Using the tricorder created a conflict between the needs of the two crews on Desilu Studios’ Stage 9. Any member of the Enterprise crew lucky enough to have been issued with a tricorder would have expected to at least be able to look at the screen to check what important output was being displayed. The Desilu crew, however, had other ideas – they wanted to show off the detail of this high-tech hand-held equipment to the viewer. In most cases, the film crew got their way. As a result, the tricorder was often held with the hood open, the screen pointing horizontally, but weirdly, away from the user, ensuring that the viewer knew for certain that the crewmember was holding a miniature portable computer, even if they didn’t actually know how to use it.
Nowadays we are used to our TV show characters looking intently at their little portable computers while all we can see is the usually featureless back of the casing. Along with the directors, we have learned the visual shorthand – the character’s faces glow and eyes glint in reflected screen light. Occasionally, the scene cuts to an over-the-shoulder view of the screen, if needed to confirm some plot-critical information. However, in the 1960s a small handheld computer was an unknown quantity and, in Star Trek, a new and significant piece of sci-fi prop magic, so it needed presenting to the audience in a way that fully showed it off, but neither the technology nor the budget favoured close-up action shots of the tricorder’s screen. In the majority of scenes where the tricorder is in play, it’s ironic that it’s mainly the technophobic McCoy who manages to hold it correctly, allowing us to imagine what he is studying – in our mind’s eye, perhaps a miniaturised version of his large flat-screen sickbay monitor back on the Enterprise.
Occasionally, scenes show the tricorder’s hood rotating past the more typical front-facing one hundred degrees into a position that, when looked down upon from above, would actually make much more sense for a piece of kit hanging off a crew member’s shoulder. Despite the comparatively few times the tricorder is shown like that, this fully-rotated functionality is a properly prophetic look at how real scientists and engineers would learn to interact with heavy hand-held data-capture equipment carried by a strap. As such, we couldn’t ignore this aspect of the tricorder’s mechanical function. Early in the design process, we wanted to make sure our hood could rotate as close to 180˚ as possible.
To ensure positive and accurate rotation, the tricorder’s hood assembly cannot rely purely on a tight fit and friction. Instead, the design of the hinge components incorporates sprung elements that can accommodate the minute variation that results when multiple parts are manufactured. This variation is called the tolerance stack-up and, as the tricorder’s hood needs to attach to and rotate inside an aluminium frame, this distribution of differing fits will mean that while some assemblies will be perfect, others could be too tight or too loose. In the case of the tricorder, a reasonably complex hinge bearing was needed.
Actually, the hinge bearing has four important functions and as a result, it is one of the key elements of the tricorder design, having both mechanical and aesthetic significance in the success of the finished product.
At the same time as accurately locating the hood and providing a positive, premium-feeling rotation, the hood bearing is also the protective guide for all the wires that need to pass through the metal side plate; it’s the sprung element for the detent mechanism; and it has features that locate the open-detection magnet securely in position. Added to that, with the requirement of being hidden in use, all these functions have to be focussed around a small hole only 10 mm in diameter (about one third of the area of a dime).
With such an important structural component, material choice is crucial. The compact hood hinge bearing is moulded in polyoxymethylene (POM), a tough, flexible, low-friction engineering plastic. It securely locates into the side plate, the bush element of it protruding through the metal and into a matching hole in the side of the hood. A strong, flexible prong, designed to provide soft haptic clicks as the hood is rotated, also pokes through a hole in the metal plate and engages with 20 detent features that partially surround the hole on the side of the hood. The prong deforms outwards over each ridge as the hood is rotated, providing resistance that is accommodating of the tolerance stack-up in the assembly. The detents’ positioning ensures that the hood rotates all the way round evenly from closed to 170˚ in 10˚ steps. We considered having enlarged detents to preferentially halt the rotation at certain predetermined angles, but our research showed that there was no single exact position, and the final design allows the user to choose an open angle that they feel matches any one of the many open angles seen in the show. Three additional detents provide rotational control when the back is removed and the hood is able to rotate further round.
The 3D laser scans we took showed us that the original tricorder hood is about 10% shallower than had previously been thought. When compared with a modern mobile phone, the prop’s hood depth is a positively massive 23.25 mm (0.92”), however, for our development, we knew that it was not going to be easy to squeeze in everything we wanted to. Three PCBs, an LCD, a bundle of wires, screen glazing and a thick aluminium front panel soon eat up the available depth and required some clever thinking to make sure everything fitted, the fixing screws were hidden and that it could be moulded and assembled on the production line.
Injection moulding is an expensive upfront cost. Simple tools for flat or shallow unfeatured pieces are easy to design and easy to make. For something as complex as the tricorder hood, the tool itself is a complicated work of art and a triumph of modern manufacturing, made up of 207 precision components. To manage the cost, where possible, tricorder parts of a similar size have been buddied-up together into what are called family tools. In the case of the hood, it shares its tool with the battery compartment.
Because the hood has features and holes that are (more or less) rotated at 90˚ to the axis of the tool’s opening action, the tool has to be designed to come apart like a three-dimensional jigsaw. The main shape of the hood is created between the core and the cavity, with the holes and features at each side of the hood created by moving parts of the tool that slide out of the way at the end of each moulding cycle so that the hood can be ejected. These hydraulically operated tool elements are called sliders and because they move from side to side, rather than in and out in the main direction of the tool, the tool is said to have a ‘side action’. As discussed before in our post #6, Cutting tools, these heavy tools have to be made with amazing precision to open and close thousands of times with watertight accuracy.
(The hood tool is not the most complicated tricorder tool. That badge of honour goes to the fiendishly-complex disc partition tool, which requires five sliding parts.)
As you study the geometry of Wah Chang’s tricorder hood more closely, you begin to understand what a lovely part it is. For something made in the 1960s it has surprisingly mature curves that wouldn’t look out of place on a 2021 smart speaker. For the prop maker, creating the hood by thermoforming a patterned plastic sheet over a wooden buck is a neat trick used to make a thin-walled casing, but it’s not exactly rocket science (although, in this case, you might argue that it sort-of is). However, spin forward half a century and it’s easy to underestimate the enormity of the task of making it real. It’s hard to fully grasp how the technology, the range of incredible skills, the global infrastructure and international commercial cooperation, work so well together to make an electronics product like the tricorder possible.
Coming next time
First shots – The mechanical build
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