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Skateboard Tricks and Topological Flips (arxiv.org)
113 points by user2994cb 26 days ago | hide | past | favorite | 66 comments

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 :)

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.

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:


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".

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.

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/

Thanks for the link... Read about Skate After School and made a donation. Great interview! http://4plymag.com/SAS/

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.


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/

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.

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...

that invalidates my deep faith for the suski grind, this is unacceptable Lemongrab screaming

Haha Suskis are still valid. They've grown on me over the years, especially when pinched on a ledge.

> - 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).

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

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.

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.

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

Kinda like how benihanas are lame, unless you're shaved-head Jamie Thomas taking it down a gap:


From this Transworld Article:


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

never push mongo too

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

i see you're a man/woman of culture as well


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/...

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.

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

That's the main reason i did it that way.

I never managed a 360 hard flip on flat, but i could do them over 2 stair steps.

If you are used to do hard flips very vertically, its really hard to do a 360 hardflip, even over stairs.

Not sure why these are considered different in the images

360 Pop Shove-it

360 Shove-it

360 Shuvit

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.

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.

Right, I know the difference between pop/non-pop in action, but the animations look the same.

Also "shuvit" distinction is just a synonym

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.

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

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

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

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)

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.

Somewhere out there Rodney Mullen smiles quietly :)

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

In which case I reject mathematics.

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.

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

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

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

Maybe you have to do

git clone --recursive

> 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?

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.

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

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.


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

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

I really like the phrase "quaternionic varial kickflip".

Like something from Snow Crash.

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?

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

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)

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).

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.

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.

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).

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.

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)?

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

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.

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

Maybe the four tricks are:


Any Shove it/varial with no flip

Any Flip with no shove it

Any flip + shove it combo


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