Magnetic Gear Torque Density

ISEF Category: Engineering Technology: Statics and Dynamics

Subcategory: Other  ·  Difficulty: Intermediate  ·  Setup: Home Setup  ·  Time: 1 to 2 Months

The Hook

A gear can move without teeth touching at all. That sounds weird until you realize magnets can pass force through a gap. Your project asks a simple but powerful question, can a magnetic gear move power like a normal gear, or does it lose too much torque?

What Is It?

A magnetic gear is a rotating system that transfers motion with magnets instead of meshing teeth. Think of two pizza pans that never touch, but still try to spin each other because strong magnets line up in a pattern. The key idea is torque, the twisting force that makes rotation happen.

You can compare a magnetic gear to a spur gear, which is the classic gear with straight teeth. Spur gears transfer force through direct contact, so they usually waste less motion in the gap. Magnetic gears trade that contact for quieter operation, no wear from rubbing teeth, and the chance to work even when a solid seal or physical barrier sits between the parts.

Why This Is a Good Topic

This topic works well for a science fair because you can measure a real engineering tradeoff, torque transfer versus distance, speed ratio, and alignment. You do not need a university lab to start, since small magnets, 3D-printed parts, and simple force tests can give you useful data. The project connects to quiet machinery, sealed devices, and contactless drives, and you can learn modeling, measurement, and data analysis in one build.

Research Questions

• How does magnet spacing affect the maximum torque transfer of a small magnetic gear?
• What is the effect of magnet count on torque density in a rotary magnetic gear?
• Does changing magnet orientation improve the gear ratio stability under load?
• To what extent does a magnetic gear outperform a spur gear in noise level at similar output speed?
• Which rotor diameter gives the best torque per unit mass for a home-built magnetic gear?
• How does misalignment between rotors change the torque curve of the magnetic gear?

Basic Materials

• Neodymium disc magnets of several sizes and strengths.
• Laser-cut, 3D-printed, or cardboard rotor templates.
• Wooden dowel or bolt shaft.
• Low-friction bearings or smooth bushings.
• Sturdy base board or frame.
• Ruler or calipers for measuring spacing.
• Digital kitchen scale with 0.1 g accuracy.
• Small hanging weights or a spring scale.
• Tape, glue, and epoxy.
• Marker and graph paper for layout.
• Smartphone camera for documenting alignment and motion.

Advanced Materials

• Neodymium disc and arc magnets with known grade and dimensions.
• 3D-printed rotor housings with precise magnet pockets.
• Precision bearings and shaft couplers.
• Torque sensor or rotary force gauge.
• Optical tachometer or encoder.
• Vernier calipers and micrometer.
• Gauss meter for magnetic field checks.
• Finite element modeling computer access.
• FEMM software.
• MATLAB, Python, or R for analysis.
• Strain-free mounting hardware and alignment jig.

Software & Tools

• FEMM: Models the magnetic field and helps you predict torque before building the prototype.
• Python: Organizes measurements, fits curves, and compares torque across designs.
• ImageJ: Measures angles, gaps, and motion from photos or video frames.
• Google Sheets: Tracks trials, calculates averages, and makes quick graphs.
• GeoGebra: Helps you sketch gear geometry and test spacing relationships.

Experiment Steps

1. Define the exact gear geometry you want to test, including rotor size, magnet layout, and target ratio.
2. Choose one independent variable first, such as magnet spacing, magnet count, or rotor diameter.
3. Build a prediction model in FEMM so you know what torque trend to expect before testing hardware.
4. Design a fair comparison against a spur gear by matching the output ratio and testing conditions as closely as possible.
5. Plan a measurement method that converts motion or lifting force into torque, then repeat it across several trials.
6. Organize a data table that lets you compare torque density, efficiency, and error bars across each design.

Common Pitfalls

• Using magnets that are not matched in size or grade, which makes one prototype look better for the wrong reason.
• Letting rotor alignment drift between trials, which changes the air gap and changes torque a lot.
• Comparing a magnetic gear to a spur gear with different gear ratios, which makes the result unfair.
• Measuring only peak spin and ignoring holding torque, which misses the main performance limit.
• Trusting FEMM output without checking the physical build, which hides modeling assumptions that do not match real magnets.

What Makes This Competitive

A stronger version of this project does more than say magnets work. You can map the full torque curve, compare several gear ratios, and test how sensitive the design is to spacing and misalignment. You can also combine FEMM predictions with measured data and report where the model matches, and where it breaks. That kind of careful engineering comparison looks much stronger than a simple demo.

Project Variations

• Test how changing the air gap alters torque density in the same magnetic gear frame.
• Compare circular disc magnets with segmented magnet patterns to see which design transfers torque more smoothly.
• Measure how a magnetic gear performs under partial enclosure, then compare that result with an open spur gear setup.

Learn More

• FEMM User Manual: Free documentation for 2D magnetic field modeling, available from the official FEMM website.
• NIST Engineering Statistics Handbook: Clear guidance on uncertainty, repeatability, and error analysis, found by searching the NIST site.
• MIT OpenCourseWare, Mechanical Engineering courses: Free lecture notes on statics, dynamics, and machine design, found on the MIT OpenCourseWare site.
• NASA Technical Reports Server: Search for reports on magnetic gears, electric drives, and torque transmission.
• Google Scholar: Search for peer-reviewed papers on magnetic gears, torque density, and magnetically coupled transmissions.
• PubMed Central: Search for open-access papers on magnetic field modeling and electromagnetic device design.