Time for a true DH Sit Ski?

[anthill]

Is it just Andy bringing it to TGR, or have sit-skiers been charging and hucking harder than ever the past few years?

Given the skis and gear they're breaking (Andy and the X games racers in general), it seems like the GS/race oriented buckets aren't enough anymore.

Suspension travel, for example: would a sitski with a 12" travel coilover be skiable?

[SnowToad]

At LL a few weeks back I saw a ski chair setup that had a sweet Ohlins shock that looked much like this one.

[anthill]

Nice. I wonder what the limits on shock travel are. Maybe your chair/ski travel can't be more than the safe extension of your arm/elbows? I can imagine some nasty shoulder injuries from landing hucks and plush suspension shifting all the weight to your hands.

Or maybe it's an edge grip/cornering/stiff ride thing?

I guess this is pointless, since Andy's the only guy around here who knows, and he has more important things to do.

[enablingtech]

guess I will add my $.02

we've been manufacturing adaptive ski equipment for over 20 years. began with monoskis in the mid-late 1980's, now focusing on biskis and outriggers. We PROUDLY sponsor Andy with his Superlite Outriggers (plug).

Shock travel can be as much as the design of your rig. Most "mass" produced monoskis have 6-8" of travel - I've heard of people having up to 12-14" of travel. The Ohlins pictured above is very popular as well as WP shocks. We used Kayaba back in the 80's.

Something to remember is that the longer the shock, the higher the sitskier is from the ground (usually) Meaning more ab muscles are needed to initiate turning, pushing yourself up from crashes etc. I can't remember what Andy's level of SCI is but some sitskier's might have to ski a biski instead of a mono because of this.

That being said, adaptive skiing has come a long way in the last 5-10 years. Guys are taking their sitsking to a whole other level than what the original design of this equipment was (which has remained basically unchanged for 20 yrs.).

Andy Campbell is THE MAN!!! Get well soon!!

-Ben

[sitskiswe]

The limit of the shock travel is dependent of the construction on the sitski. So a 12" could be used. The problem is that with a longer shock you will sit higher and that could be a problem if you are a paraplegic(bad or no balance because of loss of muscle function). Sitskis for beginners have a lower seat height and advanced/racer sitskis are higher.
Andy is using a Praschberger where the seat height is around 30 cm. Tessier scarver have an adjustable seat height from 32 to 38 cm so there should be more space for a longer shock on the scarver.
Praschberger comes with a WP shock but I think the racers can upgrade to a Öhlins shock. The scarver comes with a Öhlins shock.
The outriggers that we have in our hands can be adjusted in length so they are no concerne.

[anthill]

Hmmm, interesting. If the main performance reason for low ride height is turn initiation, is there any benefit in using a dual-rate coilover design for more aggressive sitskiers (like Andy)?

I don't know much about suspension, but I'm thinking that the stiffer (top) spring could be tuned to give good control of carving compression and kicker takeoffs, while the soft (bottom) spring could be just strong enough to get full shock extension in the >1 sec airtime before landing big jumps. That way neutral ride height could be kept reasonably nimble, while leaving some travel in reserve for hucks to flat...

[Lane Meyer]

Sorry if this is an obviously stupid idea, and no disrespect whatsoever to the talented engineers who have toiled for years to help adaptive skiers, but why are almost all of these designs limited to a coil-spring shock around a rod that snaps into a traditional ski binding? If the skis break at the binding mounting points, why not toss out the idea of using a binding at all?

What about designing a flexible carbon-fiber arch (like an upside-down ski over a ski) with the sit skier's chair at the apex of the arch directly over the midpoint of the ski? The arch would need some means of attaching at the ends of the ski, or could maybe be integrated into the ski design? Or you could even integrate a coil spring under the high-point of the arch.

I presume this idea has been discounted in the past because it would not work well with a traditional cambered alpine ski with sidecut because the ski would not flex properly and carve if the weight was spread out to the ends instead of the middle. But what about forgetting the need to flex a ski with weight in it's midpoint to carve on hardpack and build a rig designed just to schralp soft snow (the goods)? Surely you'd also need to design a different ski: perhaps a longer, super-wide rockered reverse camber, reverse sidecut ski to integrate into the design for use only while freeskiing? Something like this: (excuse the terrible MSPaint sketch, but I'm too lazy to open up AutoCAD).

[enablingtech]

Up until 5-10 years ago, monoskis did not used standard alpine bindings. Each company designed a different type of attachment system to the ski. Folks within the adaptive world pushed for years to get manufacturers to switch to monoski "boots" which could be used with standard alpine bindings allowing them to switch between skis easier. Also, much of the adaptive equipment is built for adaptive programs who see a huge number of skiers with all sorts of different disabilities and needs so they need something that will work for the largest numbers of participants possible.

As for the question about why coil-spring shocks are all the rage, I don't know. We used them originally in 1985 because we are a motorcyle shop and that's the type of suspension that we knew about. Nothing much changed in 23 years.

Andy seems to actually have 2 problems - 1. getting the rebound/compression correct so he doesn't pull the bolts through his bucket again (fixable, depending on how hudge he wants to go). 2. How to stop breaking skis due to his weight + weight of the monoski when landing jumps in non-ideal conditions (much tougher).

[Lane Meyer]

Up until 5-10 years ago, monoskis did not used standard alpine bindings. Each company designed a different type of attachment system to the ski. Folks within the adaptive world pushed for years to get manufacturers to switch to monoski "boots" which could be used with standard alpine bindings allowing them to switch between skis easier. Also, much of the adaptive equipment is built for adaptive programs who see a huge number of skiers with all sorts of different disabilities and needs so they need something that will work for the largest numbers of participants possible.

As for the question about why coil-spring shocks are all the rage, I don't know. We used them originally in 1985 because we are a motorcyle shop and that's the type of suspension that we knew about. Nothing much changed in 23 years.

Andy seems to actually have 2 problems - 1. getting the rebound/compression correct so he doesn't pull the bolts through his bucket again (fixable, depending on how hudge he wants to go). 2. How to stop breaking skis due to his weight + weight of the monoski when landing jumps in non-ideal conditions (much tougher).

Very interesting, thanks for that. For Andy to even be able to rip the skier-X course as he was doing in the XGames is no small technical feat of equipment design, for sure.

Is Andy's rig built from scratch or is it made of widely available parts from the adaptive equipment world? I ask because I spent some weekends volunteering as an adaptive instructor in Breck back in college 10 years ago and I don't really recall if his rig is similar or different to the ones we were teaching people to operate. Man those people we worked with were so inspirational!

[SkaFreak]

Cont from a tangent in a different thread:

Does the binding affix to the aluminum piece or to the ski?

If I am envisioning this properly (binding attaching to this device), wouldn't the area within the aluminum parabola be a "dead spot" where the ski wouldn't flex at all? Would using a springier material like titanium be more effective?

Or am I picturing this all wrong??

I'm not sure from what you are saying, but I suspect that you are envisioning it differently. Here's a quick and dirty Solidworks part I threw together to give a better idea of what I mean. The middle section is the false DIN sole to clip into bindings. The bars would only contact the board for about an inch past the bindings, then curve upward. The upward curve could be tailored to whatever exact dimensions were necessary.

edit: For those that didn't get linked here from the other thread, this design is meant to simply give the ski a steady curve to bend up to rather than focusing all the force on a single spot as normal bindings would. The bottom of the structure would have a shock absorbing material of some kind attached to help as well.

[anthill]

Lane Meyer's design looks kind of like a leaf spring like you would see on heavy trucks. I'm guessing you'd still need a damper of some kind to suck up the rebounds.

[dumpy]

Cont from a tangent in a different thread:


I'm not sure from what you are saying, but I suspect that you are envisioning it differently. Here's a quick and dirty Solidworks part I threw together to give a better idea of what I mean. The middle section is the false DIN sole to clip into bindings. The bars would only contact the board for about an inch past the bindings, then curve upward. The upward curve could be tailored to whatever exact dimensions were necessary.

edit: For those that didn't get linked here from the other thread, this design is meant to simply give the ski a steady curve to bend up to rather than focusing all the force on a single spot as normal bindings would. The bottom of the structure would have a shock absorbing material of some kind attached to help as well.

Ahh now I get it. That is not what I was picturing. I was thinking something more like Lane's design, but a two piece support bar with a shock in the middle, less rise and have it be independent of the mount for the carriage. I admit, it's a bit of a Rube Goldberg. If I get some spare time, I'll draw something up to post.

Your design is interesting, I admire it's simplicity and the fact that it wouldn't affect ski performance much (if at all). So the theory is that the ski will bend, but if it bends past a certain point, it will hit the curved aluminum block and not bend too far? That could work or it could push the breaking point to just past the end of the aluminum. I guess it would depend on how big of a landing.

BTW this thread is hot tits, way more fun than the average gear talk.

[anthill]

Cont from a tangent in a different thread:
this design is meant to simply give the ski a steady curve to bend up to rather than focusing all the force on a single spot as normal bindings would.

I like the philosophy of spreading the force around, but I think it might be better built as a riser plate of some kind. Getting the plate+ski geometry and stiffness right would be tricky, but it might have a more predictable feel. I'd be worried about the 'flex-limiting' approach being large and cumbersome in pow as well as the feel of the transition from ski-only to backstop being rough and startling.

As far as approaches that don't let the ski flex like a conventional camber/sidecut, that would make it pretty specialized. For $4000, a sitski's gotta be able to do everything.

I'm thinking that snowmobile and mountain bike suspension design are the places to look for inspiration. There's some talk about a (supposedly) excellent setup here. I'm not as keen on snowmobile geometry, but the shock absorber spring/damping setup sounds like it takes care of what Andy was complaining about most: kickback after big landings launching him off-balance.

Here's a question: Is it better for a sitski suspension to nudge your weight forward, backwards, or keep it centered over the ski when you hit a kicker? What about when landing a big drop?

[SkaFreak]

I had thought about a riser plate, but that would just introduce another element which would increase the number of parts that could break. Then again, it might reduce construction cost, but either way. I hadn't really thought about it being cumbersome in powder, but I guess it would be creating one more small face to dig through the powder.

As for the transition between normal flex and the limiter, I would suspect that it shouldn't be too big of a problem as the only time that it will get a jolt is on an impact that would normally break a ski. That is also the reason for the shock absorbing material on the lower side. That way should the impact be enough raise the ski up to the limiter, the dampeners would help to reduce the impact as well.

Thinking about this a little bit more, I'm thinking maybe this design, but using the tip and tail as the mounting points for the chair, with a shock system in the middle would make it more efficient and less likely to cause any issues.

[karpiel]

Sorry if this is an obviously stupid idea, and no disrespect whatsoever to the talented engineers who have toiled for years to help adaptive skiers, but why are almost all of these designs limited to a coil-spring shock around a rod that snaps into a traditional ski binding? If the skis break at the binding mounting points, why not toss out the idea of using a binding at all?

What about designing a flexible carbon-fiber arch (like an upside-down ski over a ski) with the sit skier's chair at the apex of the arch directly over the midpoint of the ski? The arch would need some means of attaching at the ends of the ski, or could maybe be integrated into the ski design? Or you could even integrate a coil spring under the high-point of the arch.

I presume this idea has been discounted in the past because it would not work well with a traditional cambered alpine ski with sidecut because the ski would not flex properly and carve if the weight was spread out to the ends instead of the middle. But what about forgetting the need to flex a ski with weight in it's midpoint to carve on hardpack and build a rig designed just to schralp soft snow (the goods)? Surely you'd also need to design a different ski: perhaps a longer, super-wide rockered reverse camber, reverse sidecut ski to integrate into the design for use only while freeskiing? Something like this: (excuse the terrible MSPaint sketch, but I'm too lazy to open up AutoCAD).

Ski lifts.

[dumpy]

Ski lifts.

This is something I've been thinking about a lot. Skiing gear, in this case, skis, bindings and chairlifts, are designed around human legs being part of the equation.

Chairlifts are the biggest issue here, no matter what other design changes are made, chairlifts will always be there.

It seems like sit ski design needs to as accurately as possible mimic the human leg in skiing position while wearing ski boots. I don't really have much to add on this design wise, but this appears to be the challenge.

Unless a purpose built racing sit ski can be made, that may not be as chairlift friendly, but can handle the rigors of sit-ski cross. something that is not designed for spinning laps at your local hill, but something for destroying race courses. I suppose it would require training at a place with a surface lift and race day would require either a sled or a regular sitski and sherpa.
Maybe something that can be retro-fitted to an existing sit ski on race day.

[Clone]

Could something along this line be worked out?

[Lane Meyer]

Ski lifts.

Helicopters and snow cats. Spatulas certainly suck on groomers as do any R/R but they certainly beat the pants off anything else in soft snow.

Why the need to respond with such a dickish tone, we're all just brainstorming to try and be helpful.