The success of this kit lies at it's foundation. So, instead of having all that fun with the top/cosmetic section first, I've decided potential walker builders must slog through the tedious mechanical bits first.
First and foremost: There are a lot of parts, and keeping them in the right orientation can be challenging to builder's not familiar with the AT-RT's geometry. This is an excellent rendition used for the Battlefront II AT-RT as well as the version that this kit was based. The pictures are excellent, and will help you keep track of things. https://www.artstation.com/artwork/lknEY
First up is the feet. They are cast from an open faced mold and are very easy to finish up. Simply sand as you would any flat bottomed part on a flat surface, but instead of using the usual 220 grit sandpaper or so, I recommend starting at something around 100. Then do a light scuff-up of all the other surfaces with 400 or wetsand 220.
Since we're already here, we might as well sand the toes. Clean up the seam lines with an exacto knife, then scuff all of the surfaces. Insert one into the foot and see how it fits. There might be a bubble or two at the base of the toe, but if it is not seen when installed, don't bother cleaning it up. Your prepped parts should look like this:
Once prepped, we can glue the toes. The left toe (left from the AT-RT's perspective, not the builders) is marked with an L and corresponds with the foot pictured below. The toes are a little different, so make sure you glue it in the correct foot or it will be a little off center.
Scuff the mating surfaces of the toe and inside the hole with some sandpaper. Then, but a few drops of super glue to glue it together. Make sure the foot is on a flat surface, and make sure the toe is also touching the "ground" at the tip, and centered. This will make the foot as stable as possible.
Moving on to the ankle joint and lower calf. Open up your parts kit, and grab these guys. Note that the caps for these bolts are stainless steel, vs the aluminum caps that came with the longer bolts. DO NOT mix those up. You need the strongest materials at this joint. This is the most important joint on the whole kit, so follow these steps carefully.
It seems a little strange, but we need to sand the both sides of the rubber spacers. Make sure they are completely sanded on both sides so there is no "shine" left on them. This will help it grip the resin.
You're going to need to scuff up the bolt posts themselves, too. The best way is to use a rotary tool with a cut off wheel attachment to scuff up the metal. I like to put shallow gashes in the metal and rough it up a little with the edge of the disk. Ideally, the underside of the cap and the first quarter inch of the post need some texture added to them. If you don't have a rotary tool, some manual sanding will have to do.
After that, put a single drop of glue on the area you just sanded, and insert it through the hole in the ankle in the direction pictured. Its ok to go light on the glue here, we're going to put more on from the other side. try and get the post as centered as possible relative to the plastic, NOT the hole drilled. The holes are sometimes a tiny bit off and are a tad larger than the post diameter.
Once the glue has dried, sand the post a little as well as the small rectangular nubs used for friction. (220) Then, glue one of those washers you sanded into place firmly against the friction plate.
Now we can simply bolt up the lower calf to test the fit. The metal post you just installed can vary in length just a tad, so a washer is included just in case. Install the calf without a washer first if you can. Then tighten it up to a moderate amount, move it around a bit. eventually the rubber will compress and you will probably need the washer to keep the tension. After break in, I recommend tightening down the ankle fairly firmly in the position you will most often use, and use the joint sparingly. When you do pose it, it will help longevity to loosen the screw, position, then re-tighten.
Give the lower calf the prep work and scuff to the level you desire.
Then, take a piece of 220 sandpaper and fold it in half, twice. The edge is firm, yet flexible, enough to get down into the circular grooves. We need to scuff those up and remove any imperfections on the surface. (and if you painted before assembly, it is probably better to get rid of any paint that made it into these grooves.)
Grab the upper calves and do the same thing. (Prep the parts, sand the circular grooves) With the upper calves prepped, we're going to install the lower fender. Look for these two little guys and flip them over to the bottoms. Then sand the bottom as pictured before vs after. Keep in mind that the area being sanded angles back a tad to fit the geometry of the leg. It is not a perfectly flat surface.
Then glue them into place on the upper calves. They go on the side with the rectangular panel. Having the fender on there before gluing the joint/pins will help easily determine which side of the calf is "up" for assembly.
With all the resin prepped and ready to go, go into your parts kit and grab these guys. Make sure to wipe down the O-rings with a towel, as they might have some residual oil/lubricant from the factory.
Rough up the metal screw posts just like you did at the ankles. Only this time, we're going to rough up the top 1/2" of the post instead of just the top 1/4". Install the O-rings into the grooves of the lower calf and press them in firmly. They will stay in place. Then carefully slide the assembly into the bottom of the mid calf. Make sure the leg is "bent" forward, and the fender you just installed is facing up!
Carefully put the joint together and put the post through as a test fit. Check the orientation of your parts. The fender faces upward when the leg is bent. Then check. Then check again. Once you glue the post, you cant go back easily at all.
Just like before, put 2-3 drops of glue at the end of the post, then push it all the way in. We don't need tons of glue here, we're just trying to stop the post from rotating during tightening, we aren't gluing the leg together directly. Get the cap for the other side, and tighten it up just a little while it dries. wait about 20 seconds, then try and bend the leg a little. If all is well, the bolt will stay in place, but the leg will still move.
We'll move on to the magnets and hips before we do the thigh joints. Get out these parts:
It is recommended to rough up all the magnets with some 220 sandpaper. I find that keeping them in a row makes it easier to sand the round edges all at once. (in progress, pictured below) Then, individually take them off (can be a challenge) and scuff up the flat side the same way you would a resin part.
Get one of the pistons, and sand the little nook at the tip of the ball joint, then glue a magnet in. There is enough clearance that after the magnet is placed, you can still drip a tiny bit of super glue along the edges to cement it even more.
Get out the other three piston parts, and do the same. Make sure the magnetic polarity is facing the identical direction on all parts. it will make your life a LOT easier.
The thigh parts have obvious mounting locations for these pistons/magnets. Rough up the cavity, check the magnetic polarity several times, then glue the magnet in. Make sure the magnet sits flush with the bottom of the cavity. (push it in with something non-magnetic) If it is too high, the ball joint won't rotate as smoothly and will be a weaker bond. The piston part with the smaller spherical end is the one that goes here. (Pictured)
Enjoy the fruits of your labor. Wiggle it around, make it extend, etc. It isn't your first time.
Home stretch. The Hip parts are last. Make sure you grab the last two stainless steel screws for the posts. (They should have came attached to the hip joints when they shipped to you) The are shiny, and magnetic. The aluminum ones are not. Rough up the track in the hips, the thighs, and a little bit of the surface of the 0-ring. (This process is the same as the lower calf joints, so no pictures required. )
Do a test fit with each of the thighs. If the aluminum post is really close to the surface, you may need to sand/grind down the edge of the aluminum about a MM or so. It is very difficult to suspend hardware in molds while they are being rotocast, so a slight variance is always possible. The one pictures below checks out, just barely but may be shortened in the future as the 0-ring compresses over time.
You can go ahead and screw it in. These joints, along with the ankle joints can be removed at any time. Here's a picture in the correct orientation for reference. As you can see, the large fender points up, and the mounts for the magnetic joints face inward. ( I don't recommend gluing the large fenders until after painting as it is easier to paint, but it is your call. )
The joints/process between the upper calf and thighs are identical as the other joint you did earlier that utilizes two O-rings. I recommend removing the calf from the hip as you assemble/glue that joint if you haven't installed it already, but the order isn't important aside from ease of assembly.
With those last two joints done, you're ready to start messing with the poses and get ready for the top half!
before you tackle the top half though, I recommend breaking in the bottom by posing it, and re-tightening the joints periodically.