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Jumping Stick Consistency (and the Dzhanibekov Effect)

Discussion in 'Beginners' started by Spartanicus, Mar 6, 2021.

  1. Spartanicus

    Spartanicus n00b

    Joined:
    Jan 9, 2021
    Hi! I've been working on making my J-Sticks as consistent as possible, and here's a crazy question for those of you who can hit them over and over:

    Do you find, overall, that you tend to flip the ken on its edge (the sarado cups facing towards you and away from you), on its face/flat (the sarado cups facing sideways) ... or does it make any difference at all??

    I ask because I'm kind of fascinated by the Dzhanibekov Effect (aka the Tennis Racket Theorem) that causes the ken to flip AND rotate when flipped in a flat position. See the video below for an example of this (with the math behind it).

    So with regard to consistent Jumping Stick landings, does the ken orientation matter in your play?

     
    Mar 6, 2021
  2. goenKendama

    goenKendama Moderator Staff Member

    Joined:
    Oct 14, 2016
    Location:
    Metro Manila, Philippines
    @Spartanicus Very interesting, thanks for sharing. For j-sticks I have better luck with the ken rotating around its cross point with the cups rotating facing me. However my 1-turn airplanes are more like the tennis racket theorem with it spinning then flipping not staying on the cross axis or the one through the sarado.
     
    Mar 6, 2021
  3. Spartanicus

    Spartanicus n00b

    Joined:
    Jan 9, 2021
    Thanks @goenKendama! That's great to know. I've been working on my one-turn airplanes and one-turn lighthouses recently (very new for me - I can only land 1 in a hundred - but working on it!) - it's good to know what to expect. It's beautiful to watch people who make it all look so easy - but making progress is tons of fun.

    FWIW, I am finding that my j-sticks tend to land more easily when I face the cups (so no extra flip a la the tennis racket theorem). I can land both, but I think I'll focus on rotating the cups in that orientation as a matter of course. I'm all about building consistency these days, and anything that helps is great!
     
    Mar 7, 2021
    goenKendama likes this.
  4. goenKendama

    goenKendama Moderator Staff Member

    Joined:
    Oct 14, 2016
    Location:
    Metro Manila, Philippines
    @Spartanicus Not saying the way I'm doing them is right, just that it's the way the turn out. I've tried to 'correct' the 1-turns to spin on the cross axis (at the sarado) but I've gotten fairly consistent (depending on the day) with the racket spin so I've not really chased the correction. If you're a consistency fan have a look at the JKA. It's kind of their thing, among others. ;)
     
    Mar 7, 2021
  5. Spartanicus

    Spartanicus n00b

    Joined:
    Jan 9, 2021
    Excellent - thanks! I was aware of the JKA, but I'd never looked carefully at their Dan levels before - thanks for the link! That's right up my alley. :)
     
    Mar 8, 2021
    goenKendama likes this.
  6. jimgrude

    jimgrude Member

    Joined:
    May 21, 2019
    Location:
    Tokyo
    The tennis racket theorem definitely plays an active role in kendama, for better or for worse. I probably take advantage of it more than most players because of how I do tama-grip tricks. Most players pull up their ken with a smooth swing with an appropriate twist needed for the cups to face however they're supposed to face. I prefer to pull the ken more or less straight up, with little to no swing. With this technique, the ken is exposed to this tennis racket effect to a higher degree because it isn't guided by tension in the string.

    To give an example, the way I get the big cup to face me perfectly every time when doing tricks like 1-up lunar / lighthouse, is that I give the ken a twist while hanging straight down, then I let it rotate PAST the point that I want to catch it at, before pulling and yanking it up. This way, I take advantage of a counter-rotation the ken gets from getting yanked when the cups are slightly askew. The ken will make a slight rotation in the opposite direction and come back to land perfectly straight.

    This, off course, takes a lot of practice, as any technique would. However, I feel that it's much easier to get consistent at because I don't have to worry too much about how I release and twist the ken. The swing technique requires you to twist and swing with a consistent and predictable force and speed for it to work, which in turn requires a lot of muscle memory. The way I do it, speed doesn't matter because I don't swing, and it doesn't matter if I twist it fast or slowly, as long as I pull up at the right time. The result is that I can do the initial release and twist really sloppy without thinking, because the trick really only starts when I yank the ken to get rotation.

    I hope my very scientific essay tickled your brain in the right places.
     
    Mar 16, 2021
  7. Spartanicus

    Spartanicus n00b

    Joined:
    Jan 9, 2021
    Thanks, @jimgrude! This is very interesting - especially as I'm just starting to get consistent with my lunars. [EDIT: and several months later they're starting to land regularly! Now to get my one-ups consistent. :) ]
     
    Last edited: May 6, 2021
    Mar 20, 2021