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Spider Tank: Difference between revisions
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The form has a number of advantages over the human shape: lower to the ground (thus less of a target). Your classic Spider Tank spreads its legs out more, making the vehicle more stable overall and allows it to traverse terrain that would give wheeled vehicles considerable trouble. All of which helps it cheat that pesky [[Square-Cube Law]] that gives giant humanoids considerable engineering problems. (Of course many settings then turn around and give it [[Rule of Cool|pointy ballerina feet]], [[Did Not Do the Research|ruining]] any overall improvement in the ground-pressure department, but hey.)
While wheels are faster and more efficient and tracks are best on a soft ground (it's hard to beat one big support area), spider legs can navigate extremely rough terrains and are more reliable because the vehicle can stand or even walk after losing a leg or two. Since "extremely rough terrains" include rubble blasted all over streets or hedgehogs made of rails and "losing a leg" includes little gifts from artillery, you see why an excavator isn't the only potential application. In fiction this means the spider design is most attractive for settings supposed to be [[Darker and Edgier|gritty and realistic]] - exactly because it can believably retain some functionality despite a lot of visible damage.
Depending on the size of the Spider Tank, it may or may not [[Rollerblade Good|have wheels on its feet]]. Caterpillar tracks are also common. If the Spider Tank is under 4 meters (roughly 12.5 feet) tall you can expect it to have wheels or tracks on its feet; if larger, you can expect it won't. It will probably have pointy feet instead. Despite the name, Spider Tanks rarely have eight legs. Four is the most common, and some have six. It's usually guaranteed that they'll have an even number of legs, though.
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* Syndrome's Omnidroid in ''[[The Incredibles]].'' Early versions had two wheels and two arms, but at some point they were mixed together and just kept increasing from there until you got the five- and six- legged, building-sized monstrosities that were actually fought.
* ''[[Star Wars]]'':
**
** AT-TE ("All Terrain Tactical Enforcer"), more of APC/UCV than a tank<ref>it got 1 mass driver cannon and 6 anti-personnel laser turrets, with 5 gunners controlling it all, spotter handling the sensor suite, and carries one medical droid(!) and 38 troopers</ref>, which is EMP-hardened and can be deployed or evacuated via air by a special dropship/gunship (LAAT/c).
** UT-AT ("Unstable Terrain Artillery Transport") - self-propelled artillery/APC - is a spider ''hover''tank: it got 16 repulsorlift skis, armored and structurally separate like a caterpillar's legs, so presumably even complete destruction of a few would not cripple the vehicle.
** On [[Attack Drone]] side of the spectrum, Spider Droids (large and small) from the prequel trilogy.
* ''[[Wild Wild West (film)|Wild Wild West]]'': The giant [[Steampunk]] robot spider.
** Producer Jon Peters repeatedly insisted a similar spider tank show up in early drafts of what later became ''Superman Returns'', as wittily recounted [http://www.youtube.com/watch?v=vgYhLIThTvk here] by scriptwriter [[Kevin Smith]]. It also shows up in ''[[Superman: Doomsday]]'' (though admittedly, it kind of looks more like an ant with one pair of legs too many.)
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== Webcomics ==
* Used in ''[[Girl Genius]]''
* In ''[[Homestuck]]'', as part of its [[Theme Table|extensive array of patterns and themes,]] each central character has some sort of futuristic vehicle connected to one of their personal motifs-- for instance, Rose's struggles with her alcoholic mother are reflected by a rocket made to look like a champagne cork. The vehicle corresponding to [[Western Zodiac|Cancer]]-themed [[Our Trolls Are Different|troll]] Karkat is naturally [http://mspaintadventures.com/?s=6&p=004412 one of these].
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* Actual vehicles have been built that use the motor configuration of arachnids. However, [[Cool but Inefficient|they move much slower than just using wheels.]]
* [http://www.youtube.com/watch?v=CJ-Q8wmYyWI Big Dog] (from Boston Dynamics) may not be a vehicle, but just you wait. [http://www.bostondynamics.com/robot_ls3.html LS3] The in progress bigger brother.<br /><br />However cool legged machines may be, there are several disadvantages. Maintenance is a major concern, and walking tanks are pretty much guaranteed to have at least 16 high-stress (hip lateral, hip vertical, knee, ankle, multiplied by at least 4 legs) compared to 4 for tanks (just the drive wheels, an M1 could almost certainly get by without a few of its road wheels given normal ground pressure of ~15 psi). That's only for cargo walkers as well, actual combat walkers (as actually fit the trope) have to factor in armour, recoil, speed, etc. most of which count against walkers.<br /><br />All of this plus the touched on, but not explicitly mentioned ground pressure issue. A tank spreads its massive weight over a pair of equally massive treads resulting in ground pressure per unit of area no higher then a walking man. An armored walker of the same weight balancing on four much smaller pads would have massively higher ground pressure and could easily bog down in any sort of soft ground (ironically much like a wheeled vehicle). You could of course try to sort of counter this by making the feet huge like snowshoes, but this would be a weak work around and could make walking unwieldy to say the least.
* Speaking of walking on soft ground...the [http://www.youtube.com/watch?v=CD2V8GFqk_Y Timberjack] hexapod deforester which can walk on uneven ground effectively (albeit has very slow turning) is proudly claiming that its feet cause less damage to ground when compare to a normal caterpillar. What kind of magic it use? Rubber dampers.
* And that's why the cheap robots they're designing to wander Mars are called 'spider-bots'. They only have six legs, though. And they're kinda small. And there will be a ''lot'' of them. They're cheap, after all.
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