I Finally Got My Solenoid Pulse Motor Running with a 24-Node Magnet Array

Hook

I cut the solenoid pulse motor down to a single solenoid and packed the disc with a 24-node magnet array. One reed switch, a light touch, and it spins up at 12 volts. This feels like the cleanest version yet.

Watch this experiment

I fired the 12.3 V solenoid and gave the rotor a tiny nudge. It took off counterclockwise, hesitated a second because of the extra weight, then smoothed out and kept climbing. At 15.5 volts the current sat at 0.0 A with the pot wide open. When I hit 20 volts you could hear it accelerate. The reed switch clicked along even though it probably misses a few nodes — the spacing is tight but not tight enough to keep the circuit constantly closed.

What you'll learn

You’ll see exactly how a single solenoid drives 24 magnets, why the extra mass slows startup, and how the reed switch behaves when the nodes are close together. I also talk through the next step — turning this into a counter rotating pulse motor with a second disc sharing the same trigger.

From the bench

The solenoid is glued to a little stand made from a bolt, washer, and two flanges. Hot glue keeps it rock solid at the perfect height but I can still peel it apart later. All the magnets on the disc are modular — no permanent adhesive yet so I can swap sizes or counts fast. Both wires on the reed switch are blue so I had to flip alligator clips a couple times before I got polarity right. Lesson learned.

How it works / what we changed

We dropped from two solenoids and two magnets down to one of each. The 24-node magnet array replaced the old smaller count. Because the magnets sit close together the rotor feels heavier, so spin-up takes longer, but once moving it coasts nicely. The reed switch only needs to catch some of the passes — enough pulses to keep torque coming. I can probably nudge the solenoid 0.5 mm closer for a tiny speed bump but I’m not gluing the rotor magnets down yet.

Counter rotating pulse motor

The next plan is to float a second smaller disc just above the big one. Align its magnets with the 24-node array on the main rotor and drive both with the same reed switch or a second one. One solenoid pushes the bottom disc, another pushes the top, creating opposite rotation. Or I can drop the upper disc low enough that the bar magnets on each rotor push each other magnetically. Either way the goal is two spirals spinning at the same time. Bearings are already in the wood but the fit is sloppy on aluminum and steel interferes slightly with the permanent magnets. Still, the distance keeps the effect small.

24-node magnet array

I was nervous the 24-node magnet array would be so dense the reed switch would stay triggered and kill the pulses. Turns out the spacing works. The switch fires often enough to accelerate the rotor even if it skips a couple nodes. The extra mass makes the start slower but the close magnets also mean a tiny touch is all it takes to get rotation going. I’m keeping this array for now — it feels like the bold move that finally smoothed things out.

Builder checklist

• One 12 V solenoid mounted on bolt-washer-flange stand
• 24 evenly spaced neodymium magnets on rotor disc
• Single reed switch positioned to catch passing magnets
• Alligator clips for quick polarity swaps
• Variable voltage supply 12-20 V
• Hot glue for temporary but stable mounts
• Modular rotor so magnets can be changed without destruction

Troubleshooting

If it won’t start, flip the solenoid wires — polarity matters. If the reed switch stays closed, increase magnet spacing slightly. Heavy rotor needs a gentle push or higher voltage to overcome inertia. Blue-on-blue wires make debugging polarity confusing — label them next time.

Safety

Keep fingers clear of spinning magnet array. Hot glue can burn if you re-melt it. Voltages up to 20 V are used here — respect your power supply limits. Wear eye protection in case a magnet lets go.

FAQ

Does the reed switch hit every magnet? No, but it hits enough to keep the motor running.

Why does it take longer to speed up? The 24-node magnet array adds weight; once moving the momentum helps.

Can I run this faster? Probably by moving the solenoid a hair closer, but I’m keeping magnets unglued for easy changes.

Will this become a counter rotating pulse motor? That’s the plan — second disc driven by same or extra reed switch.

Related on this site

• How to Build a Pulse Motor: Complete Beginner's Guide
• Pulse Motor Rotor Design: Magnets, Materials and Balance
• Pulse Motor vs Bedini Motor: What's the Difference?
• How to Maximize RPM on Your Pulse Motor

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