The R2-D2 Detail Catalogue Part C: Legs, Shoulders, and Feet

TABLE OF CONTENTS

Legs, shoulders, feet

The droid's body is supported by two outer legs and feet, and a small third retractable leg in some cases.

Shoulders: buttons

The tops of the legs are often called R2’s “shoulders,” which is a little funny, really. Since they visually appear to be the droid's upper arms, but of course he hasn't got any – his shoulders go straight to his legs! Anyway.

The curved parts are commonly called the “horseshoes”. Each horseshoe has three details on it - a pair of small squat cylinders (commonly called “buttons”) inside square recesses, and a single long multi-part cylinder that's sometimes called a “hydraulic” detail, though it barely resembles an actual hydraulic device.

ANH: The round shoulder buttons were actually “found” objects, and weren’t custom-fabricated for the film. Each consisted of two parts: a squat aluminium cylinder 1" in diameter, topped with a small flattened cone 1/2" in diameter. The cylinder had two small threaded holes on the top, set 90° apart. In most scenes these holes were arranged facing up, though occasionally you can see one or the other of the buttons rotated.

The cylinders on the ANH droids were part of the lower tone arm support for a British-built Hydraulic Reference record turntable. This luxury audio product was designed in 1964 by David Gammon, was made and sold by his Transcriptors company for over a decade, and was famously seen in Stanley Kubrick's 1971 film A Clockwork Orange. Transcriptors is thus the name of the designer's company, not a product name.

 J. A. Michell Engineering Ltd. subcontracted the manufacture of various parts for Transcriptors until 1973, when Gammon moved his factory to Ireland. The “Michell” version of the Hydraulic Reference was then manufactured under licence from 1973 until a dispute between the two firms caused the agreement to cease in 1977. Later Michell-produced Hydraulic References were cheekily badged "Michell Transcription" turntables, which I understand was one of the points of contention between the two companies.

In 1976 the Michell company happened to be located near EMI Elstree studios in Borehamwood, and ended up supplying the Star Wars set decorators with tons of aluminium components. The filmmakers, it should be said, just bought boxes of spare parts – they didn't buy and throw out high-end turntables just for a few bits!

And so Michell-made details can be seen throughout the Original Trilogy. They're on many Death Star control panels, the Blockade Runner's escape hatch buttons, R5-D4's antenna, the Millennium Falcon's bench panels, the Tatooine homestead garage, Chewbacca's bowcaster, X-wing fighter cockpits and pilot chest boxes, Boba Fett's costume, Imperial officer hats, Vader's belt boxes... the list seems endless. Finally, in addition to supplying factory parts, Michell was also commissioned to custom-build C-3PO's illuminated eyes. The eyes were machined from large brass discs that were used as turntable weights - they’re visible in the photo above.

Interestingly enough, you can sometimes see in the film and in making-of photos that the angled button (more information on that below) had a visible hole on the side, marked here with the red arrow. This is one of three mounting holes seen on the side of the actual Michell part. So if you want to be truly screen accurate, your shoulder buttons should also have these holes in the side – something most people's replicas are missing!

The real Michell cylinders are known to have this prominent hole at about 45° below the horizontal line, as it were. It's a threaded hole located a few millimetres below the outer surface ("outer" relative to the droid use of the part of the button; they were actually the bottom surfaces on the Michell/Transcriptors turntable!). The other two holes are on the other side and not visible in this photo. They're further down inside the square recesses and thus less visible in the film.

Note that hobbyist shoulder buttons are often done with curved domelike top pieces, but they were actually low cones with straight angled sides, not domes.

Now, there is one exception to this particular ANH shoulder button design. And that is the hybrid alu-fibreglass droid that was used throughout the film, including some of the pickups in California. This one has toured the world with the Star Wars Identities exhibition, so we have good photos of it. And while two buttons are now missing, the lower button on the left side is quite odd looking. It's a flat-topped cylinder with four holes drilled, seemingly at random, into it. It has the same diameter as the other button, but is about 1mm taller.

This four-hole cylinder, which was a cantilevered weight and silicone reservoir from the same Hydraulic Reference turntable, is only briefly glimpsed in the finished film, as shown below. And one photograph - the ILM team setting up the R2 data-download pickup shoot - suggests that it may have been present then as well. (the photo isn't quite clear enough to be unambiguous) Conjecture: this might have been an early prototype shoulder button, built into one of the first droids to be assembled.

ESB: All the droids had the same button design as the two-part ANH one, though it appears that they were custom-made for the film. The hero droids had aluminium pieces, but others appear to have had resin castings.

Shoulders: button-front or button-back?

So. We have the round shoulder buttons. And were they on the front side/leading edge of the horseshoe? Or on the back/trailing edge?

Unfortunately it's not a straightforward answer, owing to continuity errors in, and between, the films. The quick summary is:

ANH: mostly button-front but a few left legs are button-back.

ESB and ROTJ: button-back.

Prequels: button-back.

Sequels: button-front.

Crazy, isn't it? If you want to know the gritty details, read on!

ANH: Generally the two shoulder buttons were toward the front (first photo below), but occasionally they were to the back (second photo below; note that the front of the droid is to the left side of the second shot). This film thus has the most continuity errors in this regard.

 Fans have come up with three explanations for this discrepancy.

1. The horseshoes were removable and interchangeable, and people were sloppy. I doubt that, and I've seen no photographic evidence that the horseshoes were removable.

2. The legs were put on backwards on some of the droids. I personally think this is a bit unlikely.

3. Some of the ANH droids had two pairs of the same leg, and both were right legs. This is the most probable theory.

The photo below shows EMI studio craftsfolk working on fibreglass copies of the leg, which were done as a single unit - shoulders/horseshoes and leg. The feet were separate. Note how the casting has buttonholes on the right. Now, if only one leg mould was made to save money, then two fibreglass legs were cast using this right leg mould. That explains why on some droids the right leg is button front, but the left leg is sometimes button back.

By contrast, the photo below shows one of the all-metal droids under construction. It's button-front on the left, and has all-metal shoulders and legs. The blueprints also show button-front droids. (though note that the blueprint below has shoulder details which differ slightly from the finished droids)

There are no known scenes in ANH or making-of footage that show an R2 spinning around. However, The Making of Star Wars TV documentary, which features the ILM-updated RC metal droid from ANH, clearly shows a droid that's button-front on both sides, since it rotates around on the spot.

But the droid on display as part of the Star Wars Identities touring exhibition, which was used for some of the pickup shots in ANH, has a left leg that's button back, and a right leg that's button front. There is also a behind the scenes photo of Kenny Baker inside the buffed-up closing ceremony droid, indicating that the right leg was button-front. The actual film shows that the left leg of the same droid (unless they swapped droids mid-shoot, which seems unlikely) was button-back. So there were definitely a couple leg-duplicated droids.

Conclusion: based on this research, I think it's clear that button-front was the intended original design for ANH, and the all-metal droids were button-front. The simple reason some droids were button-back is because only one leg – a right-hand one – was duplicated in fibreglass, for budgetary reasons.

ESB: All the ESB (and thus ROTJ) droids appear to have been button-back. Why this change from ANH was made is unknown. A mistake? Someone liked it better that way?

Prequels: I haven't researched every prequel appearance, but it seems the droids in those films were button-back, ESB-style. Even known ANH-era droids used in the film seem to have had their legs reversed.

Sequels: The sequel droids were built with a button-front orientation in homage to the classic ANH look.

Shoulders: button angles

Another intriguing detail on all the original droids also involves the shoulder buttons. The topmost button of each pair is always angled up and in, by somewhere between 10° and 12°. It’s not perfectly perpendicular to the horizon, the way the lower buttons are. This isn’t a mistake - it was designed that way. Why? Nobody seems to know! Maybe it was supposed to portray some sort of socket or connector to be used by standing humans. Or something.

So if you’re building a droid on your own, or accurizing a commercial kit, then make sure to get this detail right. Even if uneducated punters point at your droid and say, “hey man - that thing’s broken! It’s all bent!” Because you’ll know better.

ANH: Closeup views of one of the unfinished metal droids show that the bottom of the upper button's square recess was actually angled internally. Some droids appear to have slightly curved internal recesses rather than straight and angled ones like this. Sometimes the ANH upper button seems to stick out a fair distance. Some hobbyist builders have designed flat-bottomed recesses and cut an angled slice into the top button to cause it to be angled, but that's technically not screen accurate.

The corner radiuses of the metal leg recesses were fairly sharp and square - just very slightly rounded. The interior of each recess was built as a sheet metal box, and appears to have been left bare. The droids with fibreglass legs, by contrast, have rounded (filetted) corners on the square recesses. Some droids appear to have silver-painted recesses.

ESB: The ESB droids also had angled upper buttons. Maybe it's just the limited photo resources we have, but the ESB robots seem to have slightly more recessed upper buttons than their ANH counterparts (ie: the two buttons look like they protrude almost the same distance despite the angling of the top one).

The recesses seem to have been either bare metal or, in the case of the fibreglass legs, painted silver. As with ANH droids, it seems that the robots with metal legs had fairly sharp 90° corners on the horseshoe recesses, whereas the ones with fibreglass legs had more rounded corners.

Prequels: Angled top buttons.

Shoulders: long details/hydraulics

The longer detail on the shoulder, sometimes referred to as a hydraulic detail, varies from droid to droid.

ANH: The original droids mostly had turned metal details, handcrafted from aluminium. Some of the cylinders were knurled, as though they were meant to be turned by someone's fingers. One droid, however, that's on tour with the Identities exhibition, seems to have silver-painted wooden pieces. Whether those were early prototype cylinders produced in wood before the later droids' metal parts were made, or whether the original parts were lost and hastily replaced with these wood pieces, is not known.

Anyway. The shoulder detail shown below left was on the RC R2 during filming of the pickups. Note how the rods are a bit shorter than in some versions of the droid, and how the rods aren't vertically aligned but are up against the top of the recess. The detail below right was on a Kenny R2, and it's not horizontally aligned. There's definitely a lot of inconsistency about horizontal placement for these details between droids - and even on the same droid. It also looks like it's set down a bit in this shot.

From my research it looks like the ANH RC R2 had a left hydraulic that was basically centre-aligned, but the right hydraulic on the RC R2 and at least one Kenny droid (see the droid auction) was "forward" (ie: it was offset to the right when looking at the right side of the droid.) The offset gap matches the blueprints, where additional wires and tubes were shown in the gap. It's as though they decided not to include those additional details after the hydraulic had been screwed into place.

This is kind of a weird detail to replicate if you're modelling the RC R2 droid, since it just looks like a mistake.

ESB: It's difficult to know for certain, but it seems that the second-gen fibreglass R2s had either turned metal or cast resin details, depending on the droid.

Note how the droid on the left has a cylinder detail which isn't centre-aligned vertically. And the one on the right isn't centre-aligned horizontally. Were they like that during filming? No idea - this detail isn't super visible in screen-used footage.

Shoulders: hub interiors

ANH: There were two different designs for the round internal detail, sometimes called the shoulder hub, that was clearly supposed to represent a kind of pivot point.

The majority of the droids seen in the film were aluminium, and had four separate internal curved wedges. The wedges were clearly separately machined parts, were positioned at 12, 3, 6, and 9 on the clock dial, and were slightly lower than the edge of the sloping sides of the detail. At the centre was a simple flat machined disc. This is shown in the left-hand rendering below, which is an approximation of the movie design.

However, there was a second design for this part seen briefly in the film. The droids with cast fibreglass legs, such as the Identities droid, have single-piece shoulder hubs with narrow curved wedges that are positioned at 45° increments. They were kind of the inverse of the first design. They weren't simply rotated, because of the differences in width of each wedge. 

They’re also flush to the top of the internal cone. Instead of a flat disc at the centre this version is equipped with a Michell turntable part - a low cone with a small hole at the centre. The walking Kenny with fibreglass legs seen briefly in the escape pod scene even lacks that centre disc.

The funny thing is that these details in the blueprints, while noticeably different in terms of proportions and angles, were actually somewhat closer to the second design! Now it's true that the shoulder details of these blueprints were for reference, and Peteric and team relied on physical legs sent to them from EMI for their work, but it's still interesting to speculate how this change came about.

 So if you see a commercial R2-D2 product that has this second design, such as the De Agostini/Modelspace kit, you’ll know where that came from.

ESB, prequels, sequels: These droids all seem to follow the first design.

Shoulders: hub interior sides

The sides around the interior of the shoulder horseshoes of most of the droids were actually layered. In other words, they were made from stacked sheets of carefully cut aluminium, of alternating sizes to create grooves. This is another amazing attention to detail on the design of the original droids.

ANH: As far as I know, all the droids had these layered hub interiors. They were also all bare metal, though of course some of them got rather dark due to weathering. The fibreglass legs appear to have had the layers, painted silver.

The one below is an all-aluminium Kenny droid during the droid auction scene. Note that the layers all appear to be the same thickness; a detail verified on the original blueprints.

ESB: The hero droids also appear to have had the layered interiors. The one below is a hero Kenny R2 from the Smithsonian collection, which seems to have metal legs.

There are differences from the ANH droids, though. First, the inner grooves seem to have been painted white, with the outer grooves left as bare metal. It's not known if that was accidental painting that occurred during a later respray of the droid, or if it was built from the start to have white grooved interiors. Second, the layers appear to be made of alternating varying thicknesses of metal, rather than being the same thickness as on the ANH droid. I don't know if any other ESB droids had this varying-thickness design.

Some droids with fibreglass legs may have a smooth interior surface, rather than the stacked/layered parts. Most commercial toys/models of R2 also have smooth interiors like this, because of the difficulty and thus cost of making a ridged near-circular detail using injection moulding technology.

Prequels: The prequel’s Uber droid, shown below, is smooth and painted silver.

Sequels: The sequel droids had traditional layered interiors.

Shoulders: under-arm details

ANH: At least one droid, the “Identities” droid used for pickup shots in California, is missing the small greebly fastened to the “armpit” area under the shoulder horseshoe. Most of the robots, however, have machined metal details here.

These details are sometimes called “leg stabilizers” by fans. I have no idea who dubbed them that, or if the original R2 designers had any intention behind them other than looking mechanical and cool. I’m not even sure what they were supposed to do since the design doesn’t make much sense. Maybe you were supposed to be able to tighten or loosen the struts using the small lower wheel? But then why knurl the upper cylinder when it couldn’t rotate at all since the struts go into it? Mysterious.

That said, one of the leg blueprints does show some angled dotted lines suggesting that the designers intended some sort of leg swing mechanism that pivoted around this point. How this was intended to work, since it was presumably abandoned as an idea, is not known.

The RC R2 has a deep cutout behind this detail. Other droids simply have shallow recesses, such as the one shown below, for the details to fit into. The recess always seems to be bare metal or silver-painted. Some hobbyists paint the recess white, but I’m not aware of any screen-seen droid like this.

ESB: I think they all had the same greeblies. Note that they weren't all installed at a consistent depth or distance from the outer angled surface of the horseshoe - there was some variation. Also many of the greeblies were cast in resin, but some may have been actual turned aluminium parts. The knurling appears to differ from the ANH parts.

Prequels and sequels: Greeblies present and accounted for.

Shoulders: pivots/flanges

There are bare-metal cylindrical parts that sit between the shoulders to the body, and they vary slightly.

ANH: The metal droids appear to have had flat sheet-metal rings that were part of the shoulder assemblies and which extended into a hole in the body barrel. They therefore differ from a lot of hobby designs, which have thick sturdy weight-bearing rings.

The Kenny droids had legs that were fairly close to the body, and no gap is visible on the body barrel side. In this regard they match the original blueprints, which specifically read “1/8" clearance leg & body.” A tight gap definitely seems to be the original intent of the designers.

The RC droid had wider spacing between the legs and body, and there's also a noticeable gap between the metal of the cylinder and the body. This is a useful way of telling the RC droid apart from others.

Since under-construction photos of the RC R2 show legs that were notably closer to the body, like the Kenny droid above, it seems that either a change was made along the way, or the damage to the shoulder pivot caused this gap to widen.

ESB: The ESB droids all had leg/body distances that looked like the ANH Kenny droids, and no gap is visible.

Legs: movement limiters

ANH: At least one, but presumably both, of the two-legged "Kenny" droids had special movement restriction grooves and brackets on the legs and body barrel, limiting the degree of travel possible on the legs. A bolt passed through to a slot on the leg. These things were an important safety feature, as they kept the legs from moving out too far. Baker would've probably fallen over if that happened. The ANH brackets appear to be rectangular with rounded ends.

ESB: The ESB Kenny droids had a similar feature, but they seem to have been rectangular.

Legs: side details

ANH: One of the important, and surprising, things to keep in mind is that R2-D2's legs were designed as telescoping mechanisms. The shoulder and leg are one piece, but fit into a sleeve in the ankle. The decorative metal rod on the outside of each leg could also telescope slightly.

The reason is partly because R2 was initially designed to walk. He never really could, but with Kenny Baker inside, the spring-loaded ankle/leg mechanisms could expand and contract a small amount to accommodate his shifting weight. The other thing was three-leg mode. With the body extended forward, the legs needed to be slightly longer than in two-leg mode.

What this all means is that photos of the droids appear to have continuity errors in terms of leg length, but that wasn’t necessarily the case. Sometimes the position of leg to ankle, or the position of rod details, would change depending on leg length. An empty Kenny R2, for example, will sit a bit higher than one containing Kenny Baker.

In terms of other details, I think all the ANH droids had horizontal grooves partway down the leg. The groove that continues over to the blue section of the leg is painted silver, or else left bare metal.

Fans sometimes call the vertical blue sections of the outer leg the “booster covers,” owing to the fact that the rocket engines seen in the prequels pop out from here, but of course this is a retroactive name when applied to OT droids. Many fan-built “booster covers” have sharply machined rectangular corners on the verticals, but the actual ANH props had slightly curved (radiused) verticals, since they were bent pieces of sheet metal.

These blue sections have two pairs of silver-coloured vertical grooves or recesses. On the metal droids these grooves extend all the way down, below the ankle bracelet or flat silver detail. However, on the “Identities” droid and the awards ceremony droid, which both had fibreglass legs, these grooves seem to terminate a short distance before that. This is because there are differences in leg length and geometry, including the position of the horizontal groove.

There are also two deep recesses at the top of the blue section. These are generally silver coloured on the inside.

ESB: Most of the ESB droids appear to have the horizontal groove on their legs, but at least one does not. Sometimes the groove in the blue section is painted blue. Sometimes the vertical four grooves are also blue and not silver.

However it isn't clear if the grooves were all silver during the original production, and then some of the droids got repainted blue years later. I suspect it may be the latter.

Prequels: The Uber R2 has the silver groove in the blue “boosters” but lacks the groove over on the white section of the leg.

Sequels: Grooves on both blue and white sections of the leg.

Legs: side rods

ANH: The turned metal rods that are recessed into the legs vary in appearance throughout the film. Look at the two photos above. Note how the first photo shows a primary leg rod (ie: the main shaft) that is the same diameter all the way down. Whereas the second shot features a leg rod that's narrower in diameter at the top, and then is wider the rest of the way down.

This is in part because the outer rod telescoped on some of the droids. They were part of the spring-loaded leg mechanism that made it easier for Kenny Baker to walk. It was quite a complex arrangement, since the leg could sink into the ankle on springs, and the leg's rod could also telescope in and out.

The shot below is of a Kenny-powered R2 hopping about in the Yavin IV base.

Or consider the shots below. The left-hand droid is a Kenny droid, photographed during the awards ceremony. Baker was inside the droid at the time, so the rod is compressed from his weight. The second shot is an empty shell droid. The third is the RC R2.

Oddly, the RC R2 droid had a two-diameter rod in Tunisia, but by the time filming began in Elstree it had acquired single-diameter rods as seen above. The famous Seidemann promotional photos taken of the RC R2 therefore show single-diameter rods. There was no reason for the RC R2 to have telescoping rods.

Finally, the sort of cube-shaped bit with a disc at the top of the rod protrudes from the blue section to different amounts depending on the droid.

ESB: Same variations as ANH - some rods are single-diameter (perhaps the resin cast ones were fixed?) and some are two-diameter.

Battery boxes: hangers

The outer feet have rounded-top enclosures that are usually called “battery boxes” since they clearly are supposed to look like interchangeable power packs for the droids. However, they didn't actually contain any batteries in the practical props, and were used to disguise either the motor mechanisms or Kenny Baker's feet.

ANH: Most of the ANH droids had hanger devices, or spacers, for the foot batteries. These hook-shaped pieces are also clearly seen on the original blueprints, and even on the wooden R2 prototype.

However the two-leg droid used at the end of filming at Elstree and at ILM - the “Identities” droid - appears to be missing the hangers. It has a vestigial hanger hook on the back side of the battery boxes, but only shaved off hooks on the front. Its boxes appear more or less stuck to its feet. Identities has a box-foot gap of maybe a couple millimetres, filled in with gobs of paint.

On regular ANH droids, each box and foot were linked by two hangers, which allowed for a narrow gap between each battery box and each foot. It also meant that the inner surface of the ankle and the inner surface of the foot are parallel vertically.

Funnily enough, the battery box hangers were then pretty well forgotten about for decades. Tons of droid replicas were made without the hangers, and in fact some hobbyists even denied they existed! Relatively few droid replicas have them, in part perhaps because they can require a little extra work to make, but at least we have them fully documented now.

ESB: The ESB droids didn't have hangers - the battery boxes attached directly to the side of the feet. The feet had slightly different geometry to compensate for the missing hangers (see the foot recesses section for details).

Note an interesting detail in the photo below. In the gap beneath the ankle detail you can see a white-painted rectangular block of plywood, and above that a narrow rectangular block of white HDPE plastic. These are not original parts - they're wedges or blocks placed inside the two-legged R2 for display purposes. They're there to prevent the ankle from rotating and R2 from falling over! For a closer look at the wedges, scroll down to the “ankle details” section.

Prequels and sequels: No battery box hangers, except for the ANH droids reused in some prequel scenes.

Battery boxes: protrusions and hoses

Each battery box has a pair of bits which extend out: one to the top, one to the bottom. I don't know if they have names, really, so I'll call them protrusions for lack of a better term. The top one is featureless and painted white; the lower one has the two battery hoses plugged into it.

Finally the battery “hoses”, as hobbyists call them, were braided copper cables, and were presumably supposed to represent high-amperage power leads from the batteries to the foot motors. They were attached to brass/copper tubes or sockets which may have been diamond-knurled. However only the Identities droid has photos high-rez enough to confirm finely knurled connectors; I haven't seen clear enough photos of the RC R2 and Kenny droids to say for certain if they did as well. All the copper was either corroded or chemically darkened to a brownish goldish sheen.

ANH: There are two notable things about the ANH era protrusions. First, the top and bottom protrusions are not symmetrical. The lower one is taller, and is effectively a half circle (or half cylinder). The upper one is not as tall.

Second, the lower protrusions have additional bare metal plates, fastened by three pop rivets, on the RC R2 and the Kenny droids. The rivets are present from the first day of filming in Tunisia. The stunt droids and the “Identities” droid do not have rivets.

This is an approximation of the battery box issue described above. I’ve modelled the ANH design on the left. You can see that the lower protrusion is much taller than the upper one. You can also see the ANH-style lower riveted plate, and the ANH harnesses, though this model has the top hinge pressed up against the upper protrusion rather than angling back into the box, which they probably did (see the battery harness section).

The box on the right follows a design commonly used by Astromech club builders. It has two protrusions of the same height (they really are the same in this model – it’s just the perspective that makes them look asymmetrical) and the battery harnesses have the really deep hinge slots not seen on any OT or prequel droid.

As a side note, you can also see that the RC R2 has two flathead/slotted domed screwheads visible at the bottom of the ankle slot. These screwheads are present in the earliest construction photos taken at Peteric. No other droid has these screwheads that I'm aware of.

ESB: The Smithsonian's Empire battery boxes are asymmetrical, with a taller lower protrusion and a short upper one. The taller box yields a more prominent upper box look. Now, it's very difficult to make out the battery box detail in the actual film. But each one I can identify in the film or in behind the scenes photos has asymmetrical battery boxes.

Interestingly, the boxes were cast in fibreglass moulds without the protrusions. These were then glued on later. You can see boxes sans protrusions in some making-of photos, and close examination of the Smithsonian ESB R2 shows visible cracks and seams where the half-moon protrusions fasten to the main battery box.

No ESB droids has the riveted metal plates. However, one hybrid droid that has been displayed at various exhibitions ("Magic of Myth", Madrid Spain, Dundee Scotland) has symmetrical battery boxes with a silver-painted thin plate, glued to the lower half-moon protrusions. It's not clear if that droid was modified, perhaps during the prequel era, to have the later symmetrical box design.

Prequels and sequels: The Uber R2 built for the prequels has a noticeable difference in battery box design. The two protrusions are both the same size, and are of the taller type. I believe the sequel droids follow the same design.

Note that the Astromech CSL/CSR specs have ANH boxes that match the blueprints and photos. They also call for ESB boxes that have protrusions of identical heights (symmetrical). But unlike the prequel version the ESB dual protrusions are both of the lower size, which isn't consistent with screen appearances.

Battery boxes: harnesses

The “harnesses” are metal bars on the front of the battery boxes, which presumably were meant to represent some sort of clamping or lock-down mechanism. They're machined aluminium (or cast resin) details with raised blue rectangular buttons that are, one assumes, release catches. A source of noticeable continuity issue in the films, they're in different positions on different droids at different points in time.

The harnesses also differ in shape.

The diagram above is based on my examination of a whole pile of photos and screenshots. So I do not claim that they're 100% accurate. They're certainly not taken from physical measurements. However, I think they get the basic idea across. As you can see, the ANH harnesses have shorter buttons, so there's more bare metal in the flat section above them. The ESB harnesses have longer buttons, and the blue details are often bare metal on the sloping sides.

It's worth mentioning that the Astromech club CSL/CSR hobbyist design is kind of like the ESB harness, but with a very large and deep hinge slot for some reason. This deep slot is an error propagated during the early days of the club and survives to this day. It's not seen on any OT or prequel droid, but is seen on the sequel droids.

ANH: The blueprints show the harnesses in line with the battery hose connectors. But the RC droid in the auction scene has the harnesses right on the outer edges of the battery boxes. Later in the film the inner pair was sometimes missing altogether to provide adequate clearance for the bracing bars. Photos of the three-legged droid being built at Peteric show the harnesses right out at the edges of the battery box, and indeed the single shot below of the three-legger heading towards the camera in the auction scene does as well. Note how the RC R2 tension wires are visible here.

The top pieces of the harnesses feature a T-shaped piece that inserts into the main piece. This is machined in a way that suggests that it's supposed to flip out on a rotating hinge, though of course we never see this in the films. The "Identities" droid and a Kenny droid show that there are small recessed holes at the top of the harness on the sides, implying a recessed pin that the thing could theoretically rotate around. I haven't seen any photos of the RC R2 clear enough to show what they had.

The original 1976 blueprints show the top T-shaped hinge piece angling up and fitting into a rectangular hole cut into the top of the battery box recess. There is some photographic evidence suggesting that this may have been done on the finished ANH droids, but unfortunately there aren’t that many photos showing this area of the battery box in much detail.

Backing this idea is this shot of an R2 under construction at Peteric. Look at the harnesses - they're weirdly long at the top, and stick out a long way. This is clearly shows that the top part of the hinge assembly is quite long. The idea is that the battery box recesses had cutouts in the top overhang, and these long bits of the hinge went into them, which is why the harnesses lay almost flat when finally installed.

This design may seem rather confusing, so hopefully this diagram will help explain how it seems to have worked. On the left is the ANH original design with the angled top hinge part which fits into a hole in the battery box. On the right is the simplified ESB design, which has a top hinge part that simply presses up flat against the top protrusion and is typically glued in place. This latter is the design most commonly seen on droid replicas. Note how the different designs result in different angles to the battery harness component.

The blue rectangular “button” detail has 90° corners, as with the RC R2 above. The Kenny photo below looks like its harness details have radiused (rounded) corners, but a different higher-resolution photo of the same droid shows sharp-edged details - the rounding is an artefact of that image.

Unfortunately many fan-made harness replicas have rounded corners on the “buttons” even though they don’t look like screen-used OT and prequel droids, simply because it’s easier for them to make them that way. (they use CNC-routed holes in the harness body, which results in round corners)

ESB: The battery harnesses are always paired in this film. I think their positions were fairly consistent - just slightly past inline to the hose fittings. The resin castings seem a tiny bit wider than the ANH ones, perhaps. They also don't appear to be quite as far out from the edge of the battery box. (ie: the ANH harnesses seem to have a little bit more of a gap) Strangely some droids seem to have slightly dissimilar pairs. Look closely at the harnesses below - the left hand one has a blue button that's slightly higher than the right, and the top part of the harness is a bit longer. The right-hand one below looks like an ANH harness, only with a longer button than those ones had.

The ESB ones often have blue facing rectangles with sloping silver sides, rather than being all blue.

The tops of the hinges angle up to touch the top of the battery box recess. Therefore the hinge tops are always flat against the recess. You can see this design in this cast resin harness that was apparently made for ESB and auctioned off later. The flat hinge top, and glue blob, is clearly visible. You can also see the sloping sides of the rectangular blue button. This particular droid seems to have had all-blue buttons, rather than a blue top with silver sides.

Battery boxes: covers

ANH: The RC R2 droid had curved pieces of thin sheet metal screwed onto the battery boxes. The three-leg battery boxes had the same cutout holes as the two-leg Kenny droids, which used the holes to accommodate Kenny Baker's feet and ankles. However, in the case of the RC R2 there was a large cylindrical traction motor that protruded slightly. So the motor's black cylinder was painted white, and a thin piece of metal was wrapped around the box to cover over the rest of the foot hole.

The second shot below demonstrates that the metal plate had an open notch (ie: open at the bottom; the metal sheet was an upside-down U shape) cut into it for the protruding bit of motor. The third shot is from the winter 1977 issue of Electronics Tomorrow, and clearly shows how the traction motor was painted white to disguise it. It also reveals that the boxes were painted white after the metal sheets were initially installed.

An important point, that Robert Jackson of OpenR2 has pointed out, is that the Lucas 17W windshield wiper motors that were used for traction purposes weren’t symmetrical. Nor were they sold as two products with gearboxes on opposite sides – they were all built in one specific and assymetrical configuration. For this to work on R2, it meant that the left and right motors on the feet were not mirrored: they were handed, resulting in protruding motor cylinders that were back of the centre line on the left battery box, and forward of the centre line on the right battery box. The photo below shows the right battery box, and you can see how the protruding motor is located towards the front end of the box.

This is a fun detail that most people have missed for years, since very few photos of the inner surface of the left battery box were ever taken of the ANH RC R2. One of the best shots, in fact, was from a promo photo taken for the infamous Star Wars Holiday Special. You can also see the protruding left motor in the studio footage taken for the Making of Star Wars TV documentary.

Sideshow Collectibles and De Agostini have both made commercial R2s which assumed the motor positions were mirrored (they got the left side correct and the right side wrong), as have many hobbyists. Interestingly, the Bandai Tamashii Nations Chogokin R2 has the handed motor locations correct. (probably because it benefitted from Seiji Takahashi’s research)

This final shot is of the empty shell R2 which was used on the landspeeder. Note how it has a metal plate to cover the battery box hole, but there's no notch in it since that R2 had no traction motor. (it also had no Kenny in it) This version of the plate has 45° chamfered cuts on the lower corners, as well. It's an odd colour and texture, so I wonder what it was made from.

ESB: The ESB droids didn't have these cover plates and protruding motor cylinders. They were just smooth, clean-sided boxes.

Battery boxes: tension cables

ANH: The RC R2, which had the 2-3 leg capability, relied on “tension wires” on each outer foot. These were clearly indicated on the original blueprints, and were intended to keep the legs from splaying out in 3-leg mode.

They're hard to see, but are briefly visible for a split second or two in the movie if you have an eagle eye, a high-resolution copy of the film, and a pause button. (you can see the wire flopping around in the Death Star closet scene after the droids are found by the stormtroopers) They run between a small hole in the battery compartment top and the edge of the skirt.

They're described in the Electronics Tomorrow article (see photo above) as “leg distance wires”. The John Stears manual says that R2-D2 “utilizes a wire to maintain each leg at the correct distance from the body. However, it fails to sustain this distance during turns, as the inside leg tends to move forward, disrupting the overall balance.”

ESB, prequels, sequels: No tension wires were required or used.

Battery boxes: angle bars/bracing bars

ANH: Sadly the cable tensioners proved to be insufficient to hold the legs together. In a handful of shots, metal bars and angle irons can be seen bolted onto the three-legged RC R2 droid, linking the lower body barrel and the ankles. John Stears’ R2 manual says, “When the robot needs to run in its three-legged form, distance struts should be fitted.”

The angle irons shown below were an improvised solution, added post-construction, for fixing the robot's shoulder pivot problems on the three-legger. These ones are heavier than the lightweight sheet metal brackets seen in the Tunisia sequences. They also required the removal of one of the battery harnesses on each side.

Weirdly, I've heard these referred to as “ILM bars”. The name doesn't make sense, since the ANH droids were built in England and not California. And the support bars were clearly added to the three-legged droids during the course of filming in England. It seems somebody incorrectly thought the bracing bars were added to the droids once they'd arrived at ILM in California for pickup shots. That, or maybe they thought ILM was involved with filming in the UK, which was not the case.

Incidentally, while this bracing bar add-on is generally associated with the all-metal RC R2, it wasn't the only time it was needed. The fibreglass body R2 that was hacked into service as R5 for the droid auction scene filmed in Tunisia also had bars. The fibreglass body was intended to be a two-legged, so the bracing was needed to keep the body tilted back for three leg mode.

As shooting progressed, various holes were added to the vertical flat recessed plate on the battery boxes on the RC R2. In Tunisia you can see the RC R2 had two holes at the very top – visible in the photo above. Two more angled large diagonal holes were added at EMI for the angle iron bracing bar.

Two pop rivets at an angle were added at EMI as well, since they don't seem to be present in Tunisia. The purpose of the pop rivets is not known for certain. Conjecture: I think it's quite likely they held a metal backing plate in place. This plate would have thickened the interior battery box wall, thus strengthening it. Since the original battery box sheet metal wouldn't have been intended to be able to handle the torsion placed on it by the bars. Same with the nut and washers that appeared on the edge of the RC R2's skirt - it also had thin metal that needed to be braced to support the angle brackets.

ESB: The revised droids had sturdier shoulders and didn't require these hacks.

Prequels: The UK-built “monster truck” R2 built for high clearance desert sand operation, officially called the “sand unit” by the production team, didn't have ANH-type bars. However, it had a bar almost at ground level, joining the outer feet. The Uber R2 had no bars.

Sequels: No bars.

Ankles: locations

ANH, prequels, sequels: All the ankles are centre-aligned with the feet.

ESB: Most of the time the ankles were like all the other droids. However, two scenes involved special gimmicks which required ankle relocation. The famous scene where a sad wet droid stands up on tiptoes to peer into Yoda's hut was one, and the scene where R2 gets to his feet after falling out of the air during the Jedi training was another.

You can see in the photo below how the ankle position was offset all the way to the back of the foot to allow the gag to happen. The droid builders had to make some hasty modifications to make it possible. In fact, in the shot of R2 getting up you can see the centre holes at the top of the foot where the ankles normally hinge. This modified ankle was also used for the scene in which R2 sits himself up after being spat out by the swamp monster.

Ankles: L-shaped details

The ankles have metal (or cast resin painted silver) details front and back. These are complex and vaguely L-shaped objects, with a curved inner edge and an angled side. They have chamfered tabs at the top, and a small rectangular recess below that. Like most R2-D2 details, they look great, but I have no idea what, if anything, they're supposed to do, story-wise! They're not easy to see in the film itself, as you rarely get closeups that show the droid's feet. 

ANH: The ankle detail has a projecting tab at the top that's almost always blue. But there is one obscure inconsistency – during filming in Tunisia the RC R2 had unpainted projecting tabs on the backside of the feet. Other than that one time, the tabs are always blue.

Another thing worth mentioning is that older Astromech club plans (CS:L) have an incorrect projecting tab design where the tab is curved at the top. No non-fan droid that I've seen has this - the tab is always angled at the top. The CS:R design fixes this error.

The horizontal recessed rectangle below the tab appears to be bare metal in the 4K film scans I've seen. However, it appears the RC R2 may have gained white-painted recesses sometime after filming concluded, as shown in this photo taken in late 1977.

There's also a recess in the white ankle surface directly above each blue tab. Oddly enough this is always slightly more narrow than the blue tab, and is painted white along with the rest of the ankle. Though because of weathering it's often fairly dark in colour.

One unusual detail on the awards ceremony droid is that there's a narrow white strip at the top of the ankle, just below the silver “ankle bracelet” detail. This is not seen on any other known droid.

ESB: Most of the ankle details have blue projecting tabs, though I've seen a couple of photos of a 2-legged ESB-era droid with unpainted silver tabs. Most of the droids appear to have unpainted silver recesses, but I've also seen photos of one allegedly ESB-era droid with a blue recess. However, it's not clear if the recess was blue when the prop was on-screen, or if the paint was applied years later, when the droid was either used in the prequels or refurbished for public display.

This shot also really shows the two blocks - white HDPE plastic and thin white-painted plywood - used to hold the ankle in position for exhibition purposes. Hobbyists often make similar parts that they use as ankle locks.

Prequels: Photos seem to show that the Uber R2 had a blue recess on the left detail and silver on the right. It does not have the rectangular recesses in the ankle just above the blue tab.

Sequels: The sequel droids have blue recesses in their details, and do not have the recesses in the ankle above the blue tab.

Ankles: cylinders

The three ankles are also equipped with cylindrical details, which in most cases are fastened to the ankle via a wedge-shaped piece. There are a few subtle differences between the ANH and ESB versions.

ANH: As shown above, the droids have smooth and continuous, or at least very subtle, joins between the wedge and cylinder. The tapered part-rectangular bit protruding at either end is almost always vertical, except in one brief one-off Yavin hangar scene where a droid seems to have horizontal details.

Another point is that the end cap is fairly large in diameter. It's the lower of the two cylinders shown below.

ESB: As shown in the first diagram, some of the droids seem to have a more visible step between cylinder and wedge.

Also, the end cap is smaller in diameter, as in the second diagram.

Prequels: It’s hard to know for certain, but in the photos I’ve seen the Uber R2 has a really pronounced step between cylinder and wedge - much more obvious than in the picture above. The step is also angled out and quite wide.

Ankles: dots and dashes, or  • —  –

ANH: The original droids have three small curved lines, arranged in a quarter circle, down on the front of each ankle. These lines appear to be recesses cut into the aluminium, and seem to be slightly rounded on the corners, though it's hard to tell. The recesses were then filled in with blue in most cases. Droids that have these lines seem to have them on both front and back sides of the ankles.

The pattern seems to vary slightly. On some units, like the ANH three-legger below left, these details seem to have lines of three different lengths, and the shortest line appears to be almost a square. The Kenny droids seem to have a similar arrangement. It's hard to tell, but it's possible that the shorter line might have been slightly longer.

Other droids, like the Identities droid below right, have two outer lines of about the same length (longer than a square) with the middle line long.

They're a tiny and subtle detail, and I don't know if all the droids had the feature, simply because so few photographs are of high enough resolution to show anything. But the ANH hero droids all seem to have it.

I find it kind of fascinating that a film as low-budget as Star Wars was (relatively speaking) still meant that people had the time and attention to make such minuscule details! They couldn't have been simple to make, given that on the metal droids they were notched into raw aluminium. Presumably they were programmed into the Strippit machine that cut out the parts.

ESB: It appears that the dots and dashes, existed on some of the droids, but may have been filled in with white paint. At least one seems to have raised equivalent details rather than recessed ones, and those are painted white. The Smithsonian's ESB R2 has almost the same basic  –  —  –  arrangement (and unpainted tabs) as the ANH Identities droid, but the ends of each line are sharp corners and the outer lines are a bit longer.

It's really hard to tell from screenshots, however, as this level of detailing doesn't show up in photos and screengrabs very well. The promo shot below suggests that that particular droid has unpainted recesses with a bit of dirt in them.

Prequels: The Uber R2 does not have this detail.

Sequels: The sequel droids do not have this detail.

Feet: outer foot “toes”

ANH: The outer feet have raised strips where the battery hoses attach. On the three-legged R2, and at least one of the two-legged Kenny R2s, an extra metal plate can be seen. This is riveted to the foot at three points, and is pretty misaligned on one side. The other droids have single strips and no rivets.

Conjecture: it’s reasonable to assume that the aluminium strips were added when there were problems attaching the battery hose ends to the toe strips. The battery box on the RC R2 has a similar half-circle/half-moon plate on the bottom.

The rear of each foot has a single raised strip, which is painted white on the ANH R2 droids.

ESB: The toe plates appear to be moulded into the fibreglass, and don't have the extra aluminium pieces on top, or the rivets. The moulded parts are tapered on the sides; more so on the top and bottom. None of the battery boxes have extra half-circle metal plates over them.

The toe plates are painted silver, front and back, on the ESB units. They are also a tiny bit wider than the ANH toe plates.

Prequels: As ESB. Note that the Uber R2 has very different foot/ankle designs from all other droids. There should be a deep recessed slot at the top of the foot, required for the ankle joint to pivot within the foot assembly. This slot is filled in on the Uber droid.

Sequels: As ESB, though there seem to be metal plates on the front.

Feet: Kenny leg coverings

ANH: The initial design for R2-D2 featured hard angled shells to conceal Kenny Baker's shins and ankles, but this didn't make it to any screen-used props. The ANH leg coverings seen on-screen were mostly some sort of dark grey ribbed plastic, like an electric dryer's waste heat hose, or the flexible ducting used for kitchen vents. I don't know if it's ever been confirmed where the hoses came from.

These also necessitated large holes to be cut into the battery boxes for Baker's legs and feet to fit. Although only the two-legged R2s required these holes, the three-legged ANH R2 appears to have large cutouts like this as well, covered by a piece of sheet metal.

ESB: These ones seemed to vary - possibly dark ones for darker sets and white leather ones for brightly lit sets, like the medical ship bay. Only the two-legged R2s have the hole openings.

Sequels: The performer R2s have leg hoses. This was a deliberate decision, since of course with modern digital technology it would have been really easy to have the performer wear green leggings and simply paint out the human legs in post production. As a nod to the original films, however, the sequel R2s have visible leg hoses in standing/two leg mode.

Feet: half-moon grooves

All R2 droids have raised semi-circular details, called “half moons” by hobbyists, on the outer sides of the outer feet, and both sides of the middle foot. Each half moon has a raised rectangle, angled differently to the outer surface of the half-moon, containing two parallel grooves at the top.

The grooves always had sharp square ends - they were perfect rectangles when viewed from the front. Some hobbyist droids, especially those which use CNC-machined parts, have round ends to the grooves.

ANH: The ANH droids (below, left) had a spacing of about 3x the width of each groove between the grooves. Each droid also had roughly the same spacing between the panel line recess of the bottom of the trapezoidal motor access plate and the details. Some droids had visible screwholes on the outer trapezoids.

ESB: The ESB droids (right, above) had narrower spacing for the parallel grooves, at maybe 1-1.5x the width of each groove. In addition the half-moons and outer raised details were set slightly lower on the trapezoidal plate.

Prequels and sequels: ESB spacing.

Feet: half-moon locations

ANH: The ANH droids had half-moons and side decorations on the feet that were slightly higher from the bottom of the foot. (see above left)

Incidentally - it seems that the middle foot's half moon details have the same geometry as those on the outer feet. However, the angle of the sides of the middle foot were different from the outer feet, which is why the top of the half moons are angled inwards on the middle foot rather than being parallel to the ground, as on the outer feet.

ESB: These droids had half-moons and side decorations that were a bit lower down the foot (see above right).

Prequels and sequels: ESB locations.

Feet: basic geometry and foot recesses

Each foot has a recess on the inner edge, curved at the bottom, for the battery boxes to fit in. The size and location of the recess differs, depending on whether or not the droid has battery hangers or not. The relative location of the ankle slot also varies slightly.

ANH: The curved bit of the recess ends right up against the base of the top part of the foot, and this design has hangers between the foot and the battery box. The outer side of the foot is also fairly narrow, and thus the ankle slot is slightly closer to the outside edge.

ESB: Since the ESB droids do not have battery box hangers, the geometry of the feet gets reworked. There's a bit of a raised ledge at the bottom of the curved bit of the recess, and the inner bit of the foot is moved over to compensate, resulting in a slightly wider outer side of the foot. The toe plate is also just a bit wider.

Feet: base skirt

Each foot has two stepped ridges at the bottom. On the original blueprints the two steps that form the foot skirt are exactly the same height: see A and B below. It’s difficult to tell if the physical props have the same design, however, because it’s rare to see a photo of a droid taken square-on with enough detail to let us measure the image.

Note that the rectangular cutouts in section A were thinner (shorter in height) on the real props than on these blueprints.

For some reason the Astromech club’s CS:L and CS:R plans do not have A and B the same height. They indicate B should be slightly taller.

ANH: The droids all seem to have same-height steps. The steps seem to be angled in at somewhere between 12 and 14%.

ESB: Same as ANH.

Prequels: The Uber droid has foot skirts that are cut back at different levels, so they are not the same height.

Middle foot: ankle length

ANH: The three-legged R2 unit has a short middle ankle design. In other words, R2 had the pair of cylinders positioned just below the bottom of the skirt.

However, in a handful of scenes in ANH, such as the Mos Eisley street scene below, a fibreglass body was used to sub in for R2. This means the middle leg had a longer exposed ankle.

ESB: The same short ankle design as used on ANH R2s was used consistently throughout ESB.

Prequels: Uber R2 has a short ankle. Some other droids in the films have longer ankles, however. The “monster truck” droid used primarily for desert and rough ground scenes in Episode I has a very long exposed middle ankle.

Sequels: Short ankle.

Middle foot: ankle type, and middle ankle cylinders

Not counting the length variants, there are two basic designs of the middle ankles – the ANH RC R2 type and the “all the other ones” type.

The RC R2 seen in ANH had ankles that are squared-off and flat at the bottom, where they approach the top of the foot. Almost all the other known droids have part-circle ankles at this point, which are not squared off. This difference makes the part-circle design very slightly sturdier, since there’s a bit more material right above the pivot point. 

ANH: The RC R2 has the squared-off ankle. Also, the sheet metal plates used to build the details were also doubled up in areas for extra strength. This thickening of material is visible on the original blueprints where dashed lines indicate the extra metal. I’ve shown this in the image above - you'll notice there’s a little line right by the ankle pivot hole; a line that’s also visible as a shadow in the photo of the RC R2 below.

The two horizontal cylinders on either side of the ankle, unfortunately not visible in this photo, are bare metal on the RC R2, with no blue. The sole photo I’ve found that shows this part of the ankle – a picture taken in Tunisia during the setup for the droid auction scene – shows that there were no blue wedge details above the middle ankle cylinders, the way the outer feet have.

However, a behind the scenes shot of the "Identities" droid, in the comedy corridor-crossing scene, is noticeably different from the RC R2. It has blue wedges on its pull-out middle ankle, and it appears to have the part-circle leg detail and not the squared-off one.

But is it that simple? Nope! A shot of the “Identities” droid, being renovated for the ill-fated 1978 Star Wars Holiday Special, shows that its middle ankle had a blue cylinder detail, the recessed horizontal line groove above that... and a squared-off ankle!

There was also the Frankendroid used in Tunisia, which was a cobbled-together droid that had an outer leg as a makeshift middle leg. Since an outer leg was used, it also had the part-circle and wedge details.

These represent continuity errors of construction, though they aren’t actually seen in the film on R2-D2. (you can’t see the feet in the corridor-crossing sequence in the movie) In fact, you can never clearly see the upper part of any short ankle in any movie. This, and the fact that most droids at exhibitions are shown in two-leg mode, means that there’s virtually no photographic documentation of the middle ankle at all.

Finally it appears that the RC R2 may have gained ankle cylinder wedges for the middle foot at some later date. My guess is that they were most likely added during the extensive refurbishments that took place for Episode I, when the RC R2 had its middle leg mechanism replaced with an ill-fated pneumatic system.

ESB: Like the Identities droid, the ESB ankles are curved at the bottom, as in the diagram above. The metal cylinders on either side of the ankle are two-colour. The middle bit is blue, with the ends bare metal or silver. There are few detailed photos of the underside, but it appears that the ESB droids had blue wedge details above the middle ankle cylinders.

Prequels and sequels: ESB style. One photo of the monster truck R2 from Episode I clearly shows blue wedge details above the middle ankle cylinders.

Middle foot: “toe” and twin holes

ANH: The rectangular plate on the sloping front of the middle foot is a bit short, and doesn't reach the tip of the foot (see above). It's painted white.

The first of the two photos above shows the three-legger. Note that it has two black-headed Phillips screwheads on the front edge of the middle foot, and a couple more on the inside of the pivot mechanism and top of the foot. Interestingly the two front screws aren't seen in either construction photos or in the actual movie anywhere. Even the pickup shot filmed in Death Valley features an RC R2 with no screws in its middle foot. However, all the public appearances from the Chinese Theatre footprint ceremony in August 1977 onwards feature an RC R2 with the two mysterious screws.

ESB, prequels, and sequels: The rectangular plate is longer. (see above) No visible screws. It's also painted white, not silver like the outer feet.

Middle foot: the RC R2’s steering mechanism

ANH: The original RC R2 steering mechanism, designed by John Stears, was a complex assembly with two wheels (one is omitted from the blueprint below for clarity) that moved on an internal frame. You can see that the two wheels were perfectly centre-aligned in the foot in shots where R2 heads towards the camera – the end of the droid auction and the post-Leia Blockade Runner shots, for example.

There is possible evidence of the mechanism working in the movie. The opening droid scene, R2 rolling past the camera in the dune argument scene, the start of the auction scene, the "come on R2" rolling scene in the Death Star - these all show the droid turning very slightly as it moves. It's possible that the Tunisian scenes simply involved R2 careening around on uneven ground, though I think that the steering mechanism was kind of working in those shots.

However, despite John Stears' fulsome praise, this active servo-operated system was complex, unreliable, and didn't permit sharp turns. These issues, combined with the weak shoulder problem which lead to the legs splaying, meant that steering calamities during filming were common.

Accordingly the twin-wheel mechanism was removed and replaced with a pair of passive casters during ILM renovations. This was done by ILM's Bill Shourt, probably after the pickup sequences were shot in Death Valley.

The new middle foot design is obvious in the Chinese Theatre cement ceremony, since R2's footprints reveal the two spherical impressions. This also shows that the casters were off-centre at the time, presumably because they were mounted on pivots and could turn on a vertical axis. And instead of a steering mechanism, the droid's directional movement was controlled by altering the relative amount of torque of each of the outer sets of wheels. This tank-like "differential steering" approach proved far more successful than turning the middle front wheels. You can see, for example, R2 turning fluidly and swiftly in the Making of Star Wars TV special.

ESB: The ESB RC droids also used a differential steering mechanism.

Prequels: The Uber droid used a combination of differential steering and a steerable middle foot mechanism. I don't know how the monster truck R2 did it.

Sequels: As ESB.

Middle foot: the Mystery Box

ANH: A couple of photos, and some in-movie footage, show that a triangular box was protruding from the back of the RC R2's middle foot during filming in the UK. This black or grey mystery box, seemingly made of folded sheet metal, was presumably there to accommodate something related to the steering mechanism. The non-steerable R5 with the undecorated middle foot has no such thing.

The puzzling aspect is that the mystery box appears to have been added to the RC R2 partway through filming, and removed after filming of the pickups was complete.

None of the scenes filmed in Tunisia (the dune argument scene, the rolling towards the Jawas scene, and the opening of the auction scene) have a visible mystery box. Instead you can see a sturdy cable with connectors at each end, linking the middle foot and the underside of the body barrel. This cable is never seen after Tunisia.

However, photos taken on the Tantive IV Blockade Runner set (below) and the Death Star set (above) have the mystery box, clearly indicating it was added during filming at Elstree.

The box is also visible in the actual movie, during two of the pickup shots filmed in Death Valley. It might have been painted white at this time.

No mystery box is evident during the Chinese Theatre ceremony, or the Making of Star Wars, both of which were filmed after the ILM modifications. Photos reveal that a white-painted metal plate was put over top of the opening where the box was.

Conjecture: so, what was the box? Given that there was a power cable on the middle foot in the Tunisian footage, it seems likely that the foot was already powered for steering at this time. However, perhaps the mystery box contained some additional components added by the EMI team in an attempt to get the steering mechanism to function reliably. This mechanism would no longer be needed once ILM had upgraded the droid to use differential steering.

ESB, prequels, sequels: No mystery box.

Feet: the “treads”

ANH: The R2 bodies which were meant as lightweight “shells”, and which could not accommodate either Kenny Baker or any sort of drive mechanism, did not have wheels. Instead, the soles of the feet were given textured “tracks”, suggesting that R2 scooted around on sort of magic tread mechanisms.

The treads were also replicated on the R2-D2 that was strapped to the miniature shooting model of Luke's Landspeeder, reflecting the appearance of the full-sized droid.

However, when R2 is loaded into Luke's X-wing fighter the droid they used is seen to have flat rectangular panels on the underside of the feet.

ESB: No tread mechanisms are known.

On to part VI: R2-D2’s Arms and Tools

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