Studio Scale AT AT With Full Animation Armature

[Big C]

Happy New Year everyone!

Been lurking around for a couple weeks and have been hugely inspired by all the incredible talent here.
Got me thinking about a project I've been wanting to do for like 30 years. A studio scale AT AT with a full machined aluminum stop motion armature. I started looking at images of the walkers used in the Empire Strikes Back and sort of went down the rabbit hole. After about a hundred hours of scrutinizing every bolt and screw hole and every possible part I could figure out, I put together a 3D model in Fusion 360 that (as far as I can tell) represents every part in the original leg stop motion armature. I'm curious what the experts here have to say!
Some big questions remain: How exactly did the mechanism work on the upper leg? Were the rotating knee plates hand animated or driven by an internal mechanism? And how exactly did the quick release pins used to secure the models during animation attach to the feet?
As far as the upper leg mechanism goes, I've got it working in the 3D model with parts that at least look similar to the fuzzy images of the original mechanisms. Work still needs to be done here before I start machining aluminum. To that end, I am planning to machine a 2/3 size prototype leg in ABS plastic to check how everything goes together. Once I'm happy with that I'll start on the really fun work!
Images show the 3D model leg so far. Gray parts would have been machined aluminum in the studio models. Tan parts would most likely have been cast urethane. Let me know what you guys think. I'm totally open and hope for input on all this.

 

[joberg]

"An island North of Seattle"...you mean Vancouver? Your renderings are beautiful and making those "pistons" going up and down the leg is something that had eluded me for decades. Eager to see your next update

 

[Big C]

"An island North of Seattle"...you mean Vancouver? Your renderings are beautiful and making those "pistons" going up and down the leg is something that had eluded me for decades. Eager to see your next update

Thanks for the kind words! The island I live on is a wee bit smaller than Vancouver. I live on San Juan island a bit to the east.

 

[Bjorn]

Beautiful CAD work there!

I can't say I have studied this in great detail like yourself, but have often wondered this when watching the film. It just looks so realistic!

However, Phil Tippett mentioned in the recent Light and Magic doco on Disney that Jon Berg had engineered both the knees and pistons to move mechanically, so as to save on work puppeteering. How he did this I don't know.

The knees moves much quicker than everything else and the motion seems intermittent. I suspect it's a bit like a tappet driven by a rocker arm and cam.
And driven close to the rotation axis for fast movement. But that's a wild guess!

Very keen to see how you go with this.

 

[JediMichael]

Very nice.
Something about this model, I would say is probably the most advanced prop/model ever used for a film.
The fact that over 40 years later, it can still baffle people, really shows that.

 

[Big C]

Beautiful CAD work there!

I can't say I have studied this in great detail like yourself, but have often wondered this when watching the film. It just looks so realistic!

However, Phil Tippett mentioned in the recent Light and Magic doco on Disney that Jon Berg had engineered both the knees and pistons to move mechanically, so as to save on work puppeteering. How he did this I don't know.

View attachment 1653967

The knees moves much quicker than everything else and the motion seems intermittent. I suspect it's a bit like a tappet driven by a rocker arm and cam.
And driven close to the rotation axis for fast movement. But that's a wild guess!

Very keen to see how you go with this.

Thanks! Yeah I suspected as much. I've found two clues that there was a knee plate rotation mechanism: A slot milled in the back of the 'shin' that I think had no other purpose than to make room for maybe a pushrod. And a gap in the 'shin' and upper leg round knee parts that could have allowed something to rotate the knee plate while still allowing the knee to bend. Its an interesting problem. One of the knee plates does about a 220 degree rotation in the film. Which would not be possible with a pushrod alone. Maybe a sector gear was used.

 

[Runner]

Anyone know what the "arms" are in the Tippett photo above are called? I know the purpose of them but was always curious what they were officially?

 

[swgeek]

Anyone know what the "arms" are in the Tippett photo above are called? I know the purpose of them but was always curious what they were officially?

They're called surface gauges.

 

[Leinads]

Wow! Way above my pay grade here, but I’m thoroughly enjoying all the hidden engineering in this. Love it!

 

[Big C]

Got the Ring Holder parts made up for the ABS plastic test leg along with a few detail parts and the shin piece (which will be redone when I figure out the knee plate rotation mechanism). Short video shows the process if anyone is interested. Eventual aluminum parts will be done in a similar way.

 

[joberg]

This is a killer project and, when finished, will be the bomb

 

[GEEK1138]

Excellent work Big C, I will be following your build with interest. It'd be so cool to see the enigma of the AT-AT motion finally solved

 

[Big C]

Excellent work Big C, I will be following your build with interest. It'd be so cool to see the enigma of the AT-AT motion finally solved

Thanks! Been following your great work on the Walker 3D model too. I know from experience how much work and time goes into a project like that.

 

[Big C]

Some upper leg parts fabricated. Hope to have the mechanism proved out this weekend. The main leg part will be redone to accommodate changes for the knee plate rotation mechanism. This one will probably get hacked a bit to get the upper mechanism working well anyway.
I think I have the knee plate mechanism worked out. Blew a bunch of my remaining brain cells on that one. I'll upload some CAD images in a few days after its been prettied up a bit.

As I work through the design, my awe and appreciation for the incredible talent, skill and creativity of Jon Berg, and Phil Tippett, grows and grows. I am truly standing on the shoulders of giants.

 

[joberg]

Yep; this guys are model makers, engineers, animators, painters...too much talent for my brain to compute
As for your model engineering Big C; it's a beauty for sure

 

[Big C]

Got the knee plate rotation mechanism up and running in my 3D model.
As far as I can tell, there is not a single public photo of the mechanism. It works in my model and jibes well with a couple small clues I have from leg images so I am going with it.

If anyone has photos or info on the original mechanisms and would be willing to share publicly or privately I would be very appreciative.

So this thing was a real challenge. Mostly because, as far as I can tell, the original models had a disc on each side of the knee joint with a screw that clamped them together pressing the upper and lower leg ends together. The clamping force and resulting friction would have been needed for the joint to hold position while being animated.
The real head scratcher was getting the internal rotating parts of the mechanism to drive the external rotating knee plate. A rotating shaft was not possible because the clamping screw occupies the center pivot point. So... I resorted to magnets. Two small magnets (chrome pucks in the images) are mounted on the internal rotating plate. These couple magnetically to the external rotating knee plate which has a small steel puck hidden in each end. This actually jibes with every walker photo I have seen that has the rotating knee plates removed. The knee disc has no holes or anything that I can decipher that could allow the knee plate to be driven through it.
Studying scenes in the movie frame by frame leads me to believe that the foot ring motion drives the knee plates so I have the mechanism set up to work that way. A thin cam plate hidden in the foot ring gap drives the mechanism. Take all with a grain of salt. This could of course be nothing like what was in the models and most likely isn't!

 

[Scarecrow Joe]

Interesting!

 

[Sym-Cha]

Does this help Big C ?

There seems to be a rubber band going over the pivot cam towards the knee cap (?)

Yet there's also an opening in the lower leg parts as seen on the right in this close-up:

Pictures Courtesy Lucasfilm Ltd.

Chaïm

 

[joberg]

Wow...this leg animation is the bomb

 

[Big C]

Does this help Big C ?

View attachment 1655471

There seems to be a rubber band going over the pivot cam towards the knee cap (?)

Yet there's also an opening in the lower leg parts as seen on the right in this close-up:

View attachment 1655472
Pictures Courtesy Lucasfilm Ltd.

Chaïm

Thanks Chaïm! I've seen those images but that is a very interesting idea. The mechanism may simply be a cord/rubber band going from the upper leg cam through perhaps a hole drilled lengthwise through the upper leg to the knee joint. A cord could then be wrapped around a spool that would spin the knee plate.