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Author Topic: Repulsatron — soon to be a magnetoharmonic top starter  (Read 237 times)

Jeremy McCreary

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Repulsatron — soon to be a magnetoharmonic top starter
« on: July 14, 2020, 12:07:12 AM »

This work-in-progress uses magnetic repulsion to transfer torque from a motorized red "driver" to a freely turning yellow "top" across a time-varying air gap. It will eventually be a no-touch spinning top starter. At this stage of development, however, the top's stem still has to be braced against the magnetic impulses delivered by the driver.

https://youtu.be/2ZVkILFdeSI

A future release mechanism will free the top to stay up on its own -- as any real top should.

Train sounds

The magnets were originally LEGO train car couplings. Because they wiggle a bit in their holders, each non-1:1 driver-top resonance turns out to have its own distinctive chug-chug, clickety-clack train sound. Didn't see — or hear — that coming. With practice, you can even recognize some of the resonances by ear alone.

Such happy seredipities happen a lot at the intersection of LEGO, physics, and engineering. In fact, they're one of my favorite things about LEGO as a scientific construction system.

See video description for more info.
« Last Edit: July 14, 2020, 12:20:59 AM by Jeremy McCreary »
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Playing with the physical world through LEGO

ta0

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Re: Repulsatron — soon to be a magnetoharmonic top starter
« Reply #1 on: July 14, 2020, 09:28:18 AM »

Ha! Half-way into the video I was thinking in asking you if  you could not lock them at a ratio of 2:1 and then you put a title saying you could lock it at ratios of 1, 2, 4, 6, 8, 10 and 12!  :o
The wheels have 4 magnets (pole spokes = spolkes ?) but I don't see why that would limit you to even ratios. Have you tried to lock it at 3:1?

The train-like sounds are really amusing!
« Last Edit: July 14, 2020, 11:23:10 AM by ta0 »
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Jeremy McCreary

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Re: Repulsatron — soon to be a magnetoharmonic top starter
« Reply #2 on: July 14, 2020, 11:15:12 AM »

Ha! Half-way into the video I was thinking in asking you if  you could not lock them at a ratio of 2:1 and then you put a title saying you could lock it at ratios of 1, 2, 4, 6, 8, 10 and 12!  :o
The wheels have 4 magnets (pole spokes = spolkes ?) but I don't see why that would limit you to even ratios. Have you tried to lock it at 3:1?
The train-like sounds are really amusing!

I only listed the resonances I've actually confrmed. If 3:1 wasn't listed, it should have been. And don't forget about 16:1 and 14:1!

Agree, other odd resonances seem like they should be possible. But some resonances are much harder to hit than others. I'll have to keep an eye out. One limitation here is that I have only 7 speed steps to work with on either side of off.

I see now that vewing the timing disks through my phone camera could be a useful tool. Or at least some entertainment.

The train sounds could be the best part. The video doesn't do them justice.

Interestingly, this approach didn't work at all with any mix of N and S poles facing outward. It was all repulsion or nothing -- hence the screwy name "repulsatron".

« Last Edit: July 14, 2020, 11:23:30 AM by Jeremy McCreary »
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ta0

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Re: Repulsatron — soon to be a magnetoharmonic top starter
« Reply #3 on: July 14, 2020, 11:36:38 AM »

Sorry, somehow I didn't see the 3:1 ratio, but it's listed there!  :-[

Somewhere I have a science toy that consists of two wheels with magnets on parallel axes in a similar setup. They exchange spin, one building up its spin while the other one slows down and then reversing the exchange, a great example of coupled systems.
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Jeremy McCreary

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Re: Repulsatron — soon to be a magnetoharmonic top starter
« Reply #4 on: July 14, 2020, 01:16:16 PM »

FermiLab just unveiled their record-breaking 14.5 tesla accelerator magnet...

https://news.fnal.gov/2020/07/fermilab-achieves-14-5-tesla-field-for-accelerator-magnet-setting-new-world-record/

Hope to use LEGO versions in the next iteration of the repulsatron -- if only they'd answer my emails. :o
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Kirk

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Re: Repulsatron — soon to be a magnetoharmonic top starter
« Reply #5 on: July 16, 2020, 11:40:45 PM »

So all the ratios are speed reduction, right?
Any chance of a speed increase?
Perhaps with fewer magnets on the target wheel.
A client of ours did some work on a magnetic gear speed increaser.  Friction of shafts and bearings ate up all the gains of having no tooth friction.
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Jeremy McCreary

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Re: Repulsatron — soon to be a magnetoharmonic top starter
« Reply #6 on: July 16, 2020, 11:44:21 PM »

So all the ratios are speed reduction, right?
Any chance of a speed increase?
Perhaps with fewer magnets on the target wheel.
A client of ours did some work on a magnetic gear speed increaser.  Friction of shafts and bearings ate up all the gains of having no tooth friction.

All speed reductions so far.

This combative system definitely has its losses, but they seem to be relatively small at 1:1 resonance.
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