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One footed leg steering

post #1 of 28
Thread Starter 
Bob Barnes has been very clear in his explanation of the physics of leg steering, and how two points of contact (read both feet) need to be pressured on the snow to allow it to be done in a pure form. Lift one foot, he says, and it can't be done. With one foot off the snow, some other form of rotary (other than leg steering) must be employed to twist the ski into a new direction of travel.

Sounds reasonable, and proves true in a carpet trial, but does it really hold true in the dynamic environment of skier on snow?
post #2 of 28
Even in a static position, if you are able to suppinate (sp?) your ankle inside the boot, can't you create a moment around the leg by using a movement similar to knee angulation? In a static position this would probably not produce any rotational movement (just a moment), but in a dynamic position on a slick surface I can see where it could create rotational movement. Would this classify as foot/lower leg rotation? I think the only way to rotate the femur/whole leg in this instance would be to move the ankle in more than just a linear path.

Later

GREG
post #3 of 28
I'm not sure right now from a purely theoretical standpoint, but I will say that sunday I was out showing javelin turns to a friend of mine. I haven't done them in a while. A couple times I felt myself steer my stance ski, while the inside ski was lifted because I didn't develop enough edge angle to get the turn shape I wanted, and also not enough angulation to balance on it. I'm not at all sure how I did it, but it was not a simple wash out, it was a rotary that I did. I doubt it was simply twisting my femur, could have been some other movements I was doing with my body that caused the ski to rotate on the snow long enough to get some angle against the turn forces, re-establish the balance points I wanted and carve out the rest of the turn. I will say, it was monumentally more difficult to steer the ski that way, but none the less, some steering did occur.
post #4 of 28
Quote:
Originally Posted by Rick
...but does it really hold true in the dynamic environment of skier on snow?
My answer: (strictly speaking) is No.

Another highly useful mechanism is always available to (and used by) us - whether we realize it's there or not.

.ma
post #5 of 28
Quote:
Originally Posted by Rick View Post
Bob Barnes has been very clear in his explanation of the physics of leg steering, and how two points of contact (read both feet) need to be pressured on the snow to allow it to be done in a pure form. Lift one foot, he says, and it can't be done. With one foot off the snow, some other form of rotary (other than leg steering) must be employed to twist the ski into a new direction of travel.
Pure means without tipping or edging? Are we talking about a flat ski?
post #6 of 28
Thread Starter 
Quote:
Originally Posted by BigE View Post
Pure means without tipping or edging?
Pure meaning done without the introduction of other gross rotary inputs to compensate for the lack of a second point of ground contact,,, such as aggressive rotation and/or counter rotation of the upperbody, shoulder, arms, etc.




Quote:
Are we talking about a flat ski?
No. Steering is a means changing the direction of travel by manually redirecting the feet. Turning of the feet while on a totally flat ski just results in slidding in the same direction while rotating to face a new direction, such as when doing 360's. To actually change the direction of travel, the skis need to be be at least slightly engaged.
post #7 of 28
Quote:
Originally Posted by michaelA View Post
My answer: (strictly speaking) is No.

Another highly useful mechanism is always available to (and used by) us - whether we realize it's there or not.

.ma
Spill the beans, please. What mechanism is it?
post #8 of 28
it takes two points of contact to create a fulcrum mechanism
post #9 of 28

Decoder ring

Quote:
Originally Posted by Rick View Post
Bob Barnes has been very clear in his explanation of the physics of leg steering, and how two points of contact (read both feet) need to be pressured on the snow to allow it to be done in a pure form. Lift one foot, he says, and it can't be done. With one foot off the snow, some other form of rotary (other than leg steering) must be employed to twist the ski into a new direction of travel.

Sounds reasonable, and proves true in a carpet trial, but does it really hold true in the dynamic environment of skier on snow?
"Into a new direction of travel" That could be anticipation-release.
post #10 of 28
Quote:
Originally Posted by Rusty Guy View Post
it takes two points of contact to create a fulcrum mechanism
Like the man said "one foot"
post #11 of 28
Quote:
Originally Posted by Rusty Guy
it takes two points of contact to create a fulcrum mechanism
Very carefully stated...!

And yet - not strictly true. This statement refers to Two Points of "Contact" but doesn't specify what is in contact with what else, nor where the 'fulcrum' is.

---
Assume a skier sliding forward on Flat terrain, with skis perfectly flat to a very-firm snow surface...

Assume also that one of their 'contact points' is on the snow (thru their foot, boot, binding & ski - which actually touches the surface).

Now if the other foot is in the air - where might their 'other contact point' be? And where might the actual fulcrum (which actually means 'pivot point') be in this case?


Taking it further; what if the skier is on that same surface but with that single ski tipped on edge (while they angulate to stay in balance over the ski)...?

This skier is able to 'twist' that foot, driving the tip of that single ski slightly deeper into the surface.

In this case, where is the other 'point of contact'? And where is the actual fulcrum?


.ma

(PS: This in no way discredits BB's discussions on the technique called a 'Fulcrum Turn' or Independent Leg Steering - it's merely a different arrangement of our contact points and the fulcrum point)
post #12 of 28
Rick,

What, in this dynamic environment, would stop Newton's: For every action, there is an equal and opposite reaction?

Quote:
Originally Posted by Rick View Post
Bob Barnes has been very clear in his explanation of the physics of leg steering, and how two points of contact (read both feet) need to be pressured on the snow to allow it to be done in a pure form.
Yeah, the examples (pivot slips, paper on the floor, barstools) seem to usually be with feet. Do they have to? I don't think so, other points will do. I think a pole (or poles) will do - drag'em or plant'em.

Would it be possible for a refined skier to make an anticipatory move and subtly set the upper body into rotation to then subtly turn the leg against it, having negligible effect (possibly seemingly no effect) on the larger upper body mass?

Quote:
Originally Posted by michaelA View Post
In this case, where is the other 'point of contact'? And where is the actual fulcrum?
I'm all ears, michealA! Where are they?

Chris
post #13 of 28
To steer a ski or overcome the ski snow interaction requires leverage of something else removed from the ski being steered. If a skier is not leveraging one ski against the other then they are leveraging their momentum or the upper body against the ski snow interaction. Just try skiing on one ski without poles in slow long radius turns and the answer will become very apparent.
post #14 of 28
How about the statement that the ability to control the rate of steering can only be accomplished through two-footed steering and not one-footed steering. With only one foot on a surface, the rate of steering cannot be regulated in the same way as with two feet. Think of every action having an equal and opposite reaction. If the one foot and leg is twisted and the other foot is off of the surface, other parts of the body react and move as a result.
post #15 of 28
I'm thinking one-footed steering can be done. I'm sure I've done it, just not sure how. One possibillty is blocking with a pole (even if it's just dragging the pole). Also, how about a form of couter-rotation? Not with the top half, but with the other leg, the Javelin turn mentioned above?
post #16 of 28
Quote:
Originally Posted by epic View Post
I'm thinking one-footed steering can be done. I'm sure I've done it, just not sure how. One possibillty is blocking with a pole (even if it's just dragging the pole). Also, how about a form of couter-rotation? Not with the top half, but with the other leg, the Javelin turn mentioned above?
That may work on the big toe side but what about the little toe side turn? Do you rotate the free leg away from the stance foot for this opposite rotation?

My own experience with one footed skiing without poles is that is possible in short high tempo turns, as we can wind up and then unwind the body against the ski's action. But this falls apart as the speed of the movements and the forces generated decrease. As I remove the normal things we use for leverage I eventually I get left with nothing to effect ski performance.
post #17 of 28
Quote:
Originally Posted by RicB View Post
That may work on the big toe side but what about the little toe side turn? Do you rotate the free leg away from the stance foot for this opposite rotation?
You could. Think Royal Christie. Obviously that wouldn't be how you'd normally ski, but when you see people trying to cheat while doing one foot drills you will see the free foot going all over the place (once you take away the poles to make them stop cheating with those).
post #18 of 28
It seem to me that you would be turning your leg against your hip.
post #19 of 28
Why wouldn't the hip move?
post #20 of 28
Could the second fulcrum point be the hip joint? I just stood on my office chair with one foot. I can cause the chair to rotate left or right without any gross body movements. Upper body stays facing forward as my leg rotates. Seems like the force causing the rotation has to be generated by muscle.

On skis I'm confident I could do the same rotation movement (think 1 footed pivot slip)(I'm not claiming it would be pretty or well controlled). Because we can't completely isolate pressure and edge movements it would be so easy to add a little of each to accomplish a direction change.
post #21 of 28
It seems to me that our muscles and connective tissues are arranged to allow us to move one body part in relation to another.

In this case some muscles would twist the leg while others held the hip still.
post #22 of 28
epic,

Quote:
I'm thinking one-footed steering can be done. I'm sure I've done it, just not sure how.
It can be, maybe not to the "pure form that BB is refering to. The weight or mass of the ski lifted off the snow gives you a folcrum point to rotate the femor in the hip socket. I stear using leg rotation doing one footed skiing all of the time.

RW
post #23 of 28
Seems like everyone is pinning this down pretty well Rick...

Remember (all) that a 'fulcrum' is the point (or collection of points) at which things pivot or rotate - an axis.

---
'Contact Point' was a term used earlier but it isn't necessarily accurate. When two 'material things' are involved in the fulcrum mechanism it's their Mass and where the CM of each such Mass is located that's important. (When in firm contact with the ground it's the Mass of the whole earth we're working with.)

This is why the proposed ideas of a Javelin Turn or a Royal Christie work so well - better in fact than keeping our lifted ski close to the central axis of our body.

---
Even when we have no other leg to wield as counter-Mass there's no reason why our own internal mass can't be used for us. Remember that each hip socket is off-center from our body's centerline which also helps.

Kazooski's office antics on his chair show this nicely. (I'm sure it was a popular show too!) The Lazy-Suzan ball bearings that permit reduced-friction swiveling are more like sliding on snow than any exploration of the idea while standing on sheets of paper.

---
Statements about Equal & Opposite Reactions above are exactly why this does work. Using our muscles, we move one body-part's Mass in relation to another body-part's greater (and possibly more axially distant) Mass.

The further from the Fulcrum (in this case the average of many internal "locations-of-partial-pivot") our base-Mass is, the more leverage we have on our moving-Mass. This means that we are more effective twisting that single leg when we have a Mass held out to the side further away from it (like the other leg & ski).

We gain even more advantage when we move that lifted leg & ski forward as we ski into the direction toward the lifted-leg-side, and added advantage when we move our lifted-leg backward when Turning away from it.

Finally, we have more leverage for this in a Flexed position than in a very straight (upright) stance because more of our body Mass is located further from the center-axis of the pivot point. In this case further fore and aft - but still further away.

---
In answer to shortcomings of this mechanism in slow, long-radius turns - yep, this is so - to a degree. But remember also that in a large radius turn the Whole Skier is actually Rotating around their turn somewhat with their skis.

In such a Turn we can systematically alternate between foot-steering (via this mechanism) and accepting some ski-induced rotation (let's call this 'Upper-Body Guidance') throughout the turn and might unconsciously 'reset' our rotational range a number of times.

Is this BB's ILS? Nope, not in the pure form he describes which specifically uses leverage from the snow surface. His ILS provides much more leverage than what is described above and more continuously as well (until you feet or skis whack together that is ).


---
One final thought is that the ski itself provides considerable turning force once on edge. If we make use of the mechanism described above and integrate it with the ski's own inputs, that's when we see the greatest advantage. and yes, this idea works best in shorter radius turns.

The purpose of the idea described above (and of ILS) is NOT to do all the Turning for the skier! Each mechanism is a skill/tool to refine and augment control of our skis. Is it Active Rotation? Yep, the best kind - the kind that makes skiing easier and more fun.

.ma

(Gee - I hope this is kinda where Rick wanted us to go.)
post #24 of 28
Hello, Rick?

Inquiring minds need you to complete this thread!
post #25 of 28
As others have said, for fast turns you can leverage the required torque against the inertia of the rest of your body.
For slow turns, it seems you ought to be able to get your CM off-axis from the desired rotation, tilt the axis some, and lever against gravity. But maybe that contradicts what you need to do to keep from tipping over?
post #26 of 28
Quote:
Originally Posted by mdf
As others have said, for fast turns you can leverage the required torque against the inertia of the rest of your body.
For slow turns, it seems you ought to be able to get your CM off-axis from the desired rotation, tilt the axis some, and lever against gravity.
Nicely said.

As to tipping over - internally, we only need to lever against Mass that is somewhat away from the Mass we wish to move. We amorphous critters can easily do that without messing with Newton.

Both Angulation and Flexion provide the opportunity to relocate Mass such that either internal Mass can better be used, or Gravity can better be used to implement leverage - without disrupting our overall balance.

We don't even need to think about it. Intent is all our cerebral motor-activators need to coordinate the action.

Cats falling off a barn roof do it without a surface to push against - and without gravity to assist because they're in free-fall. (...And no, I didnt toss them off! )

.ma
post #27 of 28
I don't find anything above to be striking one way or the other. My question is: why does the answer to the original question matter? I am not being a wiseass here (although wiseass is well within my capabilities)- I want to understand how to use the answers.
post #28 of 28
Helluva's got it right.

Tipping will lead to rotation. It can be done on dryland too.
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