Skateboard Tricks and Topological Flips

https://arxiv.org/abs/2108.06307

by user2994cb • 5 years ago

113 66 5 years ago

arxiv.org

RhysU• 5 years ago

The end of the paper points to https://github.com/holomorpheus/topological-flips

joncrane7• 5 years ago

I tried cloning it and running it but I'm missing a module; there is no requirements.txt either. :(

adrian_b• 5 years ago

Maybe you have to do

git clone --recursive

nathancahill3• 5 years ago

It needs a handful of libraries. I generated the animations here: https://imgur.com/a/SJcAvHF

psychomugs6• 5 years ago

Generated a requirements.txt here: https://gist.github.com/psychomugs/e0e298e1f82a271ef3e9eedbb...

mrspeaker• 5 years ago

Reminds me of this (less math-heavy!) analysis of "Skateboarding Science" about Rodney Mullen: https://www.youtube.com/watch?v=yFRPhi0jhGc

psychomugs6• 5 years ago

Rodney has a great TED Talk where he aptly compared the skateboarding and open-source communities: https://youtu.be/3GVO-MfIl1Q?t=741

nerdponx• 5 years ago

I really like the phrase "quaternionic varial kickflip".

nathancahill3• 5 years ago

Like something from Snow Crash.

joncrane7• 5 years ago

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?

dchuk2• 5 years ago

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.

joncrane7• 5 years ago

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.

btbuildem• 5 years ago

Wouldn't symmetry cover that? In this context, regular and switch are "mirror images" of each other.

joncrane7• 5 years ago

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)

eunoia4• 5 years ago

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).

joncrane7• 5 years ago

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)?

fokinsean13• 5 years ago

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

kevinventullo2• 5 years ago

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.

joncrane7• 5 years ago

Maybe the four tricks are:

Ollie

Any Shove it/varial with no flip

Any Flip with no shove it

Any flip + shove it combo

cj_f• 5 years ago

How is a 360 shove it not equal to an ollie? and a 540 shuv it equivalent to a 180 shove it?

nathancahill3• 5 years ago

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/...

fokinsean13• 5 years ago

Not sure why these are considered different in the images

360 Pop Shove-it

360 Shove-it

360 Shuvit

alexanderdmitri• 5 years ago

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.

psychomugs6• 5 years ago

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.

volta832• 5 years ago

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.

rawling3• 5 years ago

And then the 360 hardflip goes back to not doing the vertical bit.

fokinsean13• 5 years ago

I was hoping they would come up with a mathematical way to distinguish an impossible from a 360 shuv :)

eunoia4• 5 years ago

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)

fokinsean13• 5 years ago

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.

jbottigliero• 5 years ago

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.

joncrane7• 5 years ago

I wonder if they have somehow mathematically proven that they are the same trick?

In which case I reject mathematics.

rawling3• 5 years ago

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• 5 years ago

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.

rawling3• 5 years ago

Hah, ok. I'll go find some videos and brush up!

psychomugs6• 5 years ago

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

fokinsean13• 5 years ago

You can also steez fs flips like this as well, aka the Muska flip

ndnxmsm• 5 years ago

The biggest difference in hardflip à is where your back foot is in relation to the board during the flip.

fokinsean13• 5 years ago

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 :)

eunoia4• 5 years ago

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.

fokinsean13• 5 years ago

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.

scudd2• 5 years ago

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".

psychomugs6• 5 years ago

Mall grabs are okay as long as you just tried something huge: https://youtu.be/THcnby6b6sY?t=88

scudd2• 5 years ago

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...

rbrtdrmpc-3• 5 years ago

never push mongo too

fokinsean13• 5 years ago

*Unless it's switch mongo and you're Koston, Rodrigo TX, or Stevie Williams

5cott02• 5 years ago

therefore by induction a nollie fs 180 is not a half cab∎

axegon_2• 5 years ago

- 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).

jwilber3• 5 years ago

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.

fokinsean13• 5 years ago

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

odessacubbage• 5 years ago

all these terms originated from skating pools so you have to visualize them relative to your position on a transition as opposed to flat. fs/bs is quite literally how you are facing the the wall while fakie is simply treated as the inverse of your natural position.

kevinventullo2• 5 years ago

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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