Electronics That Last: How I Built an Heirloom Laptop
17 Ene 2016
The Novena Heirloom is a limited edition custom enclosure system I built for use with the open-source Novena computer designed by Bunnie Huang and Sean Cross. It was crowd funded in cooperation with Portland, Oregon-based Crowd Supply.
Several prototype concepts were developed for the campaign. After consulting with Huang, we decided to forgo an easel design in favor of a more traditional clam shell laptop. The requirement for user access to the internal components argued for a removable keypad and drove the final result. The thrust of the design concept is informed by, and hopefully serves as homage to, the vintage HiFi designs epitomized by Dieter Rams. The final Heirloom design remains substantially true to the original concept prototype.
The Heirloom design was developed with a composite of wood veneer, e-glass cloth, cork, and epoxy for the main panels of the enclosure. Influenced by the use of cross-banded wood laminates for my camera designs, I embarked on a series of trials with combinations of materials that led to the fabrication process used for the Heirloom computer. This material proved to have a desirable balance of durability, strength, weight, appearance and environmental impact. An additional benefit deriving from the use of cork, as opposed to wood or other hard material, for the core material, is a significantly improved impact resistance.
The Heirloom construction utilizes wood in the solid timber form along with the composite panels. While the composite material is used for the larger surface areas of the LCD panel, the bottom shell, and the rear speaker/switch panel, solid material is used where mechanical attachment is required (the lower hinge mounting points), significant shaping occurs (the top and bottom rails of the LCD panel), or where wider edge trim is required (the stiles along either side of the LCD panel).
After inspecting initial examples of the composite material, Huang decided to send off a sample to his associates at MIT for structural testing. One of his blog posts illustrates the results returned from testing.
The Heirloom composite is a layered material whose individual constituents contribute a particular set of desirable properties to the final result. Those materials, in the structural sequence, are:
0.7 mm wood veneer
5.6 oz E-glass cloth
3 mm 20 kg/m3 cork composite core
5.6 oz E-glass cloth
0.7 mm wood veneer
The combination is assembled with a high-modulus epoxy resin using custom molds in either a two-part, solid mold configuration or a vacuum bag clamping system used with a one-part mold. For curved forms, I often use a pneumatically actuated band clamp system or an air pressure clamping machine, but neither proved applicable to this set of components.
Four wood species were chosen based upon a balance their suitability for the task and the aesthetic properties they would bring to the final product. These are Makore, Walnut, Black Limba, and Afrormosia.
I looked initially to locally harvested Western Walnut. A Portland based company mills the material into both timber and veneer form — convenient for a design that uses both. With a figure and color a bit more appealing in my estimation than the more common Eastern Walnut, this material has a stunning character full of depth and color.
A recent project introduced me to the previously unfamiliar Afrormosia, a species similar in appearance to Teak but with it’s own unique color palate and character. It darkens over time to a rich golden brown and has the appropriate qualities to mesh with the feel of the Heirloom design.
A species familiar to me from my wooden camera designs is Makore. It has a beautiful ribbon figure, a rich red tone, and appropriate physical properties.
Black Limba has a strikingly unique appearance with meandering brown stripes running across a yellow-toned background. Luckily, a local supplier had a stock of the timber to go with the veneer sourced from my usual veneer merchant.
Producing an appropriate composite from these veneers required extensive experimentation. Epoxy candidates, admixtures such as cab-o-sil and microspheres, and application techniques were fine-tuned to minimize bleed through while optimizing performance. Three assembly stations were needed for cutting material to size, mixing and applying epoxy, and molding the material into final shape. The thicker Walnut veneer was dimensioned to thickness (about 0.7 mm) to match the other veneers utilizing a wide belt sander. Normally an asset, the thicker Walnut veneer posed a challenge both in matching dimensions within the process and in attaining the bend radii used for two of the composite panels.
The cork industry has been actively expanding its base of applications in recent years so that cork has come to be used in products that might have otherwise used honeycomb or balsa wood for core material. My experimentation led to a series of trials with readily available cork but eventually required the purchase of a large roll of special 3 mm cork to fabricate the Heirloom components. Long harvested as a sustainable material, cork’s natural properties make it an excellent fit as a composite core material for the Heirloom while contributing to a smaller environmental footprint.
The LCD panel and main enclosure components are assembled using vacuum bag clamping techniques. After assembling the layers of the panels at the glue station, the assembly is transferred to the molding station where it is put into a seamed bag and sealed up with a roller rod and clamps. Then a special vacuum pump is used to evacuate the bag and allow atmospheric pressure to clamp the layers together while the epoxy binder cures. For many panel applications, this is the simplest and most cost-effective technique. However, in the case of the rear panel that carries the speakers and switches and supports the back of the keyboard, the bend radius is tighter than can reliably be managed with vacuum. Although I have an air pressure laminator that is capable of much higher clamping pressures than the vacuum bag, in this instance it was simplest to create a pair of matched bending forms to laminate the parts. One face of the bending forms has a thin urethane foam surface to insure full and even pressure across the laminate as it accommodates slight variations in the material thickness. The forms are clamped together over the prepared laminations using standard woodworking clamps.
To increase the strength, improve heat dissipation, and enhance the aesthetic properties of the Heirloom’s main enclosure, I chose to use an undulating shape across the width of the bottom panel. The slight wave provides a semi-monocoque structure that stiffens the otherwise flat section of the case while providing for a measure of air flow across the bottom of the case. A visual detail discovered only on complete inspection is an added bonus.
With my extensive experience designing metal and wood combinations, and inspired by the work of German designer Dieter Rams, I chose to incorporate aluminum for the two side plates in the Heirloom design.
These plates are designed with an integral flange used to bond them to the wavy composite bottom panel of the enclosure. A second flange section supports the rear panel at either side. The left side plate is recessed and perforated to allow the PCB to pass through to a separate fitted port plate that includes openings for each connector on the port array. The port plate also incorporates small slots on the interior surface that support the port end of the PCB board where the original screw holes are inaccessible due to the depth of the side plate. A large facet along the top and bottom edges of each plate reduces mass and improves the visual appeal of the main enclosure.
Mounting the main and battery PCBs, battery, and SSD into the enclosure is slightly complicated by the undulating shape of the enclosure base. I considered installing threaded inserts of varying heights to present a flat upper surface for supporting the PCBs but rather quickly moved on to consider installing a unifying plate in the bottom of the enclosure to accommodate all of the components that would install there. Since Huang had incorporated the threaded Peek array into his design for a Novena enclosure, I decided to follow his lead and design an aluminum Peek plate for the Heirloom enclosure.
At the time I was researching possible passive cooling solutions and a large aluminum surface seemed like it might prove useful in that application. This aluminum plate attaches to the composite via three rows of threaded inserts installed into the composite using a similar approach to that used in both the LCD and Speaker/Switch panels. In each case, a bored hole accepts a threaded brass insert glued in place using either urethane and rubber-toughened cyanoacrylate adhesive.
A series of hole locations in the Peek plate accept standard stainless steel captive standoffs to provide mounting locations for the PCBs and the SSD. The remaining insert locations create the Peek array. Because of the open design, these proved problematical for the standard captive nut installation process so I designed an alternate threaded insert solution that has the added benefit of a larger top surface area for discrete mounting applications.
The battery, fan assembly, and a breakout board specific to the Heirloom occupy part of the Peek array leaving a small amount of space for user installations. I designed and CNCed custom brackets for the SSD and battery mounts.
The centripetal fan we used for CPU cooling had unworkable mounting provisions and no ready way to tie into the heat sinks that Huang had sourced. So I designed and CNCed an aluminum plate design that replaces a cover on the fan and provides Peek plate mounting locations, a mounting for the heat sink, and provision for a possible future heat transfer plenum.
The LCD chosen for the Novena project has a relatively large non-imaging surface across the bottom which required a solution to cover that area and provide for cable routing in the panel design. In addition, the hinges needed attachment through a relatively shallow thread capture space while providing long term rigidity for the pivoting action. I decided that an aluminum plate would neatly resolve both issues. The design is hollowed out on the inside surface while providing full depth locations to mount the hinges and mounting screws that attach the hinge plate to the larger LCD panel housing.
The resulting hinge plate is veneered to match the rest of the Heirloom enclosure and has the solid bottom LCD panel rail bonded and mechanically fastened to its lower edge. Hinging the LCD panel to the main enclosure would prove interesting.
A particularly challenging aspect of the Heirloom design process was sourcing hinges suitable to the design concept. There are perhaps four major suppliers of the special torque hinges needed to hold a laptop display in any chosen position. The majority of these are designed to be hidden within the molded plastic components of a typical laptop design and are thus not particularly presentable in a design like the Heirloom. Some of these designs also include provision for LCD cable routing which further complicates their appearance. In addition, the means of attachment are usually based on hidden metal components that are used to absorb torque forces exerted on the small-area hinge leaf commonly found in these standard hinges. I was looking for a hinge that would resemble a standard jewelry box hinge. Combining that idea with the small Heirloom production run created a challenging sourcing proposition.
A bit of research finally turned up stock hinges that met the appearance requirement. But the devil-in-the-details proved just how few hinges had a suitable leaf design. Months passed as discussions with suppliers over semi-custom hinge options transpired. Eventually I was able to arrange a custom order without overly egregious minimum order demands or unit part costs. Following an anxious wait for their arrival, the resulting hinge design happily met all the requirements. After designing and implementing a cable routing solution and CNC fabricating the lower mortises for the hinges, the LCD panel was successfully united with the main enclosure.
Because the torque friction of the hinges will not allow the LCD panel to fully close against the lower enclosure, a set of magnets embedded in the wooden frame members of the LCD panel and the aluminum sides of the enclosure provide just enough magnetic attraction to encourage the full closure of the lid.
Early discussions with Huang led to a shared desire to create a passive cooling solution for the Heirloom case. The open enclosure used in Huang’s Novena case design meant that there was little need for an enhanced cooling system. Although the Heirloom is designed to allow for opened application with the keyboard placed in front of the enclosure (which would allow for plentiful cooling air), it will perhaps more frequently be used with the keyboard resting in the enclosure. This creates a closed system with little natural airflow. Testing in this closed configuration confirmed that heating of the CPU could become an issue.
So I began to research possibilities for a passive cooling system for the Heirloom. Eventually I started a lengthy series of discussions with engineers from cooling systems providers such as Aavid and Enertron regarding the transfer of heat from the CPU to a larger heat sink area via heat pipe technology.
The initial target of inquiry was the significant mass of aluminum present in the side plates, particularly the left side plate closest to the CPU. So I began designing a series of evaporator and condenser plates and creating heat pipe paths between them. The first attempt, with a set of cooling fins (calculated by an engineer) cut into the top or bottom edge of the side plate ultimately proved unsatisfactory due to the short length of cooling surface engagement with the condenser end of the heat pipe and the extensive machine work required to implement the cooling fins.
With the right side plate deemed too far away from the CPU for a heat pipe solution, a further series of concepts was generated in cooperation with two engineers. In each case, a critical requirement would fall short of expectations. The slow pace of this design process, and the potential impact on critical design elements of the remainder of the case, led me to consider only one last option before concluding that some sort of active cooling was going to be required.
I had just completed the first iteration of the Peek plate design in aluminum and still wondered if this fairly large aluminum surface might itself serve as a heat sink. I drew up yet another concept with a heat pipe path leading to the uncommitted area beneath the SSD. There was plenty of area to get significant length of attachment for the condenser end of the heat pipes. And the arrangement was reminiscent of photos sent me by one of the engineers who referred to it as a “cold plate”. But when presented for review, one of the two engineers indicated that the lack of supply and exhaust air and attendant flow across the plate would make this an unsuitable solution. The other engineer indicated that it did indeed look like a possible option. Faced with this difference of opinion, and with a substantial amount of time invested in what might be a dead-end, I decided to see what Huang would think about using an active cooling solution.
I had earlier contacted yet another engineer regarding a new, small form-factor, diaphragm-based cooling technology being developed and he was fairly confident we might find it suitable to the task. It had the advantage of being a simple addition to a standard CPU mounted heat sink, so spatial constraints were minimal. But continued glitches in the production development process for the fan left it off the table for consideration. So after a consultation with Huang, he sourced the small centripetal fan that we worked into a solution.
Fan-based heat dissipation
When Huang arrived in Portland for a week to work out some of the details of the Heirloom, we had already worked out the general layout for a fan/heat sink/heat pipe assembly. A possible concern was how to route the exhaust air out of the case. We began testing without a solution in place, essentially moving air within the case. The tests indicated that the system was performing as desired even without the custom condenser plate thermally attached to the heat sink or the heat sink properly ducted to the fan. The aluminum side plates of the case seemed to be doing a reasonable job of dissipating the heat with any special accommodation. So I began to work on a solution for getting the fan attached to the peek array and the heat sink. After a couple of quick CNC prototypes in aluminum, a final version did the trick while allowing for retrofitting an exhaust plenum should it prove necessary.
Huang has a cool thermal imaging device for his phone that he used to make this photo of the Heirloom showing the heat distribution. The right side plate and speaker vent indicate escaping heat while the left side speaker vent shows the cooling effect of air drawn into the enclosure.
The Heirloom sound system initially involved sourcing suitable speaker drivers. Space would be limited, so I ordered a selection of driver designs that might be useful given that constraint. Simple testing quickly narrowed the field down to one promising candidate with a tuned port. It was adequately proportioned to find its way into the enclosure design so I set out to incorporate it into the drawings. A composite panel intended for the task occupied the space between the back edge of the keyboard and the hinge rail at the back of the enclosure. All that remained was to allow for sound transmission past that panel surface. I knew that a perforation pattern was my preference so the drawing began. It quickly became apparent that the round shape I wanted provided some challenges to conjuring a visually appealing layout. But at one point I realized that my vintage HiFi inspiration had something to offer.
The brilliant Dieter Rams had used a round speaker grill layout in many of his sound equipment designs. I tracked down some examples and discovered the design was so efficient that I decided to offer homage to this seminal designer and use his design with only slight tweaks. Once I had determined how best to cut the hole pattern in the tricky composite material, I was able to add the necessary switch and threaded insert holes and PCB pin clearances. The drivers are resiliently mounted with a slight gap against the bottom of the panel which allows the grills to serve double duty in system cooling needs. The final result has the vintage touch I was looking for and pleasing soul qualities for a simple sound design.
I initially thought about using touch switches with actuation locations laser engraved into the rear panel top surface. Initial testing with an off-the-shelf breakout board seemed to indicate it might work, but a custom application board Huang designed showed there might be some reliability issues associated with inadequate grounding. With the realization that this approach was technically tricky, it also began to seem that a tactile switching application might be both more reliable and more in keeping aesthetically with the overall concept.
I had a sample set of dome switches from Snaptron so I selected a design with appropriate properties and had Huang work up the PCB to support them. The actuators needed to be flush with the top surface of the rear panel. I designed and CNC fabricated a recessed switch base and an actuator with the specified pin design at the bottom to properly interact with the dome switch and a larger smooth button shape at the top. The resulting combination nicely integrates with the rest of the Heirloom design and provides a satisfying audible and tactile click when pressed. Additional on-board switches are accessible upon lifting away the keyboard.
Finally, the addition of a magnetic sensing circuit into the speaker support PCB serves to allow the user a choice of lid closing actions in response to the corresponding magnet mounted in the aluminum hinge plate.
The Novena computer is designed for experimentation and includes a variety of access points to the hardware system. Numerous pinouts, switches, an FPGA port, and a pair of USB ports are all available within the enclosure of the Heirloom model. The Heirloom laptop had to have provisions for easily accessing the internal space. To meet this requirement, the Heirloom design makes use of a small footprint ThinkPad keyboard with a form factor fairly ideal for the task.
To create the Heirloom design I chose to cradle this keyboard between a rabbet in the solid wood front rail and a curved lip along the front of the rear panel that carries the speakers and switches. A secondary goal was to leave the rear keyboard feet in the lower position when placed on the enclosure. The lowered feet aid in returning the keyboard to its cradled position.
An interesting feature of the ThinkPad is a subtly curved front edge where a user’s palm would rest while typing. I took advantage of this detail by matching and continuing the curve along the front rail to create a comfortable ergonomic element for the Heirloom design.
A final element of the keypad integration is a single finger slot at the front rail which allows for the easy removal of the keypad and offers a second avenue for airflow within the interior of the enclosure.
It is common for laptop computer designs to include adhesive-backed elastomer feet applied to a cast-in recess on the plastic or aluminum enclosure. Due to particular details of the design I chose to find another means of incorporating feet into the Heirloom design. After considering a variety of concepts, I settled on a system which utilizes a small, relatively high durometer (a measure of hardness) urethane ball. It is inserted with a modest press fit into a hole in which a set screw has previously been installed, thus providing a means of adjustment. The balls are relatively easy to replace for wear and make a minimal visual impression in the overall design. The relatively high load exerted on the small footprint of the set of four balls seems to insure a good grip on most working surfaces.
I endeavored to make the Heirloom design as successful as possible given the large scale of the challenge and very small scale of production. It in no way addresses issues of consumer-grade design or production. Each of these computers is essentially a one-off project. I believe the Heirloom accomplishes most of the goals I set for the project and should serve users well both as an unusual, useful tool and as a unique, if very small, part of computer design history.
Special thanks to:
Bunnie Huang – genius hacker
Sean Cross – co-genius hacker
Josh Lifton and the whole crew at CrowdSupply.com
Darrell Rossman (now at CrowdSupply)
Zane Grey (shop forebird)
Lisa Cenotto – the only one.
Portland, Oregon 2016