The R2-D2 Detail Catalogue Part A:
the Dome

TABLE OF CONTENTS

Continuity

Famously, R2-D2 is not the most consistent robot in terms of his physical appearance. Because multiple props were used to represent the character there are a lot of continuity errors from film to film, and even within the same scene! The original Star Wars film of 1977 is particularly rife with such detail issues. Here are just four of the dome configurations seen in the film.

So. What to do if you're trying to make an authentic R2-D2 replica? Well, there are really four basic approaches.

1. Replicate one specific prop as it appeared at one specific moment in your favourite film.

2. Make a composite droid that basically amalgamates all the features of R2 as he appears in just one of the films.

3. Make a composite droid that contains select features as they appear across all the films. This is the approach historically taken by the R2 Builders Club, which devised “club spec” standards which incorporate aspects from ANH, ESB, and prequel droids.

4. Just build a droid that looks however the hell you want.

Which is correct is up to you!

The dome

R2's head was usually a dull aluminium dome. Famously it wasn't hemispherical, as it's often misrepresented in cheap toys and stuff, but was a slightly tall ovoid shape.

Dome: materials

ANH: The R2-D2 domes were all spun aluminium with a fairly matte finish. A wood former was created, and aluminium sheet was pressed against it as it turned. Spinning is a metalworking method commonly used to create lamp shades or the bells for brass instruments such as horns. It differs from lathing. When you turn something on a lathe you cut metal away from the object. With spinning you reshape the metal sheet and no metal is lost.

The dome had the blue neck ring permanently attached, but not the unpainted metal one. The bare aluminium neck ring stayed linked to the body barrel, but it could rotate. This neck ring mated with the blue neck ring of the dome using pins and holes. Thus the most visible gap in this design was between the two neck rings.

Some supernumerary robots, that rolled through sets or sat behind fighter cockpits, had painted fibreglass domes. The fibreglass domes were cast from a mould created from the original lamp bell used as a model for R2’s head.

ESB: The domes for the “hero” ESB droids were also spun aluminium, just like the ANH droids. The dome was mounted differently, however. The two neck rings were attached to the dome assembly, and the whole thing was lowered onto a support rail that extended up from the body barrel. Therefore the visible gap appeared between the body barrel and the bare metal neck ring, not between the two neck rings. In fact, there are a number of moments in the film where you can see the dome's internal lights visible in this gap.

However, at least one and probably two Empire droids had vacuum-deposited chrome finish on their (probably fibreglass) domes. You can sometimes catch a glimpse of a stunt droid with a shiny dome like this, and once or twice briefly in the Bespin sequences. That said, you have to look pretty hard to see a non-aluminium R2-D2 dome in Empire.

However one of these shiny droids was used for public and promotional appearances, such as on the Muppet Show and Sesame Street, which has perhaps contributed to the erroneous idea that R2-D2 should have a polished chrome dome. That, and the Kenner R2-D2 toy, which also did.

Some secondary droids had fibreglass or vacuformed plastic (many transparent) domes.

Prequels: Many of the prequel droids were equipped with metal domes recycled from the Original Trilogy props. Apparently some of the prequel domes were also made to look metallic through the use of Rub'n Buff, which is carnauba wax mixed with fine metallic powder. The wax was applied to the domes and polished to a fairly convincing metal look. This works quite well, and many R2 builders have used it since, but isn't the most rugged and resilient finish.

Sequels: The sequel droids had spun aluminium domes.

Dome: condition

ANH: A lot of the ANH R2 domes, made from ductile aluminium, were in perfect shape on the first day of filming in Tunisia. But by the time filming moved back to England, some pretty beaten-up domes were put before the cameras. Serious dents abound! Which would be narratively okay, but there are also a lot of continuity errors in the film. A badly dented dome can appear in a scene, followed by a less damaged one in the same scene.

The poor ol’ Kenny dome below, seen in the Blockade Runner sequence, looks like a brick or something dropped on it at some point.

ESB: The ESB domes are mostly in reasonable shape, by comparison.

Dome: panel lines

Each panel is outlined by a thin, shallow recess.

ANH: Most of the original droids were metal. Each alloy dome actually consisted of two parts – an inner skin and an outer skin, one nested inside the other. They were thus two-layered constructions, and this gave a more sturdy structure than single-ply sheet aluminium.

The dome holes were cut out by hand, and accordingly there is some variance in position and placement from dome to dome. The panels, which were the same thickness as the outer skin, were then cut slightly smaller than the holes. This resulted in a narrow recessed line around each one; effectively a thin groove of exposed inner skin.

ESB: The hero ESB domes were spun metal, and had recessed panel lines as with the ANH domes. Other ESB domes appear to have been made from fibreglass.

Dome: panels

ANH: The top panels on the dome are never seen open, or opening, in this film. However, there is evidence that the plan may have been to make them openable on at least a couple of domes. There are photos of some aluminium R2 domes with completely smooth inner domes, and there are also photos of domes with separate internal panels, such as the one below. There's also a photo of a dome with provisions for maybe just one openable internal panel at the top. The plaster former above says "all panels removable" except for the ones marked X.

There is also the “magic panel” on the side of the dome, which is shown open at one point. An improbably long arm is depicted protruding from here, fixing Luke's X-wing during the final battle. Closeup views of the dome that was used for this shot reveals a rather obvious hinge, held in place with flathead screws, that isn't present on any other version of the dome that I've seen. The hinge is even visible in the film itself, such as the moment when R2 is seen trotting into the escape pod at the start of the film.

ESB: There are a couple of scenes in the film with protruding dome accessories. The lifeform scanner on Hoth is one notable one, as is the periscope in the Dagobah swamp scene. The latter actually used a specially constructed dome on a wheeled frame for a pair of divers (frogmen in those days!) to operate, though you don't see the dome in the finished film.

Blue areas

ANH: All blue areas were constructed from aluminium. The metal was then treated using “layout blue” or “engineering blue,” as discussed in a previous chapter.

ESB: Blue parts of the ESB droids were painted blue. The specific brand and formulation of paint is not known, though droid build supervisor Ron Hone has said that they used transparent “candy” automotive paint imported from the US. Dykem dye is not believed to have been used. Some of the R2 units in ROTJ look pretty dull, suggesting they may have been later repaints.

This approach, incidentally, is why the ESB domes had blue that was in pretty good shape. ANH-era layout blue is nowhere near as resilient as automotive paint!

Prequels: Painted. The Episode I droids had a flat opaque blue that wasn't as rich as the original trilogy droids. However, for Episode II the droid team at ILM spent some time developing a paint job that more closely resembled the OT droids.

In 2002 ILM's droidmaster Don Bies made a suggestion for how one might want to paint an R2 unit in Episode II/III prequel style, using complex and expensive custom automotive paints. This has become known in R2 building circles as “hypothetical blue”.

You know, if I were to paint an R2 -- and this is just hypothetical, mind you -- I would order a brand of paint called Shimrin Kolors from House of Kolor, located at 2521 27th Avenue South, Minneapolis, MN 55406 (800 328 5139). I think I might order Pavo Purple, Zenith Gold and Orion Silver as basecoats, mixing them with a ratio of 50% purple, 25% Gold and 25% silver. I then might coat it with Kandy Oriental Blue, and probably wouldn't put a clear coat on it, though it would add some more depth. I'd guess that a quart of the basecoats each cost about $26.55 and the top coat about $31.49 per quart. Of course, I would have to buy a quart of catalyst at $35.40 and a quart or two of reducer at about $9.80 per quart. I bet if I did all that, I'd have a color that's pretty close to the real color.

But that's just me.

Don

Sequels: Painted. Official formulation not released.

Bluescreen photography

Special effects sequences, where stuff has to be overlaid, requires some method of identifying what areas are going to be replaced later. The original Star Wars films used coloured background screens, known as bluescreens. Of course, if you put a blue-detailed R2-D2 in front of a bluescreen you'd have a problem! The blue areas of his dome might show through as holes, which isn't exactly what you want. So for the scenes where R2 is in space, the blue panels were painted black.

This issue occurs in both ANH and ESB – at least the original cinematic releases. The Special Editions of both films digitally recoloured the domes to blue.

ANH: The Death Star space battle seems to have featured a black R2.

ESB: The approach to Dagobah also had a black R2 which was colourized back to blue in the Special Edition.

Prequels and sequels: Always blue.

Radar eye

ANH: R2-D2's visual sensor was described as a “radar” eye in the original scripts, as far back as 1974, when R2 was called A-2 and C-3PO was C-3. The term was also added to the 1977 Ballantine Books edition of the blueprints, though the original studio blueprints didn't refer to it as anything. The novelization ghostwritten for Lucas by Alan Dean Foster called it a “mechanical” eye.

“Radar” is an odd name for the final design. After all, it's clear that the robot had a transparent optical lens in there, not an antenna used by radio waves! Obviously the eye was transparent so that Kenny Baker could peer out when he was inside. It also gave a point of visual reference to the viewer, giving a stronger sense of personality to the droid design. It’s not known where the lens used in the original props came from. The photos I’ve seen show that it was just a curved piece of glass or plastic and not an actual lens, as such.

The raised blue surround around the eye lens is one of the most complex components on the whole droid, geometrically speaking. It’s a surprisingly complicated shape to replicate. There are also some variations in appearance (mainly paint and positioning on the dome) from film to film and even scene to scene.

ANH: The boxy “radar” eye surround is pretty massively beaten up in some shots in ANH. Sometimes the data slot under the eye is so bent from toppling droid injuries that it couldn’t actually have accepted any Death Star plans! The surround’s position also varies slightly from dome to dome.

Incidentally, it appears that the ANH eye surrounds were boxes made from welded metal sheet, with flat stock for the narrow side piece. This is why the eye surround is often so badly damaged and dented in the surviving ANH droids - the metal was relatively thin and easily crushed or deformed by impact, and the surrounds were mostly hollow.

Note that the dome below was from an exhibition some years ago; the bashed-in holoprojector has since been repaired. This is the droid that toured with the “Star Wars Identities” show.

ESB, ROTJ: The ESB version looks pretty sharp and clean most of the time. But check out this crazy one from the sail barge scene of ROTJ. Not only does the blue paint look flat and dead, but the radar eye surround is totally crooked. You're supposed to be serving drinks, not embezzling them, R2!

Radar eye: surround colour scheme

ANH: All the eyes have exposed metal in the round cylindrical recess around the lens. The two horizontal grooves on the right side (the left side from R2's point of view) are unpainted metal, as is the vertical recess between the main body of the surround and the lower narrow section, sometimes called the “hinge” by fans even though it’s never seen behaving as one, to the side.

Incidentally, the bare metal interior had an interesting visual effect. Several shots in the movie, mainly when things were brightly lit, show what appears to be a metal ring on the interior of the lens. It isn't – this is actually a reflection of the surround’s bare metal interior! At least one commercial R2-D2 kit has put a flat ring on the inside of the lens, thinking this was a real thing.

The data slot under the eye (the one that Leia puts the Death Star plans into) is always shadowed in the film. The edges of the slot are blue, but the rest of the slot is just hollow space underneath. In some shots you can see the dome beneath, and in the case of the Identities dome the line cut into its surface to accommodate the data card.

The bottom edge of the narrow section is bare metal on the Kenny droids, as shown above.

But it’s blue on the RC R2, as seen below. Oops! However, both versions have bare metal inner edges of the horizontal slots.

 ESB: There is some variation from droid to droid in ESB and ROTJ in this regard, though the lens is often in shadow and it's hard to tell if it's silver or blue in there. A few of the ESB droids seem to have silver recesses, complete with the “inner metal ring” illusion as above.

However, check out this ROTJ droid! The whole surround is blue, including the lens recess and the two grooves. It seems blue surround interiors were common on this generation droid.

The ESB droids appear to have the same paint scheme for the narrow section as the RC R2 in ANH - inner edges bare metal, but bottom edge blue.

Prequels: All blue radar eye surrounds; no recessed silver lines. Some droids appear to have cast resin surrounds and so they're solid rather than hollow.

Sequels: Blue with recessed silver lines.

Radar eye: surround location

There are a lot of subtle differences in panel size and location between the ANH and ESB domes. One of the most obvious ones is the position of the radar eye surround.

ANH: The radar eye surround is a bit lower down than on the later robots. On many ANH droids the surround is roughly 2/3 of the way down between the top of the logic light panel and the two panels below the eye. This matches, more or less, the original 1976 blueprints (blueprint 60) for the dome. 

However the RC R2 seems to have an eye surround that's just a bit higher. Not quite halfway.

ESB: The surround is noticeably higher than on any of the ANH droids. It seems to be about 1/3 of the way down. Perhaps the front holoprojector, which is located higher than on the ANH droids, got in the way.

Radar eye: toggle switch

ANH: At one point after filming, the RC R2 prop had a tiny toggle switch added under the radar eye enclosure. No other droid is known to have had such a switch, though it's not easy to see because it's on the underside of the radar eye and R2 is rarely viewed from below.

The purpose of the toggle is not known, nor is it known exactly when it was added. However it’s only visible in publicity shots taken after filming was complete, so it was added after pickups were done. It would, therefore, have been used in promotional public appearances and so on. There’s no evidence at all that the switch was present during filming of the original movie. The only evidence I’ve seen of it, aside from these promo shots, is a hint of it during the R2/3PO/Vader footprint ceremony in Hollywood. It seems clear that this switch was a post-filming add-on.

Conjecture: it was added to simplify the process of turning R2’s dome lights on and off. A published diagram from 1977 indicates that the dome light switches were actually inside the body. This would be quite annoying during filming – they'd have to lift the dome on and off to power the lights. And since the lights used incandescent bulbs and electric motors, they must have drained the batteries quite a bit. Accordingly, an external switch would have been very handy – just reach over and flick it right before the clapper loader steps in front of the camera, or before R2 rolls out before the adoring crowd of children at the shopping mall.

ESB, prequels, sequels: None of the droids have this switch.

Width of the narrow panel

There’s a narrow vertical panel right next to the logic lights on the front of the dome. This one varies in width.

ANH: The RC R2 seems to have a fairly narrow panel that’s about as wide as the gap next to it. This dome’s layout seems to more accurately reflect the plaster dome template than the Kenny ones, for what it’s worth. (ie: I think this layout represents the designers’ original intent a bit more closely)

 This arrangement is close to what's shown on blueprint 60.

The Kenny droids seem to have a slightly wider skinny panel, which is also a bit wider than its gap.

ESB: These droids have slightly wider panels; possibly slightly wider than the Kenny ANH ones. It’s also a bit wider than its gap.

Holoprojectors

ANH: The original airplane reading lamps that served as R2's holographic projectors were stamped aluminium, with nozzles (or grasps or shrouds - they didn’t blow air or anything, so technically weren’t really nozzles) made from Bakelite plastic, all painted a uniform glossy grey.

The use of hard brittle Bakelite, incidentally, is probably why a lot of the holoprojector nozzles on the ANH droids are cracked and damaged. It’s worth mentioning that many hobbyist replica holos are bare machined aluminium, which looks great but isn’t actually screen-accurate. No movie R2 had anything other than painted holos.

And, speaking of screen accuracy, a lot of early hobbyist replicas use holoprojector designs where the four raised sections of the outer sphere, the sort of bumps on the housing, are all the same height. This is a legacy fan error, probably caused by someone eyeballing a few photos and going from there. The actual detail parts used in every single movie had two taller bumps and two lower bumps, making a nearly oval cutout when viewed from above (and not a squircle).

The Astromech club plans have now been updated to fix this error, but it was around for a long time and a lot of parts were made with the previous design.

The real reading lights were nested spherical shells so they could, of course, be adjusted by passengers: a person sitting in the airplane seat below could reach up and adjust where the light was pointing. However, the ANH holos are never seen moving around.

Well, almost. An amusing detail from the first film occurs right after Leia gives R2 the Death Star plans. The Kenny R2 is shown shuffling about, and the top holo can be seen wobbling around loosely. The original reading lights contained felt strips which served as friction pads, keeping the lamp from moving except when adjusted by the user. But in this shot it appears the felt strips were missing!

ESB: Many ESB droids had cast resin duplicates, but some droids used real lamps. The holoprojectors that can be seen wiggling around in ESB and ROTJ were most likely actual Viscount lamps – they had L-shaped rods attached to the back for Kenny Baker to operate. The resin ones appear to have been one piece and thus fixed in place. The ESB front holos were all centre-aligned between the flanking panels.

The ESB-era droid used in media appearances in 1980 was capable of moving its holoprojector under remote control. You can see this easily in the Sesame Street appearance. However, it’s not known if this motorized holo was seen in the actual film, or if every occasional holo move was performed by Kenny Baker.

Holoprojectors: front locations

ANH: The front holoprojector location varied very slightly from dome to dome, presumably since the circular opening was cut by hand between the panels. The original blueprints, plaster prototype dome, and RC R2 all had front holos which were offset slightly to the left (looking from the front). Some of the other ANH R2 domes had more centre-aligned front holos. The ANH era holos are located just slightly above the baseline of the panels.

ESB: All the front holos appear to be basically centre-aligned. They are also slightly higher in position than the ANH holos.

Prequels: I think the holo is closer to to ANH, but not as far over to the left. Maybe. Other droids: unknown.

Sequels: As ESB.

Holoprojectors: colours 

As noted above, the original airplane reading lights were painted a glossy industrial grey, with a slightly metallic sheen, at the factory. This is why both the stamped metal bits and the Bakelite plastic bits were the same colour. One minor detail of note is that the internal ring at the bottom of each nozzle - the bit that touches the glass lens - was a lighter shade of grey, and seemingly not subtly metallic.

None of the original lamps were bare machined metal, or painted with shiny sparkly silver paint – two common approaches taken by hobbyists. There existed pale green reading lights of a slightly different design, used on different Vickers aircraft models or a different generation of Viscounts, but that type was never used in a screen-used droid. It was only ever used on the wood-body prototype droid.

ANH: The droids in this movie have holoprojectors with different colours. Some parts are painted blue or black, but other parts are left factory-issue glossy grey.

The situation is a bit confusing, but both the Kenny and RC R2 droids seen in Tunisia on the first days of shooting (the droid “auction” scene) have the same arrangement of colours on the holoprojectors’ outer shells and nozzles.

However, as filming progressed and the chaos of on-set damage and repair occurred, some of the holoprojectors were replaced or repainted. There are definitely photos showing projector nozzles, made of brittle Bakelite, with chipped and broken edges. So the droids used later in Elstree typically have one or two holos that differ from the original Tunisian arrangement. Two of the droids were then shipped to California, refurbished and repaired by a different team, and used for the pickup photography. These have further variation in holo colours.

Holoprojectors: colour variants

I count five obvious variants in the handful of scenes in ANH where you can see all three holos. There may well have been more variations, and obviously each dome was used in many more scenes than listed here.

Variants A and B below appear to have been the designers’ original intent.

Version A. Kenny two-leg; Tunisia and Elstree, 1976.

Where: Droid auction scene, the “whoa - just where do you think you’re going?” Tatooine canyon scene, Leia data upload scene as Leia backs off to hide, boarding the escape pod.

Front: black (possibly blue over black) outer shell with black nozzle.

Top: blue outer shell with glossy grey nozzle.

Back: glossy grey outer shell with black nozzle.

Version B. RC R2 three-leg; Tunisia, 1976.

Where: Jawa attack, end of droid auction scene. 

Front: black outer shell with black nozzle.

Top: blue outer shell with glossy grey nozzle.

Back: glossy grey outer shell with black nozzle.

Version C. Kenny two-leg; Elstree, 1976.

Where: Garage/hologram scene, Death Star computer bay.

Front: black outer shell (possibly blue over black) with black nozzle.

Top: glossy grey outer shell with glossy grey nozzle.

Back: glossy grey outer shell with black nozzle.

Version D. Identities droid in Elstree, 1976.

Where: Crossing the Blockade Runner corridor scene.

Front: blue outer shell with black nozzle.

Top: blue outer shell with glossy grey nozzle.

Back: black outer shell with black nozzle.

Version E. RC R2 three-leg; Death Valley pickup/post ILM modifications in 1977.

Where: Tatooine dunes argument scene, Bob Seidemann photo shoot, Making of Star Wars documentary.

Front: black outer shell with glossy grey nozzle.

Top: blue outer shell with black nozzle.

Back: black outer shell with black nozzle.

Identities droid as exhibited today:

Front: blue-black outer shell with black nozzle.

Top: blue-black outer shell with black nozzle.

Back: blue-black outer shell with black nozzle. The interior shell also has some blue on it.

Unfortunately we don't have enough data to know whether each dome had its own fixed combination of holos, and if specific domes were always paired up with specific bodies. It does appear that domes may have occasionally been interchanged from body to body – one instance of this appears in the opening footage (“there’ll be no escape for the Princess this time”), where the badly dented Identities dome seems to be on a Kenny body barrel.

Holoprojectors: black or blue?

Some of the ANH holos are obviously body-panel blue. Others just seem black. But when viewed closely some of the black ones seem faintly blue on the edges. The outer shell below definitely looks entirely black, but notice the area where the paint has been scratched off - it seems to reveal a little halo of blue underneath. So were they one colour and then painted over? Or were they multiple layers of blue dye, which can seem black? I don't know, but personally I think considering them black is the easiest option.

Finally, some the nozzles/handgrips of the holos were painted a scuffed-up black on the outside, like the one above, but some were left factory-issue glossy grey.

ESB: Although some production photos show droids being built with a few differently coloured projectors, all the R2-D2 droids that actually appear in the movie had identical glossy grey-painted projectors. No crazy colour combos!

It seems these droids had a mix of factory-issue Vickers Viscount reading lamps, and cast resin replicas carefully painted to resemble the originals.

 Prequels and sequels: All had standard glossy-grey/silvery holoprojectors.

Logic displays

Each R2-D2 dome had three rectangular frames filled with shimmering dots of light, generally referred to by fans as “logic displays” or “logic lights.” They’re simply called “fibre optic displays” in the Stears manuals.

Each display consisted of a rectangular frame made of flat aluminium bars, packed with a grid of simple optical fibres, much like a novelty household fibre lamp, described in part II of this document.

R2’s logic light fibres were wrapped into rope-like bundles that were then glued together into resin blocks. The block ends were cut flat, sanded, and polished to form a smooth surface. Some logic lights have a slightly dished interior, however, owing to the resin not hardening flat, thanks to surface tension.

The fibres in the bundles were also twisted and shifted around prior to gluing down, creating a semi-random distribution of the illuminated dots. This created, in theory, a sweeping pattern to the shimmer. The application of paint to the disc, combined with the unpainted clear fibres, meant that each point of light could change in both brightness and colour.

Sitting between the fibre bundle and the light source was a transparent rotating disc – a colour wheel – arranged so that the cable tips of the logic indicators would pulse and blink, supposedly reflecting the internal state of R2’s brain.

The front lights were pale blue and white, whereas the rear lights were mainly green, orange and red. Note that the colours were determined by the painted areas on the wheel – the fibres themselves were all colourless and untinted, and a standard white tungsten bulb was used. 

The shot below is one of the better views of the ANH-era light setup that I've been able to find. You can see how the fibre assembly is fairly thick, and consists of numerous smaller-diameter fibres, plastic-sheathed into bundles. The end of each bundle didn't physically touch the light fixture – there was a gap of a couple centimetres. The light assembly appears to be a metal plate to which the geared-down motor was fastened. The photo was taken in Tunisia, and so is as close as we can get to a factory-issue dome.

Logic displays: front

The dome had a pair of small rectangular frames on the front. The frames were made of four pieces of aluminium, with parallel boxlike outer sides and angled sides sloping inwards on the interior. The pieces were mitred with 45° angle joins. The two front frames were aligned to the curvature of the dome - they weren't parallel to each other - but weren't curved themselves.

The two small front lights were framed by simple angled aluminium bars, and each of the rectangular lit panels was basically flat (though sometimes, since it was filled with epoxy resin or something similar, slightly concave).

ANH: The ANH logic light fibres were lit by 50 watt 12 volt tungsten incandescent light bulbs. The Stears manuals refer to the bulbs as “QI” lights for “quartz iodine;” what we generally call today a quartz halogen bulb. The rotating colour wheel between each bulb and the fibre ends was driven by a small 6 volt DC motor. The wheel was powered by a small geared-down motor and a pulley drive; a mechanism, incidentally, which made the dome interior pretty noisy for poor Kenny Baker.

The points of light are a little wonkily arranged, and don't align neatly to a grid. In the case of one notable dome – the one typically paired with the three-legged ANH droid – there were four rows of dots in the upper box and five in the lower, even though both frames were the same size. The top box seems to have 8, 9, 8, and 8 dots. The lower box seems to have 8, 7, 7, 7, and 8 dots.

The ANH logic lights seem to have a thin metal frame around the black rectangular back.

It didn’t always work – or perhaps wasn’t always turned on – in ANH. When functioning it mostly alternated between a kind of shimmering bright white and dimmer pale blue. I imagine the halogen bulbs would draw down the batteries quite quickly.

ESB: The ESB logic lights had fibres as well, but the flickering sequence was faster. I'd love to know more about how the sequencing of lights was done, because it actually did result in swirling, sweeping patterns. It seems likely that they used the same rotating wheel mechanism as ANH.

The arrangement of fibres was cleaned up and tidily arranged compared to their ANH predecessors, and both top and bottom lights had an even grid of points that's 5 rows tall and 9 columns wide. The ESB logic lights don't seem to have the thin frame around the black plastic fibre-optic holder.

Prequels: The Uber R2 appears to have had four rows of LEDs in each light. The Episode I droids apparently reused the same mechanisms as the earlier films.

However, for Episodes II and III the logic light electronics were rebuilt by the late lamented Grant Imahara, a former ILM employee and later Mythbusters TV star. He created a small box of electronics containing a number of white LEDs which would vary in brightness over time, pulsing. The fibres, which were the original OT fibres, were lit by these devices.

Note that the Episode II/III fibre ends were also coloured with transparent paint, so the finished design involved light points that varied in brightness but did not change colour the way the original droids did. However, it meant that the lights were silent, and thus a great relief to the on-set sound recording team. (of course, if he’d done the work today he would have used microcontroller-operated RGBW LEDs, for both colour and brightness shifts!)

Logic displays: rear

The long rear display had more complex geometry than the two front frames, since its frame was curved, inside and out. The back of the dome had a wide rectangular strip, using the same fibre optic system as above. Unlike the front logics, which were relatively simple angled and mitred pieces of metal, the rear logic frame is surprisingly difficult to make correctly. Because the internal fibre optic surface was curved, and the frame's outer edge is basically parallel to the dome, a lot of complex shapes had to be cut into the metal pieces.

The rear logic frame was essentially a rectangle cut into a cylinder. The four outer edges of the frame matched the curvature of the dome. And the fibre optic surface was effectively a section of a curved cylinder that matched the curvature of the dome in the vertical axis. These differences of geometry are why the rear PSI frame looks oddly wonky when installed into the dome! 

Incidentally, many fan replicas have a flat surface mounted inside the frame, which is a lot easier to make but doesn't look as good as the curved cylinder section seen on the actual props.

PSI lights

The round “processor status indicator” lights are a pair of recessed light sources on R2's dome. The front PSI is located right beneath the radar eye, and the back PSI is located on a special panel at the rear of the dome. They generally blink or glow in different colours to give a suitably robotic look to R2’s dome.

PSI lights: front

The front PSI is about 1/2" smaller in diameter than the rear PSI. Photos of an ANH dome suggest that the front PSI's plastic surface was mounted behind the inner of the two domes, making it slightly more deeply recessed than the rear PSI.

ANH: The front PSIs were equipped with blue and red transparent lighting gels (thin flexible sheets of tinted transparent plastic, probably taped together to form a single piece), and there was usually a sharp and near-vertical line between the two colours. Generally the Kenny droids had red on the left and blue on the right, whereas the RC R2 had blue on the left and red on the left.

So the question is, was the gel designed to slide? The main possibilities are:

1. Some droids had motorized mechanisms that could move the red/blue gel from side to side, but the mechanism never worked in the film. I think this is unlikely since there isn't really any visible slider inside the dome assemblies that we have photos of.

2. Some droids had manually movable red/blue gels as part of some sort of sliding mechanism, and Kenny Baker could manually push it back and forth. Or in the case of the RC R2, the effects team could reach in and adjust the gel position when the head was off. This theory is possible, and aligns with the fact that we see filter gel movement in a Kenny droid but never in the RC R2. However, we don't see any slider bracket or anything in internal dome photos.

3. The droids were not designed with intentional gel movement in mind. Any seeming changes in red/blue gel appearance, therefore, were purely accidental as the production went on, or else happened simply because different domes had different static gel positions. This theory is also possible, and it could be that the gel movement we see was just because Kenny grabbed the PSI light housing to turn the dome, and bumped the gel filter inadvertently. It was cramped in there, after all, and he didn't have long fingers.

Until we get more hard evidence, I'd say that the proverbial jury is out between theories 2 and 3, though I’m currently leaning towards 3.

As for lighting, the front PSIs were lit internally by a pair of 12 volt tungsten light bulbs with bayonet bases, probably off the shelf automotive bulbs. Generally the Tunisia and EMI footage show the bulbs operating in a pulsing fashion. It seems that the two bulbs glowed steadily at a low brightness, but would also alternate back and forth in a high brightness mode. There seems to have been some sort of power-ramping circuit causing them to brighten and dim over a second or two, rather than flashing on and off instantly. (ie: the brightness change seems slower than the warm-up/cool-down time of a typical tungsten bulb)

The specific device or circuit type is not known at this time. The Stears manual calls the pulse devices “pulsating light drives,” but it’s not known if they actually used motor drive mechanisms with rheostats, or if he used the word “drive” metaphorically and they were wholly electronic devices. There are also some points in the film where one side doesn't seem to pulse, suggesting that a bulb might have burned out for some scenes.

The 1977 pickup footage shot in California does not show pulsating PSI lights, on either the RC R2 or the “Identities” droid. The front PSI basically just glows mostly red during the pickup footage.

However, when the RC R2 was modified for public appearances in 1977 it gained an alternating flashing left red/right blue front PSI and lost the bright/dim pulses. ILM's William Shourt performed this modification at the same time he installed a tape player for audible R2 beeps, and the flashing lights can be seen in the Making of Star Wars TV documentary. This flashing look is similar to how the PSI looked on the Empire droids built a year later (though the Empire robots had a more diffuse surface, so the apparent motion caused by left and right light bulbs isn't obvious)

As you can see in the screenshots above, a diffuser with a hexagon pattern was used internally on some – but not all – of these lights. The exact type of material is not known, and for many years people have speculated that it was some sort of perspex/plexiglas prismatic diffuser from a fluorescent lamp, or something similar. However, such materials don't really give the exact look we see in the film, where there are bright hotspots on a hexagonal grid. The apparent shape of the hotspots also seems to change depending on the viewing angle.

One recent theory that's come to, well, light is that a lens from a photographic light meter was used. Droid researcher Mark Kiger has made the suggestion. Unfortunately the Weston lens could have fit into a front PSI, but is too big for the rear PSI. But the idea of a hexagonal grid of small lenses is a very convincing theory!

ESB: The ESB front PSI lights are slightly larger in diameter, and thus taller, than those seen in ANH.

The ESB lights were lit differently than the original droids. They implemented colour changes the same way the refurbished ANH RC R2 did — by switching between two different light bulbs (blue LEDs did not exist in 1980) but, unlike their predecessor, they did so pretty consistently and evenly across the surface of the round screen. These second gen droids did not appear to have hexagonal lenses but smooth diffusers. The lighting was therefore brighter and less blotchy, and the colour changes were more abrupt and less pulse-like. No red/blue dividing line is visible on the front, and so the light tends to alternate smoothly between red and blue, sometimes looking a little bit purple as the colours transition. Once exception was Jabba's palace hall in ROTJ, where the lights appear to alternate from one side to the other.

PSI lights: rear

The rear PSI lights are similar to those in front, but differ in details. The most obvious is that the rear ones are slightly larger in diameter. They also appear to have plastic surfaces mounted directly behind the outermost of the two domes. As a result they're not mounted as deeply as the front PSIs.

ANH: The rear PSI lamps were mostly yellow and green. They did not have colour gels up against the surface of the diffuser, and thus didn't have a visible colour divider. They also had two white incandescent bulbs mounted at right angles to each other, and 45° to the surface of the dome. Each bulb was equipped with a yellow/amber or green gel  (except for the scene where R2 hides from the sandpeople: the back PSI is red and green, for some reason), and backed by a round dished reflector that bounced light around, yielding a mottled effect. The bulb placement and alternating “pulsing” of the ANH design mean that the rear PSI colour change seems to shift slowly from one side to the other.

ESB: As with the front PSIs, the Empire rear PSIs have a smooth frosted look to their surfaces. They typically blinked yellow and green; no gradual pulsing.

Compartment hinges and the “magic panel” or “picture panel”

ANH: Some of the ANH droids have small but visible hinges on the outer edges of the compartment doors and also the “magic panel” which, in ANH, opens up for the scene where R2 is repairing Luke's X-wing in flight.

The magic panel, also known as the picture panel, never lights up in this movie, but sometimes it's filled entirely with blue and other times it's a blue rectangle with a bare metal interior. Most of the time its interior is bare metal, but in a handful of scenes (the bit where R2's head spins around while arguing with C-3PO, post escape pod landing; the Jawas carrying him off) it's solid blue.

It looks like one of the empty shell R2s hoisted aloft by the Jawas in the Tunisian-filmed section of the movie had a filled-in magic panel. This was actually a fibreglass lightweight dome, not an aluminium one. The ANH fibreglass domes had deeper recesses to their magic panels than the metal domes.

Finally the three-legged RC droid gains a solid blue panel for the pickup shots in California, and for post-film appearances, such as the Holiday Special and the Making of Star Wars.

ESB: Some second gen droids have no visible hinges on their magic panels, and others have much smaller ones. The magic panel neither opens nor lights up in ESB (I think it’s blue-framed with a bare metal interior the whole way through), but does improbably light up red, via an optical (not physical) effect in ROTJ.

Hence the name “magic panel” - how is a piece of metal supposed to glow like this? Note that the screenshot below is how R2 appeared in the original sequence in ROTJ. This scene was altered for the Special Edition with additional tools popping out, steam emerging from the holoprojector, and so on.

Dome buttons/bumps

ANH: The back of R2's head has twin raised circular details, commonly referred to as “dome bumps”. There were two versions of these things on the ANH droids.

All R2-D2 scenes filmed in Tunisia and England feature droids with two small convex bumps.

Incidentally this shot is really useful for showing how the holoprojector surround is glossy grey, and not metallic silver or bare metal.

The bumps were both an opaque glossy black, and don't seem to represent light sensors or anything like that. Of course, a lot of hobbyists use these bumps to house small pushbuttons.

Some domes are a little worse for wear these days after years of touring and storage. The bumps below, photographed at the Star Wars Identities show in London, look a bit grubby and dirty.

While convex, the bumps are also slightly recessed below the surface. This is because they were mounted behind the interior dome, not sandwiched between the interior and exterior domes. (the ANH domes were made of two layers of metal)

However, the dome used with the RC R2 for the California pickups, and subsequent public appearances, had shallow black recesses instead of bumps. It looks to me that the outer dome was punched with two round holes whereas the inner dome never had openings there. The inner dome was just painted black in that area, and since it's a small area appears to be flat.

This dome's flat recesses are first seen in the movie during the Death Valley-filmed shots in the Tatooine dune argument scene, but are also highly obvious in the Making of Star Wars TV show, and in the Holiday Special, both of which used the pickup-shot RC R2 only.

 This pair of flat non-bumps is also suggested in this under-construction photo. Was this before plastic bumps were glued into place? Who can say?

So when exactly did the RC R2 dome lose the convex bumps and gain flat recesses? Well, the back of the RC R2’s dome is seen in a number of pre-ILM scenes. Those are the “being zapped by the Jawas,” the start of the “droid auction”, and the “entering the Death Star control room” scenes. All of those moments show either obvious raised bumps, or subtle curved reflections on the bump surfaces, such as the brief glimpse below.

This suggests that it’s just the pickup shot era dome on the RC droid that had the flat recesses, rather than convex bumps. Presumably the flat recesses were a result of the droid renovations that took place in California in 1976.

ESB: The ESB droids all had raised convex bumps. None had flat recesses that I've seen. The ESB bumps appear slightly less recessed than the ANH ones.

The interior shot below shows what appear to be found items - small plastic domes made from grey ABS or similar plastic, glued into position. Note the object with the ring of holes - that's what a Vickers Viscount reading lamp looks like from the back. The black bundles on the right are logic light fibres.

Some people claim that the bumps were dark blue on the ESB robots, but I can’t find any evidence of this in the original film. All the ESB movie screenshots and behind the scenes photos that I've seen have black buttons. One scene – the hangar doors closing on Hoth – features bumps which briefly look intensely dark blue as R2 turns his head, but that's more a reflection of the surroundings than colour itself. Plus all the Hoth scenes were colour-timed blue to make things look cold.

The 1997 Special Edition of ESB does show blue bumps in one scene – the scene where R2 is shown in space in Luke’s X-wing. This is because the dome panels were all painted black in the original film, to avoid problems with the bluescreen process. The black panels were recoloured blue digitally for the Special Edition, and they erroneously turned the buttons blue. So this does not count because the actual bumps in front of the camera weren’t blue.

Prequels: The prequel droids clearly had raised blue dome bumps. Indeed some ESB-era droids were revamped for the prequels, and have gained blue dome bumps that way, long after they were initially created. This latter may be why a lot of people seem to think that all movie droids had blue bumps, when it was a uniquely Prequel feature.

Sequels: The sequel trilogy also had raised blue dome bumps on its droids.

Bare metal panels: pickup continuity

ANH: The large (slightly taller) dome panel, located between the magic panel and the rear PSI light, is always bare metal in the first movie.

However, there is a continuity error involving the metal panel to the left of the magic panel. Throughout most of the movie it's blue. However, for some reason the RC R2 has a bare metal panel on the left for the California-shot pickups and thereafter. This is the same RC R2 droid used in the Making of Star Wars and the Holiday Special, as shown in the picture in the previous section. Incidentally the magic panel on this dome is also filled in, rather than being just an outlined frame as it is on all other domes.

ESB: All the ESB droids I've seen in pictures had blue panels to the left of the unframed magic panel, and bare metal panels to the right, just like most of the ANH ones. However, some droids modified for exhibition purposes etc, do seem to have blue panels on both sides of the unframed magic panel.

Prequels: Many if not all of the prequel droids have blue panels on both sides.

This prequel R2 from the Phantom Menace has a bunch of differences from the Original Trilogy domes. The panel to the right of the framed magic panel is blue and not bare metal, the two dome bumps are blue and not black, and the panel around the rear PSI is bare metal with a blue frame, rather than the other way around. Were these mistakes? Or were they deliberate differences from the narratively later droids?

Rear logic display panel

The back right side of the dome has a large panel made up of three smaller panels. Two gaps, of the same width as the outer gaps, run between those panels. The largest of the three panels contains the rear logic display assembly.

Dome topper

Finally we get to the very top of the dome, where there are two concentric rings and a small flat button; parts collectively known as the dome topper or pie topper. These are difficult to get details on, because most pictures and views of R2 do not show the droid looking from the top down. And there are few, if any, closeups in the film.

About the best view I’ve been able to glean so far is this crop from the 4K scan of ANH. It’s a Kenny dome from the “droids bickering on the dunes” scene, shot in Tunisia. This was very early in on the shoot, and so most likely represents the intent of the original designers and builders.

Interestingly, the 1976 blueprints do not document the topper at all. Instead, they describe two features that never made it to the finished droids. The top was to incorporate a scooped-out carrying handle, and also a threaded hole for optional installation of antennae, etc. The conceptual R2 designs drawn up by Ralph McQuarrie nearly all had disc or bar shaped antennae protruding from their domes. But in the end a simple blue disc with a smaller bare metal ring was used on all the droids. Perhaps the ring was a washer. I don’t know if it’s certain, though it does seem to be aluminium like the dome, so wouldn’t have been an ordinary steel washer.

Anyway. Instead of an update being drawn to the blueprints, it appears that the plaster dome that was created at EMI as a template, and sent to Peteric for construction of the metal domes, was used by the machinists to draw in the topper directly. 

ANH: My survey of photos and still frames from the film shows that almost all the droids had identical dome topper details. The Kenny and RC R2 robots shared the same proportions.

Here’s my rendition of the relative proportions of the different parts of the topper, based on the photo of the plaster dome above. It aligns with the screenshots.

But there is one exception. The lightweight aluminium “stunt” droid that was tied to the Landspeeder for the “these aren’t the droids you’re looking for” scene filmed in Tunisia (the first two screenshots below) had a slightly larger silver ring and a slightly smaller central blue button. The dimensions of this version are close to the “CSR” dome blueprints created by the Astromech builders club.

ESB: For Empire I took a series of screenshots for every shot that showed the dome topper. Unfortunately none are particularly high resolution, but I was able to calculate the ratio of blue to silver to blue for each dome, and each one turned out to be identical in terms of proportions. And they match the Kenny/RC ANH dome topper proportions, even though they don’t all look like they should in these screencaps!

However there do seem some outliers. One ROTJ under construction photo seems to show a droid with a wider silver ring. And some droids exhibited publicly seem to have different dome topper details. One has two holes drilled into the silver ring, for example. However, it isn’t known if these droids were built that way, or if the modifications were done post-filming.

On to the R2-D2 Detail Catalogue Part B: the Body

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