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Harb's Carver Ski Trainer - Page 2

post #31 of 59
I should say that I have no doubt about the great value of the Harb Carvers as a great simulation of skiing in the summer. But if people think that the tight turns displayed in SkierSynergy's videos will happen with zero steering, then somebody managed to re-invent physics.
post #32 of 59
Quote:
Originally Posted by TomB
Nice try, but we are not talking about a single wheel tipping. Give me a bicycle with a fixed front wheel and I will show you how it won't turn at all by only tipping.
Quote:
Originally Posted by TomB



Yes, it will turn, just ask any track cyclist, or take it to the extreme, watch the motorcycle track racing to see how those racers handle the curves/corners.

Quote:
So let me repeat: several wheels that are in-line and connected to a common axis CANNOT turn by tipping. They don't bend, they have no sidecut. Comparing them to skis from that perspective is wrong.


Yes, though they don't bend, and have no sidecut, they turn nicely under the influence of the "weight," (if that's what you mean by "tipping,") just like skiing.

"To make the blades running straight, one must tilt/straighten the blades back by standing almost on the outside edges of one's feet, and keeping them parallel, so the running blades become the 'flat bottom.' Now, the inside/outside edges are referenced to the body and the "flat bottom," and the inside/outside blades are referenced to the turn, we have all our necessary terms for the 'flatboarding,' so all the flatboarding techniques can now be applied."

In rollerblading, skiing, or any sliding sport for that matter, the thing that moves/turns the people is not what they wear under their feet, but the net-force of centripetal force, centrifugal force, and gravity; the skis, snowboards, rollerblades, and etc., all are "devices" serve the purpose of reducing the "friction" so to make these sports possible.

Skiing is a sport of gravity, all techniques aside, the simple principle is to "trade the potential energy for kinetic energy," or simply put, "trade elevation for speed." Skiing is all but playing the "forces" which the "trade" generates. However, as skiing is all but twists and turns and not all parts of the body experience the uniformed force/same acceleration, how to balance the whole body in the balance of [angular] acceleration and the speed become the tricks of trade, such as "Five Sames," PSIA, PMTS... Watching them wrangle those equipments and terminologies only leads one lose sight of the fact, a good skiing is simply to "move your butt/CM downhill in balance."

On the flat, the influence of gravity is minimal, nevertheless, we still have the good old centripetal force and centrifugal force to play with, so,

"Where the wheels convert the gravity into G-force, Tai Chi Rollerblading brings the mountain to the flat,"
--from a previous post.

So we flatboarding on, an endless skiing season?


IS
post #33 of 59
taichiskiing : Yes, it will turn, just ask any track cyclist, or take it to the extreme, watch the motorcycle track racing to see how those racers handle the curves/corners.


You clearly don't know what you are talking about. When I said "fixed front wheel" I mean a wheel that does not turn. You can tip your bike/motorcycle until you touch the ground. It will not turn if the front wheel is fixed. And the rest of your post is sheer stupidity. Drop the flatboarding bullshit already, it is embarassing.
post #34 of 59

Railroad turns on carvers in a circle

Quote:
Originally Posted by TomB
So let me repeat: several wheels that are in-line and connected to a common axis CANNOT turn by tipping. They don't bend, they have no sidecut. Comparing them to skis from that perspective is wrong. :
TomB - you can keep saying this as much as you want. Or, you can get on a pair and tip them and push yourself with your poles and see what happens while keeping your body/feet/legs in a completely fixed position. Then you'll have to figure out what about your assumptions is incorrect.

I just posted a note over on realskiers about how you can tip carvers left, but have them turn right - all sans any pivoting/steering. When you can do that and turn them either way by playing with the pressure/contact patch effects on real asphalt, then your theoretical opinion will have to be jived with your experience. I'm not sure how you will be able to do that since based on your premise the effects I play with and have experimented with cannot be possible.

As Jay said:
"I will always be available for anyone in my area (or when I travel) to demo them. That is free. Just give me a call and play for an hour. Theoretical discussions aside, the real proof is what they are like in use."
post #35 of 59

TomB - here is an explaination that may make sense

I don't really have much time or exp in inline skates TomB, so I can't comment on them. But I did just realize that we are missing a big design differents that would be an explaination as to why carvers turn in response to pressure and tipping much like a ski does.

The contact patch offsets that occur when they are tipped is the key. Now, what your (TomB's) point is, is that in inline skates the contact patch would be parallel and the same on each wheel so there could be no turning effect. I posted a link to an article that describes why there still is a turning effect do to differentially shaped contact patches even on an inline skate.

BUT, in the carvers you have something quite different. You have 2 sets of back wheels, a space with no wheels, and a single pair of front wheels. This means that the contact patch on the front wheel will always be a different shape and size than the much less deformed real wheels. This explains why the carvers turn so easily and why playing with fore/aft pressure can even make them turn the wrong way. This is a much different design then the evenly spaced wheels of an inline skate.

Because if your actually on the carvers they will turn you when tipped and pressured. The little time I've spent on inline skates do not have this very noticible effect that I feel on the carvers. I should probably put my inline skates back on and compare now that I have basic skating skills. (I only used my inline skates 2 times in the past over the years briefly - before I learned to ski in fact).
post #36 of 59
Quote:
Originally Posted by TomB
taichiskiing : Yes, it will turn, just ask any track cyclist, or take it to the extreme, watch the motorcycle track racing to see how those racers handle the curves/corners.
Quote:
Originally Posted by TomB

You clearly don't know what you are talking about. When I said "fixed front wheel" I mean a wheel that does not turn.


Or just you don't know what you are talking about. A bike's wheel doesn't spin on its axial doesn't make sense, so I assume that your "does not turn" means the wheel cannot be steered to change the bike's direction, and what I was saying is that you don't need to "steer" the front wheel of the bike to change the bike's direction. So a bike will turn/changing direction if you tip it properly, even with a "fixed front wheel."

Quote:

You can tip your bike/motorcycle until you touch the ground. It will not turn if the front wheel is fixed. And the rest of your post is sheer stupidity. Drop the flatboarding bullshit already, it is embarassing.


As there's no functional "fixed front wheel" bike in existence, your counter rebuttal is as stupid as it gets. The stupidity is yours.

As for flatboarding? You don't have a clue.


IS
post #37 of 59
John Mason: The contact patch offsets that occur when they are tipped is the key. Now, what your (TomB's) point is, is that in inline skates the contact patch would be parallel and the same on each wheel so there could be no turning effect. I posted a link to an article that describes why there still is a turning effect do to differentially shaped contact patches even on an inline skate.

Remember that I mentioned new wheels with no specific wear. Take such a new skate and tip it and roll it on the ground with you hand. Does it turn? No! You can then put any amount of even pressure and you will see it still does not turn. Its physics, plain and simple. The only way to turn them is through steering. In line skaters know that sharp turns will happen when you pressure through the heel (effectively reducing the friction area). On Hard Carvers this is really easy as there are only 2 wheels in the back. Thus turning is MUCH easier. That would be my explanation.
post #38 of 59
taichiskiing: ...and what I was saying is that you don't need to "steer" the front wheel of the bike to change the bike's direction. So a bike will turn/changing direction if you tip it properly, even with a "fixed front wheel. As there's no functional "fixed front wheel" bike in existence, your counter rebuttal is as stupid as it gets. The stupidity is yours."

The "fixed front wheel" bike is a metaphor for the skate. Same principle, same laws of physics. But in your universe things are different, huh?
post #39 of 59
The front wheels on my rollerblades spin freely, so it is not like the bicycle you describe ("front wheel doesn't turn"). Try some flatboarding! Physics can't explain what a lot of people are doing. Don't let science stop you from doing anything!
post #40 of 59
I have the Harb Carvers Pro model (I started with the pros to get the feel of carving on pavement, I'll upgrade to the Comps shortly and hand these over to my wife).

They simulate a snow carve surprisingly well. I find that they are less forgiving than a ski so they will emphasize problems with ski technique.

You do not have to steer them to turn. You just flex and tip, let your cm follow the tipping and you crank out a very nice carved turn. I think they are a great training tool.
post #41 of 59
Quote:
Originally Posted by TomB
taichiskiing: ...and what I was saying is that you don't need to "steer" the front wheel of the bike to change the bike's direction. So a bike will turn/changing direction if you tip it properly, even with a "fixed front wheel. As there's no functional "fixed front wheel" bike in existence, your counter rebuttal is as stupid as it gets. The stupidity is yours."
Quote:
Originally Posted by TomB

The "fixed front wheel" bike is a metaphor for the skate. Same principle, same laws of physics. But in your universe things are different, huh?


That was to say your metaphor didn't carry meaning if it didn't conform to a real experience. "Same principle, same laws of physics," but your interpretation of them is shallow, so is your world.


IS
post #42 of 59

Nope - they do turn when you test them this way

Quote:
Originally Posted by TomB
You can then put any amount of even pressure and you will see it still does not turn.
Acutally you can do this with Carvers and they turn. You have to press down hard enough to deform the wheels though. Heel pressure alone makes them turn the oppisite direction they are tipping too. New wheels or not doesn't matter as it's the offsetting size - thus line of contact - caused by deformation of the wheels that create the turn forces. This is why a statically held body/foot position will allow you to push with your poles and turn in a circle in carvers.

You may be totally correct that none of this happens with inline/same wheel type/ no roundness to the frame - inline skates. I'm only talking about carvers and how they turn here.
post #43 of 59
Quote:
Originally Posted by John Mason
Acutally you can do this with Carvers and they turn. You have to press down hard enough to deform the wheels though. Heel pressure alone makes them turn the oppisite direction they are tipping too. New wheels or not doesn't matter as it's the offsetting size - thus line of contact - caused by deformation of the wheels that create the turn forces. This is why a statically held body/foot position will allow you to push with your poles and turn in a circle in carvers.

You may be totally correct that none of this happens with inline/same wheel type/ no roundness to the frame - inline skates. I'm only talking about carvers and how they turn here.
Thanks John, I think this makes sense to me. What you are saying is that the Harb Carvers have some flexibility in the chasis (through the placement of front wheel and back wheels. I could see that deformation causing the wheels to effectively form a "sidecut". Very clever!
post #44 of 59

not saying quite that

No - the chassis is totally rigid. The wheels themselves are not. They deform in reaction to pressure. Because of the extra wheels in the back (and actually different sized wheels on the comp model) vs the front, the deformation and thus the contact patch is different. This makes them sensitive to fore/aft balance and tipping and pressure.

The little wheels up front and the fact they are a single wheel instead of a pair of wheels will have a contact patch offset more off the center line of the chassis compared to the back wheels which will deform much less since there are 2 sets of them instead of one. Less deformation makes their contact patch closer to the centerline of the ridgid chassis. This offset in contact patches compared to the theoretical line of the chassis create the rotary force. When tipped left and pressured the front wheel contact patch will be more left of this line than the back wheels. In a bike, this contact patch offset is created by turning the wheel. But it's the contact patch offset that creates the rotary force.
post #45 of 59

importance of two rows

Because there are two rows of wheels for each foot and the wheels are just outide the edges of the boots, there is a leverage for deforming the wheels that is way beyond what you have on an inline skate -- a ski boot helps here also.

And then there is also the emphasis in PMTS technique on articulating the ankle laterally inside the boot . . . laying it over against the side of the boot to create leverage inside the boot.
post #46 of 59

Skate Roller Skis

Quote:
Originally Posted by madbee
Yes my question was off-topic. I started inline skating last summer because I missed skiing. I have seen people with those nordic type skates and they look like a good workout and fun. I was just curious if they were easy to use if I know how to skate.

And I'm not a guy. Madeleine
Madeleine,

Both classical and skate rollerskis are not that difficult to use, particularly if you are a good skier or a good inline skater. Rollerskis offer more resistance than inline skates so they closely simulate a cross-country skiing workout. As I said in my previous post, skate rollerskis develop many of the skills we use in downhill skiing (balance and weight shift). Unlike from what I understand the Harb Carvers can do, rollerskis are not that easy to turn when going down hill. Most rollerskis have speed reducers (kind of like gradual resistance brakes) that help get one down the hill. They are geared to Nordic skiing rather than Alpine, but they do have benefits for Alpine skiers too.

Tom
post #47 of 59
Quote:
Originally Posted by TomB
Thanks John, I think this makes sense to me. What you are saying is that the Harb Carvers have some flexibility in the chasis (through the placement of front wheel and back wheels. I could see that deformation causing the wheels to effectively form a "sidecut". Very clever!
The chassis is totally stiff. I made a pair, using oak for the chassis.

They are not adjustable, since I made my own bindings. I have purchased aluminum for the next upgrade, (from the metal supermarket) , because oak is so darn heavy.

The hardest part is finding bolts for axles that would not bend under my weight. You can get them at a Brafasco outlet store. Still, the front axle bends a bit, especially when skating back uphill -- I must be careful not to push off the toe too much....

I used 82A wheels, which work fine for me. I'd go for softer wheels to enhance the turning effect for lighter folks.

IMO, the important stats are to ensure that the centerline of the wheels are directly under the edge of the boot sole. That will model a ski with a 64 mm waist.

I don't think that the fore and aft position is too important, just so long as the front wheel is infront of the ball of the foot, and the back wheel is behind the heel -- else you fall over. It's not too important because the wheel position does not need to be adjusted for your shoe-size.
post #48 of 59
Quote:
Originally Posted by BigE
IMO, the important stats are to ensure that the centerline of the wheels are directly under the edge of the boot sole. That will model a ski with a 64 mm waist.
69mm?

It would be fun to model binding lifts with this.

I don't know what the cross section of your Al looks like, but I would be tempted to use split axles with 2 U channels next to a trapezoidal center section. Tilt the top side of the wheels a few degrees inward. Base bevel!

It might improve the uphill skate as well.
post #49 of 59
My first version had a 3.5" wheel-base -- I was experimenting with binding options only. It was very very hard to turn.

Using 76mm wheels means the boot needs to clear nearly 3 inches. On top of that I used "1 by" oak to make supports under the heel and ball of foot. Using a rabbet to join the wood, that makes the top of the device about about 4" above the ground. (clearance is require

The Al cross section is rectangular. Wouldn't tilting the axles into a V shape make it more turny? OTOH, an "A framed base bevel" would need to be tilted more to carve a turn, 'cuz the wheels need to pass over the vertical.

I used roller-blade wheel spacers and washers up against the oak. IIRC, the axles are 4", but not mild steel. And I think I should replace with even stiffer metal.
post #50 of 59
Quote:
Originally Posted by BigE
OTOH, an "A framed base bevel" would need to be tilted more to carve a turn, 'cuz the wheels need to pass over the vertical.
Yes, that is what I am thinking.

Quote:
IIRC, the axles are 4", but not mild steel. And I think I should replace with even stiffer metal.
I think you should pass some of the vertical loading to the outer side of the wheel, by putting the wheels inside a U channel. Effectively, bolt a skate frame on either side of a T-shaped binding support. Bolt the 'frames' from the top, and the vertical of the T is under compression only, you can make it from yellow cedar if you like. And you can use hollow 6xxx Al axles.
post #51 of 59
I was originally going to put each row in a channel, but got concerned that the U channel wheel holders could trap a stone and stop a wheel from turning. Keeping the wheels open stops that from happening.

The bolt grade at home depot is the mild steel grade 8 bolts. I used grade 9. A grade 10 is available too, but was far more expensive than the 9.
post #52 of 59
Quote:
Originally Posted by BigE
I was originally going to put each row in a channel, but got concerned that the U channel wheel holders could trap a stone and stop a wheel from turning. Keeping the wheels open stops that from happening.
.
I'm not sure it is a great risk: most skate wheels don't have tread blocks to trap stones and you'd have a hard time accelerating any dry objects upwards without some sort of adhesion to the wheel, or significant deformation of the wheel.

In a line of multiple closely spaced wheels the next wheel acts as a sweeper anyhow, and twigs and stuff drop back out most times. Easily deformable objects such as leaves the big exception. K2 early speed skates all had U-channel frames, closed at the top.

I've some spare Rblade off-road (Coyote) bearing shoulders, LMK if you'd like them.
post #53 of 59
John and Jay have done a great job explaining the theory and practice of Harb Carvers. I've had mine for about three months, overlapping the end of the ski season. I found my skiing improved dramatically. I've come up with several theories on why they are such a great ski training tool. My current favorites are:

-The extremely predictable surface of smooth asphalt exposes technique issues much more readily than snow. It's often difficult to isolate the effect of technique versus variable snow conditions. With Carvers, it's always technique.

-For all practical purposes, its impossible to skid a turn. Good technique is much more necessary, and rewarded, than on skis.

Steve
post #54 of 59
The physics is quite simple really, once you think about it.

The simple cone model of a turning wheel (or wheeled vehicle such as a motorbike, bicycle, unicycle, rollerblades, or carvers on edge):

The part of the wheel that comes into contact with the road has a cross section, the bottom of a "U".

When the wheel is vertical the left and right side of the wheel meet the road at the same distance from the axis of ratation. For one revolution of the wheel, both the right and left side travel the same distance, 2 * pi *r.

When the wheel is tilted to the right, the right side of the wheel touches the road at a point closer to the axis than the left side. The right side travels a distance 2 * pi * a smaller r, while at the same time the left side travels a distance 2 * pi * a bigger r.
Hence the right side does not cover as much distance as the left side. Hence the wheel turns to the right when it is leaned right. It is just like rolling a cone along the ground; the cone turns in the direction of the smaller end. The tire when it is leaned over, as far as the ground knows, is a slice of a cone.

BTW, it is very hard to get a bike to lean over with a non-steerable front end, especially at speed. Countersteering is usually used to induce and control the amount of lean.
post #55 of 59

More on Carvers turn mechanincs

Ghost,

You are describing the turning of a single wheel.

The carvers turning mechanics have more to it. If you watch the tracks of the turning carvers you will see two separate tracks with the front wheel going on the shorter turn radius. The turn radius of a single wheel depends on the amount of deformation of the wheel. That is why carvers have one wheel in the front and two wheels in the back. The Comp model goes even further in this respect since the front wheel is much smaller then the back wheels (I believe the front wheel is 76 mm and the back wheels are 100 mm). So if the person’s weight is applied in the middle of the boot the weight force applied to the front wheel is roughly twice as large compared to the back wheel load.
post #56 of 59
SkierSynergy said-I regularly go out free carving in huge neighborhood developments or on appropriate secluded highways. Many of them are over 2 mile runs and a few go as steep as 25 degrees.
I'm calling you out on this one. Lets see that would be about a 46% grade. On Mt. Scott,Or. paved. I don't think so. :
post #57 of 59
Hobbit,
Yes, it is slightly more complicated. However, the MAIN mechanism for the turn is the coning effect of the wheels when put on angle, as the videos show. The carvers touch the pavement at the wheels. The wheels are turning. The inside point of contact of the front wheel is running a smaller radius than the outside point of contact. The front wheel turns. The front of the carver turns.

When the carver is tipped way over, one back wheel is touching simulating one "edge". The inside point of contact of the back wheel is running a smaller radius than the outside point of contact; the back wheel turns in an arc; the back of the carver turns.

When the carver is only slightly leaned, the front wheel turns and the back wheels must follow.

In-line skates have several wheels, each turning in their own arc to affect a curved path of the skate.

Motorcycles have two wheels. When leaned over they turn in the direction of the lean.

A second order model involving elastic tire deformation certainly goes a step further, but is not helpful given the level of physics training of most members of this form.
post #58 of 59
Ghost, have a look at Fila's new design


Now, of particular interest to me is the phase shown by the red arrow in the diagram:

Now, if we assume that a sizeable fraction of the weight is already transfered to the landing foot on the inside, and that the outside skate is being increasingly edged, what do the precession forces do for the steerable front wheel?
post #59 of 59
Fascinating.

Not being much of an in-line skater, I'm not interested enough to get into the steering aspects of the new design, vis a vis steering around obstacles, though I can see how it would improve the ease with wich you could turn; it add a steering component to the cone effect by having the wheel point in the direction of the turn (a secondary model).

I think the bigger advantage in their design, which permits the wheels to be no longer colinear, is that the "suspension" and "frame flex" (a tertiary model !) allows the wheels to aquire an orientation, as the suspension bends, that allows them to put more forward thrust on the power stroke.

Edit: What will they think of next? Flexible blades for speed skates?
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