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Electric top spinner/elastic winder/axle tester
This simple battery-powered tool is handy for spinning up LEGO tops, winding up LEGO rubber band boats, and making sure that axles that look straight really are.
About this creation
Please feel free to look over the images and skip the verbiage.

I use this handy battery-powered tool mainly to (i) spin up LEGO® tops, (ii) wind up LEGO® rubber band boats, and (iii) make sure that Technic axles that look straight really are. The first 2 applications are demonstrated in the video below.



The very simple design takes full advantage of the speed control built into the Power Functions rechargeable 7.4V Li polymer battery in the handle.



Cross-axles slide easily into and out of the yellow trigger of the rapid shooter magazine and trigger assembly (18588c02) serving as the "chuck" for top spinning and boat winding. An axle joiner replaces the chuck for axle testing.



Top spinning and boat winding require different motors. (The former demands very high speed but doesn't need much torque, whereas the latter needs a good bit more torque and much less speed.) Both of the selected motors work for axle testing. Motor changes take less than a minute.

Warning! Always wear eye protection when working or playing with high-speed LEGO® rotating machinery and keep valuables and bystanders (including pets) a safe distance away -- especially when testing new designs. Really.




Top spinning

A powered top spinner can enhance the play value of any top. This is especially true for tops that prove difficult to spin up by hand.1

Though not quite the fastest, this is by far the most convenient electric top spinner I've tried. (Some of the others are shown here).







A very high no-load speed of ~4,100 RPM at 7.4V makes the original 9V Technic motor (2838) of 1990-2002 vintage the LEGO® motor of choice for spinning tops. Its low torque is more than adequate for even heavy tops if you're willing to be a little patient.





Friction within the chuck and along its drive axle reduces the spinning tool's no-load speed to ~3,700 RPM2, but aerodynamically clean tops with narrow tips on low-friction surfaces still reach speeds of well over 3,000 RPM -- provided they don't fly apart first.

Warning! Use the battery's speed control to build up speed slowly in untested tops, as the shrapnel from a high-speed failure poses a real danger to anyone or anything nearby. Always inspect tops afterward for signs of impending failure.

For 2 reasons directly related to the fact that drag increases rapidly with speed, powered spinners tend to yield only minor gains in spin time with aerodynamically dirty tops like the Klingons below.



For starters, rapidly mounting drag eventually overcomes the motor's torque during spin-up, and maximum attainable speed suffers accordingly. After release, aerodynamic braking then quickly eats up any gain in speed the motor might have provided.

Hence, an electric spinner similar to this one increased Klingon top release speeds by 120-195% but spin times by only 7-35%.



The cleanest top of the bunch (last in the video and bottom center in the photo) benefitted most from motorized spin-up WRT both speed and spin time, while the dirtiest top (first in the video and top center in the photo) gained the least.




Elastic (rubber band) winding

An electric winder takes the drudgery out of testing and playing with LEGO® boats powered by elastics (rubber bands).



The video below shows my lovely assistant toiling away with X-ray, my first rubber band boat.



An electric winder really shines with boats powered by several long strands of the "sport rubber" (latex strip) favored by serious rubber band airplane enthusiasts.



The short segment showing this winder in action with the boat above starts at 8:20 in the video at the top of this page. Of course, the prop spins a lot more slowly -- and therefore a lot longer -- when it's underwater.

In my limited experience with rubber band boats to date, the lightweight Power Functions M motor (no-load speed ~320 RPM at 7.4V) offers the best combination of torque and speed for winding purposes.







Unlike the spinner, friction in the chuck has no significant impact on performance here.




Axle testing

(Sorry, no axle-testing video or photos.)

High-speed devices like tops, flying rotors, and propeller-driven carts (below) demand "true" (straight) axles.



Few LEGO® axles are perfectly true even when new, but some come closer than others.3 The only reliable way to separate the wheat from the chaff here is to test in a way that makes subtle curvatures conspicuous.

To test axles with this tool, first replace the chuck with a new axle joiner on a new 2L axle. Either motor will do. Then turn the battery speed control to the lowest setting (±1/7) and leave it there. You'll be using the battery's power button from here on out.

After convincing yourself that the joiner itself runs true, turn the battery off and load one end of an axle into the joiner. Then turn the battery back on and watch the axle closely for tell-tale wiggling at the free end.

If the free end wiggles too much for the purpose at hand, reject the axle. Otherwise, test the other end. Accept the axle for high-speed use only if both ends pass muster.




Specifications

Overall dimensions:[] mm (LxWxH)
Mass:[] kg
Chuck for spinning and winding:Rapid shooter magazine and trigger assembly (18588c02)
Motors:Original Technic 9V (spinning and winding), Power Functions M (axle testing)
Electrical power supply:7.4V from PF Li polymer battery
Modified LEGO® parts:None
Non-LEGO® parts:None
Credits:Original MOC





Footnotes

1 The often interrelated factors most likely to make a LEGO® top hard to "twirl" (spin up with a twirl of the fingers) areFor example, the twirlability of the updated version of Asteroid below suffers from the last 2 factors.



High moment of inertia remains a hurdle to twirlability in the Round Up top below. Ground clearance is much more forgiving, but the CM is that much higher.



The importance of recent practice can't be overstated. Having twirled tens of thousands of tops in the last year, I have no trouble with the tops above, but folks who haven't touched a top in a long time will have little luck with them at first.

Top twirling involves 2 different skills -- (i) building up the necessary speed, and (ii) keeping the stem close to vertical in the process. The latter is by far the more important of the two.

The good news: Twirling skills improve very quickly if you start small, work your way up in size and weight, and focus on staying vertical along the way.



2 A little silicone lubricant in the chuck and the pin hole behind it will increase the tool's no-load speed by >100 RPM.

3 I don't buy many sets, so "new" axles come to me mainly via BrickLink. Not sure why so many of them arrive out-of-true, but I suspect that shipping trauma and seller storage practices may have something to do with it. Generally, the longer the axle, the less likely it is to be true, but 10L axles may be the worst.





Comments

 I made it 
  November 4, 2017
Quoting Angelo Filipelli Very cool Jeremy! I actually built something extremely close to this a while back for winding up a rubber-band powered model airplane. All I did was attach a PF M motor to a battery box and made a hook that caught onto the propeller. It worked well until the plane crashed...
Thanks, Angelo! This is still my best winder for rubber-band boats, but I've since made a much more powerful top starter turned by an RC Race Buggy motor geared up 1:5 and powered by an old 9V train transformer. The extra voltage relative to the PF LiPo (only 7.4V) makes a noticeable difference. This new starter has a no-load chuck speed of 9,600 RPM and enough torque to take even relatively heavy low-drag tops to over 8,000 RPM. Amazing how many of my tops actually stay in one piece at such speeds, but you can never assume that and must test =very= carefully.
 I like it 
  November 3, 2017
Very cool Jeremy! I actually built something extremely close to this a while back for winding up a rubber-band powered model airplane. All I did was attach a PF M motor to a battery box and made a hook that caught onto the propeller. It worked well until the plane crashed...
 I made it 
  September 30, 2015
Quoting David Roberts Brilliant. I love how detailed your write ups are. This format just wouldn't work on Flickr and is a great example of what MOCpages is great for doing. The elastic band boat video is super. To my shame, I still haven't built a band powered boat, having been busy with Decisive Action 2 and work.
Thanks, David! I think the long write-ups select out a lot of potential likes and comments, but "going public" with the thinking behind my MOCs forces me to think harder, which only adds to the fun -- at least at my end. And you're right: MOCpages is the best public venue for that. While rubber band boats are still in queue, order some "sport rubber" latex strip (3/16") from a model airplane supplier. Huge improvement over regular rubber bands!
 I like it 
  September 30, 2015
Brilliant. I love how detailed your write ups are. This format just wouldn't work on Flickr and is a great example of what MOCpages is great for doing. The elastic band boat video is super. To my shame, I still haven't built a band powered boat, having been busy with Decisive Action 2 and work.
 I made it 
  September 14, 2015
Quoting Topsy Creatori In watching your videos I had an image of you building a top while meticulously weighing each piece! Ha, ha! I bet you have a spreadsheet of every potential top-usable LEGO piece and its weight and probably who knows what other pertanent data! So, then is LEGO's QC on part weights pretty consistent? ;) Oh, that's a handy device you've built too :)
No need to be quite that meticulous, Topsy. I do weigh each top I post here and on YouTube, because mass is such an important parameter. However, I take the uniformity of parts for granted, and they haven't let me down yet. That's one of the things that makes LEGO such a great medium for tops: If you can find a reasonably straight axle, get the parts into at least a 3-fold rotational symmetry around it, and make the entire assembly rigid enough, the top's guaranteed to balance and spin smoothly.
 I like it 
  September 14, 2015
In watching your videos I had an image of you building a top while meticulously weighing each piece! Ha, ha! I bet you have a spreadsheet of every potential top-usable LEGO piece and its weight and probably who knows what other pertanent data! So, then is LEGO's QC on part weights pretty consistent? ;) Oh, that's a handy device you've built too :)
 
By Jeremy McCreary
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LEGO models my own creation MOCpages toys shop Electric top spinner/elastic winder/axle testerTechnic


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