POTENTIAL SOLUTIONS FOR THE FREEMOTION SKI BOOT


The  3 main features that appear to be limiting the performance of the FreeMotion boot are the lack of a hard rear stop and forward lean adjustment for the exo cuff and an adjustment means for the U spring that would allow a range of low resistance rotation of the cuff before the resistance provided by the U spring is introduced. It is also important to have a monoplanar boot board with a ramp angle in the order of 2.5 to 2.7 degrees or, preferably, the ability to substitute boot boards with different ramp angles to allow experimentation to determine the optimal angle or range.

In researching the history of the FreeMotion ski boot, it appears to have evolved out of the Kneissl Rail soft boot introduced around 2002. Perhaps Simon can confirm this.

The Kneissl Rail is shown in the graphic below.kneissl-rail

Like the Freemotion, the Kneissl Rail does not appear to have a hard rear stop for the exo cuff. But the Rail appears to have a  dial on the spine that suggests some sort of adjustment for the U spring that might permit a range of low resistance rotation before it is introduced or perhaps a tension adjustment for the u spring. The Rail also has a constraint plate over the instep that is secured with a buckle, a feature the FreeMotion shown below in Figure 1 from the patent, lacks.fig-1Since the investment in prototypes and production molds is substantial, aesthetic considerations and production costs typically take priority over functional considerations.

Because of this, my preferred option is to use purely functional, low cost prototypes that are easily modified as research vehicles to prove out the functional aspects of a technology. Prototypes such as the Birdcage (shown below) can be designed and fabricated at minimal cost compared to the costs of sophisticated aesthetic and production prototypes.

birdcage

The photo below is of an early research prototype called the Lab Rat that was developed for a recent project. The open architecture of Birdcage and Lab Rat formats permit instrumentation to be incorporated and visible observation of the effects of the technology on the foot and leg to be conducted, something that is difficult, if not impossible in aesthetic prototypes, especially ski boots.

1

The photo below shows a second generation version of the Lab Rat call The Fit. It is more compact and much lighter than the Lab Rat.

2

The 4 photos below show the modifications I made to address structural inadequacies and interface issues of the first generation mold generated post Birdcage prototype called the P1. The instep was reinforced with a formed stainless structure and the internal plastic components were replaced with reinforced fibreglass and Tig welded stainless steel components. While these modifications did not lead to a marketable prototype, they validated the conclusions of the analysis that explained why the prototype failed to deliver the expected performance.

scan

In my next post, I will offer some suggestions for potential grafted-on modifications for the FreeMotion ski boot that may clarify the options required to address the issues that I flagged that were confirmed by Simon. It would be helpful if Simon can provide his comments on whether this approach is viable from his perspective.

3 comments

  1. Dear Dave and Simon,

    Thank you for posting the running dialogue between you.

    The focus of my curiosity is on keeping the foot snug with the foot board. I’m given to understand the boot cuff mechanism has a different importance.

    One question I have had since reading Dave’s patent 5,459,949 pertains to the heal counter. There seems to be no mention of it with the FreeMotion ski boot but it shows up in the Lab Rat, second generation Lab Rat and the P1. It looks like a function of this counter is not only to snug the heal to the boot laterally left, right and to the rear but also vertically. That the heal counter would resist the tendency of the heal to rise vertically from the foot board or AKA snug the heal to the foot board.

    Is restraining the heal vertically with a heal counter possible? It seems a more effective way to keep the foot in contact with the foot board is instep retention. It seems you are suggesting there is significant importance to allowing the foot free to move within this structure but at the same time confined to being in close proximity to the foot board. I say close proximity because the foot will oscillate between being waited and unwaited.

    Can the heal counter by its self keep the heal from rising vertically? Or is the instep retention of greater importance?

    It seems that ski boots generally squash the instep so if I understand your work it is to design instep retention that holds the foot to the foot board but does not interfere with foot mechanics. In that light the heal counter snug-retain the heal lateral left right and aft but are there other functions? thomas

    1. “Is restraining the heal vertically with a heal counter possible?”
      > No.

      “It seems a more effective way to keep the foot in contact with the foot board is instep retention”.
      > Bingo!

      “It seems you are suggesting there is significant importance to allowing the foot free to move within this structure”
      > No. “Forward sliding of the foot (on the boot board) should not be possible. There should also be no loss of contact of the sole (of the foot with the boot board) and no decrease in the feel. Correct positioning of the foot is more important than forced constrain and “squeezing” the foot.” – Kinematics of the Foot in the Ski Boot; Professor M. Pfeiffer, Institute for the Athletic Sciences, University of Salzburg, Salzburg, Austria.
      The heel counter establishes the rearmost position of the foot in relation to the boot board and ski running surface.

      “I say close proximity because the foot will oscillate between being waited and unwaited.”
      > Bingo again. The foot will tend to oscillate between the loaded and unloaded states (between being waited and unwaited) unless the associated movement is dampened. Everyone talks about the need to support the foot. But was far as I know, I am the only one who has recognized the need to dampen oscillation between loaded and unloaded states. I will discuss this in future posts.

      “Can the heel counter by its self keep the heal from rising vertically? Or is the instep retention of greater importance?”
      > Instep retention is primary. But it is dependent on the heel counter for its effectiveness.

      “It seems that ski boots generally squash the instep”
      > They can. But in many cases there is a void space over the instep of the foot.

      “so if I understand your work it is to design instep retention that holds the foot to the foot board but does not interfere with foot mechanics.”
      > Bingo again. It doesn’t interfere with foot (bio)mechanics required for skiing. The instep counter acts like a transistor in that it filters out undesirable biomechanics.

      “In that light the heal counter snug-retain the heal lateral left right and aft but are there other functions?”
      > It provides a force transfer surface for a horizontal torque couple in conjunction with the vertical face beside the ball of the foot. This is described in detail in US Patent 5,265,350.

      You are getting there Thomas. Keep going. Best of the Holiday Season to you.

      In that light the heal counter snug-retain the heal lateral left right and aft but are there other functions? thomas

      but at the same time confined to being in close proximity to the foot board. I say close proximity because the foot will oscillate between being waited and unwaited.

      Can the heal counter by its self keep the heal from rising vertically? Or is the instep retention of greater importance?

  2. Dear David,

    Thankfully I never went to college and am not the ‘sharpest knife in the drawer!’ Too little of the time I fly by the seat of my pants and trust my intuition. Ski equipment is one place I do that well but it is for me a very slow process. From my experience with ski equipment, I knew the first time I read your accumulated info and saw the video of the motion of the foot and shin in a ski boot that “this guy really knows his stuff.” For me more proof has accumulated as I have ‘stumbled’ through experimenting with your ideas; they work so well for a novice (me) in those areas that it has to be nothing short of miraculous when applied by one with years of experience.

    Now seeing for the first time that you made it to the prototype stage of a ski boot has me even more impressed. I had come to the conclusion the best ski boot would be a literal ‘Bird cage’ with a little extra insulation to keep the cold air and moisture out; I would ski in a pair of those because they look very stable but allow the human anatomy to move freely.

    So this last paragraph is about your critics. I marvel about those who have PHDs from the ‘best’ universities in the world and I guess they have to belittle everything they doesn’t agree with their way of thinking(?) Ran into that mentality with farmers; they’d tell me how great something like their milking machine worked; after I bought the same model and found out they were terrible went back and complained and was told; ‘we actually don’t like them either!’????

    Educated ignorance to me is a sin!!! Changing the world one mind at a time would be fun; changing it one molecule at a time can get tedious:) Keep on plugging and I’ll do my best to do the same!! mpupko

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