Keyboard Builders' Digest /
On the DES keycap profile
Pseudoku, the self-proclaimed ergo madman, rants about development of his ergo keycap profiles.
Published December 18, 2023
Introduction
Hello, I am Pseudoku, MemeticDevices or one-man operator of Asymplex. I make a living off selling obscure keycaps at an obscene price. You may also remember me from such posts as Keyboard that remind you of teeth, ergo abomination, and or switch/keycap mutilator; here to talk about the Distorted Ellipsoidal Saddle (DES), a keycap profile that I've created and its derivatives and variation.
A Very Brief History
The motivation behind creating a keycap profile began around mid-2019: I had crudely played around with designing and printing pre-cut keycaps through the ErgoWarp project, and I wasn't thrilled with commercially available caps, especially when it came to the thumb cluster. It then dawned on me: where are the ergo-centric keycaps, and what's stopping me from designing them? Thus, the alpha version of DES came to be: a testing ground for trying out the unique top surface, simulating the keywell via profile's sculpting and the potential benefits of per-key customization, including the thumb cluster aimed for the use on flat columnar staggered (col-stag) keyboards.
Having enough confidence from the initial result, what transpired next was getting into resin casting keycaps for higher quality and durability. This required a more streamlined and production-friendly version, and during that process, I made further iterations on the sculpt and dish shape. Then followed were Chicago Stenographer (CS), a low-profile Choc derivative of DES with more focus on vertical chording, a foray into the thumb cluster varieties (Corne → Kyria → CS T1 → Cornelius → Skeletyl → Ortho 1u) to improve their typing experience, and re-exploring sub 1u keycaps: Philadelphia Minimalist (PM) and Liminal Chimera (LC) for minimal Choc spacing and minimal MX spacing, respectively. Some I've created strategically, most haphazardly, all to fill what I perceived to be in demand in the niche that is the ergo-mech keyboard community.
The Dish, The Crux of It All
Now, let us get into the nitty-gritty of the design behind DES. The criteria that I wanted DES to fulfill are as follows:
- Robust pressable top surface: allows wider area and angles to strike the key without distraction and instead assist switch actuation.
- The smooth self-guiding transition between rows, consistent with typing motions and flexion of a finger. Much like that of keywell design.
The key profile's most vital component, and the source of its name, is its dish. The DES can be visualized as a heavily distorted cylindrical profile. Instead of a circular base shape, it utilizes an ellipse with a parametrically varied axial radius. Additionally, the projection of this shape follows a saddled trajectory rather than a straight one.
Such a trajectory generates a central concavity while preserving the cylindrical profile characteristics of smooth and extensive longitudinal transition. Yet, akin to a spherical profile, its large central cupping surface gives grippiness and centers the finger when pressed. Moreover, with a saddled trajectory, the leading edge seamlessly transitions to a smooth downward arc into the adjacent row, eliminating distracting edges that limit pleasant off-center and off-angle presses.
Another aspect of DES's dish is the hourglass-like transformation of the ellipse in the lateral direction. With a static dish radius, one must either prioritize flexibility and accessibility by widening the dish or prioritize better cupping by having tighter dishes. DES has circumvented this by adapting such a transform, and its central dish is kept tight to preserve the hugginess, while a widened contour provides an accessible and softer off-centered and off-angled press. The widening dish also guides fingers into the key center when transitioning into adjacent keys in an off-kilter manner.
Additionally, this dish design has resulted in two unintentional but beneficial features. The combination of saddling and widening the dish creates a subtle but distinct texture on the surface of the keys. This texture provides noticeable touch awareness and guidance to the hand's position in relation to the key. It isn't easy to prove the effect, and it may seem anecdotal, but it does appear to improve situational awareness when typing and leads to a smidgen higher accuracy.
The other benefit is its ease of vertical same-finger presses, i.e. same-finger chord and combo. This is a critical feature on sub-40% boards for efficient keymap management and reduces the user's memory space on ever-encroaching keymap and layer complexity at lower key counts. While there are historical precedents for using flat keys with uncontoured transitions on stenographer boards, local minima, or as I like to call negative frets generated between saddled caps, is a more effective indicator that prevents mispress. While DES has decent enough benefit, CS profile exploits it further by reducing the sculpt angle and smoothing the transition further.
The Sculpt, Keywell Mimicry
For the ergonomic approach to keywell design and keycap profiles that imitate it, we assume that metacarpophalangeal (MP) and conjoined distal and proximal interphalangeal (DIP and PIP respectively) flexion and extension are the predominant actions used to select keys out of home rows instead of the typical in-plane hand and arm motions used on flat boards and profiles.
This is accomplished by placing the keytop's surface along the finger flexion path, whether through switch placement or, in my case, through keycap sculpting. In addition to prioritizing flexion as a means for row transition, with such an approach, in-plane translational motion now generates motion to actuate the keys.
When balanced properly, this coupling of translation and actuation motions between finger flexion and hand motion reduces the overall effort needed to type compared to the segregated actions required on a traditional planer keyboard and profiles. I prefer this view of the potential benefit of keywell design over the often-used reduced travel argument. Following this logic, the tightness of the keywell's curvature will dictate the strength of the coupling, but designers must consider the switch orientation to that of the finger flexion path as well as take on a more holistic view of hand and arm motion to ensure there isn't an overreliance on one particular motion over another to the point it would obstruct them. Following are some observations made through per-key customization of DES alpha and ErgoWarp:
- Take interference of inter-finger enslaving into account when designing keywell. Enslavement is further exaggerated when typing rapidly, and this undeliberate conjoined flexion and extension of nonparticipating adjacent fingers can cause typos on a deeply or ill-fitted keywell and col-stagger. To an extent, we mitigate such interference by disengaging/lifting nonparticipating fingers, but this only leads to inefficient and awkward hand position and motion, nullifying the ergonomic benefit gained.
- I'd advise against excessively tuned column height correction. For fingers excluding the middle finger, some arm pronation (i.e.motion used for turning a door knob) may contribute to key actuation along with the predominant out-of-plane arm and hand motion. Excessively tuned column height can lock such motion, reducing efficiency and mobility. Moreover, the amount of keyboard tenting and tilting will subtly shift the distal transverse arch and MP flexion. The ring and pinky finger's neutral positions will drift. Therefore, slightly loosened designs are preferred to accommodate such changes in typing positions.
- One should take caution in designing keycaps at a higher cap sculpt angle; unlike the keywell, the coupling effect loses efficiency due to the key actuation axis and keytop orientation deviating from one another. Taller caps exacerbate the inefficiency, and the switch stems may snag from the torque.
Based on these observations, the streamlined version of DES adopted the following traits on each row design:
Home row (R3): Considering the downward thrusting nature of reaching the top row, the home row key has a negative tilt to avoid interference with the home row during such a transition. This will also avoid inter-finger enslavement from engaging the wrong keys. Furthermore, the top surfaces of the home and top rows are shifted away from one another slightly to reduce the chance of nails interacting during home key actuation.
Top Row (R2): While I tested more aggressive top row angles during the alpha phase, I ultimately opted for a shallower pitch to reduce the abovementioned issue and prevent nails from snagging the key.
Bottom row (R4): It has an even milder sculpt to maintain a relatively low height and profile to prevent fingers from interfering with the R4 key during the top row press with predominantly extended fingers, which can occur on shorter index and pinky fingers, especially when a user types with more extended neutral hand position. It will also accommodate shallower press angle when a user prefers in-plane motion over flexion.
In addition to the pitch angle, yaw, and roll angles can better match the face orientation to the finger and simulate a tenting. Though not a unique attribute to DES, as other recent ergo-centric keycaps have shown, additional angular corrections do indeed contribute to increased comfort. Nevertheless, unless it involves lateral thrusts or heavy sprays, such as the outer index or two of the pinky columns, minor angular corrections do not significantly improve the typing effort to warrant the design and implementation complexity that per-key sculpture induces.
Therefore, instead of per-key sculpts, I opted to simplify them into a single lateral column specialization that applies additional roll and yaw angles and minor height corrections on R2~4 keys. The yaw angle helps better align the sprayed finger to the dish faces. Roll correction would induce lateral motion and actuation coupling and work as a reasonably optimized correction needed on the pinky column from the distal transverse arch. This simplifies the kit's complexity while maintaining flexibility, and the board design should integrate the tenting and per-column heights for better adjustability.
Also, just as the keywell overcorrection issue mentioned above, the roll angle and lateral bowling, its keywell analog, can induce locked lateral motion, especially from the pinky column. It will interfere with reaching the secondary index column or fanned-out thumb key, and one should take similar caution.
The Thumb, SubOptimization Hell
Thumb keycap designs consist of specialization to the chosen cluster design (say a Corne) and designing workarounds to circumvent issues arising from hand-to-board mismatch and the resulting shift of thumb position relative to the intended orientation of the board. Unless you aren't creating your perfect board from scratch, here are some of the woes involved:
- How well columns stagger and spray fit to the user (notably on index and pinky columns stagger) will affect the arm pronation and yaw alignment relative to the board, thereby shifting the thumb away from the ideal home key position and orientation. This may cause Ulnar deviation on a unibody, so take extra caution.
- The height correction needed on the thumb and the part of the thumb that strikes the key depends on the extent of the abovementioned mismatch and the amount of cluster fanning, regardless of the board designer's intent.
- As mentioned previously, the amount of tenting will shift the distal transverse arch, MP flexions of fingers, and both palmer and radial abductions of the thumb. A more aggressive tent will force the thumb to a more tucked position.
- The lateral locking is also true for opposable thumb cluster design and aggressively sculpted thumb keys in such paths compared to the out-plane motion of normal thumb clusters. They may hinder overall typing motion and run counter to the intent of ergonomic design if naively implemented.
With the above in mind, assuming a good board fit and utilizing the tip of the thumb to strike the key, we can generalize thumb keys into three categories: radially abducted keys (fanning outward or untucked), radially adducted keys (fanned inward or tucked), and the home position key (specialized version of above two).
Unlike the alpha columns, we can get away with a more aggressive sculpt angle because of the pre-existing deviation between the actuation axis and thumb pulp orientation.
Fanned-out key: Much like pressing the regular spacebars, a bladed (lateral) portion of the distal pulp strikes the key; hence, shallower roll and pitch should suffice as a contacting surface to prevent overshooting the key during the transition. Any more than necessary will likely reduce the contact surface to the pulp and potentially interfere with the nail. Yaw adjustment can assist in matching the cluster fanning angle and actual thumb angle if there is deviation.
Tucked: Unlike the tilted opposable thumb cluster design, which aligns switches directly toward the actuation axis, flat boards can greatly benefit from more aggressive yaw and roll correction for the adducted keys, especially when IP flexion is involved in reaching the keys.
Home key: While it involves similar consideration as above, the sculpt needs to be subdued depending on the presence of adjacent keys to prevent it from becoming an obstacle during transitions. Of course, the designer can disregard this suggestion to prioritize home key optimization if their key usage frequency and keymap allow it.
Let us consider two cases: Corne and Kyria. DES thumb keys for Corne consider 1.5u Fanned-out and center keys as home position candidates. 1.5u's gentle sculpt reflects that of the Fanned-out Home key. The central key has an adequate sculpt to balance the ease of access to adjacent keys. The inward key has sharper yaw and roll angles to match the IP and MP flexions needed to reach it. While I'd prefer lower overall key heights, the current iteration's heights avoid interference from the hi-pro cases.
As for Kyria, working on the 2x2 cluster brought an interesting challenge. I wanted them to retain the ease of vertical chords while reinforcing key distinguishability (nonparticipating keycaps, not hindering press motion): upper rows' yaw and roll angles, height adjustment, and lower rows' dish trajectories accomplish the two goals. Inward keys take more aggressive sculpture than Corne as it involves more opposable, DIP flexion and pronation to reach these keys.
I prefer two central keys as candidates for the home key. However, I have prioritized thumb optimization of the central cluster over transitions to the infrequently used outlying keys, and firmer sculptures reflect that.
These two clusters approached a more naive dish design by widening the dish and softening the curvature to match the larger thumb diameter; however, much like the longitudinal saddling, lateral edges need to be filleted to allow wider pressable surface and open up lateral chords on the thumb keys. CS 1u asymmetrical thumb pair first applied the fillet as trends on two thumb-keys boards grew within the split board community, and relevance for combo rose as QMK implementation matured (and the later rise of ZMK).
These fillets, or secondary dishes as I call them, have a wider radius near the key center to facilitate smoother transition and chording. At the same time, it takes tighter curves near the edges to retain wide concavity to match fingertips better and a comfortable press at the corner of the keycap. As I improved my understanding of them through design iterations, Cornelius thumb caps implemented this feature satisfactorily and adapted a non-rectangular key shape.
An issue arose when users adapted the Cornelius thumb caps onto the Skeletyl and Charybdis thumb clusters. While the key shape had a reasonable match for some users, the height and portion of the thumb used to strike the key were off for many users: the thumb's proximal pulp and interphalangeal joint made primary contact with the key.
Along with adapting 1.25u length and more asymmetric shapes, I opted to dish shapes that have inflection and concavity transitions into convexity near the edge of the cap where the cap makes contact with the IP joint. Compared to the trajectory-generated inflection, the new method allowed a more gradual transition, better conforming to the shape and suppleness of the pulp to the bony joint.
Designing keycaps specifically for thumbs requires additional complexity, as shown. While designers and users may take the easy route by adapting full convex keycaps, they do not match the comfort of well-designed concave dishing. Furthermore, most convex designs have rather skimpy top surface coverage and don't fully support frequent off-center presses associated with the thumb cluster keys.
Minimal Spacing, The Electric Boogaloo
Omitted due to poor time management, but here are some pics.
Shill Time Conclusion
DES meets design goals set out, producing an engaging but forgiving typing experience that follows my ergonomic beliefs. I've open-sourced the parametric design if you wish to change or modify some parameters to your needs. If you want cheap 3rd party printed caps (at your own risk, I am not liable), kind users have print-ready files available (I know there are several of you out there, sorry if I didn’t include you). If you have the cash to burn want to support me or enjoy slightly better materials (porcelain polyurethane composite, metal powder composite, epoxy with fancy inks, etc), my shop is open for now. I’d like to thank the ever mad and creative ergo community.
What's Next?
Complete the ergo unholy trinity: keyboard, palm rest, and pointing device.
| Pseudoku |
|---|---|
| Handle | Pseudoku, MemeticDevices, Asymplex |
| Location | USA |
| Description | ErgoWarp |
| Occupation | Burnt Out |
| Joined (the hobby) | Circa 2017 |
| Niche | 30% Split Ergo, DIY Keycaps, Minimal spacing |
| Fav. switch | linear with ~30g spring, lubed, silent preferable, though UHMWPE or POM stems are wonderful. |
| Fav. keycap profile | Avoiding this question at all costs |
| Other hobbies | Caffeinating, eating & sleeping |
| Links | Store, xtwitter, insta |
Published on Mon 18th Dec 2023. Featured in KBD #2023.
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