Power Kite Forum

STRUGGLE WOBBLE !

flexboardz - 9-12-2010 at 07:48 AM

Recently, we have initiated a research on wobble : understanding causes and finding solutions.

So, we are gathering information on this matter (feel free to contribute) and make them available on Flexboardz.com/Technicz.
In fact, there is a lot of information available but it implies a lot of (high level) mathematics

So we decided to summarize it in an understandable way in a video in particular for the young riders.
The first part is a general presentation of the phenomenon (comments from wikipedia/videos from youtube).



Next we will enter into details : rider's behaviour and dynamic analysis...

Last point : this is a "WTF!! Drop the brain and ride" Free Area ! :)

We remind that each year, +- 20.000 head injuries are treated in emergency room due to skateboarding ! Wear your helmet !

jbentley - 9-12-2010 at 08:12 AM

I watched the video up till the truck began to role over. Sorry flexboardz, I will not watch any more.
You succeeded in convincing me NOT to get into this sport, I don't want to end up on some youtube video.

PHREERIDER - 9-12-2010 at 08:36 AM

reality is strong. the weak close their eyes and prayer for a hero. ..our desperate minds want a resolve for the WHY?

intellectual gaps are the gods play ground.

JBENTLEY welcome or is that good bye.

thanks flex ...question on! a self destructive equation will arrive shortly

flexboardz - 9-12-2010 at 09:26 AM

Sorry JBentley, my purpose is only to make our sport safer...(all videos are widely available on youtube). I certainly do not want to make fun of victims (I cut the trashy part of the crash)

However, I agree that the truck sequence is irrelevant (cars dynamics is different from skate) but I just wanted to point out that skate/mtb are the only vehicles to experience instability within normal operating range...

Personally, all sequences shocked me because wobble is a dangerous issue...and as a board-maker (and a father), I feel concerned !
Now as said Phreerider, we can choose to close your eyes or face the problem...
Apologies again if I hurt your feelings,

kiteline - 9-12-2010 at 09:43 AM

Nice video. Your pauses are too short though for reading your text. I had to keep rewinding to read everything you got on there.

That being said, I really like the word "perturbation."

Thanks for the video.

-Mike

indigo_wolf - 9-12-2010 at 10:11 AM

Did anyone else notice a conspicuous lack of safety gear in a lot of segments?

ATB,
Sam

erratic winds - 9-12-2010 at 11:13 AM

That video seemed more to shock than inform.

NJLandboarder - 9-12-2010 at 03:08 PM

wow ive been riding skateboards since i was five

the first time i experienced speed wobble was on my longboard and form then on i kept my trucks tight when i was riding for speed skateboards and mountainboards are very alike everything about about them is adjustable to your preference or riding style i keep my longboards trucks just tight enough so i dont wobble but i can carve

but tightness will not prevent wobble it will only up the speed at which you begin to wobble at

on my mountainboard i keep my trucks really tight because i ride at the skatepark alot and have been getting alot of wheel bite on all four wheels its kinda pisses me off because when i contacted ground industries about the problem they didnt want to help but thats not the point

whenever i started experiencing speed wobble on my longboard i found that crouching down low to one knee and keeping my front foot adjacent with the board and its center

my theory is that when riding at high speeds center of gravity plays a big part also your control over the board because if you begin wobbling you can shift yourself to prevent it from wobbling even faster and throwing you off

also i agree there there is a big problem with adolescence these days.... they don't wear helmets because its not cool, and even when they are forced to wear a helmet at the skate park they buckle it around the back, i don't see why people don't wear them
i mean yeah they don't look that cool but one fall and you could have serious brain damage i personally would rather be the kid who looks stupid then be the person being called "retarded" because they have brain damage (no i have nothing against the mentally challenged or developmentally disabled)
/\
wow i feel like that was a little strong but, i fell once while riding with my beamer on a windy day when i first started and hit my head then went out and bought a motocross helmet the next day (yes i had a helmet on it was bicycle helmet not as protective)
and thank god i had that motocross helmet on the day i had my accident..... it may be the reason i'm alive or not a vegetable

Kamikuza - 9-12-2010 at 05:47 PM

I used to skateboard WA-AAAY back in the day ... this was before the cool, wide freestyle boards got to NZ and we all had those funny looking plastic things from the 1970's cos erm it was the 1970's :o we never went fast enough to get speed wobbles but I do remember falling off a lot ... there was no such thing as helmets then, I swear! Fast forward to this century!

Ol' Faithful is a Flexifoil Kava, the big one ... got speed wobbles on it once when I got surprised riding toeside by a gust and shot off through the carpark ... somehow rode it out but I don't know how. I suspect that because I was standing straight up and down on it, as opposed to loading from "behind" like when kiting, was the reason I wobbled.

Advice on how to avoid wobbles, or correct once wobbling? Do Flexboards not wobble?

g-force junkie - 9-12-2010 at 05:54 PM

Seems like some kind of strut that goes from wide on the front axle back to about the middle of the board on each side similar to what you see on the steering dampner on a crotch rocket.

snowspider - 10-12-2010 at 08:35 AM

From what little I know 2 things come to mind , 1 pilot induced occillation (poi) you should be able to google it. The other is "flutter" or harmonic vibration which could lead to POI. I have exprienced motor cycle wobble which is undoubtably some kind of harmonic issue and had an ultralight trike develope a poi which the instructor was immediatly able to stop. In the video every thing but the motorcycle looked like poi. I just finished a buggy build and my primary concern is , at what speed will it wobble out of control. 35mph down the road , still good. I'm no engineer but I've been on a lot of things in motion , interesting topic.

PHREERIDER - 10-12-2010 at 09:01 AM

i believe the same SNOW SPIDER, some type of threshold oscillation freq. PILOT INPUT INITIATION for the reaction to start. this momemtary imbalance vibration i think has RATE and balance tittering as from numerous sources , WHEEL SPIN imbalance and gyro effect with steering points. really can play havoc with home brew items. thankful for real engineers keeps the buildings standing, the bridges suspended and things from just dismantling with you in it, light planes, trains and things !

the two "ends" (and i use that term in a general sense) oscillate til collision( at theoretical points). threshold rate and energy must be exceeded for control to resume before rider balance point is lost . which is about the blind of an eye.

i always power through it with positive strong side pressure ASAP for recovery.

flexboardz - 10-12-2010 at 11:21 AM

thanks for the pilot induce oscillation /pilot input initiation leads ...I will follow these tracks ...

flexboardz - 10-12-2010 at 12:24 PM

To Indigo wolf :"Did anyone else notice a conspicuous lack of safety gear in a lot of segments? "

You are right ! Regarding boards (the segment I know a bit), the problem is that very few company enter into R&D : generally they only ask to their supplier to do the same products with a different colour and their brand on it !

it's a bit sad but our industry is very conservative ! Simply consider that the skate trucks has been invented in 1863 and we keep copying it ! even if it's an intrinsically unsafe design !

There is a similar topic about wobble on silverfishlongboarding and you have always the same comment : "stop thinking and keep buying !
Difficult to progress with such a mindset !

Kamikuza - 10-12-2010 at 07:29 PM

Re. PIO ... I did some reading on gyrocopters for a while cos I want one :D all of them can do it but those with certain setups are more prone - thrust line above CoG IIRC. Same with bikes - the steeper the steering head angle and the less the amount of trail, the worse they are. Those are compromises for design and handling though ... skateboards wobbles I always thought was nature of the beast - you couldn't avoid it with the design elements being used.

... although I do remember watching some longboard/flexboard video of guys carving down massively long hills at a great speed with no issues ... I'll see if I can find it ...

van - 11-12-2010 at 08:39 PM

Kami,

To answer your question : Do flexboardz not wobble?

My experience has only been my Scrub Rush and then today a MBS ( not sure which one - borrowed it from Darren today) to compare against the flexboardz. My board always wobble when I'm gettign any kind of speed out of it. So far with the flexboardz, I've experience no wobbles at all. But then , I have not gotten it up to the limit on speed yet ... :crazy: One thing I noticed is that I can put more tension against my kite at speed which helps with the wobble. The flexboardz also has a much lower center of gravity. The board rides really low (adjustable) when you put any weight on it. I guess that's why they call it the flexboardz.

snowspider - 13-12-2010 at 08:32 AM

Riding a board straight and level is like being on a tight rope , rope/trucks loose increased difficulty, tall straight up walker/rider same result. So the comments about crouching down and tight trucks easily apply to reducing wobble.
Straight rolling puts board and body in a neutral balance in order to go straight, and neutral is not stable.
Adjusting truck tension and lowering center of gravity have obvious benefits.
Another option is to have the rider a exert a constant force in one direction to go straight.
A little toe pressure or heel pressure to go straight and have the neutral balance point located some where in a turn.
If I'm not mistaken "toe in " on a car and "center of gravity ahead of the center of lift" in aircraft are both design features that eliminate/reduce unstable characteristics and allow no input to go straight and also provide a degree of self correction.
I wish I had paid attention in school .... whole careers are made of this stuff!

43patrick - 16-12-2010 at 04:33 PM

Every one who has spent much time skateboarding has eaten it pretty bad due to speed wobbles. It is always a bummer and can make for dangerous crashes. If you board is set up for the style of riding you are doing it should not be a problem. For example when street skating or at a skate park I ride loose trucks, in a swimming pool or half pipe tighter trucks. Over the last couple years I have been tightening my trucks for kiting cause i like to go faster. When the speed wobble start you can put a stop to them by turning hard in one direction or the other as that that will take you out of the harmonic resonance oscillation if you catch it soon enough and still have enough control to turn out of it. Going straight and trying to ride it out rarely works out. After i get them I usually crank the trucks down a little more cause i wont ride slower.

zero gee - 16-12-2010 at 05:08 PM

I always wondered why my Outback Mountain Board had no speed wobble. This has helped answer that. Thanks.

Bladerunner - 16-12-2010 at 05:33 PM

Gee, Jbently I hope you mean skateboarding and not kiteboarding ?

I really don't get what a video showing how wobble is induced would be the " thing " that puts you off of kite sports?

If sharing a sport with people who have an inferior safety standard bothers you then perhaps you are making a good choice ? I had to learn long , long ago that I can only lead by example. I used to carry a spare helmet but after a couple of people taking it to avoid the " talk " took it off ASAP I realized it is a losing battle.

Can't legislate common sense!

I get speed wooble on my Coyotes at about 39mph. I'm interested it the idea of pushing through now I have stronger rims but wonder how much faster I need to go to get over it ? On mountian boards how much faster do you need to go to punch through?

erratic winds - 16-12-2010 at 05:47 PM

Quote:
Originally posted by Bladerunner
On mountain boards how much faster do you need to go to punch through?


Plaid speed, of course

Bladerunner - 16-12-2010 at 05:51 PM

Quote:
Originally posted by Bladerunner
On mountian boards how much faster do you need to go to punch through?

;-)

flexboardz - 7-1-2011 at 02:21 AM

Wobble tests are ongoing : beside maths and calculation, we have built a dummy rider to make real live simulation.

Here is the first video of the test making a comparison between a skateboard and a Flexboardz...(which was not very fair for the skateboard...)

Now that we have validated our dummy rider, we will make an off-road session with a mountainboard...(main difficulty now is to find a hill where we can drop a 80 kg dummy rider w/o causing accident :)

PHREERIDER - 7-1-2011 at 06:24 AM

its own mass sustains the reaction to collision point.

like a swing with the sustaining kick. the two ends eventually start colliding and fighting over the swinging mass.

the points of curvilinear acceleration is the magic..the resistance of the wheel and surface create power return with the momentum from forward movement and direction change. this translate through the whole device including the "rider".

pendulum mechanics, rebound energy should produce good models

the distance from center line pivotal elements contains the threshold #'s you are looking for initiation and sensitivity . the fragile balance points(2) become excited (no 'unstable' is better?)when they theoretically start colliding into one another then the system starts fighting with its on mass and motion.

have fun proofing all that!

Kamikuza - 7-1-2011 at 07:30 AM

Quote:
Originally posted by erratic winds
Quote:
Originally posted by Bladerunner
On mountain boards how much faster do you need to go to punch through?


Plaid speed, of course

Oh no, not again!

flexboardz - 7-1-2011 at 11:33 AM

to Pheerider : that's precisely to avoid all that complicated science (well, we are still trying to sort it out) that we have decided to make a "dummy rider".
It certainly do not take into account all the biomechanic but it somehow simulate a ride (in fact the worst rider with rigid ankles) well enough to make comparison between various boards...

erratic winds - 7-1-2011 at 12:21 PM

Quote:
Originally posted by Kamikuza
Quote:
Originally posted by erratic winds
Quote:
Originally posted by Bladerunner
On mountain boards how much faster do you need to go to punch through?


Plaid speed, of course

Oh no, not again!


If you have nieces/nephews/etc, it's a dirty, dirty trick on the parents to give those kids a copy of "Spaceballs" because it's PG.

flexboardz - 11-1-2011 at 04:15 AM

Here is a capture from the wobble video above (black line is the skateboard trajectory, red line is the dummy rider position).
Next, we will measure the roll angle and compare it to our calculations in order to validate them...

snowspider - 11-1-2011 at 10:04 AM

Wow ... maybe I wont make that land luge out of skate board parts.
Good board design will make body armour even more necessary as more riders will be going much faster.

flexboardz - 16-5-2011 at 08:19 AM

An interesting and complete article about speed wobble in ConcreteWave Mag :

SPEED WOBBLE-CONCRETEWAVE MAG

PHREERIDER - 16-5-2011 at 09:15 AM

nice read, thanks

flexboardz - 5-6-2011 at 01:56 PM

first result from Simpack wobble simulation (wait till 0:20 to see the wobble appearing).
The model seems to be working for the skateboard. Next step will be for the flexboardz

Kamikuza - 5-6-2011 at 10:54 PM

That'd be without rider input?
Interesting ... sims are cool!

flexboardz - 6-6-2011 at 01:42 AM

I have not yet all the info about simpack simulation hypothesis but , yes, I think that it involves a rider but it is not represented on the video...more info soon...

flexboardz - 22-11-2011 at 01:04 AM

Simpack analysis of the Flexboardz stability is progressing...here is the output video and we will have some detailed analysis soon.

Again, you need to wait 30 sec before it starts wobbling...

At the end, you can see a small cube; it represents the rider weight (the hypothesis is that the rider is rigidly linked to the board like a dummy or a beginning/frightened rider (rigid ankle / no dampening)...

it must be noted that, under this hypothesis (no dampening), all board will wobble at some stage...

flexboardz - 12-1-2012 at 03:35 AM

Here is the report from Simpack Stability analysis :

I hope to get more explanations from them soon...and to introduce some rider control/dampening to get a more realistic simulation (keep in mind that rider's weight is rigidly linked to the board which increase the instability)

I don't know why the pics are so small (you can get more details here :Flexboardz.com/Wobble )