Harb Carver question

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Harb Carver question

Postby Matt » Wed Mar 30, 2011 12:40 am

We have about a month of skiing here, and after that I'm thinking about dry-land training.

One option is Harb Carvers. One thing I don't understand about them is how they actually turn. How can a straight line of weels turn when they are tipped?
Or do you have to steer them in some way?

If I tip my inline skates they do not turn.
I can turn quite aggressively with my inlines, but I cannot figure out what I am actually doing. I was trying to teach my son to inline, but I couldn't describe the movements. He can carve fine on skis, but it doesn't work on inlines.
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Re: Harb Carver question

Postby Carl R » Wed Mar 30, 2011 3:24 am

With inlines I think what we are doing is pointing the toes where we want to go, or as tdk6 usually says rotating the femures.
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Re: Harb Carver question

Postby Bolter » Wed Mar 30, 2011 5:06 am

The only way to turn a Harb carver (if you want to keep your skin) is to tip, CB, CA, bend (flex to release); use the Essentials!

Pointing your toes and or rotating your thighs will send you to the blacktop in a flash of blood and pain.

Tip and balance- they will turn. Rotate and extend - you will flounder.

Search the web to learn how inline skates turn (big time waste IMO).

This tool for training and learning is fun as well as beneficial because of how well it reproduces the actions, sensations, and forces of skiing.

Actions mean movements, carvers require the same as skiing. TTS movements are the worst thing going on carvers and skis. The immediate feedback given when you make the wrong movements is what makes carvers a great tool for learning the correct movements.

Carvers carve they don't like to skid!

Go to the Quick Start Guide to learn how to do it.
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Re: Harb Carver question

Postby Matt » Wed Mar 30, 2011 7:16 am

I did search the web on how inlines turn, but I didn't find any useful answers. I'm an analytical type of person, I want to understand how stuff works. I understand that you can use the essentials on carvers, what I don't understand is WHY is works. On skis it is simple to understand that you ride the sidecut and use the essentials in order to tip and not to twist the ski out of the groove. But why does a straight line of wheels turn when tipped?
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Re: Harb Carver question

Postby ToddW » Wed Mar 30, 2011 7:59 am

Matt,

There are two big differences between carvers and inline skates.

1. The carver wheels are spaced irregularly. Two pair in the back and one in the front, so the front wheels carry more load (if you are balanced fore-aft.) This means they will turn harder than the rear wheels because they have a larger contact patch, hence a larger induced torque when tipped. "contact patch" is the key phrase for a Google search if you want to dig into the mechanics more. If you carve through a water puddle and then look at your tracks you will see that the rear and front wheels follow different paths.

2. There are two rows of wheels, just as a ski has two edges. This makes the lateral balance game the same as in skiing -- you try to tip and the skate tries to restore you to neutral. On inlines, there's no mechanical tendency to return to the neutral position, so you are relatively limited in your tipping ability. As with skis, it is that last little bit of tipping that makes a turn tighter and to tip that much you must counterbalance.

As Bolter said, trying to twist or steer carvers is asking for road rash. Which brings up an important point: protective gear. Use the search function to find several old posts describing protective equipment (helmets, crash pants (hillbilly dirt gear is a good brand), wrist guards, knee and elbow protectors, gloves, etc.) and also rubber tip protectors (or a short segment of rubber automotive hose) for your poles.

Here's an excerpt from the first Google hit on "tire contact patch torque" The basic issue is that when a tire is tipped, different parts of the rubber that are in contact with the road travel different distances because of the varying effective radius for each surface element of rubber, shearing and twisting this large "contact patch."

As a lateral load is applied during cornering, the tire generates a lateral force to oppose this load. As it generates this force, the tire begins to distort. The carcass flexes and distorts laterally. As a result, as the tire rolls, it "crabs" sideways a little each revolution.

The rubber in the tire tread (which forms the contact patch) also distorts, flexing sideways so that the contact patch is displaced laterally from its position at rest. The trailing part of the contact patch is displaced more than the leading part.

The result is that a tire under lateral load does not travel down the road in a direction parallel to the tire's centerline (i.e. perpindicular to the axle's centerline). It travels at an angle to the tire's centerline. The difference between the tire's centerline and the direction of travel is called the slip angle.
.
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Re: Harb Carver question

Postby Matt » Wed Mar 30, 2011 1:42 pm

Todd, I am quite familiar with rubber creep, but it makes the radius larger not tighter. If you corner with MTB with course tires it will creep/slip towards the outside. It is quite noticeable.

I don´t question the usefulness of the carvers and the difference the lateral displacement of the wheels make, I simply want to understand why/how the turn.

I just went out in my garage and tried some turns with inlines, and there is no problem to tip them one way and turn the other way. If I ride on one leg and tip, nothing happens. I also tried various states of fore-aft and it doesn´t make a discernible difference. I think the majority of the turning is done by the interaction of the two skates. Similarly to the front and back wheel of a bicycle. If the skates are not parallel they will initiate turning.

Without trying carvers I can imagine that they turn because when you tip the inside foot it diverges slightly from the other one, and by making an effort to keep the distance between the skates the same they will start turning.

Can you do one-legged turns on carvers by simply tipping?
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Re: Harb Carver question

Postby ToddW » Wed Mar 30, 2011 2:35 pm

LOL. I hear your doubt. The first time I ever got on carvers, I wasn't sure the darned things would ever turn. They actually can turn one-legged.

The tightest turn I have ever done on carvers was with one leg. I was trying to avoid a storm sewer and counterbalanced so hard that the inside skate lifted high off the ground, still tipping hard. A little motivation didn't hurt... There is video in one of the carver threads of Harald and Skiersynergy doing one footed carver turns. Also, Arothafel has posted video of a few turns with one foot lifted, so turning on one leg isn't limited to black level pmts instructors.

Simply by tipping? Barely. CB and a neutral to forward position are very important to making carvers turn well. Said differently, you can turn simply by tipping and balancing over the stance carver.

Make some cross hatches with a pen on an inline skate or carver wheel and then roll it at an angle over a plexiglass or other transparent panel. You'll get a good intuitive idea of where the turning comes from by watching the contortions of the ink lines as they roll under the bottom. You'll need to apply some downward pressure. Less if you use a soft inline wheel. The basic phenomenon is present in one wheel. There is a coupling between multiple collinear wheels and this is the reason for the front-back asymmetry of axle spacing in the carvers.

I have also experienced what you mentioned -- turns due to divergent alignment of two weighted carvers. That's an unpleasant experience and the carvers sometimes buck around or skip on the ground. It's altogether different than the sensation of two carvers turning due to tipping.
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Re: Harb Carver question

Postby HighAngles » Wed Mar 30, 2011 3:20 pm

On the same topic - what's the idea behind the larger rear wheels on the comp model? Why does that change make them more suited to higher speed turns?
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Re: Harb Carver question

Postby Max_501 » Wed Mar 30, 2011 7:10 pm

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Re: Harb Carver question

Postby Hobbit » Wed Mar 30, 2011 7:47 pm

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Re: Harb Carver question

Postby kirtland » Wed Mar 30, 2011 10:05 pm

Matt,
I think the simplest demonstration is take a bike wheel, or spare tire or even a coin and tilt it and roll it, and it will roll in an arc, not straight.
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Re: Harb Carver question

Postby Matt » Thu Mar 31, 2011 12:39 am

kirtland wrote:Matt,
I think the simplest demonstration is take a bike wheel, or spare tire or even a coin and tilt it and roll it, and it will roll in an arc, not straight.
Kirt


It does not really prove anything. in this case you also have the conservation of angular momentum to take into account. What would happen if you could connect two coins with a rigid frame?
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Re: Harb Carver question

Postby Matt » Thu Mar 31, 2011 12:46 am



I don't really buy into the theory of camber thrust. How much torque can a a rubber patch of 1 mm^2 transfer. Not a lot I'd think, and to make things even worse the connection to the other wheels will effectively counter the torque.

Sorry, I still have not seen a good enough explanation why inlines or carvers would turn simply by tipping. What happens if you stand on your carvers and make an effort to only tip, no CA,CB or anything else? Do they turn? Be sure do do it on one leg in order to avoid interaction between the two carvers.
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Re: Harb Carver question

Postby Bolter » Thu Mar 31, 2011 5:28 am

Matt wrote:I don't really buy into the theory of camber thrust. How much torque can a a rubber patch of 1 mm^2 transfer. Not a lot I'd think, and to make things even worse the connection to the other wheels will effectively counter the torque.

Sorry, I still have not seen a good enough explanation why inlines or carvers would turn simply by tipping. What happens if you stand on your carvers and make an effort to only tip, no CA,CB or anything else? Do they turn? Be sure do do it on one leg in order to avoid interaction between the two carvers.




BB says "they turn because we steer them"

OMG Matt have you have found the achilles tendon of PMTS? :shock:

http://www.epicski.com/forum/thread/113 ... kates-turn

Please excuse any hint of sarcasm in my post.
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Re: Harb Carver question

Postby dbillo » Thu Mar 31, 2011 6:09 am

Never mind how they turn...how do you STOP!
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