WOZZ - an extreme spinning top

Show off your FreeCAD projects here!
ASenger
Posts: 6
Joined: Tue Nov 29, 2016 3:39 pm

WOZZ - an extreme spinning top

Postby ASenger » Thu Mar 02, 2017 9:29 am

Hi all,

this project is not terribly complex but I think it is a lot of fun:

KreiselSchraegOben.jpg
KreiselSchraegOben.jpg (349.91 KiB) Viewed 889 times

KreiselSchraegUnten.jpg
KreiselSchraegUnten.jpg (390.28 KiB) Viewed 889 times

KreiselExplodiert.jpg
KreiselExplodiert.jpg (79.65 KiB) Viewed 889 times


The spinning top consists of three custom parts: disc, handle and cap. The disc is mounted in a ball bearing onto the handle. This enables to use a string (to be wound onto the the spool-like protrusion on the bottom of the dics). When pulling the string, the disc can be spun up to close to 10000 rpm (that's about 160 km/h at the circumference of the disc).

This makes for an extreme spinning top: made in steel this beast can spin for more than 30 minutes unassisted. You can also do all kinds of balancing tricks: spinning upside-down, spinning upside down on your finger, a very interesting 'dancing spin' and others.

WozzAufFinger.jpg
WozzAufFinger.jpg (364.29 KiB) Viewed 889 times


All parts were designed using FreeCAD 0.16 running on an Ubuntu-OS (14.04). Basically all shapes were constructed by rotating sketches around the Z-axis.

For optimization the tools for calculating volume and matrix of inertia came in very handy. It's a pitty these seem to be only available from the python console.

If you like to see the spinning top in action, please have a look here:

https://www.kickstarter.com/projects/12 ... h-a-twist/

It is currently an active campaign on Kickstarter and features a video showing how to spin the top. I think it's fun to watch.

Enjoy!

Alex
Jee-Bee
Posts: 614
Joined: Tue Jun 16, 2015 10:32 am
Location: Netherlands

Re: WOZZ - an extreme spinning top

Postby Jee-Bee » Thu Mar 02, 2017 5:00 pm

reminds me on the video of Veritasium see https://www.youtube.com/watch?v=GeyDf4ooPdo
ASenger
Posts: 6
Joined: Tue Nov 29, 2016 3:39 pm

Re: WOZZ - an extreme spinning top

Postby ASenger » Thu Mar 02, 2017 7:59 pm

Actually - yes! It's kind of a scaled down version.

You can also do similar things, like holding the axle on the outer end with the spinning top pointing sideways and turning around (ok, here it's enough to twist your hand). Just like in the Veritasium-video you'll also experience an odd sensation: depending on the directions of your hand turning and that of the spin of the disc the spinning top will either tilt upwards or downwards - and quite forcefully so.

These are well known physical effects and there is nothing mystical about it. But to experience in real life is baffling and at first totally counter-intuitive.
We are just not used to the physical effects of fast spinning bodies.
User avatar
r-frank
Posts: 1962
Joined: Thu Jan 24, 2013 6:26 pm
Location: Möckmühl, Germany
Contact:

Re: WOZZ - an extreme spinning top

Postby r-frank » Thu Mar 02, 2017 9:58 pm

Hello.

Very impressive project, thanks for sharing.

ASenger wrote:It's a pitty these seem to be only available from the python console.


For displaying the volume of parts you could use the survey tool from arch workbench.
But people designing mechanic/plastic/metal things will of course have as first thought "Why should I use arch workbench ?".

Roland
Deutsche FreeCAD Tutorials auf Youtube
My GrabCAD FreeCAD-Projects
FreeCAD lessons for beginners in english

Native german speaker - so apologies for my english, no offense intended :)
User avatar
NormandC
Posts: 12066
Joined: Sat Feb 06, 2010 9:52 pm
Location: Québec, Canada

Re: WOZZ - an extreme spinning top

Postby NormandC » Fri Mar 03, 2017 3:33 am

Or use Macro FCInfo.

Good luck with your Kickstarter!
Jee-Bee
Posts: 614
Joined: Tue Jun 16, 2015 10:32 am
Location: Netherlands

Re: WOZZ - an extreme spinning top

Postby Jee-Bee » Fri Mar 03, 2017 10:47 am

r-frank wrote:For displaying the volume of parts you could use the survey tool from arch workbench.
But people designing mechanic/plastic/metal things will of course have as first thought "Why should I use arch workbench ?".

I didn't know that... except the last question(i would vote for moving to Part workbench or measurement)
ASenger
Posts: 6
Joined: Tue Nov 29, 2016 3:39 pm

Re: WOZZ - an extreme spinning top

Postby ASenger » Sat Mar 04, 2017 12:46 am

Ok, I would have never searched for the volume tool in the arch workbench.
+1 to shift it to measurements.

I thought I share a bit more technical information about development of the spinning top. IMHO this part has a few interesting points.

KreiselP1.png
KreiselP1.png (49.66 KiB) Viewed 609 times


This is the first iteration of the design in FreeCAD. If you want to see a picture of the real thing (It's ugly!) I recommend having a look at the prototypes gallery at

https://www.kickstarter.com/projects/1246976965/the-wozz-a-truly-amazing-spinning-top-with-a-twist/

The fly wheel is mounted onto a ball bearing (shown in green) which in turn is mounted onto the axle/handle (shown in orange). A string can be wound onto the spool on top of the fly wheel. When the user holds the axle in one hand and pulls the string, the flywheel starts to spin on the ball bearing while the axle is kept stationary.

My first thought was that to achieve full behavior of a spinning top (where fly wheel and axle spin as one) I need a 'connector' to block the axle inside the flywheel. That's what the strange object above the fly wheel is for. The idea was to drop this connector over the axle into the cone-shaped opening of the rotating fly wheel. On its way down the prongs on the connector would eventually be stuck between axle and fly wheel and would thus block the axle inside the fly wheel.

Well, it turns out this idea is pretty crappy: the necks of the prongs need to be really thin so that the weight of the connector is sufficient to make them bend and adapt to the axle. In reality they would need to be so thin that they would break easily. Or the connector could be extremely massive to put enough force onto the prongs. However the spinning top would then become top-heavy and wouldn't spin nicely anymore.

Luckily the connector isn't needed at all: the friction in the ball bearing (even in a bearing of very high quality) is way higher than the friction between the tip of the axle and the underground the top is spinning on. So what happens when you spin up this top and put it on a hard surface is that at first the fly wheel rotates around the stationary axle. The axle then quickly gets dragged along by the frictional force in the ball bearing and spins at the same rate as the fly wheel after only one or two seconds: voila, the behavior of an ordinary spinning top. Sounds nice, too!

It was clear from the beginning, that the tip of the top needs to be exchangeable. With the top spinning at high speeds (several thousand rpm) even very hard materials degrade quickly.
At first I thought about using bearing needles with rounded ends as tips: hardened steel in standardized geometry with extremely tight tolerances - perfect! It turns out everything about these needles is well defined and controlled to exacting standards - except for the rounded ends. These are just 'as is' and one can find all kind of variation here. However, the tip of the top needs to have a perfectly symmetric shape, otherwise the top will wobble badly. So bearing needles fall flat.

KreiselP2.png
KreiselP2.png (31.4 KiB) Viewed 609 times


That's why the second design utilizes a hardened steel ball (from a ball bearing) as tip: these are also standard parts, available in extremely good quality for reasonable price. Furthermore they feature a near-perfect symmetric shape which can easily be centerd in the tip of the top - another very important point. To make the ball exchangeable a small cylindrical neodymium magnet (small bright yellow rectangle on the right side in the picture above) is incorporated into the lower end of the top. The magnetic attraction (most ball bearing balls are made from magnetic material) is strong enough to hold the ball in its bed for all but most extreme bumps. At the same time the ball can be easily extracted with another magnet and swapped with a new one.

Why this is a good idea is visible from this picture:
Kugelvergleich10.JPG
Kugelvergleich10.JPG (577.2 KiB) Viewed 609 times

The ball on the right side is a pristine bearing ball while the one on the left was used as a tip for a few hours. With these defects on its surface it's not yet useless but spinning time is noticeably down.

Else the spool went from the top of the fly wheel to it's bottom. This way the diameter of the spool could be made smaller, which is important to reach the highest possible spinning speed. Also the handle was made bigger to give a more convenient grip (roughly the size of a pencil).

This iteration of the spinning top still features an axle going all the way through the fly wheel. In later iterations the axle was shortened to end inside the fly wheel and the lower tip of the spinning top was formed formed onto the fly wheel. This is because when the spinning top is dropped while it is spinning it will keep its orientation and will hit hard right on its tip. This gives an extreme shock for the ball bearing (the tip is pretty sturdy) which leads to the balls in the bearing punching little dimples into the groove they are running in. Not pretty!

The final version has a few more details and refinements I would like not to share at this moment, but from the principle it is pretty close.

All in all this was a fun project, both from the design work involved as well as from the result.
chrisb
Posts: 1649
Joined: Tue Mar 17, 2015 9:14 am

Re: WOZZ - an extreme spinning top

Postby chrisb » Sat Mar 04, 2017 12:58 am

Thanks for sharing, I like the idea of the "external" tip. Whenever I tried to make a tip on the lathe it is not perfectly centered - and it is not hardened too. I think I will order one.
ASenger
Posts: 6
Joined: Tue Nov 29, 2016 3:39 pm

Re: WOZZ - an extreme spinning top

Postby ASenger » Sat Mar 04, 2017 1:20 am

Machining parts for a spinning top is *extremely* challenging!

The parts for the first prototype were made by a well-known prototype company - and were not very good. They managed to have a shift of roughly 1/10th of a millimeter between upper and lower half of the fly wheel (unfortunately not really possible in one clamping) which gives really bad imbalance.

The parts for the other prototypes were made by Swiss precision machine shops - these were of course way better, still there was a learning curve to be mastered!

The best spinning tops I have seen so far are the one made by an extremely accurate japanese machine shop (here is a video of the 'spinning top challenge':)

http://www.dailymotion.com/video/x3l1kcx

and hand-optimized models made by Youtuber lacopo Simonelli:

https://www.youtube.com/channel/UC6hdkJe42pULEkA7SsVMYag

The japanese machine shop ground their top to 1 μm accuracy, totally crazy but the result is impressive. However, they had problems with the tip, too.

Simonelli seems to hand-tune every one of his tops utilizing a very neat procedure. This guy is really good and his tops spin for almost forever.

So, I think it is nothing to be ashamed of, if the tip of your top doesn't come off perfect from the first runs on your lathe. Perfect tops are almost impossible to make.
chrisb
Posts: 1649
Joined: Tue Mar 17, 2015 9:14 am

Re: WOZZ - an extreme spinning top

Postby chrisb » Sun Mar 05, 2017 12:46 am

ASenger wrote:http://www.dailymotion.com/video/x3l1kcx
Although I like the (digital) FreeCAD models, and I am a fan of the Path Workbench, this is only to hide my own deficiencies.
I admire craftsmen, who really know by heart what they are doing.