Spin the top fast enough that it won't immediately fall over, and it will continue spinning faster and faster.
Perhaps a bit more detail:
A solar cell powers up a capacitor. A simple circuit involving a basic magnetometer (ie: a coil of wire) decides at what point in the spin, and at what polarity, to discharge the capacitor into a copper-wound iron rod that stretches across the diameter of the top. Every revolution of the toy, the top's "rotor" twice encounters the Earth's magnetic field "stator" and a little more energy is added to the spin.
And a few footnotes for the entranced:
From 3sq.in of solar cell we should be able to get 1W on a sunny day; not much but more than enough to keep a small gyroscope gyrating.
A coil-of-wire magnetometer produces a sine wave when spun, which fits in nicely with the application. When the waveform crosses zero we discharge the capacitor into the electromagnet.
The electromagnet is powered only when it's perpendicular to the Earth's magnetic field, which gives the optimum rotor:stator interaction.
[bigsleep] suggests using the same coil for both. And it works :-) : the "crossing zero" point of the coil sensor is right when we want the magnet to power up, ie: as it's perpendicular to the Earth's magnetic poles.
Depending on the size of the solar-cell, more electromagnets could be added at various angles... either that or the extra power could be used to make giggling noises.-- FlyingToaster, Jan 08 2011 That would work!-- AntiQuark, Jan 08 2011 Very cool...I think.How does the capacitor know to fire just after the sine wave has switched directions?-- 2 fries shy of a happy meal, Jan 08 2011 I'm not an electronics guy but I'm sure a circuit that can tell when a waveform changes direction exists...HOWEVER I can actually picture a circuit that fires the cap in the right direction when the waveform crosses zero... I think I'll go with that instead.
Thanks for the poke.-- FlyingToaster, Jan 08 2011 heheh, the link had me scared there for a second but it turns out they use a cell-phone vibrator motor to spin it up.
To which I reply that a Geomagnetic electric motor is ***much*** cooler.-- FlyingToaster, Jan 08 2011 hahahahaha. Let me think about that "use the same coil" bit for awhile.
[2fries] I've changed my annotation on how the sensor works.-- FlyingToaster, Jan 08 2011 [bigsleep] you're right... and it coincides with the "crossing zero" bit, so right after the waveform crosses zero, the coil-magnet switches into magnet mode, fires off the capacitor and returns to sensor mode. Depending on how long it takes the iron rod to get to peak flux, it might be a little less efficient than a standalone sensor-coil (which could be at an off-angle a bit).-- FlyingToaster, Jan 08 2011 that v.a.t. would precess itself into oblivion pretty quickly, the music on the other hand: microphones do utilize piezoelectric crystals.
But as far as using one for power generation? nah.... the Earth's magnetism isn't very strong, permanent magnets would be better: this is just a bit of fun to make a "no moving parts" top.
Turns out there is a "geomagnetic motor" on the Interweb... not much to do with this idea.-- FlyingToaster, Jan 08 2011 how will i be able to tell if i'm dreaming?-- DIYMatt, Jan 08 2011 My father had one of the vibrating ones for Xmas.
How would this top keep spinning at night? Could the solar cell charge a battery enough during the day? Exactly how little power do we need?-- pocmloc, Jan 08 2011 //spinning at night// Originally I was going to post this as a top that kept spinning as long as you watched it (since if you were watching it, it was either daytime or you'd have the lights on).
//Solar cell charge a battery?// //Exactly how much power...//I'm actually going to test some of this stuff out, so I"ll probably be able to answer that at some point.-- FlyingToaster, Jan 08 2011 Very nice!
A watt is definitely overkill if the top is well-balanced and not overly big. I'm guessing a well-balanced top - or a vertical flywheel held between two jewel bearings - could be kept spinning with a few milliwatts or less.-- MaxwellBuchanan, Jan 08 2011 I bet you wouldn't even need feedback to control the electromagnet. Just alternate it as if the top is spinning at 1800 RPM. Then start the top spinning at a higher RPM. It will slow down, until it reached 1800 RPM, then the electromagnet will start "pushing" it to stay at that speed and not slow down. (IMHO).
SOMEBODY, PLEASE BUILD THIS!!!-- AntiQuark, Jan 08 2011 Yes, but then I'd have to add "Synchronous" to an already lengthy Title. Though there are possible complications with the sensor depending on how much residual magnetism remains in the rod after the current is removed.
//vertical flywheel// for sale at McKinley Station ? [edit] whoops.
1W is pushing it of course: that'd be high noon during the summer at the equator... perhaps 50-100mW would be a more reasonable figure to design around.-- FlyingToaster, Jan 09 2011 //To tune, add an LED//
If there's enough power to run the electromagnet and the LED at the same time, you could make this device into a compass - it'll always flash at the same point in the top's rotation, so by putting it in the right place, it'll indicate magnetic north and/or south.-- Wrongfellow, Jan 09 2011 If there were a whole flock of spinning tops, and each had a bar magnet plus an electromagnet, they could use each other's magnetic fields for leverage.-- ldischler, Jan 09 2011 Put the "top" inside of a frame, making it into a toy gyroscope. This allows it to be picked up and moved while running.
Also, if we add permanent magnets to the frame, it can run in any orientation relative to earth's magnetic field. The original top won't work if played with too close to the north or south poles.
Timing can be accomplished any number of ways; my favorite is to have a photocell and photosensor next to one another on the edge of the spinning part, and a reflector located inside the edge of the stationary part. When the sensor sees the reflected light, the circuit discharges the capacitor into the electromagnet.-- goldbb, Jan 09 2011 //won't work if played with too close to the north or south poles//It would spin, but be gradually more useless as a top. At the pole the orientation would be sidewards (ie: at the N pole, N would be down and S would be up).-- FlyingToaster, Jan 09 2011 I'm curious as to how much the switching losses would sap.-- RayfordSteele, Jan 10 2011 This is a really nice idea.
Begs for the: Solar Powered Geomagnetically Driven "Perpetual Motion" Spintop (with no moving parts)-controlled clock.I know I'd bun it.-- methinksnot, Jan 11 2011 hmm... how would that work ?
//switching losses// energy required to combat residual magnetism from the previous polarity ? It's a consideration.-- FlyingToaster, Jan 11 2011 Note to self : must add strategic "" around all further "Perpetual Motion" ideas [+]-- RattyBunyip, Jan 11 2011 In any DC/AC converter or power electronics controller there are switching losses in the process of trying to create the waveform which result in simple heat rejection, as the switching device cannot flip instantaneously from negative to positive or open to closed etc without some physical limitations, even the high-switching-frequency ones.-- RayfordSteele, Jan 11 2011 I haven't taken pen to paper on the schematic yet, mostly because of general sloth, but tentatively:
There's a capacitor which stores energy from the solar cell. It's fired off when the rod/coil is oriented east-west for the optimum power usage.
Then there's the sensing circuit which relies on the Earth inducing a sine wave in the coil as the top is spun. The waveform crosses zero when the rod/coil points east-west.
If we use a diode bridge we can send the current from each half of the waveform to charge its own little capacitor. Also tucked in there is a couple transistors. The transistor on one side of the bridge discharges the capacitor on the other side. So after the waveform crosses zero, the new polarity's current discharges the cap on the old polarity's side, which momentarily opens the power cap to discharge into the rod at the desired polarity. Once the little cap has shot its load that circuit close and the power cap can continue storing up energy from the solar cell until the next time, when the other side opens up. Or words to that effect. Also in there is circuitry to prevent the power cap from discharging into the sensor caps.... and some more to keep from backwashing the solar cell.
I'm expecting lossy in two regards: the power, due simply to circuit losses, and timing... I'm just guessing the top won't be spinning fast enough for that to be critically affected.-- FlyingToaster, Jan 11 2011 So, if you happen not to be at the magnetic equator, what direction is the torque from the coils? Will it still tend to be around the rotational axis of the top, or will it instead have some tendency to tip it?
Other than that, this seems very feasible.-- NoOneYouKnow, Jan 11 2011 I was under the impression that in general the Earth's magnetic field runs more or less parallel to the surface of the Earth. If not then there would some precessional losses.-- FlyingToaster, Jan 11 2011 See "grid dip".
At the equator, yes, it's sort-of parallel, but that changes progressively as you move North or South.
It's "kind of complicated".-- 8th of 7, Jan 12 2011 Well, offering a mechanical solution would defeat the main source of niftiness in mine eyes: a "no moving parts" motor, so I'll settle for a little jitter.-- FlyingToaster, Jan 12 2011 Since this all rests on a nicely balanced rotating heterogeneous body, is it going to be cheap?. I don't think I can afford those globes.-- wjt, Apr 09 2021 [a1] note the title - "geomagnetic" : the top is a one piece, no-moving-parts thingy.-- FlyingToaster, Apr 09 2021 This'uns the rotor of an electric motor that uses the Earth's magnetic field as a stator.-- FlyingToaster, Apr 10 2021 Heheh, yeah I noticed where I said that, a bit upstream. Believe me, if I actually built one, everybody'd know about it. I'm pretty sure it'd work... possibly only at the equator, but still.-- FlyingToaster, Apr 10 2021 //there’s a “Shop”// with a button that says 'Contact Sales' for me to ask. I'm am right.
I still think to have such a low energy pulsing maintain the balance, will take a very precisely made top. It would be a gem though.
Nature of course, would chuck in a few more oscillations such as a ferrofluid balancing ring and put the waste heat to use in the control system.-- wjt, Apr 11 2021 //or what the top speed would be// Well, it'd be manually started : not enough power to spin while remaining upright from scratch ; the solar cells just keep it spinning. Top speed is limited by aerodrag and the strength of interaction between the coils and Earth's mag field.
//But the faster it spins, the less time there is to recharge, so that’s a limiting factor// and that.-- FlyingToaster, Apr 11 2021 Moving a magnetic faster through the coil increases output Wouldn'r moving the PV cell faster through the EM field collect more photons? or a least change the magnetic component. The cell motion is perpendicular to the light, not in line.-- wjt, Apr 14 2021 I think that's similar to the theory that scrolling faster through the halfbakery makes you more intelligent.-- pocmloc, Apr 14 2021 The higher the velocity the more area is covered in a shorter time, more photon capture? even if the odd one is missed along the way. All the photons, that the PV can capture, are the same right? none are special relative to the others.-- wjt, Apr 17 2021 Doesn't time dilation cancel this out?-- pocmloc, Apr 18 2021 random, halfbakery