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So, there’s a couple of posts around mecha body language around that are very focused on bauplan, build and social status as the reasons for why some mecha act and comport themselves the way they do, and… I always find those posts overly reductive and kind of bio-essentialist and think they lack consideration for what kind of social spaces – both the conditions and the actual physical space – and social conditions mecha are used to.
Heavier construction and thicker armour, like the type you see with warframes like Optimus or Ultra Magnus, does generally linearly correlate with less subtle body language, but more so because a large percentage of heavy labour mecha are used to being tightly packed together, in mines and on assembly and refinery straights, so they rely on EM background radiation and verbal cues for communicating close up what medium freight and service frames communicate at a distance with body language. When you’re used to everyone standing within touching (or at least shoving) distance, verbal and subverbal cues become more important than visually distinct posture.
The one time you do get big, expressive body language out of heavy warframes and labour frames is in a conflict situation. Social conflict, see, is very bimodal for labour frames. If you’re already stuck on shift with someone, it’s in both of your best interest to bear down and just cope, resulting in social interfacing with zero friction as both mecha try to get away from each other as fast as they can. But if you aren’t already stuck with someone, then the best way to ensure you won’t be is to make them back off by laying on the physical intimidation.
This is also why minibots and lightweight service and custodial mecha (as well as most scientific instruments) generally have body language more recognisable to heavy industrial and warframes. Along with their tough construction leaving little mobility in their substructures, they’re similarly used to working in tight corners, under floors and inside vents – spaces that share physical traits with mine shafts and refineries more than the broad dock grounds or office buildings – so their body language does tend towards either understated or overbearing.
Similarly, large haulers, terrestrial shuttles and civillian airframes – all of whose works involve high speeds and large distances – converge on the body language typical of high performance ground frames. Partially because high-performance ground frames are what they mostly interact with, but also b/c the access to a physically larger social environment allows for communication that is better parseable from a distance, as well as favouring frames who are capable of making microadjustments to their own aerodynamics. As social flexibility increases, so does the necessity for being able to adjust your presentation and posture to match, too – not all high-performance frames are highly physically expressive, and not all industrial frames are laconic, but rather there’s a sort of a happy medium that frames from various classes codeswitch into with each other.
Although, honestly, airframes are sort of their own mess, because generally the spaces they operate in, the only times they’re in such close quarters with each other that body language and posture (rather than verbal or radiant communication) become significant are if they’re working in a cross-frame environment, or if they’re operating as a flight – and that latter requires an absolutely astounding clarity of communication, because manoeuvers at the high general cruising speeds they have to maintain even one person lagging on a turn can cause a crash at pulverising speeds for everyone else.
As a result, to ground frames air frames seem extremely prone to large physical displays, getting the maximum utility out of their middle-of-the-pack aerodynamic flaring (yes, wings and rotors can move, but generally airframes are already optimised to a certain kind of aerodynamic profile, and the rest of their plating can be quite rigid), but amongst themselves, even seeker body language can seem quite subdued to an outsider, because a lot of the necessary communication is done as radio and radar communication, and by maintaining a flight-wide EM equillibrium. Maybe seeker tendency to trine up is partially to create a more malleable social space, instead of every time having to match up the communicative needs of whole six individuals.
Also – the majority of air frames kind of wrap back around to sharing traits with heavy warframes, whose social distances match airframes on the ground, but who suppress a lot of that body language in order to be able to function as a part of a team or a squad, creating a lot of that same no-friction conflict you see with industrial frames. Rabbit-like displays of “I’m so much happier than you are” are not a seeker trait, they’re a warframe trait.
Beastformers have hands down the widest variety of body language expressiveness, and have similarly different ranges of body language and posture depending on whether they’re operating as individuals or in a group, but unfortunately their bauplan makes a lot of that body language hard to parse for bipedal mecha, and also their lack of reliance on radiant communication (both radio and verbal, which is why even large beastformers are often stealthier than equivalent weight class mecha from other frame types) creates huge gaps in communication.