New Ultracortex owners will find this an easy, inexpensive (<$200), high quality solution for sourcing an M4 frame, and M3 owners can now upgrade to the new design.
Since Ultracortex M4 launched earlier this year, it has been available from the OpenBCI store as a pre-assembled product and as a kit. The Dev Kit files have also been made available for those who would like to print their own frame, and complete it with components from the Electrode-only kit. One can also produce electrode assemblies by purchasing the non-printed parts (FRI electrodes, Dupont jumpers, springs, fasteners) as described in the M3 guide. These options, available in three adjustable sizes, meet the needs of most customers, but offering SLS nylon versions makes it possible to improve current products, offer more specific variations, and reduce cost to increase accessibility.
The ULTRA Store
In the interest of simplifying the creation of Ultracortex headsets, I’ve created a shop for M4 frames and other BCI accessories on Shapeways. This has a number of advantages. The products are produced on demand, so they arrive quickly (~10 days) and don’t need to be in inventory, so they can be updated constantly. The nylon material is higher quality than PLA, stronger/tougher and less brittle. The parts cost less, and they look, feel, and even sound nicer than parts made on a desktop FDM machine. Frames are now available in more variations: five sizes, two head shapes (brachycephalic or mesocephalic), and with M3 or M4 threads. Another big difference in the frames offered on Shapeways is that they have integrated threads, so they do not need node inserts. Since the SLS process has better detail than desktop printing, the headset is printed as one piece with threads in place. This makes the design less expensive, lighter weight, and less labor-intensive to assemble.
The head shape variants are a response to the feedback I’ve received about fit. While the headsets are adjustable with a generous range, natural variation in head shape can reduce this range. Some peoples heads are longer or shorter relative to their width. It turns out this head shape variation is nearly as important as size in determining fit. I was aware of this issue when creating M4 and used many more head samples to create the headset shape than with M3. The results are generally much better, yet for ideal comfort and best results it helps to have the headset shape close to the users natural head shape (and also improves accuracy of 10-20 locations). The head shape used for M4 is right in the middle of the cephalic index (Mesocephalic). Users of Asian or Pacific heritage, or those who will be using the headset on several subjects within Asia, will find that a brachycephalic shaped headset will work better, and be more stable, than adjusting a larger headset to fit.
This offering also fixes this issue for the large number of M3 headsets already in use. The M3 shape tended toward dolicocephalic (long head) because of the small number of (Caucasian) head samples used in the initial design. Customers who find their M3 too narrow on the sides might consider an upgrade. The chart below shows where to measure to find your size and cephalic index.
Note that the electrode assemblies in M3 and M4 are different sizes. M4 “bolts” are smaller because they needed to fit more tightly together on the headset due to the large number of nodes in M4 (35 possible electrode locations). In the SLS printed version, this node size limitation does not apply because the threads are printed along with the design, eliminating the needs for the inserts, allowing more space for nodes.
Having five sizes available (as well as various bolt lengths) also means you can buy a frame closer to your head size, so the headset will be less bulky and more stable. Here are the actual reference measurements for the “virtual” heads used for each design:
S size (standard minus 1cm offset):
8.0cm High from circumference line
M size (average):
9cm High from circumference line
L size (standard plus 1cm offset):
10.0cm High from circumference line
On the Shapeways shop page, choose your size using the drop-down menu on the right (In this listing choose: “Extra, Small” for “S”, “Small” for “M-S”, “Medium” for “M”, “Large” for “M-L”, “Extra Large” for “L”).
Other Ultracortex compatible parts are also available, such as longer and shorter bolts, and several other accessories like battery holders. They can be purchased in a variety of colors and finishes. Keep an eye on the ULTRA store for more wearable electronics case designs, and if you want a design you don’t see, let me know. If there’s enough demand I’ll create it.
Shapeways is extending their Cyber Monday sale! 10% off + free shipping through Tuesday the 28th.