The feedback we received has been invaluable, both in terms of encouraging and inspiring us and in highlighting three major areas that need revision (as well as several smaller points that can be improved). What was most impressive was the general consistency in comments between many climbers. Multiple climbers, though separated by testing sessions and geography, said:

 1. they would like to feel more support in the arch,

2. the shoe's asymmetry range was larger than necessary, and

3. one's toes can still flex more than desired in the aggressive position. Additionally, over half of the climbers stated that the shoes were very comfortable.

The most common reaction, however, was to immediately explore the flexibility of the shoes. As Mak pointed out, we'd "never seen climbers wiggle their toes so much!" Some trip highlights: One climber exclaimed, "oh yeah, this is totally useful!" while finding the exact perfect adjustment for his shoes before beginning an overhanging problem. While at WPI, several climbers sat down and held an impromptu brainstorming session about what they'd like to see in the next set of prototypes. SFT is extraordinarily lucky that a lot of climbers are the improve-it-on-the-fly duct-tape-carrying types, so they've always got ideas to contribute.

Slip-testing results which compare the off-the-shelf ladder lock (shown in gold in the image) to the custom ladder lock are documented in the graph below.

On the proof-of-concept alpha prototypes, we had problems with friction in the tension system. Combinations of high friction coefficients and too many lacing points meant that adjusting the shoe into the aggressive state almost always left slack somewhere in the tension system. While climbing, this slack would redistribute and the whole shoe would relax. So we minimized the lacing points and spent a great deal of time making bearings to provide a low-friction surface for the tension system to run through.

On the beta prototypes, the friction in the system has been decreased enough that tightening and loosening the shoe is quick and the tension is distributed evenly. This is great progress. However, only once the system had been optimized for low friction, did it become clear that there may be an issue with how the shoe is locked into a certain state. We've been using ladder locks on webbing to secure the shoe state, and the first time I climbed in the beta prototypes, the locks slipped, allowing the shoe to relax. Same failure as with the alpha prototypes, but a different cause.

After inspecting the ladder locks in different states on the shoe, it became clear that because of the curvature of the shoe side, tightening the tension system put the ladder lock on the heel, resulting in a self-unlocking position.

I shortened the travel of the ladder lock so that it remained on the side of the shoe and this appeared to resolve the slippage issue. However, after testing these prototypes on longer duration climbs, it became apparent that there was still a very slow slippage rate. Estimating the force carried by the tension system for a person of my proportions and weight yielded a loading scenario of about 2 kN. The company which manufactured the ladder locks and webbing we're using rates them for 440 lbs before they slip, which converts to about 1.96 kN.

I am a small person, so my characteristic load should be lower than most of the population. Therefore, load forces are almost always going to exceed the rated load for these ladder locks.

But this does not mean total failure! Note that the load forces should exceed the rating for these ladder locks. In fact, this is an excellent development, since now I have a metric to spec the locking mechanism for this tension system. And if there are no ladder locks which are small enough with high enough ratings, then I can always deliberately reintroduce friction into other parts of the system.

Since the last post, I've simultaneously been drafting our patent application and modifying the Beta prototypes that fit me. Dan was able to take some nice shots of the Beta prototypes in action while I was testing them at Indian Rock in Berkeley this weekend. I'm proud to say that this pair of Betas is now passing 14 of the 17 tests which I've been using as a metric for prototype performance. This is up from the original 8 tests it passed when I first tested them a week ago.

Next steps:

When we have an official filing date from the USPTO, I plan to put up more detailed photos of SFT's prototype shoes to satisfy everyone's curiosity.

Once I've optimized the Betas that fit me, I'll modify the pair that fits Mak. Then I'll get in touch with everyone who's offered to try out prototypes and organize opportunities for some user feedback! This first round will necessarily be limited to volunteers who fit the two pairs of Betas available, so we'll play Cinderella. If you want to help out (and haven't already let me know) and think you'll fit the glass slipper, email sftclimbing@gmail.com with your contact information and foot size.

From a manufacturing standpoint, that would mean two less parts (+1 DFM), but would require a tool to create the recess in the rubber (-1 DFM) and a tool to mold the grommet in (net 0 DFM since a separate grommet also needs a tool). However, the in-place grommets will likely need to be cast before rubber is applied to the shoe, which means that the bond between grommet and rubber will have to withstand flexing and temperature cycling during assembly. Therefore, durability of the cast material and bond adhesion will probably determine how we proceed. Laura's pair of shoes will be used to test the cast-in-place grommets for durability side-by-side with the pre-cast ones.

While Ray is building Mak's shoes, work continues apace at the California office to get a patent for the shoe design. We've found an attorney and are working with him to conduct a rigorous prior art search to help scope our final patent application. Since prior art searches are less than photogenic, here's a consolation picture of the Continental Divide from Boulder Mountain, CO:

Last week was last week: we drove to Las Vegas to learn about last- and shoe-making from Ray Klose, who makes beautiful custom climbing shoes. He taught us a couple fancy tricks to make perfect lasts that we can't share, but the basic process goes as follows:

Cast a one-use material around your feet. Pour a hard plastic in the one-time mold.    

Remove the hard plastic cast. This is the basis of the custom last. Trim and adjust the last as needed. For example, I didn't do a perfect job of holding my feet in the same position, but Ray was able to adjust the left to match the right by skilled trimming and gluing. Mak and I tried to help out where an extra pair of hands was needed, but much of the artistry we just had to watch, document, and absorb.

Roughen the surface of the cast lasts and sculpt out the final shape of the shoe. For SFT, we wanted shoes that were more generic in shape that the ones Ray usually makes. This will let us share the first pairs of shoes made on these lasts with user testers who have similarly sized feet. This means that many of the peculiarities of our lasts were smoothed out so that the final shoes wouldn't be too customized for other people to wear.

Ray showed us how to make quick masking tape patterns from our lasts to check sizing. He made up a couple of slippers that we tried on. They fit like gloves! Since the lasts passed this test, Ray will begin making two pairs of shoes in our design. We'll be working with him remotely for the next week as he builds them, and then he'll ship them to us for climb testing.