Motor Solenoid Basics: All You Need to Build a Pulse Motor & Demo

Hook

I finally got a clean-running pulse motor going with just a motor solenoid, a marked-up rotor, and a high-frequency reed switch. Here's everything I used plus the live demo.

Watch this experiment

I spin the rotor by hand, connect the 12V solenoid, and the motor takes off. You see the reed switch clicking and the whole thing speeding up on a lithium battery. Later I hold a second coil next to the spinning magnets and LEDs light up with no power supply attached.

What you'll learn

You'll see the exact starter parts, how I mark a rotor for even magnet spacing, why a high-frequency reed switch beats the cheap ones, and how a passing magnetic field lights LEDs from a plain coil. All from the bench, no theory overload.

From the bench

I started with a plastic disc rotor. On top I drew 24 lines from the center. Underneath sits another disc with magnets spaced at 32.72 degrees each — that gives 11 evenly spaced magnets. I chose 11 because I saw another build done the opposite way and wanted to try it. The rotor spins like the wheel on The Price is Right instead of a merry-go-round.

Another rotor concept uses 12 sets of neodymium magnets, 24 lines total, placing a magnet on every other line. A plain CD works fine if you at least mark four cardinal directions and glue on four magnets to start. I use a Sharpie and ruler to make notches every 15, 30, or 5 degrees so even numbers line up perfectly across the disc.

How it works / what we changed

Power supply first, then the coil. I tried both a homemade coil wound by hand with 32-gauge wire and a store-bought 500-turn 12-volt solenoid magnet. The coil is the heart of the pulse motor. Winding by hand doesn't need to be perfect — just even across the form. You can wrap the ends first then the middle or do one solid layer then another. The wire is so thin you can barely see it while winding.

The reed switch is the brains. I use a normally-open high-frequency reed switch with an indicator light. It keeps up with fast spinning where cheaper mini reed switches eventually stay closed, kill the pulse, and the motor stops. The high-frequency ones are more sustainable.

The base is four-by-two pegboard with quarter-inch holes. Shaft nipples from the double-stacked bearing discs drop right into those holes for a simple, stable mount.

magnetic ring

I used a magnetic ring setup on the rotor — basically 11 neodymium magnets arranged in a circle at 32.72 degrees each. This gives even spacing and consistent pulses as the ring passes the solenoid. One build I saw used the opposite magnet orientation with the same count, so I copied the idea but flipped it. The ring spins smoothly once balanced and the reed switch triggers cleanly on each pass.

solenoid pulse

The solenoid pulse is what drives the whole thing. Power flows from the battery or 12V supply into the solenoid coil, the reed switch times the on-off cycle, and each pulse kicks the rotor magnets. I found the store-bought 12-volt solenoid gives a strong, clean kick. When the high-frequency reed switch stays reliable the solenoid pulse stays sharp and the motor keeps accelerating instead of locking up. You can feel the difference immediately once the pulse is timed right.

Builder checklist

• Rotor disc (CD or plastic) with even lines drawn from center
• 11 or 12 neodymium magnets placed at equal angles (32.72° for 11 magnets)
• Motor solenoid or hand-wound coil (32-gauge wire, at least one pound to start)
• High-frequency normally-open reed switch with indicator light
• Power supply — lithium-ion battery or 12V wall supply
• Connectors and basic wiring
• Pegboard base with quarter-inch holes and bearing stack with shaft nipples
• Optional second pickup coil for generation demo

Troubleshooting

If the motor stops suddenly the reed switch is probably staying closed — swap to the high-frequency version. If pulses feel weak, check magnet spacing and coil gap. Hand-wound coils work even if messy as long as the turns are roughly even top to bottom. If the rotor wobbles, re-glue magnets and balance it.

Safety

Use eye protection when spinning rotors at speed. Lithium batteries can get warm — watch for heat. Keep fingers clear of the spinning magnet ring. Start with low voltage and increase slowly. When experimenting with generated voltage from the pickup coil, remember the output is AC and low current but still treat it with respect.

FAQ

Do I have to wind my own coil? No — a store-bought 12V solenoid works great as the motor solenoid and is easier to start with.

Why 11 magnets instead of 12? I saw another build using 11 in the opposite orientation and wanted to try it. Both even and odd counts can work if spacing is even.

Can I really generate voltage with no extra power? Yes — when the magnetic ring spins past a second coil it induces current. I measured up to 11 volts AC on the multimeter and lit LEDs with zero extra hardware.

What if my reed switch sticks? Cheap mini ones often stay on and kill the pulse. The high-frequency reed switch with indicator light handles the speed much better.

Is a CD rotor good enough? Absolutely for starters. Mark at least four cardinal points, add magnets, and go. Later you can upgrade to a stiffer disc and bearings.

Related on this site

• How to Build a Pulse Motor: Parts, Coil Gap, First Spin
• Pulse Motor Rotor Design: Magnets, Materials and Balance
• How to Wind Coils for a Pulse Motor (Step by Step)
• Pulse Motor vs Bedini Motor: What's the Difference?
• Using a Hall Effect Sensor in Your Pulse Motor Build

Watch this experiment on YouTube

• ▶ Watch full on YouTube