Luggable PC Screen Hinge

In the previous post we have established all the desired traits of the ideal screen layout, and how it’s impossible to meet them all simultaneously. The only solution is to design a mechanism allowing us to convert between two different configurations, each designed to provide the traits desirable for its corresponding condition.

  • Closed: the travel configuration.
    • Compact: We want to be able to lug this around without too much worry of catching on things, so the screen should align with the rest of the case (vertical or portrait orientation.)
    • Protected: To protect the screen, it should be facing inward so the glass surface is less vulnerable to damage.
  • Open: the computing configuration
    • Landscape: Unlike phones and tablets, desktop computer applications are not designed for the possibility of vertical/portrait orientation, so the screen needs to be in horizontal/landscape orientation.
    • Ergonomic: Unlike laptop screens that sit at table height, we can turn our extra heft into an advantage as support to hold the screen up to eye height. Ergonomically superior to the tabletop height of laptop screens.

To transition between these two states, we need movement along at least two axis:

  • Flip: The screen needs to move from facing inward (protected) to facing outward (visible)
  • Rotate: The screen needs to move from vertical/portrait orientation to horizontal/landscape orientation.

My ideal was to devise a mechanism that can execute both of these movements in parallel, so the user sees a single continuous movement from one configuration to another. After quite some thought and experimentation without success, I decided to postpone this ideal for later. For now, I’ll implement a hinge that has two separate degrees of freedom so the two desired axis of movement can be accommodated.

front-open
The open in-use configuration, with the screen offset to the left instead of centered

Originally the open configuration would have the screen up and centered relative to the rest of the body, and I had a few overly complex mechanical linkages attempting to make this happen. But then I realized it isn’t really necessary: the body has enough heft to hold up the screen even if it is not centered left-right. If we accept that the screen can be offset to the left, the rotation axis becomes a very simple hinge, leaving plenty of room to implement the flip axis.

front-closed
The closed travel configuration

This “ah-ha!” moment of realization, letting the screen be offset, greatly simplified the design. With the side bonus of reliability as simpler designs tend to be more reliable.

 

closelid
Demonstrating the open-to-closed transition. (Animated GIF by Shulie)

In the back of my mind, I will continue to dream of a continuous single degree-of-freedom unambiguous movement between open and closed. Maybe I’ll have another “Ah-ha!” moment to make it happen. I’m happy with this as the first draft.

Luggable PC Screen Layout: Challenges

The previous two posts discussed the design reasoning behind the positioning for the power supply unit and the motherboard. Now we get to the most interesting problem: Where do we want to position the screen?

The easiest approach is to line the screen up with the existing components, so I tried that first. A 17″ screen is almost the same length and width as the ATX motherboard plus PSU. But that means the screen would be at a vertical (portrait) orientation. While common for phones and tablets, it is not a typical layout for a desktop PC. (Historical trivia: The Alto by XEROX PARC, recognized to be one of the first computers with a graphical user interface, uses a portrait orientation.)

threadrodboxisoThe easiest solution to that problem is to rotate the whole works 90 degrees. I tried it for a while and the upright screen sitting at table height level was ergonomically poor.

Laptops also have their screens at table height (one of my peeves against laptops) but at least their screens can tilt. I wanted to do even better than merely tilting: I aim for the OSHA ergonomic recommendation raising the top of the screen to eye height.

spaceThe wasted volume between the screen and the motherboard was another problem exposed by this prototype. The space looked small in CAD because the CAD model blocked out all the volume allocated by ATX spec. Since the actual motherboard consumed only a fraction of the allocated volume, the real world example had far more wasted space.

screenwingsI had the idea to solve both issues by raising the screen high to eye level, oriented horizontally, and tilt it into the empty volume. I never got as far as building it. Looking at the CAD layout, it is quite clear that the horizontally-oriented screen sticks out on either side of the case. This makes for a shape awkward to transport and also leaves the screen extremely vulnerable to damage. The screen height was good, but everything else was bad.

Plus, there was one more problem not addressed by any of these ideas: The screen glass surface is exposed while in transit. Laptops fold closed to protect the glass while travelling, but all these designs leave the glass exposed.

It became clear that no single static arrangement will have all of the desired qualities. Similar to a laptop, we will need some kind of mechanism to switch between two states.

  • Closed: A compact configuration for easy transport while protecting the screen from damage.
  • Open: An ergonomically desirable screen position.

Next post: The mechanism to address these challenges.

Luggable PC Motherboard Layout

a360mobopsu2The previous post described how I decided to position the PSU (Power Supply Unit). Once the position was decided, the next task is to determine the motherboard position.

The first challenge is my desire to accept a full-sized ATX motherboard. Full-sized boards are the easiest to work on and has the best feature set. They also have highest sales volume, which usually mean less expensive. I knew my project would be easier with a smaller microATX or Mini-ITX motherboard, but I wanted to accept full-size.

However, accepting the full size board doesn’t necessarily mean I intend to use all the expansion slots. In fact, I am happy to block the majority of them, leaving just the primary PCI-Express slot available to the GPU.

selectcardsThe GPU itself is the next challenge. The primary slot is close to the CPU, which means it is going to stick up in the middle of the board, making the whole assembly awkward to fit. Again, I have an escape if I want it: there are PCIe extension ribbons available for purchase that allows more positioning flexibility for the GPU. They range from $89 well-regarded units from Digi-Key to $7 roll-of-the-dice units via mystery retailers on Amazon. I want to make this idea work without use of an extension, and avoid the variable that introduces to the system.

While researching the layout, I learned the primary slot is not in the same position across all motherboards, adding to the challenge. While most boards position them in the slot closest to the CPU (all of the Mini-ITX boards have to by necessity) some of the boards place it in the second position. And since high-powered GPUs are two slots wide, that means I need to allow for three expansion slots worth of space.

selectcomponentsThe GPU in the middle of the board leaves two rectangular volumes on either side: Both volume are candidates for use. One volume sits over the remaining expansion slots, and the other volume sits over the CPU.

The volume over the expansion slots are predictable. ATX spec restricts height of motherboard components in order to maintain clearance for expansion cards. If I’m OK with the absence of cards, that entire volume can be reclaimed.

In contrast, the volume over the CPU is less predictable. While the ATX spec allocated volume to CPU and accessories (most significantly, the CPU cooler) that volume is highly variable. Stock CPU coolers typically take much less volume than allocated, and many fancy CPU coolers exceed the volume.

Given those two choices, it was an easy choice to snug the PSU up against the motherboard in the volume allocated to expansion cards that won’t be there.

The last factor in positioning the motherboard is which direction I wanted the ports to be accessed. Pointing down is inconvenient to access. Pointing up makes ports vulnerable to damage from dropped items. So that leaves pointing left or right. Since the PSU power cable port is already on the right, I decided to face all the ports that way as well so everything the user needs to plug in is facing the same way.

All of the above considerations resulted in the PSU+motherboard layout I used.

Next post: Positioning the screen.

Luggable PC PSU Layout

To help optimize arrangement of Luggable PC components, I sketched them out in Fusion 360 so I can experiment with layout in CAD space. I was able to find the specification for the ATX motherboard and power supply, which allowed me to use official dimensions. Unfortunately I wasn’t able to do the same for the PCI-Express cards, because I needed to be a member of the PCI SIG to access the official specs. So I measured and guessed dimensions from the specific implementation I have on hand.

Power Supply Unit (PSU)

As the heaviest single component, I wanted the PSU at the bottom so the overall system is not top-heavy. The question is then: which way to orient the PSU? There were two considerations:

  1. PSU cooling intake: The standard ATX case layout places the PSU at the top of the case, drawing air from beneath. I can’t do that with the PSU at the bottom since a downward-facing intake would be blocked by the table surface. I tried the upward-facing intake once, in the Mini-ITX “Easel Frame 2.0” design. That turned out to be a bad idea because every time I dropped something (usually a screw) it would fall inside the PSU and I have to retrieve it to avoid short-circuiting the internals.
  2. PSU wiring: One side of the PSU takes the standard IEC AC cable. The opposite side is where all the DC wires go to the rest of the components. The decision is then whether to point them front-back or left-right. I didn’t want either of them to point towards the user, so I went with a left-right orientation for the wiring.

Taking care of those two considerations leave two good orientation for the PSU. One with the cooling intake facing front towards the user, or facing away from the user. In the current design, facing backwards allows an unobstructed air path so that’s the preferred position today.

Next post: Positioning the motherboard.

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