from Hacker News

Skateboard Tricks and Topological Flips

by user2994cb on 8/23/21, 7:26 AM with 66 comments

• by fokinsean on 8/24/21, 3:33 PM

  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 :)

• by nathancahill on 8/24/21, 2:55 PM

  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/...

• by mrspeaker on 8/24/21, 1:08 PM

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

• by fokinsean on 8/24/21, 3:02 PM

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

• by RhysU on 8/24/21, 12:42 PM

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

• by rawling on 8/24/21, 3:20 PM

  > 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?

• by nerdponx on 8/24/21, 1:35 PM

  I really like the phrase "quaternionic varial kickflip".

• by joncrane on 8/24/21, 1:53 PM

  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?

• by kevinventullo on 8/24/21, 3:38 PM

  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.

• by joncrane on 8/24/21, 2:18 PM

  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)?