Rotor Bifilar Test: 4-Magnet Results in Our Pulse Motor Speed Challenge

Hook

In our speed challenge we ran a rotor bifilar test on a 4-magnet rotor. Two bifilar coils, dual SG circuits, fixed 12 volts — here’s exactly what happened on the bench.

Watch this experiment

We fired up the 4-magnet rotor with one bifilar set using 20-gauge drive and 30-gauge trigger, the second using 26-gauge and 30-gauge. Two SG circuits fed from the first pulse motor to the second. Everything stayed at 12 volts.

What you'll learn

You’ll see the actual RPM numbers we got, how the MagLab alignment tool affected readings, and why the 4-magnet setup landed in third place. All facts taken straight from the bench session.

From the bench

We started with the first 4-magnet rotor. Initial readings were 622, 621, 614 RPM. The tac meter battery seemed weak so we called it around 600-650 RPM being generous. Current draw showed about 2.9-3 amps. Lights were blinking well although one was a little off as usual.

How it works / what we changed

We removed the MagLab alignment tool completely. That dropped the reading by seven RPM, so we put it back to keep the magnets dead center for optimal readings. Then we swapped to a second 4-magnet rotor that used bigger, stronger magnets. They lined up nicely with the MagLab and gave us 645, 600-605 RPM — we settled on 630-650 RPM max for that rotor.

4 magnet rotor

In the motor mayhem 4-magnet part of the speed challenge the 4-magnet rotor came in third place. We recorded 720-750 RPM with the 12-magnet and 6-magnet rotors at the same 12 volts, while the 4-magnet setup topped out around 650 RPM. Even after swapping to stronger magnets and cleaning up alignment we couldn’t beat the 6-magnet leader.

Bifilar coils

During the motor mayhem magnet testing we noticed the second set of magnets on the 4-magnet rotor felt bigger and stronger than the first set. They lined up nicely with the MagLab tool and produced virtually the same top speed of about 650 RPM. The first rotor’s magnets gave slightly lower and less stable readings, so magnet strength and rotor balance clearly mattered in this motor mayhem magnet comparison.

Builder checklist

• Two bifilar coils: one 20 ga drive / 30 ga trigger, second 26/30 ga
• Dual SG circuits feeding first pulse motor to second
• 12 V fixed input, 2.9-3 A draw
• MagLab alignment tool for centering magnets
• Tac meter (check battery)
• Second 4-magnet rotor with stronger magnets ready

Troubleshooting

Tac meter gave inconsistent numbers — we blamed a dying battery. One trigger light stayed a little off the whole time. When the MagLab tool lifted the rotor too high we lost seven RPM until we recentered it. Alignment and battery condition were the biggest variables.

Safety

We briefly tried a small DC voltage booster that pushed the circuit to 78 volts. The video notes it might not be safe so only experienced builders should experiment with voltage boosters on these setups. Always watch for overheating transistors and coils.

FAQ

Why did the 4-magnet rotor place third? At 12 V it reached only 630-650 RPM while the 6-magnet hit 730-750 and the 12-magnet 680-720.

Did removing the MagLab tool help? It dropped RPM by seven so we put it back for centered alignment and optimal readings.

Were the two rotors different? Yes — the second 4-magnet rotor had bigger, stronger magnets and lined up better, but still topped out at the same 650 RPM range.

Related on this site

• How to Build a Pulse Motor: Parts, Coil Gap, First Spin
• Pulse Motor Rotor Design: Magnets, Materials and Balance
• Best Neodymium Magnets for Pulse Motor Rotors
• Pulse Motor vs Bedini Motor: What's the Difference?
• How to Maximize RPM on Your Pulse Motor

Watch this experiment on YouTube

• ▶ Watch full on YouTube