I Finally Understood Stacked Magnet Disc Polarity Explained

Hook

I grabbed a bunch of acrylic discs and neodymium magnets to figure out stacked magnet disc polarity explained once and for all. What I felt with my own thumbs surprised me — the force is huge even when the magnets never touch.

Watch this experiment

I dropped smaller discs into larger ones, flipped polarity, stacked them two and three high, and tried to get the whole thing spinning on a central pole. You see the levitation, the sudden stick, and why a Christmas-tree stack idea didn't work.

What you'll learn

How same-polarity magnets create both lift and drag, why staggered stack heights kill spin, and that less magnets can actually give longer run times when you factor in weight.

From the bench

I started with a 4-inch acrylic disc that grips the magnets nicely with its edge. The central pole is just a simple rod. I nested a 4-inch inside an 8-inch, then tried 6-inch and 10-inch combos. Most fit with only a couple glue mistakes stopping perfect drop-in. When polarity lines up for repulsion the inner disc levitates in the middle; flip it and it slams down into the hole. The push against my thumbs was strong enough I had to adjust my grip.

I counted 72 magnets on the 8-inch and same on the 10-inch. Some spots have stacks of two, others three, and a few single. The copper tape around the 8-inch disc lets me pick up voltage — it handles 12.1 V without burning up. I timed one balanced 8-on-8 levitation run at eight minutes and 34 seconds before any bump in the road stopped it.

How it works / what we changed

The law of physics shows up quick: you lose a bit of that original force every cycle. Without adding energy the spin dies. I found that less is definitely more on this stick type of thing. When I loaded the top disc with extra weight it was like walking the same trail with a 20-pound backpack — the calculation changes but the distance (runtime) can actually improve if balanced right. Staggered magnet heights create uneven force the system eventually feels as a bump.

Magnet stick

The magnet stick feeling is real even when the magnets do not overlap anywhere. I could feel the pull or push against my thumbs like they were glued. On the pole the inner disc either levitates or gets sucked in hard depending on which way I flip it. Only a couple spots where I glued magnets too close actually touched. Everywhere else the stick is pure magnetic force.

Magnet hill

The magnet hill shows up when you try to stack in a Christmas-tree shape. I tried building it up like steps but the polarity made it unstable. One side would levitate while the other stuck to the ground. The hill effect creates peaks and valleys of force that the spinning disc feels as bumps. Any stagger between stacks of two and stacks of three eventually gets transmitted through the whole system and slows it down.

Type of magnet

I used standard neodymium donut magnets — the exact type that lets the acrylic edge grip the pole nicely. They are strong enough that two discs with 72 magnets each can levitate one another for over eight minutes. I did not test other types but these neodymium ones give the push, the stick, and the levitation I was after. The copper tape on the 8-inch disc works with them to pick up voltage without problems up to 12 volts.

Builder checklist

• Start with 4-inch, 6-inch, 8-inch, and 10-inch acrylic discs
• Glue neodymium donut magnets evenly — avoid overlap
• Use a smooth central pole that fits the inner hole
• Mark polarity on every magnet before stacking
• Add copper tape to at least one disc if you want voltage pickup
• Test both polarities — note which gives levitation vs stick
• Weigh the top disc and factor it into your runtime calc
• Keep stacks even or accept the bump that comes with stagger

Troubleshooting

If it sticks to the ground instead of levitating, flip the disc over. When spin dies fast, check for uneven stack heights — that creates the bump you feel. If the inner disc won't drop in, look for glue that sits too high. Voltage too low on the copper tape? Make sure the disc is spinning close but not touching the pickup. Remember any road bump eventually reaches the whole system.

Safety

These magnets are strong — keep fingers clear when flipping polarity because the snap can pinch. The spinning discs have real mass; a 10-inch with 72 magnets carries momentum. Wear eye protection in case anything lets go. The copper tape can handle 12 V but watch for heat if you push higher. Always unplug any drive coils before adjusting by hand.

FAQ

Do the magnets have to overlap to get strong force? No — I felt full push against my thumbs with zero overlap.

Why does it stop after a few minutes? The force diminishes each cycle; without added energy it slows. Bumps from uneven stacks make it worse.

Can I run it longer than 8:34? Yes if you keep stacks even, balance the weight, and give it a clean wrist flick start.

What size discs work best together? The 6-inch and 4-inch nest nicely inside the 8-inch; the 10-inch sits on top in levitation mode.

Related on this site

• How to Build a Pulse Motor: Complete Beginner's Guide
• Pulse Motor Rotor Design: Magnets, Materials and Balance
• Magnetic Levitation on a Pole – Experiment 1: Push, Pull & Balance
• 7+ Minutes of Motion: Magnetic Disc Spinning With Just a Wrist Flick
• Less Is More — Clockwise vs Counterclockwise

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