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Could the approximate weight ot AT-AT's be deduced by the scene in Empire Strikes Back where C-3PO is in the corridor and snow falls on his head in time to the vibrations from AT-AT steps?

No because we do not know the composition of the material the AT-AT is walking on. It was clearly a layer of snow and then…. We don’t know. Likewise the Rebel base is cut into ice, but is this ice part of a continuous glacier the AT-ATs are also walking on, or sitting on top of rock? We don’t know that either. This makes it impossible to do meaningful calculations on the kind of vibration energy that would have to be transmitted. We also don’t know the distances with any useful precision. We also don’t even know how much of the AT-ATs weight is on the walking foot when it impacts, it might be very little as they have the other three legs to balance on. A lot of the energy may be coming from the act of forcing the foot down like a stomp. That would kind of fit with the role of the AT-AT as a giant impractical terror weapon. It stomps when the Empire is angry!

All that could be concluded is they must be pretty damn heavy, but not so heavy that they sink into ice or completely smash through a snowspeeder of unknown construction.

On top of that, weight reduction or repulsion technology is well within the capabilities of the Empire. It's entirely possible that through there exists technology that can throw the machine's center of gravity to it's feet, or indeed, below it, or just reducing it's weight like a big snowspeed with feet. There is no reason it couldn't also use tensor fields in the bottom of it's feet to step on more ground than it's footstep covers, though we can tell by the way the snow displaces that it doesn't do this.

We also don't know if the shock waves/vibration are actually from the AT-ATs walking or from explosions.

open_sketchbook wrote:On top of that, weight reduction or repulsion technology is well within the capabilities of the Empire. It's entirely possible that through there exists technology that can throw the machine's center of gravity to it's feet, or indeed, below it, or just reducing it's weight like a big snowspeed with feet. There is no reason it couldn't also use tensor fields in the bottom of it's feet to step on more ground than it's footstep covers, though we can tell by the way the snow displaces that it doesn't do this.

Reducing its weight isn't unlikely. In fact this gives me a theory. The walkers may employ a repulsorlift device to reduce weight for normal movement. They’d only a dump fraction of the weight onto the ground. However they still need to retain the ability to support all the weight on the legs, so they can walk through shield barriers. Otherwise it makes no sense to build the things rather then just a flying tank. The big shocks we saw may have been from when the AT-ATs turned off the repulsors to walk through the Hoth shield, before turning them back on inside of it to get more agility. That would explain snow falling down early on when the walkers are far away, and then nothing more like that occurring latter on inside the base.

Havok wrote:We also don't know if the shock waves/vibration are actually from the AT-ATs walking or from explosions.

Also entirely possible. That was before the battle started, but Imperial engineers may have needed to do something like blast large chunks of ice out of the way of the walkers. It’s also possible the vibration was from the Imperial transport ships landing to unload the walkers.

If the AT-At was as heavily built as a Challenger 2 MBT, the body less legs should weigh around 1700 tons give or take 20%;

Challenger 2, 8,5m hull length, x4.2m with applique armour, x 2.5m to turret roof- yes, there are a lot of odd corners and empty spaces here, but there are also for the AT-AT- at 62.5tons;

and the dimensions I'm going with for the AT-AT are belly at least 20m off the ground based on Luke's height, body about 25m long, 12m tall and 8m broad.

The legs-show me a real world walker transmission for comparison; but say 50% of the mass of the body riding on them? Gut says that's high, but as an estimate that ends up around 2250- 2500 tons.

Now, this could be an order of magnitude estimate at best because of the materials the thing is supposed to be made out of, but if anything I'd expect it to be on the low side.

Mainly, though, that's an excuse to make the following point; AT-ATs moonwalking.

Think about it; what else is a mass-reduced, repulsor- suspended AT-AT bouncing along going to look like? Apart from utterly ridiculous...seriously, I reckon they must lose a lot of their intimidation value manoeuvring like that. And you can imagine what a bunch of bored, poorly supervised squaddies would do with it- it would be like a herd of hippopotami doing ballet.