[HN Gopher] Skateboard Tricks and Topological Flips
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Skateboard Tricks and Topological Flips
Author : user2994cb
Score : 109 points
Date : 2021-08-23 07:26 UTC (1 days ago)
(HTM) web link (arxiv.org)
(TXT) w3m dump (arxiv.org)
| RhysU wrote:
| The end of the paper points to
| https://github.com/holomorpheus/topological-flips
| joncrane wrote:
| I tried cloning it and running it but I'm missing a module;
| there is no requirements.txt either. :(
| adrian_b wrote:
| Maybe you have to do
|
| git clone --recursive
| nathancahill wrote:
| It needs a handful of libraries. I generated the animations
| here: https://imgur.com/a/SJcAvHF
| psychomugs wrote:
| Generated a requirements.txt here: https://gist.github.com/ps
| ychomugs/e0e298e1f82a271ef3e9eedbb...
| joncrane wrote:
| Correct me if I'm wrong, but the whole beginning of the article
| implies that the skateboarder is "regular" in terms of foot
| placement, meaning the right foot is on the tail and the left
| foot is at the front.
|
| The fact that each skater can reverse their stance (aka
| switchstance), doesn't that double the possible number of flip
| tricks?
| dchuk wrote:
| Not really, the flipping maneuver remains the same, the stance
| is more of a modifier. A 360 flip and a switch 360 flip are
| both still just 36 flips, you're just facing a different way in
| each.
| joncrane wrote:
| They specifically talk about "left handed" rotation for a
| kickflip and a heelflip being right handed.
|
| However for a goofy skater, the opposite is true.
| dchuk wrote:
| The mechanism for a kick flip and a heel flip are
| different, it's not about the spin of the board in relation
| to the earth, it's the spin of the board in relation to the
| skater.
|
| A kick flip uses the front toe to rotate the board towards
| the skater. A heel flip uses the front heel to rotate the
| board away from the skater (you're basically pushing it
| away from you by sliding your heel up and out off the edge
| of the board).
| btbuildem wrote:
| Wouldn't symmetry cover that? In this context, regular and
| switch are "mirror images" of each other.
| joncrane wrote:
| I suppose. Maybe I missed a part where they say they're using
| a regular stance skater for the sake of simplicity.
|
| Note that a goofy skater could also do the moves described in
| the paper, but it would be a different trick because he's
| doing it switchstance.
|
| (Source: the rules of SKATE per Battle of the Berrics, the
| skater has to declare his stance ahead of time for the
| purposes of normal vs switch tricks, aka the "Skategoat"
| (Leandre Sanders) rule)
| eunoia wrote:
| Essentially the same trick. Best metaphor for "switch" tricks
| is basically doing something left handed (assuming you're right
| handed and have always done the "thing" with your right).
|
| It's the same trick but you essentially have to relearn it with
| your other "hand". Tricks are then flagged with the "switch"
| qualifier to indicate the rider wasn't in their normal stance.
| Example: a regular (footed) skater skating right foot forward
| (switch) doing a kickflip is simply doing a switch kickflip
| (switch flip).
| mrspeaker wrote:
| Reminds me of this (less math-heavy!) analysis of "Skateboarding
| Science" about Rodney Mullen:
| https://www.youtube.com/watch?v=yFRPhi0jhGc
| psychomugs wrote:
| Rodney has a great TED Talk where he aptly compared the
| skateboarding and open-source communities:
| https://youtu.be/3GVO-MfIl1Q?t=741
| nathancahill wrote:
| Generated the animations from the repo linked in the paper:
| https://imgur.com/a/SJcAvHF
|
| The specific tricks with their matrices are here:
| https://github.com/holomorpheus/topological-flips/blob/main/...
| volta83 wrote:
| Really interesting to see the hardflip animated vertically but
| the inward heelflip isn't.
|
| I always did hard flips as varial kickflips, but with fs-shuv
| instead of bs-shuv.
| rawling wrote:
| And then the 360 hardflip goes back to not doing the vertical
| bit.
| fokinsean wrote:
| Not sure why these are considered different in the images
|
| 360 Pop Shove-it
|
| 360 Shove-it
|
| 360 Shuvit
| alexanderdmitri wrote:
| I always thought the difference is with a normal shove-it the
| board pivots on the back trucks, whereas with a pop shove-it
| all wheels are off the ground for the rotation. They seem to
| be depicting only the latter in the animations.
| psychomugs wrote:
| Popping, i.e. hitting end of the board on the ground, to get
| height is the difference.
|
| A pop shuvit will be higher while a non-popped shuvit may
| barely leave the ground. Popping can actually make it easier
| to keep the axis of rotation closer to the center of the
| board.
| fokinsean wrote:
| Right, I know the difference between pop/non-pop in action,
| but the animations look the same.
|
| Also "shuvit" distinction is just a synonym
| psychomugs wrote:
| The transformations are only rotations; the vertical
| translation in the animations is just hardcoded as a
| half-period of a sine wave.
|
| Setting the `vertical` flag to `False` in
| skateAnimation.py:generate_frames removes the pop.
| nerdponx wrote:
| I really like the phrase "quaternionic varial kickflip".
| nathancahill wrote:
| Like something from Snow Crash.
| joncrane wrote:
| So what are the 4 tricks?
|
| Kickflip, heelflip, flip + shove it in the "natural direction"
| (e.g. varial kickflip, 360 kickflip), and flip + shove it in the
| unnatural direction (e.g. hard flip)?
| fokinsean wrote:
| I'm guessing it's kickflip, heelflip, bs shuv, and fs shuv.
|
| Your definition leaves out varial heels and inward heels.
|
| Edit: On second thought I'm still not sure, I saw this in the
| paper, and I'm guessing they're classifying both direction
| shuvs as the same, and kick/heelflip as the same
|
| Below we list these four tricks with their corresponding
| residue class in Z/4Z.
|
| 0 - Ollie
|
| 1 - 180 Shove-it
|
| 2 - 360 Shove-it
|
| 3 - 540 Shove-it
|
| Another interesting choice of representatives is given by a
| combination of the shove-it and the kickflip.
|
| 0 - Ollie
|
| 1 - 180 Shove-it
|
| 2 - Kickflip
|
| 3 - Varial Kickflip
| cj_f wrote:
| How is a 360 shove it not equal to an ollie? and a 540 shuv
| it equivalent to a 180 shove it?
| kevinventullo wrote:
| The main result of the paper seems to be saying that
| kickflips and heelflips are homotopic, and therefore
| equivalent. Fs shove it is just the inverse of a pop shove
| it.
| joncrane wrote:
| Maybe the four tricks are:
|
| Ollie
|
| Any Shove it/varial with no flip
|
| Any Flip with no shove it
|
| Any flip + shove it combo
|
| ?
| fokinsean wrote:
| Here's a fun one to debate with your skate friends, nollie and
| fakie tricks are "swapped".
|
| For example:
|
| - nollie fs 180 and fakie fs 180 (fs half cab) are two different
| directions: nollie fs 180 is in front of you and fakie fs 180 is
| behind you going blind
|
| - nollie 5-0 and fakie 5-0 (fakie switch nosegrind) lean
| differently on the grind: nollie 5-0 you pop off your nose and
| land on your back truck, fakie 5-0 you pop off your tail and land
| on your front truck
|
| - nollie noseslide and fakie noseslide are different motions to
| get into the slide: nollie nose you pop off nose and land on the
| nose in the ledge, fakie nose you pop off tail and land on the
| nose but you do a sort of half cab
|
| The key distinction in the argument is that in fakie, your tail
| is always considered your "tail". Therefore you treat any derived
| tricks as being "backwards". In the 5-0 and noseslide examples,
| you're still popping off the front of your board, but you
| classify it as nose or tail based on if it's nollie or fakie.
|
| There are caveats though such as "fakie crook" where if you kept
| the rule it should be "fakie suski", which no one says.
|
| There's a million arbitrary and nonsensical rules in
| skateboarding which is part of the reason to love it, especially
| for something that "has no rules".
|
| And remember, never carry your board by your truck :)
| rbrtdrmpc- wrote:
| never push mongo too
| fokinsean wrote:
| *Unless it's switch mongo and you're Koston, Rodrigo TX, or
| Stevie Williams
| rbrtdrmpc- wrote:
| i see you're a man/woman of culture as well
| 5cott0 wrote:
| *swongo
| 5cott0 wrote:
| therefore by induction a nollie fs 180 is not a half cab[?]
| eunoia wrote:
| Ah don't forget the same variation of foolery that comes around
| if you 180 into a grind.
|
| What most people would call a nose grind or 5-0 is inverted if
| you 180'd into it.
|
| > And remember, never carry your board by your truck :)
|
| I miss skateboarding :). My ankles don't though.
| fokinsean wrote:
| Ah yes! and
|
| One of my other favorites:
|
| On circle rails there is "no such thing" as fs overcrook,
| just fs nosegrind, and there is no such thing as bs
| nosegrind, but there is bs overcrook.
|
| At least that's how magazines seem to classify it.
| rbrtdrmpc- wrote:
| that invalidates my deep faith for the suski grind, this is
| unacceptable _Lemongrab screaming_
| fokinsean wrote:
| Haha Suskis are still valid. They've grown on me over the
| years, especially when pinched on a ledge.
| jwilber wrote:
| And these are just for street! Transition has its own set
| of weird names (losi, andrecht, g-pivot, etc.), including
| some slight street overlaps (varial, pivot, etc.).
|
| I have a little passion project where we log pro's tricks
| and interview them called 4ply[0]. The naming convention is
| something we always have to get right to make the logged
| data at all useable. I actually grew up skating with Erick
| Winkowski but can't do an article on him because he does so
| esoteric transition tricks and we can't name them all (or
| find someone who can).
|
| [0] http://4plymag.com/
| fokinsean wrote:
| That's awesome! The site seems down for now but I'll
| check again later.
|
| Also I'll go ahead and plug the site I'm helping rebuild.
|
| https://skatevideo.site
| axegon_ wrote:
| Holy!!! That site still exists??!?!?!?!?!! I remember
| when this was filled with videos which were mostly hosted
| on what were google videos back in the day(and a small
| number on vimeo). Must have been 2006-7-8-ish...
| jwilber wrote:
| Yo! That's awesome you're working o skatevideosite! O
| just read your guys interview on Jenkem [0]. I used your
| old data years back for an article for The Pudding [1]
| years ago - invaluable resource. Growing up I would spend
| so much time on the site just finding music and skaters.
| If there's an issue board or something please plug it,
| would love to contribute!
|
| [0] https://www.jenkemmag.com/home/2021/08/16/meet-minds-
| behind-... [1] https://pudding.cool/2018/06/skate-music/
| fokinsean wrote:
| Woah! That's so random, I recently came across your
| article a few months ago. Great work and small world :)
|
| I have a private discord and github for the project I can
| add you too. I eventually plan to open up the discord for
| anyone once we get a little further in the rebuild.
|
| Wish there was a good way to DM on HN, I can send you a
| discord invite. Or if you happen to be on slap let me
| know.
| magicink81 wrote:
| Thanks for the link... Read about Skate After School and
| made a donation. Great interview! http://4plymag.com/SAS/
| scudd wrote:
| I always thought names like "180 nosegrind" made no sense.
| Why not "180 switch 5-0"? That seems so much more intuitive.
|
| It made so much more sense when I learned a lot of these
| tricks were first invented in the 1980's, when most boards
| had an obvious nose versus tail difference. Like this one:
|
| https://i.etsystatic.com/6865693/r/il/f51835/361296329/il_15.
| ..
|
| So even though you we're grinding in a switch 5-0 looking
| position, you would be clearly grinding on the nose, hence
| "180 nosegrind".
| psychomugs wrote:
| Mall grabs are okay as long as you just tried something huge:
| https://youtu.be/THcnby6b6sY?t=88
| scudd wrote:
| Kinda like how benihanas are lame, unless you're shaved-head
| Jamie Thomas taking it down a gap:
|
| https://i0.heartyhosting.com/skateboarding.transworld.net/wp.
| ..
|
| From this Transworld Article:
|
| https://skateboarding.transworld.net/photos/tws-10-most-
| memo...
| axegon_ wrote:
| > - nollie fs 180 and fakie fs 180 (fs half cab) are two
| different directions: nollie fs 180 is in front of you and
| fakie fs 180 is behind you going blind
|
| That is till this day(12 years since I last set foot on a
| skateboard) the most illogical thing. Especially when combined
| with board slides which were also not apparent from the
| start(for years on I called front side board slide back side)
| and from a logical perspective the lip slide names made a lot
| more sense. That said, I never figured out how to classify
| nollie/fakie board and lip slides front or back. As far as
| experience I also never understood why were hard flips called
| hard(I learned how to do them in less than 15 minutes after I
| first decided to give them a go).
| jwilber wrote:
| The rail tricks are simple if you just think of whether it's
| your toes (fs) or heel (bs) facing the obstacle and ignore
| any body turn motion.
| fokinsean wrote:
| Well, the "logic" for fakie is that your tail remains the
| reference even though you are popping backwards. Therefore
| you would spin the same direction for fakie fs 180 as you
| would for regular fs 180.
|
| > I never figured out how to classify nollie/fakie board and
| lip slides front or back
|
| Yep this one still trips me up to and is great argument over
| some beers. Especially when you introduce flip tricks into
| them as well :p
| fokinsean wrote:
| I was hoping they would come up with a mathematical way to
| distinguish an impossible from a 360 shuv :)
| joncrane wrote:
| I wonder if they have somehow mathematically proven that they
| are the same trick?
|
| In which case I reject mathematics.
| jbottigliero wrote:
| I was curious about this as well and gave modeling the
| Impossible a try... the foot drag seemed to be best mimicked by
| a half-kickflip, followed by a 360 shuvit, then a half-
| heelflip.
| eunoia wrote:
| I don't know about mathematical, but I've always thought of it
| as a vertical vs horizontal motion with the front foot used as
| as kind of rotation axis for an impossible...
|
| "I know it when I see it" (maybe)
| fokinsean wrote:
| Yeah for sure, the way the foot wraps with the board is the
| visual cue. It has led me and friends to some fun debates in
| a game of skate i.e. "that wasn't an impossible", so I was
| hoping to be able to point to some ridiculous mathematical
| definition the next time it comes up.
| eunoia wrote:
| Somewhere out there Rodney Mullen smiles quietly :)
| rawling wrote:
| > As a last example we will describe the hardflip. This is a
| simultaneous half kickflip (a 180 degree rotation about the axis
| joining the tail to the nose of the skateboard) and a 180 degree
| rotation about the x-axis in the right-hand orientation.
|
| Is it? Isn't a hardflip just a mirror of the varial kickflip they
| describe, and rotation around their x-axis something else
| entirely?
| throwawaypqr123 wrote:
| It both is and isn't. Technically the rotation is just the
| inverse of the varial kickflip (a frontside varial kickflip as
| opposed to the "normal" backside varial kickflip").
|
| The problem comes around that your front foot is very much in
| the way of the board if it is only doing an "inverse varial".
| The vertical (end over end) rotation comes out of necessity to
| get the front foot out of the way.
|
| Plus it looks really cool.
| rawling wrote:
| Hah, ok. I'll go find some videos and brush up!
| ndnxmsm wrote:
| The biggest difference in hardflip a is where your back foot is
| in relation to the board during the flip.
| psychomugs wrote:
| Varial kickflip = 180 backside shuvit + kickflip
|
| Hardflip = 180 frontside shuvit + kickflip
|
| The hardflip is unique in that it has two main variations. One
| is the end-over-end style that I think they're describing,
| where the board only does half a kickflip. The other is
| "flatter," and explicitly a 180 shuvit with a complete
| kickflip. In practice the end-over-end style is much more
| common, easier to perform, and nicer looking.
|
| https://www.youtube.com/watch?v=QNlKad9vzng
| fokinsean wrote:
| You can also steez fs flips like this as well, aka the Muska
| flip
| kevinventullo wrote:
| So if I understand correctly, letting "~" denote homotopy
| equivalence, Kickflip ~ 360 shove it
| Ollie ~ 720 shove it ~ double kickflip
|
| I may have missed it in the paper, but does anyone have intuition
| about how to visualize these homotopies? I don't get how to
| continuously deform a 720 shove it into an Ollie.
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