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Subject: Advantages/Disadvantages of a walking tank
theBird    5/22/2007 1:05:43 AM
Similar to a mech, (or mecha for the Japanesse minded), an armoured walking vehicle anywhere from 5 to 15 meters tall and armed with a variety of heavy and light weapons, either with a single pilot or multi-person crew. Alternatively a walking bradley armed with bradley type weapons and able to deliver a squad to the room of shorter buildings.
 
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aidan110       4/25/2010 10:08:31 PM
Personaly, I think that a walker is really a fantasy. An armored exo suit ala starship troopers is more realistic. The largest that such a suit would probably get would be aproximately the height of a tank. Big enough to carry a fairly large weapon or weapons, while still able to hunker down behind most terrain features. Again as previously stated a TOW type system would probably supply the heavy firepower with an automatic cannon (25mm?) as an alternate for getting those hard to reach places.
 
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StobieWan       4/26/2010 3:59:41 AM
Well, I'm starting to think the first application of a walking exo might be SWAT or similar - as a breaching system on a dynamic entry, providing the thing is small enough to fit through a door, can waddle at reasonable speed and light enough to make it up some stairs, then you could hang enough armour to stop small arms, a taser, bean bag gun, some other less-than-lethal systems plus a lethal option and bang, you've got your point man.

 With the BattleTech stuff, you have to remember that FASA got the rights to use the pretty pictures and stuff from Robotech but no rights to the IP for the backstory so they just took the pictures and wrote their own background around it. Most of the writers didn't know one end of a gun from another which is why most of the calibres are stupid etc.

Best quote I heard, on interview with one of the writers for one of the source books, when asked to explain how ammunition got up the very thin connecting tube to the autocannon on a Marauder, said "oh, hey, tell them it's magic or something" - that encapsulates how "realistic" it all is :)

Ian

 
 
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WarNerd       4/27/2010 5:31:14 PM
I am a professional mechanical engineer.
1. Mechanical complexity.  Other than the governing components, possible gyro, mandatory reactor, the drive train is relatively simple to engineer. 
 
A typical wheeled vehicle typically has a single power train with a hydraulic torque converter and geared transmission to supply limited variation between the speed and direction of the contact surfaces on the 2 sides of the vehicle.  Modern track vehicles have a more complex dual hydraulic only transmission because it is also the means of steering, but the actions are not fully independent.  In both cases the suspension system is entirely separate from the drive system.
 
A bipedal walker for rough ground needs a minimum of 8 independent ranges of motion (hip, knee, ankle, plus leg rotation and side-to-side flexing at hip and ankle joints).  In addition, the drive system is also your suspension system and the continuous impact loads will destroy any geared system in short order, so your alternatives are very high pressure hydraulics or some kind of contractile fiber.  The former has some 'interesting' limitations and problems, the later is still in the very early stages of development.  Either way, the design will NOT be simple.
 
Scientists and engineers have been trying to replicate bipedal motion for over a century.  The best we have been able to do reliably, so far, is a slow walk.
2. Ground pressure. In war, who cares about the road being tore up? Oh maybe tracked/wheeled vehicles. In that case, the mobility awarded to a walker wins. A stout wall will stop a vehicle, not a walker. Deep rivers will stop a vehicle, not a walker. 
 
4. Speed. A quick search got me 75 kph or 45mph for the Abrams. which model I don't know. Good baseline. We know the Abrams is somewhere around 75 tons. A 'mech of similar weight could probably move about as fast. Factoring in less ground contact (less friction) and adding more friction due to servos, artificial musculature or if any gearboxes are used in the legs/hip area. I am a BT advocate, but from an engineering point of view, yes a mech is possible with straight motors/ gearboxes, pistons, gas/diesel engine(s), etc... but THAT machine would be deathly slow and bulky. To lighten the design you need to increase the strength of the legs and therefore it's mobility. Upscaled heavy-duty high-strength servomotors and artificial muscle is the way to go, as FASA originally thought up. Legs that can pull alot of tonnage faster will get you up to speed, support torso weight, etc.. Speed shouldn't be an issue if the vantage point for target location is significantly higher than a groundpounder. If they need to travel X distance just to crest a hill for a firing solution, time is wasted. A walker has LOS to the target and can fire at it while standing next to the tank that is between hills or LOS blocking terrain. 

5. Toppling. Cockpit dampeners, and industrial shock-resistant servos, artificial musculature and ruggedized components will allow such a walker to be fielded. It is a challenge but a simple one of engineering components correctly with the proper material selections. EZ mode. If you are talking sci-fi crap like anti-gravity suspensorlift junk, then yea that's not possible. A bipedal 'mech that falls will get back up if it's locomotive components are not damaged. 

6. Unmaneuverability. I don't need to go there because a walker that could only move its legs in a rigid pattern such as is coverened by a gearbox/driveshaft system would be silly. Pistons/hydraulics would also be pretty useless. 

All these are influenced by ground pressure.  To give you an idea of what 10x normal ground pressure would do strap on a pack with half your body we
 
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AThousandYoung       5/22/2010 1:21:41 AM
Bipedal human sized robots are a good idea because they can use human infrastructure.  However a biped is an easy target and is not naturally stable.
 
One of the advantages of the human bipedal form is the fact that it allows a very energy efficient mode of transportation.  We're apparently really good endurance runners and long distance walkers compared to other animals.  Whether it's more efficient than wheels I don't know (for a bipedal truck or something).
 
A biped goes hull down by standing in fighting holes, kneeling behind obstacles or lying down on the ground.  This is doable but takes away mobility unlike for a tracked vehicle.
 
A walking spider-tank might work in swamps...or in extremely rough terrain...I suppose.
 
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WarNerd       5/22/2010 5:19:29 AM

One of the advantages of the human bipedal form is the fact that it allows a very energy efficient mode of transportation.  We're apparently really good endurance runners and long distance walkers compared to other animals.  Whether it's more efficient than wheels I don't know (for a bipedal truck or something).

Humans are better endurance runners than other species because they have a better cooling system (no fur and copious sweat glands).  Animals start panting heavily after just a little exercise, humans just sweat.  The bipedal gait helps a little, but the fact that we do not easily overheat to the point where the body is about to shutdown is the major factor.
 
A walking spider-tank might work in swamps...or in extremely rough terrain...I suppose.

Two words: Ground Pressure.  Walkers and swamps don't mix, unless their feet are larger than ours proportional to their weight.
 
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flamingknives       5/22/2010 7:34:43 AM
Like many things science fiction, the feasibility of walkers depends on available technology.

At the moment, technology does not support large walkers.

Start throwing in devices that limit inertia and mass effects, energy fields, neural linkages, energy weapons etc. and the balance may change.
 
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StobieWan       5/23/2010 7:21:21 PM
Take a normal human being and park them on a bicycle and you can get them to cycle at 10mph quite easily - while burning the same calories as they were at a 4mph walk.

We *are* a very efficient species for long distance running but sticking everything on wheels or treads is far far more efficient.

Ian

 

One of the advantages of the human bipedal form is the fact that it allows a very energy efficient mode of transportation.  We're apparently really good endurance runners and long distance walkers compared to other animals.  Whether it's more efficient than wheels I don't know (for a bipedal truck or something).


 
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Mikko       5/24/2010 7:49:51 AM
The con's seem to be well enough covered here so I throw in a few perks a walker might have:
 
1) Ability to alter height, vertical maneuvering. A bipedal war machine could use terrain in a more flexible manner than a tank due to its ability to squat and stand up straight. I could take cover and fire briefly from behind an obstacle like a helicopter, yet being better protected and fuel efficient than a helicopter. Maybe I'd design my mech very light but able to alter height from 3 meters to 20 and back in just few seconds.
 
2) A walker is sensitive to terrain and ground pressure, but in different ways than a tank. Normally you plan using your AT-assets in terrain that allows efficient use of tanks; so walkers could force the enemy to expect breakthrough attempts almost everywhere.

3) Having limbs provide opportunities. Could it get down on the ground under a barrage? Could it support infantry in urban combat by kicking in doors, and by creating platforms from which infantry could climb over directly to rooftops and third floors (become a ladder when needed)?
 
M
 
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WarNerd       5/25/2010 2:04:49 AM
Why bother when a telescoping crane arm with some end accessories can do the job, only better?

1) Ability to alter height, vertical maneuvering. A bipedal war machine could use terrain in a more flexible manner than a tank due to its ability to squat and stand up straight. I could take cover and fire briefly from behind an obstacle like a helicopter, yet being better protected and fuel efficient than a helicopter. Maybe I'd design my mech very light but able to alter height from 3 meters to 20 and back in just few seconds.

Attach a weapon and sensor pod to the end of the crane.  The Germans once proposed a similar idea for using MANPADs inside forests.
 
3) Having limbs provide opportunities. Could it get down on the ground under a barrage? Could it support infantry in urban combat by kicking in doors, and by creating platforms from which infantry could climb over directly to rooftops and third floors (become a ladder when needed)?

Swing the bucket through the door, if the hole is not big enough rip the wall out.  Attach a ladder to the back of the boom and some hand grips and shackle points to the end of the arm.
 
Instead of arguing for a bipedal walking machine, why not just add an engineering squad and a couple vehicles to the TOE at the company level.  It's cheaper, and has many additional benefits.
 
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Mikko    @WarNerd   5/25/2010 4:46:26 AM
Yeah. I wouldn't sign a development budget for a walker for a long time. Surely same benefits can be met in a more cost efficient manner.
 
Still, the first real combat arguments that will support the develpoment of a serious walker will probably be due to their role as a flexible and multi-use support unit (able to take cover better than a wheeled/tracked vehicle, better protected than a trooper), secondarily as a shock unit in urban environment.
 
As western blood becomes costlier and costlier to spill for those interested in waging a war, a device that could alone substitute an entire combat engineer squad, risking only the operator, might become handy one day.
 
A nation's sensitivity to both blood and treasure and the ratio between the two, as well as valuation of objectives, greatly determines whether inefficient but life-saving walker-kind units get on the drawing board in 20 or 150 years or anywhere in between. 
 
M
 
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