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Skateboard Tricks and Topological Flips
- RhysU 5y agoThe end of the paper points to https://github.com/holomorpheus/topological-flips https://github.com/holomorpheus/topological-flips
- joncrane 5y agoI tried cloning it and running it but I'm missing a module; there is no requirements.txt either. :(
- adrian_b 5y agoMaybe you have to do git clone --recursive
- nathancahill 5y agoIt needs a handful of libraries. I generated the animations here: https://imgur.com/a/SJcAvHF https://imgur.com/a/SJcAvHF
- psychomugs 5y agoGenerated a requirements.txt here: https://gist.github.com/psychomugs/e0e298e1f82a271ef3e9eedbbb6f4a66 https://gist.github.com/psychomugs/e0e298e1f82a271ef3e9eedbb...
- mrspeaker 5y agoReminds me of this (less math-heavy!) analysis of "Skateboarding Science" about Rodney Mullen: https://www.youtube.com/watch?v=yFRPhi0jhGc https://www.youtube.com/watch?v=yFRPhi0jhGc
- psychomugs 5y agoRodney has a great TED Talk where he aptly compared the skateboarding and open-source communities: https://youtu.be/3GVO-MfIl1Q?t=741 https://youtu.be/3GVO-MfIl1Q?t=741
- nerdponx 5y agoI really like the phrase "quaternionic varial kickflip".
- nathancahill 5y agoLike something from Snow Crash.
- joncrane 5y agoCorrect 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 5y agoNot 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 5y agoThey 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 5y agoThe 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 5y agoWouldn't symmetry cover that? In this context, regular and switch are "mirror images" of each other.
- joncrane 5y agoI 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)
- joncrane 5y agoSo 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 5y agoI'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
- kevinventullo 5y agoThe 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 5y agoMaybe 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 5y agoHow is a 360 shove it not equal to an ollie? and a 540 shuv it equivalent to a 180 shove it?
- nathancahill 5y agoGenerated the animations from the repo linked in the paper: https://imgur.com/a/SJcAvHF https://imgur.com/a/SJcAvHF The specific tricks with their matrices are here: https://github.com/holomorpheus/topological-flips/blob/main/matrixTricks.py#L52 https://github.com/holomorpheus/topological-flips/blob/main/...
- fokinsean 5y agoNot sure why these are considered different in the images 360 Pop Shove-it 360 Shove-it 360 Shuvit
- alexanderdmitri 5y agoI 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 5y agoPopping, 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 5y agoRight, I know the difference between pop/non-pop in action, but the animations look the same. Also "shuvit" distinction is just a synonym
- psychomugs 5y agoThe 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.
- fokinsean 5y agoI was hoping they would come up with a mathematical way to distinguish an impossible from a 360 shuv :)
- eunoia 5y agoI 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 5y agoYeah 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 5y agoSomewhere out there Rodney Mullen smiles quietly :)
- jbottigliero 5y agoI 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.
- joncrane 5y agoI wonder if they have somehow mathematically proven that they are the same trick? In which case I reject mathematics.
- rawling 5y 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 5y agoIt 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 5y agoHah, ok. I'll go find some videos and brush up!
- psychomugs 5y agoVarial 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 https://www.youtube.com/watch?v=QNlKad9vzng
- fokinsean 5y agoYou can also steez fs flips like this as well, aka the Muska flip
- ndnxmsm 5y agoThe biggest difference in hardflip à is where your back foot is in relation to the board during the flip.
- fokinsean 5y agoHere'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- 5y agonever push mongo too
- fokinsean 5y ago*Unless it's switch mongo and you're Koston, Rodrigo TX, or Stevie Williams
- rbrtdrmpc- 5y agoi see you're a man/woman of culture as well
- 5cott0 5y ago*swongo
- eunoia 5y ago
- kevinventullo 5y agoSo 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.