MythBusters does the AT-ST log smash

[2046]

For their Jan 4 Star Wars Special, the secondary team featuring Kari the redhead in an R2 dress replicated the log smash from RoTJ. Grant used a figure of two megajoules for the energy but their logs were rather different in shape. However, the armored truck they used held up better than the AT-ST did.

Generally speaking it seemed to all largely confirm my old findings.

Thanks to blog reader Vorus for pointing it out.

[2046]

From my blog:

Quick Review: Mythbusters AT-ST Log Smash

So, did the Mythbusters get it right?

In broad strokes, yes. As reader Vorus noted, my old 2002 page on the AT-ST log smash held up well compared to their scrutiny.

In short, they build a rig with telephone poles and hang logs beneath them, pulling them back and letting them smash a test vehicle and then a full-on (and nicely painted) armored truck of the sort you might expect to haul bank loot.

There were some great moments beyond the eminently television-friendly Kari's various attire, such as Grant Imahara describing "back of the envelope" calculations suggesting that the energy involved per log was going to be about a megajoule, followed by a quick flash of assorted scenes from the show of megajoule scale, like car crashes and so on.

The total for both logs of two megajoules falls in line nicely with the notations on my AT-ST log smash analysis page in which, as always, I heap the benefit of the doubt upon Star Wars and basically double the likely figures. The Mythbusters team, unencumbered by claims of bias from a group of Star Wars fans bent on maximizing Star Wars technology at every turn, felt perfectly at liberty to simply follow the facts and not inflate the figures in favor of Star Wars.

But, there were also some oddities.

"Aren't you a little short for a chicken walker?" - The AT-ST height is given as 20 feet (a rather low figure given that the full-scale mock-up in the film was over 8 meters, or 26 feet), and for some reason they felt it necessary to then hang a Ford Econoline test vehicle at that height for smashification. Not only was the altitude completely unnecessary, but it put undue stresses on their rig to move the logs about at that height. Fortunately this was abandoned for final testing, otherwise they would've had to rebuild it.

"Aren't you a little short for an Ewok log?" - Also, despite having a fake log of proper length to width ratio at the beginning of the episode, it is somehow decided that the logs in the film are about ten feet long and five feet wide, which makes them entirely too short. In the scene below, for instance, the logs would not even extend all the way to the edge of the frame.



On my page I came out with 1.5 meters by nine meters, or about five feet in diameter and 30 feet long. And, since their targets were quite a bit shorter than the AT-ST cab section, the five foot logs looked a bit monstrous.

"Aren't you a little short for a log nose?" - The logs themselves were unfinished, in the sense that they were straight or nearly-straight cuts and had no pointed/rounded tips. In the first hit against the armored truck, this seemingly resulted in the left side (as viewed from the front) not actually penetrating the side of the vehicle since it hit the roofline broadside.

"Aren't you a little far back for a logsmash?" - The first strikes were against the flat sides of a van and then the flat side of an armored truck. In the case of the truck the right side simply caved in, which makes sense given that there is likely very little actual vehicle structure back there. The second hit, however, was aimed more forward, and literally tore the roof off of the vehicle and smashed the cabin. There is likely a pillar just behind the driver's door, making that more of a fair test. After all, armored trucks of that nature are mostly intended to be bulletproof rather than structurally strong.

Of course, comparing that to the actual AT-ST's structural failure is interesting, since the first hit, as noted, only poked a hole in the truck. The general structure appeared to remain fairly intact. Compare that to the logsmash itself, in which the AT-ST literally crumples. I guess in an age of blasters, the notion of kinetic impact may seem altogether quite foreign.



"Aren't you a little hard for a log? Wait, don't answer that." - For some unexplained reason, eucalyptus logs were selected explicitly for their hardness. Presumably this was intended to allow repeated strikes without fear of log failure . . . the rig, after all, would've been rather difficult to 'reload'. Nevertheless, it seemed odd when watching initially.

This does bring me back to my page, however. I did assorted calculation via forces and whatnot, but never really got into the actual pondering of hardness of the AT-ST hull. Given the malleability against logs it would be nice to review that ancient page and see what I can come up with in that regard. Presumably I dismissed it back then as relatively unimportant, given that I had already concluded that AT-STs were more or less bulletproof.

In any case, I'd say the Mythbusters team did a great and very entertaining job, and it was great fun to see things get smashed and have Grant Imahara generally confirm my old figures.

[Mr. Oragahn]

Those war wagons were nothing more than humvees on legs, and I would say the kind that's not really much armoured, like if the Empire didn't lend an ear to the cries of army troopers falling to rebel traps, all that in order to cut costs, or retain some speed and agility considering the pedestrian mechanized mobile system, or for propaganda purposes (although you'd need a good program to compensate for the obvious corridor rumours about the chiken legs' suckage). They'd come with a similar ability to be outfited with a variety of supplementary heavier weapons attached outside of the structure. A somewhat "real" military vehicle in other words, but still with a terrible, terrible thought process as you move from quadri or hexaleg designs and a relative low profile, to something standing high on two sticks. You see the decadence in design, as the AT-TEs were very well designed in comparison. Although their front cabin provided no protection to the pilot and was not better than any tree cutter.

Outside of repulsorlift technology (and eventually with strong reactionless engines like on the Trade Federation troop transports which mowed Naboo trees down ... although those were thinner than Endorian trees), walkers are best suited to move around uncleared forest.

We're certainly not looking any kind of APC or IFV here with the AT-ST.
It's almost like some idiot bureaucrat had a moment of coolness and then pragamatic engineers rushed and went through blank nights to make the thing suck less as much as possible without hurting the sensibilities of the office moron. The AT-ST, definitely good against infantry rifles, but would fantastically suck against rocket launchers or massive momentum-based strikes. You wouldn't want those tinboxes on matches in Mogadishu.

Anyway, humvees weren't meant to be heavily armoured either. As a replacement for the jeep, they were already much better and well suited for the job.
Now, the Empire has the advantage of not having to explain much to families losing their sons. It is more sovietic right there. All the Empire needed in the movies was some kind of clear comissar figure... other than Vader, of course, who can't be everywhere at once, even if he can choke you through video-conference (take that, chatroulette).
That said, I'm pretty sure humvees wouldn't fare any better against those logs either.

All in all, that certainly does not make the AT-ST totally terrible machines. Again, against lightly armed infantry, in forest, having a higher point of fire is actually an advantage.
Assuming you actually use the advantage of firepower and the extra mounted weapons, and assuming you still get some intel, scouting and flank cover from infantry moving along, coupled with real scouting (aka scout bikes), AT-STs turn out to be more a good compromise for some kind of backseat infantry support and low intensity mop up operations.

They're however bad choice in case of a guerilla. But the shield was supposed to prevent the deployment of any troops.

On the MB test itself, considering how they somewhat changed parameters at the last moment, one could think that their results aren't relevant. But if I get it right, their choices actually brought them to work with rather conservative premises, right?

[2046]

Well, I'm thinking I need to analyze the video of their work, and possibly re-check my own.

We're told that their short logs weigh 10,000 pounds, or about 1/6th of my highest end estimates for the RoTJ logs. Even using more reasonable figures for log density, it seems that their testing was most likely rather less energetic than the actual log-smash, and thus it cannot be said (as I said earlier) that the armored truck held up a bit better . . . in other words, if it wasn't as hard a hit, we must acquit.

I want to check the speed of their short logs at impact and get a better sense of the energy actually involved, since Grant's back-of-the-envelope calculations of a megajoule each may not reflect the test as performed.

For instance, just before his energy figure is given, there's talk of a 45 degree angle being used in the film as the drop height, as if to suggest he derived the speed from the angle. I don't know if they actually got that angle or if the speed so derived matches the film.

Also, while watching their replays of the clips, it really did look like the logs were swinging faster in the actual film in the release shots (i.e. the short cuts after the Ewoks cut the vines or whatever those are holding the logs) than in the final impact scenes. I haven't checked against the actual film to be sure that they didn't monkey with the speed for editing purposes, but if it's true then the final impact scene is probably in slowed motion.

[sonofccn]

Expanding off of the "Why" of the AT-ST rather than a bulked up AT-TE it could be construed that the Imperial armed forces, who would be geared towards the offensive expansion of the Empire, expects to enter engagements on the far side of logistical chains and deployment bottlenecks and needed a fighting vehicle it could mass produce and transport in quantity alongside its Stormtroopers/Soldiers which could not only bolster the firepower of their infantry squads but which, potentially, could act as glass cannons against the heavier armor a well entrenched foe might have at the ready. Something not unlike the German Weasel "Tankette".

Granted the Empire doesn't seem inclined to air portability, and tactically had the airlift capacity for a Tactical Enforcer, but strategically speaking its offensive force would be limited by its starlift capability where every soldier, gun and piece of equipment would first have to be loaded onto a starship, flown to the enemy planet then deployed either by landing the transport ship or intermediary vessels to ferry them down and I would suggest you could cram more of the tall but scrawny AT-ST into a given space than you could the AT-TEs.

Further the fact its drive system is two legged rather than the, IIRC, six of the Tactical Enforcer might lend further logistical advantage to the humble AT-ST. In terms of replacement of parts worn by wear or enemy action the AT-TE would have three times the complexity of a Chicken Walker resulting in a greater demand on, relatively, finite supplies.

In terms of its actual combat performance I still think this was the best discussion on the subject stressing both the vehicles strengths and weaknesses and will only add that on the forest moon of Endor that the Empire lost two, IIRC, AT-STs to Ewok traps, had one captured by an irate Wookiee and the last destroyed by said captured AT-ST. Most of which can be accounted for by the overconfident and sloppy actions of the Imperials, essentially blundering incoherently after the Ewoks without any concern or plan, rather than an inherent weakness in the design.

[Lucky]

Expanding off of the "Why" of the AT-ST rather than a bulked up AT-TE it could be construed that the Imperial armed forces, who would be geared towards the offensive expansion of the Empire, expects to enter engagements on the far side of logistical chains and deployment bottlenecks and needed a fighting vehicle it could mass produce and transport in quantity alongside its Stormtroopers/Soldiers which could not only bolster the firepower of their infantry squads but which, potentially, could act as glass cannons against the heavier armor a well entrenched foe might have at the ready. Something not unlike the German Weasel "Tankette".

Granted the Empire doesn't seem inclined to air portability, and tactically had the airlift capacity for a Tactical Enforcer, but strategically speaking its offensive force would be limited by its starlift capability where every soldier, gun and piece of equipment would first have to be loaded onto a starship, flown to the enemy planet then deployed either by landing the transport ship or intermediary vessels to ferry them down and I would suggest you could cram more of the tall but scrawny AT-ST into a given space than you could the AT-TEs.

Further the fact its drive system is two legged rather than the, IIRC, six of the Tactical Enforcer might lend further logistical advantage to the humble AT-ST. In terms of replacement of parts worn by wear or enemy action the AT-TE would have three times the complexity of a Chicken Walker resulting in a greater demand on, relatively, finite supplies.

In terms of its actual combat performance I still think this was the best discussion on the subject stressing both the vehicles strengths and weaknesses and will only add that on the forest moon of Endor that the Empire lost two, IIRC, AT-STs to Ewok traps, had one captured by an irate Wookiee and the last destroyed by said captured AT-ST. Most of which can be accounted for by the overconfident and sloppy actions of the Imperials, essentially blundering incoherently after the Ewoks without any concern or plan, rather than an inherent weakness in the design.

The Myth Busters declared the AT-ST a bad design that could be destroyed with a block of C4 which the Rebels should have had for such a job in the M7 after show videos.

[Lucky]

Well, I'm thinking I need to analyze the video of their work, and possibly re-check my own.

We're told that their short logs weigh 10,000 pounds, or about 1/6th of my highest end estimates for the RoTJ logs. Even using more reasonable figures for log density, it seems that their testing was most likely rather less energetic than the actual log-smash, and thus it cannot be said (as I said earlier) that the armored truck held up a bit better . . . in other words, if it wasn't as hard a hit, we must acquit.

I want to check the speed of their short logs at impact and get a better sense of the energy actually involved, since Grant's back-of-the-envelope calculations of a megajoule each may not reflect the test as performed.

For instance, just before his energy figure is given, there's talk of a 45 degree angle being used in the film as the drop height, as if to suggest he derived the speed from the angle. I don't know if they actually got that angle or if the speed so derived matches the film.

Also, while watching their replays of the clips, it really did look like the logs were swinging faster in the actual film in the release shots (i.e. the short cuts after the Ewoks cut the vines or whatever those are holding the logs) than in the final impact scenes. I haven't checked against the actual film to be sure that they didn't monkey with the speed for editing purposes, but if it's true then the final impact scene is probably in slowed motion.

This might be relavent
http://dsc.discovery.com/tv-shows/mythb ... ershow.htm

[Mr. Oragahn]

Well, I'm thinking I need to analyze the video of their work, and possibly re-check my own.

We're told that their short logs weigh 10,000 pounds, or about 1/6th of my highest end estimates for the RoTJ logs. Even using more reasonable figures for log density, it seems that their testing was most likely rather less energetic than the actual log-smash, and thus it cannot be said (as I said earlier) that the armored truck held up a bit better . . . in other words, if it wasn't as hard a hit, we must acquit.

I want to check the speed of their short logs at impact and get a better sense of the energy actually involved, since Grant's back-of-the-envelope calculations of a megajoule each may not reflect the test as performed.

For instance, just before his energy figure is given, there's talk of a 45 degree angle being used in the film as the drop height, as if to suggest he derived the speed from the angle. I don't know if they actually got that angle or if the speed so derived matches the film.

Also, while watching their replays of the clips, it really did look like the logs were swinging faster in the actual film in the release shots (i.e. the short cuts after the Ewoks cut the vines or whatever those are holding the logs) than in the final impact scenes. I haven't checked against the actual film to be sure that they didn't monkey with the speed for editing purposes, but if it's true then the final impact scene is probably in slowed motion.

MythBusters' test

We have two factors here. The logs and all the parameters relevant to the trap on one side, and the vehicles on the other.
Since the vehicles are different, what should have been made is to use the most identical trap system to the one seen in the movie.

Because if the system is different, there's not much to compare to: an overall weaker weapon system doesn't tell us much. OK, it does this and that against known vehicles, but we just don't know what it would do against an AT-ST.
For the weaker system to be relevant, they'd need a real AT-ST. Which I think represents an obvious problem.

Now, with a weapon system more powerful than the one seen in the movie, ONLY IF some real vehicles had been capable of withstanding the shock, at least we could have concluded that they're better than the AT-ST, since we'd know that the AT-ST had been pulverized by a weaker weapon system. And that would be it.

So if their weapon system is weaker, then I think it is totally useless.


Assessing the ROTJ trap's effectiveness

The first log to go is the best one to confirm that they start falling at 45° or so.
The second log is good to know their speed something like halfway.
What we notice with the second log's swing is that there's a narrow and brown dead tree on the ground. With my video software player, very conveniently, the tip of the log happens to "touch" the low tip of that fallen tree on the screen.
It takes precisely 9 frames (@ 25 fps) for the end of the log to pass the same point on the screen, and the log still has lots of distance to cover since we don't see the AT-ST, located presumably offscreen (I mean, documentary-wise, that's where it would be located).
But in the impact sequence, neither logs cover their own length even before touching the vehicle (they both have 3 more frames to go and even by then, we wouldn't see the tail of each log since we don't even see the other cords supporting the aft sections).
So the impacts could definitely be considered shot through slowmotion (if we were to assume this to be documentary-reliable, SoD and all that).

So the calculation to make, both for energy and angular momentum, is to start at an angle of 45°, work with a given mass (I think you got a good approximation of it), and know the radius of the swings. Finding the radius will be the hardest part and you'll be better off starting with several distances.
We don't even see if the "hinge" is fixed or if the cords are attached to supple branches, which would mess up calcs.
One thing that can be done to get the radius is use the impact sequence and draw an arc by pinpointing, on each frame, the location of a given point on each log. I'd say, obviously, to pick a point on the lower side of the edge of the beveled extremities (the "penetrator" flattened cones), because that's the part of each log we see the most.
Then, pick your one screencap where you've reported all those points for each frame, and insert it at the bottom of a huuuuuuuuuuge canvas. Then the rest is about basic trigonometry to find the point of origining of that section of the circle that the swinging arc represents.
Not perfect but can't get any better.

But you can already apply a correcting factor to your calcs since you know that at the very least, you should work from a length-covering speed of 9 fps out of 25.
Or 0.36 seconds instead of whatever time you used. That would be the low end, in terms of speeds, of course.

[2046]

9 meters log length in 9 frames at 25fps is 25m/s, or twice my calculated speed.

[Mr. Oragahn]

And that's the low end. Even a theoretical calculation based on a 1g gravity would probably provide a greater impact speed. The logs in the impact sequence really come in too slowly. It's too striking now that I've thought about it.
Can't say that makes me feel happy... :/

[2046]

Just for sake of comparison, I've estimated the volume and density of the Mythbusters logs in metric.

Their logs are five feet wide and ten feet long, or about 1.5m in diameter by 3m in length. That gives an approximate volume of 5.3 m^3. At the stated weight of 10,000lb (4536kg), then the density of their eucalyptus logs is 855.6 kg/m^3.

At the size calculated for the Endor logs, then, we're talking about 15.9 m^3 times that density, for a total mass of 13,600kg.

Also . . .

Found an online calculator just so numerous possibilities can be explored easily.

http://www.endmemo.com/physics/spendulum.php

For example, if the hanging vines were a mere 25m long, and using 13600kg for the mass (only needed for the calculator's integrated KE calculation), and a 45 degree angle, and at 1g, the velocity at the bottom of the swing would be 11.98 m/s, which is weirdly close to my original figure.

Other notable facts are that it would take almost exactly 5 seconds.15 for the center of mass to reach bottom, and that the kinetic energy at the bottom of the swing would be 977 kJ.

(Note that I am not accounting here for the length of the logs, which would mean they could strike well before the center of mass had reached the bottom of the swing.)

If we double the length of the vines, the speed climbs to almost 17 m/s, and the KE hits 1.95 MJ, and we're looking at 7 seconds to the bottom. At 75m vines, we get to 20.75 m/s with a KE of 2.9 megajoules . . . but now it takes over eight and a half seconds to reach bottom.

Thing is, not only are we not up to 25m/s yet, but even then that would be 25 at the bottom . . . but the 9-frames-to-pass-a-point thing happened in mid-swing.

I think the trick here is that the forty five degree angle is not a required component. We see Ewoks cutting vines and then we cut to the swinging logs but the logs meet exactly at the bottom with the same energy despite the fact that we saw Ewoks cutting seconds apart from each other.

Sure, we could say one log was wet and the other wasn't and the Ewoks managed to figure out the difference in timing, but I really rather doubt that. So, I think it best to assume that scene is edited somewhat, which makes sense since we're already thinking slo-mo.

Thus, let's try a 75 degree angle. Notably, the total time period remains pretty stable.

At 25m length, speed goes up to 19 m/s and energy to 2.5 MJ.

At 50, speed is 27 and KE is 4.9 MJ.

At 75, speed is 33 and KE is 7.4 MJ.

So, there is a range of possibility, and it'll take some more looking to check in on it.

[Picard]

A somewhat "real" military vehicle in other words, but still with a terrible, terrible thought process as you move from quadri or hexaleg designs and a relative low profile, to something standing high on two sticks.

In other words, just the same though process as moving from tracked to wheeled APC (M113 to Stryker), except far worse. Main advantage of tracked vehicles over the wheeled ones is mobility: low ground pressure and good grip on the surface allow it to traverse areas where wheeled vehicles, with their high ground pressure and slippy wheels would get stuck. Secondary advantage is that tracked vehicles typically lay lower, presenting a smaller target. Walkers are worse than either: they have both higher ground pressure, higher profile and worse stability than any wheeled design.

At 25m length, speed goes up to 19 m/s and energy to 2.5 MJ.

At 50, speed is 27 and KE is 4.9 MJ.

At 75, speed is 33 and KE is 7.4 MJ.

Just for a reference, Leopard 2 A6 has L55 gun capable of firing 8,35 kg tungsten penetrator at 1.750 mps, so just under 12,8 MJ.

[Firmus Piett]

So the show might have low balled the energy of the event a little, its still order of magnitude. That page happens to be one of my preferred, 2046, my only real complaint was ever that you arbitrarily decided that the armour is likely fallible by energy weapons of similar energy.. like phasers.. despite there being evidence to the contrary. You'd need the Breen rifle at least.

[Firmus Piett]

Suffice to say, anti-tank ballistics would certainly annihilate the chicken walkers lol/

[Picard]

my only real complaint was ever that you arbitrarily decided that the armour is likely fallible by energy weapons of similar energy.. like phasers.. despite there being evidence to the contrary. You'd need the Breen rifle at least.

Well yes, it is entirely probable that armor works far better against energy weapons than against kinetic ones. But in modern tanks, ceramics are made to be useful against both HEAT and KE rounds, though they are not equally effective against both.