar things -- except by Fontaine or Sofia Lamb, later ).
What all was involved in becoming a Big Daddy may have been truthfully spelled out in the recruitment -- Instead of Life Exile for Major Crimes - a chance to become useful, get rewards, or jump into Oblivion ( without really committing suicide ).
What was the actual life for Big Daddies ??? - an actual society that might be a bit alien to us normal people.
It is also possible that there were terminal medical cases which even the new ADAM technologies couldn't fix, who might volunteer, if it meant continuing to live ( again possibly to live in something more than some mindless state, or in a endless nightmare ). Yes, something like the Handymen in Columbia, except no constant pain... Jack was partially converted to a Big Daddy, so there were Degrees of that Conversion involved.
Crazy people ( by our present day legal standards ) cannot volunteer (or be volunteered). There may be a grey area about this for the criminally insane, who constantly have to be restrained -- Wouldn't getting "Daddied" similarly be a restraint ( as well as allow them to pay their own upkeep ). 
Possible major body system failures ( rather than mental issues ) requiring 'Cyborging' for the patient to stay alive ( they hinted at that for the Handymen in Infinite BS ).
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Delta's Potential for Surviving :
Not sure if the Daddy-Lil Sister link being broken would have been the cause of Delta's death (like what happens if it is reestablished - seemed to be a combination of mental conditioning and physiological).
That final explosion may have severely damaged Delta ( the hamburger making effect of powerful blast compression wave - it might have been more realistic to have his suit appearing well mangled afterward ) - and his body damage beyond the capacity of Med-Kits to repair.
At the end of BS2, our little group was out in the Ocean and they went upwards quite fast, so allegedly were not close to any Vita-Chamber ( WHY NOT one in the 'LifeBoat' ? -- we found them in every other strange place previously ...), and it would take a long time to get back near one ( We're not given any data on how long you have for that 'resurrection' system to do its work ... )
It is actually possible that as Delta 'died' and floated back down to Rapture to have had a Vita-Chamber intercept him. It is all largely unexplained how that Vita-Chamber mechanism really worked -- Flying Monkeys/Lock Box Gnomes carrying/dragging your still warm corpse into it, to be repaired. That is a bit easier to explain than real 'Teleporting' ( or worse, Delta's being reconstructing entirely from nothing but DNA and INCLUDING his diving suit/equipment - which is definitely NOT part of your DNA). Unfortunately, that game-play 'crutch' ( handling of Player 'death' ) they chose to include made it part of the plot/Canon/Lore.
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Technical Details of Big Daddy Suit Equipment :
Iconic Big Daddy
* Air Reservoir (large tank - high pressure) Can also be filled at Oxy-Fill stations for extended outside operations ( I would assume that they don't have to pay the "$5" ). Fancy finial on top of tank is a manual 'emergency' valve control.
* Recharging compressor pump + motor (below tank) to recharge air reservoir while inside Rapture, so can go back outside in water for extended periods. The spigot there might be a coffee dispenser, but more likely is a tap to run air operated tools and/or an inlet off a stationary air recharger ( found at minimum in the Big Daddy Maintenance Depots ).
* Various metal tubes/pipes connect the components and mechanisms which are rigidly fixed to the suit body.
* Top canister thingee, external intake filter + valve for external atmospheric air charging
* Bottom canister thingee - exhaust system for spent air
* Filter/pressure regulator (left side) feeds air from tank or external air intakes into helmet.
* Big circular disk ( fastened to helmet on the BD - but originally (real diver) a disk shaped weight tied to the chest that could be easily cut with the divers knife to allow the diver to quickly rise to the surface. ) Contains Battery/electrical/electronics and compensation systems ( adjusts to varying water/air pressures ), bypass valves. There are some things that look like wingnuts at its lower part ( perhaps are condensation or cleaning drains ).
* Filler valve for external compressed air/oxygen supply ( with various safety valves ). While resting or having routine maintenance done, Big Daddy is connected to a electrical and air charger, to get them ready for their next shift of work.
* Foot weights ballast ( to force upright orientation in water via higher buoyancy of the upper section ), the armored (metal encased) boots also protect the feet and wide tread acts as a stable base.
* Joint reinforcements on arms/legs - to help support/steady equipment/armaments ( particularly when out of the water when the heavy weight of the suit is not neutralized by buoyancy ).
* Control unit to regulate and backup ( including emergency supplies ) - BD is conditioned/trained to control the system which has many automatic adjustments.
* Food port on helmet - for caloric/nutritional intake for the biological components remaining in the Big Daddy. ( Standard auto cooker/grinder for basic fish/seaweed consumption ). Big Daddies have Cuisinart-like devices they feed fish into ( it is how they eat - they do eat you know ... ). Incorporates a 'flash cooker' to deal with most bothersome microorganisms. 
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Big Daddies Did Not Swim : ( You can see all the seafloor pathways we walked thru outside in BS2, including railings and stairways ). So much of their equipment is designed to keep them upright when in the water, with large weights on the boots to offset the other equipment weighing down their bodies. Traction on the seabed surface is the important issue.
If there is a 'fluid' medium in the interior -- various straps tied to restrict the ballooning of the fabric ( no point in carrying excess liquid when walking around OUT of the water when buoyancy is no longer cancelling the weight ). Originally (for real divers) the ropes in an emergency could be cut and the suit fill with a larger volume of air and the diver would rise to the surface.
Big Sisters don't seem to have anywhere as much mechanical apparatus as the Big Daddy Suits do ( looks mostly just the 'tank'and helmet ). Perhaps they don't/can't spend as much time out in the ocean -- as Big Daddies did heavy repairs and reconstruction, and also had to power/support the tools they used.
Since the City's ( Old Rapture and New one ) survival is dependent on keeping the Big Daddies going ( at least until sufficient Citizen replacements are found and enough hard suits ), there will be Quests/Missions to assist the BDs work, and to locate spare parts which the BD maintenance requires to continue functioning. Their remaining handlers/maintainers will be contacted to negotiate assistance so that the Big Daddies may continue to function.
"The suits also give the Big Daddies the ability to resist deep ocean pressure to a depth of six miles" http://bioshock.wikia.com/wiki/Big_Daddy. Well even well short of 6 miles down, if they are compressed to match water pressures, then its the Big Daddies Plasmids/Tonics/implants that do most of that.
Implies liquid (perfluorocarbons) filled units?? ( may explain them not being hardsuits as liquid doesn't compress ). That yellow fluid seen in tanks in the Big Daddy production facility ( Failsafe Armored Escorts in BS1) was probably related to this. Unfortunately also makes the suits that much heavier when they are filled with fluid ).
Abyss work (what depth capacity?) Slug harvesting, mineral gathering (robot servicing) 2000-3000 ft likely.
Harvesting Polymetallic nodules from locations at 13,000 and 20,000 feet ( manganese/nickle/copper/cobalt ) thought that would better be done by machines.
Suits accommodate a variety of repair tools/machinery used by the Maintenance Daddies to do their work.
4 Big Daddies at a table playing Poker - at least a painting of this somewhere ( if not a glance of this in a Quest - likely at a Big Daddy Depot ) ...
Big Daddy maintenance facility ( numerous locations - building basement at several main plazas ) :
* Who did the repairs when Rapture was falling apart ?? - Eventually the only properly operating repair center was at Minerva's Den (?). But then not everyone in Rapture turned insane and Factions like Ryan's would help support their continued operation.
* Repairs to suits (including the tools) - the sea-pressure suits at least remove the worst of the complexities required by Hard Suits ( which maintain Rapture-Pressure for unaltered humans ).
* Supplies (consumables/air/fuel/fluid replenishment ) - Fuel station outside in water has a nozzle&hose so must be self-serve ...
* Tuning/diagnostic adjustments, recharging/topping off fluids ...
* Medical treatment and Plasmid/Tonic maintenance
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Sinclair as a Alpha had small Red and a Blue glass vial/tanks on his back (ADAM and EVE supplies ? ) :
* That would imply that at least some Big Daddies needed to consume these elements to function ( Alphas used combat Plasmids, most others models don't seem to have - ADAM shortage probable reason ). The Blue makes sense if an Alpha is a Plasmid user ( and who says there aren't other things that consume EVE to function ).
* Tonics may just use EVE much slower. For Red, frequent boosting of ADAM might be needed, but again there may be other arrangements of ADAM usage that we didn't have as Jack/Delta ( like Big Daddies using it for self repair ... ). Or it is actually something different than ADAM (red kool-aid ? ) .
* Do all the Big Daddies need these and what happens if they run out ( possibly the Big Daddy Depot has a supply and its own mechanisms for generating them (and Lil' Sisters give some to Daddy ... ). We didn't seem to get ADAM from Big Daddies/Alphas we terminated ( do get EVE vials and Med-Kits ) despite those nice already separated vials on their backs... 
* One expects they were not glass but something unbreakable ( like the window material ). Otherwise a Splicer could do a quick attack on the vials and then sop up the spilled ADAM after the Big Daddy left the scene. You have to be pretty hard up to inject something you squeegeed off the ground into your veins.
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Bodyguard Bill :
Consider that 'rich' citizens might want their OWN 'Armed Escorts' like the heavily armored Big Daddies (and they could afford them ... something to add to the MMORPG - in Flashbacks).
NOTE - Failsafe Armed Escorts ( thus a title predating the whole Little Sisters thing ... )
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Likely there would also be Private Maintenance for building Owners ( original use for BDs - "making the criminally insane 'Useful Citizens' again" ). Probably contracted as an extra service of Rapture's Maintenance Department. Use of Resources and access to external systems outside 'the building' causes alot of problems IF it isn't all integrated together/coordinated.
Just like for your house, the interface between the external utilities and internal are well defined - with limited liabilities for the Utility Companies for what goes on (and what YOU do) PAST that demarcation/boundary.
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THIS IS A LOGICAL IDEA - to assist the story in explaining WHY the technical development could happen for the game's Big Daddies in a rather short time.
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Real Diving Suits :
Diving Suits - what we are shown in the Game in places like Atlantic Express near the airlock. 
Rubberized canvas ( rubber sandwiched between cotton twill canvas ). Other stronger 'cloth-ish' materials might be used, but cant be too stiff and need to resist salt-water corrosion ( no real strength is needed as these suits have equal pressure on both sides ). Flexible means it DOESN'T keep the water pressure out.
The air pumped from surface was kept slightly higher than the depth's water pressure ( so the air wasn't squeezed out of the helmet and the body pushed into it ). The interior of the suit always is at a slightly higher pressure from the water depth's.
That is the limitation - Generally real divers using such equipment didn't dive in those suits much below 100-150 feet with normal humans ( Nitrogen narcolepsy, nitrogen narcosis cause fatalities much below those depths ). Thus to be used any deeper, Tonics and Plasmids would be required to increase the capacity of the 'human' for the depths Rapture is at (600+ feet). Remember, when much of Rapture was built ADAM didn't yet exist so it wasn't using suits like this ( except work within 100 feet of the surface ).
The suit's damage resistance ( armor value ... ) might be similar to the Brute's, but with the thicker covering and some projectiles bouncing off the various metal bits ( covering about 1/3 the surface ? )
These suits are heavy and the over-sized helmets and devices on the back ( that real human divers didn't have, air supply/pressure pumps was thru air tube from surface/elsewhere ... ) add even more weight ( add tools/weapons ). They would require alot of strength to carry all that outside of the water -- So likely needed a combination of Brute strength Plasmids/Tonics. The pressure could be handled similarly ( 600 foot depth I estimate typical for Rapture environs is about 19 atmospheres ) and so some additional Big Daddy's Plasmid enhancements could allow them to work much deeper ( and survive constant transitions back to sea-level pressure (one atmosphere) when re-entering Rapture (via airlocks), which is when you would (in Real-Life) get the bends and die excruciatingly ).
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Big Daddy 
Daddy Suit System Elaborations Needed :
Big Daddies who all operate out in the cold ocean water needed insulation which will then "mess them up"(tm) when they come OUT of the sea water ( overheating problems ) unless yet another system is integrated. We really didn't see big blowers/heat-exchanger on the various BD suits, did we ??? They might be cranky when we saw them because inside they might not be overly comfortable ( maybe that's why they walk slow, except for short intervals of raging violence ).
The alternative is them having to burn calories like crazy with the attendant food intake, and then the matching waste disposal ( and increased Oxygen use ) when staying 'warm' is required. We likewise didn't quite see the mechanism which allowed this bulk consumption (( Did we ??? Scarfing down food/drink/ciggies instantly was a game mechanism as it wouldn't do to have to delay gameplay while the BD takes 5 minutes to eat a sandwich )).
Other BD systems ?? :
* Communications - Suit Vocal transmission. How would you like to have to scream with your head inside a metal can to be heard by your Little Sister ??? So a mechanism ( doesn't even have to be electronic ) to facilitate you doing that. Being a Maintenance Cyborg, you probably also need some communication method to Central Dispatch to get your repair assignments. Possibly there could be 'call boxes' located at many locations, but direct radio links might be more effective (or with radio signals being interfered with by water - more being signals to 'Call In').
* Power Tool power system ( and multi-attachment storage )
* Waste disposal ( It has to go somewhere and finding 'steaming piles' might be a bit too much realism for the MMORPG )
* Air Generation - BDs have to come inside to replenish their Air ( You could have Compressed air taps outside for emergencies - We saw an in-water Air Station in BS2 )
* Sleep Time For Daddy ( REM sleep is good, and we don't need that problem )
* ADAM and EVE replenishment ( seems mostly its Tonics for them, so not so much EVE ?? )
* Repairs (Big Daddy Depots at strategic spots in Rapture, with attendant personnel ?
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Seen : Big Daddies Welding, But None Carry Welders ... :
New Big Daddy flavor with welding torch that cranks up like short range flamethrower... ( gas tanks on its back - nice vulnerable spot ). Welding torch doubles as a cutting torch used to cut debris up into manageable chunks.
Rivets ?? Rivets went out when ?? Gas wending, arc welding was largely in use by WW2. Rivets for airplanes ( aluminum welding wasn't developed/widely used til later ).
Except rivets can connect dissimilar materials ( and some materials may not be weldable - ie- Ryanium ). Look at the viaducts and bolts with nuts are used in those structures ( maybe that was just to facilitate the double-paned glass -- The inner is normal glass that breaks as we can do in the game, and the outer is the unbreakable 'clear' Ryanium (that you don't seem to be able to break no matter how much you try ).
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Do Big Daddies Have a Delusional View of Their World, Similar as We Saw the Little Sisters Had ? :
Many Big Daddies (Maintenance Cyborgs) had brain damage from Splicing ADAM, and others were the product of Fontaine's experimentation. They had to do complex work for repairs, so they aren't 'mindless', and so "motivation" rather than being 'will-less' might be the case.
What exactly they see ( or different ones see ) is one of those perceived reality things that you can do with computer games ( "FarCry 3" had some very interesting 'drug' induced trips the main character went thru for example, and we saw the Little-Sister-Vision in BS2 ).
Such BD conditioning would have predated the 'Protector' Program, to be used to create and keep the City's Maintenance Cyborgs working effectively.
Yet another aspect to explore for the Creative ones amongst the MMORPG Player Creators.
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Yellow Liquid :
It is possible that the Big Daddy's suit is liquid filled ( and they breath an oxygenated liquid ?? -- That yellow stuff in the Big Daddy factory in BS1 ??? ). That kind of mechanism lowers the deep sea compression/decompression effects somewhat (liquids don't change volume under pressure). Having fatal bubbles form in your blood/tissues is still there -- with the kinds of depths involved around Rapture. SO a Plasmid/Tonic to take care of that problem would still be a solution - possibly to very great depths ( Sea-depths OFF Raptures's underwater volcano could go down to 10000 feet deep and more - - - 300 + atmospheres of pressure - requiring utter fantasy technology ).
Ever notice : IF you shoot the tanks filled with the Yellow Liquid that the leak stops flowing after about 5 seconds -- self sealing ( probably a good idea for use by something that works underwater ... )
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Thats "Mr" Big Daddy To You, Mac ... :
Given the lack of proper supervision and maintenance for all the remaining Big Daddies, some may have their conditioning failing, and their free-will ( not 'Free Willy' ... ) reasserting itself. By the time of the MMORPG ( fairly soon after Sofia Lamb's departure and Tenenbaum's return ), you will no doubt be running into these chappies who no longer are limited to the typical Big Daddy behavior. You are not really supposed to be attacking them anyway, but Rogue units may need 'apprehending'. Report any unusual Big Daddy behavior seen to the City Hall Office of Cyborg Management.
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Separate Cyborgs
Note - Big Daddies CANNOT be Conditioned to be TOO Anal-Retentive about their Work Tasks as they NEED to be able to 'Prioritize' their tasks - Daddy CANNOT be obsessive about taking that little last patch of scum off that window WHILE that potentially catastrophic Leak is growing 'over there' ... ( Note : There is a 'Big Daddy Central' where tasks are assigned to the city's maintenance workers. ) 
Having them Obsess about Little Sisters would be Worse. SO there likely was a whole OTHER set Cyborgs doing ONLY Maintenance ( The MMORPG could have a Audio Diary Arc about this subject ... )
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BD Seen Outside Repairing Leaky Window (BS2) :
Seen in BS2 as you are moving through the Adonis Spa/Resort past the Therapy section. You see a Big Daddy outside a nearby window doing repairs. ( SO its obvious some if not many continued to exist doing those chores for the City ).
It makes sense to plug holes from the outside - the inward Water Pressure would pop out 'plugs' if they were applied from the inside. Like tire repair, the 'plug' type patch is done with as a bulk material ( wedged into the hole ) and usually is applied with a glue to solidify and seal the leak.
As I've mentioned elsewhere, the unmodified 'Rivet Gun' may be an injector ( like for Epoxy glue ) which can fill small cracks in leaks (or fill in a sealer around a 'plug' on larger leaks). ( Rivets actually were mostly long gone by Rapture's time and don't really work in water anyway ).
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Not Much Was Talked About This Issue (In Polite Company ...) :
"In WWII a number of soldiers died of well, farts. When ascending in an unpressurized plane to 20,000 feet, it causes intestinal gas to expand 300% . I guess some guys couldn't fart quickly enough. They should have brought pigs along with them. Then when Porkie was ready to blow, fly over the enemy's plane and drop him. When Porkie goes Blammo you blow the enemy to hell !!"
Amusing, but think of a related problem for Big Daddies ( and Big Sisters and the Little Sisters we saw out on the Ocean ). Compression of the body in the water ( which "all of those above" apparently had to be immune to ), and THEN the subject coming INSIDE Rapture where the pressure is 1 atmosphere ( 14 lb/in^2 versus 19+ atmospheres at 600 foot ocean depth ).
* Air mixed with 'methane' - potentially instantaneous explosion at high pressure (like in a diesel engine). 
* Massive expansion of the gases when the pressure gets reduced (inside) - 19 atm to 1 atm quickly ...
* Needs some pretty tricky ADAM magic to handle these problems ... Tonics for 'bloating' ... ( They can't hold their breath like whales do -- who are subject to similar pressure changes ).
* Animals, like fish, in the water of the AE train airlocks had similar issues. The gases dissolved in their body fluids often would bubble like soda.
Imagine Suchong's Audio Diaries on THIS subject ...
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Origins :
Alot of exterior maintenance might have originally been more the 'remote control' of machines ( as probably was much of the city's construction ). The city was probably even all designed to make that possible/optimal - with only a few niches/exceptions requiring more manual labor work by divers.
The ADAM-possible Maintenance Cyborgs' may have become more cost effective, once possible ( fitting with the way Eapture's Philosophy ran ).
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I would expect there to be the Handyman equivalents made from people so physically debilitated as to be useless too from the general Rapture population. ADAM of course likely eventually created MANY of such unfortunates.
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