So how do the inline skates turn?

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Postby Harald » Mon May 31, 2004 2:41 pm

How Harb Carvers Turn

When a Harb Carver is tipped on one set of its wheels the skier?s Center of Gravity (CG) begins to fall toward the center of the instantaneous arc, if enough tipping force is applied. The front wheel sets a different radius than the back wheels; this is proved by the wheel marks left on the pavement. Each track left by the Harb Carvers has two lines, one from the front wheel and one from the back wheels. The front wheels describe a smaller arc; the back wheels a slightly larger arc. It?s the force developed from the front and back wheels working in unison that allows the Carvers to turn and skid through a turn. The force generated by the wheels is called ?lateral or side force? also called grip, produces the turning. Here grip and skid are closely related.

As the skier goes through a turn the wheels produce lateral force using slip angle. Slip angle is the difference between the direction of the wheels or where the wheels are pointed and the actual direction of the Carvers. This is produced when the wheels are tipped on to their sides. Since the wheels flex and deflect, slip angle is possible. The shape of the wheels helps to create tipping once forces are applied. The wheels are able to grip the surface, but they also slip, yielding somewhat to the pressure developed from the turn and body weight on the wheels.

When pressure is reduced or taken away by flexing the stance leg, the angle of the Carvers is reduced easily and the Carvers come out of the turn. Momentum from the act of releasing helps move the CG toward the downhill side of the lower Carver (downhill leg or stance foot) at the end of the turn. This helps to put the Carvers onto the new wheels, for the new direction. Lateral foot tipping and allowing the GC to move freely across the wheels, creates the turn in the new direction. Momentum is the secret to getting the skiing feeling on the carvers. If you release the edges (wheels) from one turn and let your CG move toward the new turn, your Cavers will easily develop tipping angles for that turn. If you are stiff or hold onto the turn too long, the momentum will disappear, which doesn?t help to tip the Carvers for the next turn.
Harald
 

Postby Jeff Markham » Tue Jun 01, 2004 6:47 pm

I've been doing some research since this topic came up. Because of my motorcycling background, I have been searching the Internet for motorcycle-related explanations of turning (since there are precious few references to inline skate turning and the tire/wheel cross-sections are similar).

It appears that motorcycles and inline skates have something in common called "camber thrust". Basically, it is the "cone effect" that Mr. Baum dismisses in his article. If I understand his objection to the "cone effect", he is saying that the skate axles are fixed parallel and would, due to the wheels' grip, therefore resist the turning effect. If the axles could be turned toward the center of the turn, as on a motorcycle, then they would converge to the center of the turn. They are obviously prevented from doing so by the skate frame.

I disagree with this objection on the basis of 1) the relative shortness of the skate wheelbase and 2) the deformability and slipping action (i.e., non-perfect grip) of the contact patch. The shorter the wheelbase, the less wheel deformation/slipping required for a given radius turn. The converse is true for longer wheelbases, e.g., those for a 5-wheel racing speedskate

Example: If you consider a theoretical two-wheeled inline skate with the wheels very close together (i.e., almost touching), it would turn very easily in response to tipping. The angular difference between the parallel axles and the center radius of the turn would be relatively small. On the other hand, if the front and rear axles were separated by 36 inches, it would be comparatively difficult to make a tight radius turn. In this situation, the angular difference between the front/rear axles and the center radius would be relatively enormous. Obviously, a normal pair of skates is somewhere in between these two extremes.

By the way, the actual radius of the turn is not solely influenced by camber thrust, because centifugal forces tend to increase the radius dictated by camber thrust.

For those of you who are interested, google "camber thrust" and "motorcycle" to see some interesting references. In particular, the following links discuss camber thrust (as well as other motorcycle turning issues):

http://www.tonyfoale.com/Articles/Tyres/TYRES.htm
http://www.ommriders.com/read-ride/adva ... eering.htm

From what I can determine, camber thrust is consistent with Harald's description.

Comments welcome.
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Postby Harald » Wed Jun 02, 2004 9:50 am

Yes, this is consistent with my understanding.

I have resently designed a steering mechanism (very simple) for the front wheels of the Harb Carvers. It may make them too easy to turn, but it's worth a try. I hate applying for patents, but if this additional twist to the Harb Carvers could make them available to rank beginners, we may have something for everyone, not just dedicated skiers. I won't be able to start on this project until July.
Harald
 

Postby Hobbit » Wed Jun 02, 2004 7:05 pm

Harald wrote:Yes, this is consistent with my understanding.

I have resently designed a steering mechanism (very simple) for the front wheels of the Harb Carvers. It may make them too easy to turn, but it's worth a try. I hate applying for patents, but if this additional twist to the Harb Carvers could make them available to rank beginners, we may have something for everyone, not just dedicated skiers. I won't be able to start on this project until July.


Just a thought...

I don't know if this is applicabale, but it would be nice to have just one model of carvers ( Comp ) with the steering mechanism.
If you would be able to enable / restrict / disable steering there would not be a need to step through the models as you progress on carvers.
Start with the steering enabled (beginner), than make it a more restricted steering if possible (intermediate) and finaly disable it (expert).
This would allow combining the features of all existing models in one.
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Steering may not be the solution

Postby Harald » Sun Jun 20, 2004 5:10 pm

This is true, but skiing improvement is dependant on tipping not steering. If the Carvers turn with such ease that tipping is no longer the focus, we may end up with the same problem we have with skiing on snow. Skis turn so easily that skiers don?t see the need to improve until they run into terrain and snow where steering no longer works and tipping is essential. Then they realize they didn?t spend enough time on the right basics (tipping). The amount of tipping required to make Carvers turn easily is minimal. Making the grade on cavers is like a right to passage into the performance skiing world.

We are instituting a trade in or up grade program for those who are ready to move up to Comps or Pros.
Harald
 

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