The text and pictures were provided by Arnd Riedel, who can be found here:
The development of this giant model project started in 1986, when I wanted to have a full-size (then nonmoving) R2-D2 as a special piece for my collection. I had been building some remote-controlled model ships before, but nothing of this dimension. In the beginning, my R2 was just planned to be a stand-up, a non-moving model without any mechanical or electrical interiors. But, as always, when his exterior "shape" was finished, I longed for more. I wanted to have Artoo moving like he did in the movies. This was not an easy feat, since my "model" weighted in at 80 pounds. Finding motors that would move this mass was not going to be easy. But letīs start from the beginning:
Data-collecting
To make my R2-D2 model as realistic as possible, I had to collect anything about R2-D2. I especially searched for blueprints, drawings and pictures of the interior, but these were, understandably, very rare. The best lead the Artoo-builder may find to start with will be the "StarWars Blueprints", published by Ballantine Books. They contain ten blueprints of various StarWars props and stages, among them an (early) side elevation of R2-D2. This blueprint includes one dimension of the step distance, which makes it possible to calculate the scale of the blueprint (1:2.566) and from that the diameter and a lot of other dimensions.
From the Blueprints one does calculate a height of 107,8 cm (about 42 1/2 inches). I measured a height of the R2-D2 at the Smithsonian Exhibition in Washington, D.C. of about 107-108 cm, which very nicely confirms the Blueprints.
What you donīt get out of it are dimensions in width. These you will get from the blueprints in issue #1 of the "StarWars Technical Journal" by Shane Johnson, published by Starlog Press. I calculated a body diameter of a bit over 18 inches (46.3cm). However, for my project I had to resize it slightly, because you only get plexiglass spheres in metric sizes overhere and the next size was 48.0cm. But the difference is so small, nobody (except Tim Ketzer of course) notices it.
Building the model:
The Fiberglass Parts:
I started the model by building moulds for the legs and for the "head dome", which I planned to do in fiberglass. I used a styrofoam dome for the head, covered it with vaseline and then with lots of plaster. In this negative mould I laminated the head dome with glassfibers and polyester resin. Some weeks after I had finished the detailing on this glassfiber dome a friend and co-R2-builder, Alexander Landgraf from Nuremberg, Germany, called me to tell that he had found a very light plexiglas coupola in the right diameter. This would save about a kilo (two pounds) of weight, so I ordered it and redid the whole detailing process. For the legs I built a `positive shapeī out of wood, plastic sheet and other stuff, then I constructed a rather complex negative five-piece-plaster mould. This was necessary, because the legs have a quite deeply recessed shape that would probably destroy a one-piece mould. After all, I would need the mould at least twice, since R2 has two legs.
I "pulled" two glasfiber leg parts out of the mould, but after that the mould was finished. You would really need silicone moulds like the pros to get more pulls from a mould. The glasfiber parts were completed with several fittings for the attachments of the feet and for attaching the legs to the body.
The Body:
The body, or hull, as a shipbuilder like me would call it, consists of an interior structure made out of aircraft plywood and an outer shell made of several layers of 1mm (approx.1/16") polystyrene sheet. This has the advantage of providing a very rigid, yet quite lightweight body. The body has to take considerable forces when R2 is driving around, and with the plywood inner structure one has, as we engineers say, defined load paths, which means you know which part carries which load and makes it easier to calculate the neccesary thickness.
All the little doors and flaps on R2īs body are moveable. I am planning to built lightweight versions of all the tools from the movies behind the doors, but so far I finished only the blue arms at the front and two of the arms in the vertical doors at Artooīs frontal sides. These arms are moved by small electrical motors that retract the arms via a very thin nylon thread that is almost invisible. The doors are closed by spring action. Beneath the left front door (as seen from R2īs direction) is the main electrical control panel. Here you will find all the main power switches for the batteries, fuses, LEDīs to indicate power on, and so on. I used seperate circuits, switches and fuses for every electrical thing R2 has onboard to be able to switch off circuits if they are not needed or if they donīt work as planned in a critical moment.
The Feet:
Once again the feet have a force-carrying structure and a rather light outer shell. Yet in case of the feet I finally used quite thick (1/8 inch; 3mm) styrene because my experience shows that whereever he shows up, R2-fans try to hug him and invariably step onto his feet. The force-carrying structure consists of a 1/4 inch (6mm) acrylglass plate. To this plate the motor and the ball bearings that carry the shaft of the main drive wheels are fixed. The drive wheels have a working clutch mechanism inside which enables me to push or pull R2 around when these clutches are free. The feet are open at the bottom to give access for maintenance and repair. Additionally the rounded boxes at the inside of the feet are detachable. Inside are the electrical drive motors which only fit because of their canted reduction gear. There is space provided in the feet for little microswitches which are supposed to stop R2 automatically if he runs against an obstacle.
The Mechanical And Electrical Interior:
R2-D2 is propelled by one windshield-wiper-motor (from the car scrapyard) each in the two lateral (side) legs. These have the advantage of having a built-in reduction gear. The motorīs torque is transferred to the wheels (modified RC-car wheels) by a toothed belt, which provides very silent operation. The motors can be run on either 12 or 24 Volts, remotely switchable, so you have a kind of a speed-shift. On 12 Volt, Artoo moves slower but has longer battery endurance; on 24 Volts he is quite fast yet empties his batteries rather quick. Steering is done by switching on just one of the two motors or by switching one off while R2 is moving (exactly as a tank is steered). At first I planned to use proportional electronic speed regulators for each leg motor, so one would be able to do smooth curves. But later I decided to use just on/off and reverse switches, because a) they are way less expensive and b) they actually provide a somehow better looking way of motion, since you really expect R2 to do abrupt motions and cornering.
The head is turned by another windshield-wiper-motor, but a very small one. This drives the head via two sprockets from a bicycle and a bicycle chain. The bearing for the head is made from a large turntable-style ball bearing used in swiveling stands for TV sets.
Pictures
Blueprints
Foot Mold
Partially Finished Leg
Leg-Almost done
Head Setup
