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Ninjago finger top
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This small, simple finger top based on a Ninjago spinner stays up 1.2-25 times longer than my other finger tops. It runs smoothly, loves to sleep, and walks much less than Ninjago spinners with their usual tips.
About this creation
Please feel free to look over the images and skip the verbiage.

When this page was first posted, this small, sturdy top based on a Ninjago spinner was the longest- and smoothest-running of all my finger tops by a wide margin. At the time, it was also the only one capable of staying up more than 60 sec. (Since then, I've made dozens of finger tops lasting longer than a minute -- in most cases, without resorting to a Ninjago spinner base.)





Its best spin time of 102 sec in the configuration shown here made it the first of my LEGOŽ tops to break the 100-second barrier when twirled -- i.e., when spun-up with a twirl of the fingers. Subsequent modifications focused mainly on its tip bumped spin time to 158 sec -- my longest LEGOŽ top spin time ever!

This top opens the video below and reappears many times thereafter.



NB: Eye protection is an absolute must when working with any LEGOŽ gizmo spinning at high speed.

The Ninjago top owes its outstanding performance to a combination of factors:
  • High release speeds (routinely >1,300 RPM by hand and >4,200 RPM by motor)
  • Moderate overall mass (0.046 kg)
  • A very low center of mass (CM) just 22 mm above tip
  • A custom tip with small radius of curvature and point-like contact patch at all inclinations
  • Low air resistance (mostly smooth surfaces with low total surface area)
This Goldilocks combination translates into run times many times longer than those of the much larger Asteroid top, whether spun up by hand or by motor.




Photos

Not much to it, really. The superstructure is just there to provide the central axle the spinner itself lacks. The infrastructure supports the custom tip shown below.





The best stem for spinning this top up by hand is a simple axle. Since the starting torque needed to get it going from rest is substantially lower than that of my Asteroid Spintop, the stem needs no axle joiner for added grip.



Walking is a big problem with the Ninjago spinner's intended tip (2x2 round plate with rounded bottom, 2654) but minimal with the replacement shown above. My Asteroid top also used this tip when its MOCpage was created.

All of my tops now use even narrower tips cut from the ends of round-tipped 4L antennas (3957), lances (3849), or ski poles (2714). The photo below shows an example from my Klingon top MOCpage, but the mount used there is too high for Ninjago tops.



When mounted securely, these narrower tips outperform tips from 6L bars with caps in all respects.

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Design notes

The Ninjago spinner at the heart of this top accounts for 74% of its total mass and nearly all of its rotational inertia.

As noted by Walter Lee in his comments on my Asteroid top, the Ninjago spinner has 3 features of interest to the LEGOŽ top maker:
  • If the spinner remains low to the ground in the finished top, its internal weight will lower the top's overall center of mass.
  • The internal weight also allows the spinner to pack a fair amount of rotational inertia into a small diameter (only 46 mm).
  • The spinner is nicely balanced.
The first feature improves run time by reducing the lever arm of the gravitational torque acting on the top. The second feature improves run time directly while promoting hand-spinnability. The 3rd feature reduces losses to unwanted motions and friction.

However, the Ninjago spinner also has 3 major drawbacks:
  • It lacks a through-going axle hole.
  • All available attachment points are studded.
  • The large radius of curvature of its intended tip -- the 2x2 round plate with rounded bottom (2654) -- results in too much walking for my taste.
The first 2 disadvantages severely limit superstructure and tip options. And while walking may be desirable in a battle top, it cuts into run time by diverting rotational kinetic energy into translational kinetic energy.

As this MOC shows, the drawbacks can be overcome. Of the countermeasures employed, the most important by far was abandonment of the usual spinner tip in favor of a custom tip. Seemingly small tip details can make huge differences WRT both run time and top behavior (details here).

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Specifications

Construction:Studded
Stem:Simple cross-axle
Rotor:Ninjago spinner
Tip shown:Cut from 6L bar with cap (61680)
Overall dimensions:46x66 mm (DxH, including axle)
Mass:0.043 kg
Center of mass height:~22 mm
Tip axial radius of curvature:~3 mm
Spin-up time:~2 sec by motor
Release speed:>1,300 RPM by hand; >4,200 RPM with motor
Topple speed:~600 RPM
Run time as shown:102 sec by hand; 165 sec by motor
Run time with subsequent modifications:158 sec by hand
Grounding angle:~30°
Spin-up motor:Original Technic 9V (2383)
Spin-up motor no-load speed:~4,400 RPM
Electrical power supply:Old 9V train transformer
Modified LEGOŽ parts:Tip
Non-LEGOŽ parts:None
Credits:Original MOC

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Comments

 I made it 
  July 8, 2018
Quoting Sam Sanister I was twirling two soup cans that were identical in size and shape, but with a weight difference of maybe an ounce or so. (yes, I know cylinders are not good tops). Would you happen to know how the ever-so-slightly heavier can couldn't really spin at all, while the lighter can actually spun for several seconds?
Need more info. Email me at mocpages@cliffshade.com. If possible, send photos of cans exactly as they were when you tried to spin them, identifying the heavier one. Were cans empty? What were you using for tips?
 I like it 
  July 8, 2018
I was twirling two soup cans that were identical in size and shape, but with a weight difference of maybe an ounce or so. (yes, I know cylinders are not good tops). Would you happen to know how the ever-so-slightly heavier can couldn't really spin at all, while the lighter can actually spun for several seconds?
  September 3, 2015
Thanks for your concise response to my inquiries in the comments. It is truly amazing to read about the design engineering challenges you faced in making a Lego hand top. btw: NHK World TV's "Supreme Skill" will be broadcasting yet another episode - this time it a spinning top competition (Battle of the Tops Part 1) It will be broadcasted this Today Thurday Sept 3 2015 8:30 EST and on Friday Sept 4 2015 2:30AM 9:30AM 2:30PM EST. If you don't get the broadcast locally - the video streams online at ...www3.nhk.or.jp/nhkworld/en/live
 I made it 
  January 30, 2015
Quoting Walter Lee Good Gravy that's a very long spinning time! That's enough for me to grab a cup of joe and come back! You are doing fantastic design work! :-) With respect to the spinning tip - have you ever tried using a common Technic ball joint (bricklink 32474)which can fit on the tip of a Technic axle? That is -- When does the diameter of the semi circle of the spinning tip start to impact the performance of the spin?
Very kind, Walter. (i) Did you happen to notice your credit WRT the use of Ninjago spinners in tops? (ii) It took me a while to realize that tip design is my one and only opportunity to influence how a top interacts with its supporting surface prior to falling. Tiny tip details can make huge differences. In my experience, the greater the tip's axial radius of curvature (RoC), the greater the tendency to precess and walk as opposed to sleep -- i.e., spin quietly in place with spin axis perfectly vertical. All other things being equal, sleeping tops stay up longer. The 3 mm RoC of the tip used on this top equals that of a towball, but there's a critical difference: My tip is uniformly convex, whereas towballs have nasty little flats right at the contact point a sleeping top would use. Technic balls have a 5 mm RoC with a smaller flat (dimple, actually) in the same bad location. Such flats and concavities only exacerbate the effect of greater RoC, and they greatly reduce the odds of spinning up a sleeper by hand. To complicate matters even more, the rougher the supporting surface or the greater its coefficient of friction (e.g., matte porcelain tile vs. polished marble or granite), the greater the influence of tip RoC and convexity on top behavior and spin time. Tip choices are further complicated by mounting issues. As you know, the lower the top's center of mass (CoM) to the ground, the longer the spin time. The importance of this relationship can't be overstated. Secure, perfectly coaxial tip mounts are also a must. These 2 constraints severely limit the elements one can use as tips in practice -- at least when maximum run time is the goal. Tips cut from round-tipped antennas have the smallest RoCs I've found (1.5 mm) with no flats or dimples, but the contraints just mentioned limit their use. Finally, one must also keep an eye on grounding angle -- i.e., the angle between spin axis and the vertical when the rotor first strikes ground. For a given rotor diameter, grounding angle varies directly with CoM height. Dropping the CoM too far turns spinning up by hand into a severe test of skill, as the small grounding angle then leaves no wiggle room. Bottom line: If you enjoy an engineering challenge with your LEGO, and I know you do, top-building won't disappoint.
 I made it 
  January 30, 2015
Bingo! Video showing all 19 tops in action finally embedded successfully.
 I made it 
  January 30, 2015
Quoting Verticus Akkron Fascinating. That 6l bar looks just like the front of a spring missile. I should try something like this soon. Interesting information on the laser timer, too. I am extremely intrigued by your careful computations. No doubt I will be looking out for more. By the way, I generally don't ask this question (I don't like answering it myself) but how old are you? Don't feel obliged to answer.
(i)The "6L bar with round cap" (61680) I usually use for tips has been out of production since 2008. I cut it down to just the cap and 2-6 mm of shaft. The cap on the "spring shooter dart" (15903) is out, as it's off-center on its shaft. Though a bit harder to mount, the very best tips are cut from round-tipped 4L antennas, which are dirt-cheap and plentiful.(ii) I expect to see some good tops out of you.(iii) I'm officially 66 years old, but my wife says I act more like a 12 year-old. I take that as a great compliment, but I'm pretty sure that's not how she means it.
  January 30, 2015
Good Gravy that's a very long spinning time! That's enough for me to grab a cup of joe and come back! You are doing fantastic design work! :-) With respect to the spinning tip - have you ever tried using a common Technic ball joint (bricklink 32474)which can fit on the tip of a Technic axle? That is -- When does the diameter of the semi circle of the spinning tip start to impact the performance of the spin?
  January 30, 2015
Fascinating. That 6l bar looks just like the front of a spring missile. I should try something like this soon. Interesting information on the laser timer, too. I am extremely intrigued by your careful computations. No doubt I will be looking out for more. By the way, I generally don't ask this question (I don't like answering it myself) but how old are you? Don't feel obliged to answer.
 I made it 
  January 29, 2015
Quoting Verticus Akkron This is very interesting. I appreciate the detail on this model as well as all your others, though this is the only one I have undertaken to read completely. I am quite intrigued by the part you modified for the spinner tip. Is it http://brickset.com/parts/4618270 that you shaved the antenna off? I am interested to try out your specifications. Also, I am insanely curious how you calculated a 1,300 rpm spin, much less a 4,200 rpm one. Did you video it in slo-mo or something? Great creation, and I will doubtless be looking out for other statistical Lego models from you!
Verticus, thanks for the interest and like. You deserve a medal for "Valor in the Face of Overwhelming Verbiage" for reading even this one. (i) The tip is cut from the 6L bar shown on my "Asteroid spintop" page. Thanks for pointing me to the Mini Rapier, which has potential if not too thin. (ii) Direct measurement of RPM using (a) a cheap laser hand tachometer ($12 on Amazon -- see my MPC3 page), and (b) a small piece of timing tape on the 4x4 cone capping the superstructure (present but not visible above).
 I like it 
  January 29, 2015
This is very interesting. I appreciate the detail on this model as well as all your others, though this is the only one I have undertaken to read completely. I am quite intrigued by the part you modified for the spinner tip. Is it http://brickset.com/parts/4618270 that you shaved the antenna off? I am interested to try out your specifications. Also, I am insanely curious how you calculated a 1,300 rpm spin, much less a 4,200 rpm one. Did you video it in slo-mo or something? Great creation, and I will doubtless be looking out for other statistical Lego models from you!
 
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