Collaborate:  wiki


makeSEA Analysis - Brushless Motor - Selecting the Magnets

Brushless Motor: Selecting the Magnets

(see also, Brushless Motor)

The force of the magnets is categorised in grades: N35, N45, N50, N52 are very common, whereas N52 is the strongest. I have the impression, that suppliers are not very accurate with their specifications. Absolute values are difficult to measure (it also depends on magnet size), so you can’t check, if sellers exaggerate. They probably don't even know, what they are selling, but since the price is so cheap, you can't complain. Also the variation between the "same" magnets can be huge - I've measured +/-20%.

Select the strongest magnets:

I'm using this simple setup to compare magnetic forces of magnets relative to each other. It allows to select the strongest. The magnet is placed onto a wooden bar on top a small scale. The scale is tared together with the magnet, and then a probe with a ferromagnetic block is pushed beneath the magnet. I’m using some ferrite as a probe, but an iron bolt probably works a s well. Make sure that the position of the magnet and the position of the probe is always the same. The scale shows the force for the magnet. Since the scale contains magnetic components, it's important to measure the magnets at some distance from the scale, and keep away other metals.

It would be possible to calculate absolute values by applying the law of the lever, but for only comparing and selecting magnets, this isn't important. However it is important to repeat the measurements exactly the same way - I’ve used tape and some indication marks. In addition it matters to measure all the magnets with the same orientation of polarity (e.g. south up, north down). The measurements change, if the same magnet is flipped. I'm not sure about the reasons, but it could be the earth magnetic field, or some magnetic field in my room, or the ferromagnetic probe remains a bit magnetised, or the field lines on North and South of the magnets are not perfectly symmetric, …

For getting the brushless motor running, this selection isn't relevant. It's an optimisation, but since the setup is so little effort and I've ordered 20 magnets (8 spare / waste), I've done it.

Balance the magnets:

A similar setup can be used to measure and compare their weights. That’s more important, since an unbalanced rotor can generate big vibrating forces, and it makes a horrible noise. The ferromagnetic probe isn’t needed here. But the bar can be reused in order to keep the magnet away from magnetic components of the scale. The scale is tared without the magnet, and then the magnet is placed onto the bar.


I’ve first measured the weight of the 12 strongest magnets, and then created a ranking from 1 (lightest) to 12 (heaviest). The scheme below shows, how to assemble the magnets sorted by their weight. It’s probably not THE optimum, but it’s a good and simple guess.

0 Attachments
Average (0 Votes)
No comments yet. Please sign in to comment.

Check Out the makeSEA Mash Market for a collection of useful designs related to this Wiki article.

makeSEA R&D

makeSEA is more than a service, it's a platform for Digital Transformation. Here's a hint at whats coming . . .

makeSEA Proudly Sponsors Construct3D 2018 Conference at Georgia Tech

We are thrilled to be proud sponsors at the 2018 Construct3D conference for 3D Printing in Education at GATech in Atlanta this coming weekend! Come visit and see me, Chris Stavros, Chief Maker...

Is 3D printing good or bad for construction jobs?

(Quartz/Mike Murphy) Now You can now 3D-print a house in under a day   I love this discussion thread  about the recent article by Mike Murphy at QUARTZ  on 3D...

Move over Moore . . . there's a new law in town!

illustration by ZOHAR LAZAR According to this article by Clive Thompson of WIRED Magazine , there is a new law in town:  Lass' Law.  Moore's law has accurately predicted...

3D Printing and the Olympics

Whether you strive for Olympic gold downhill skiing, or couch-surfing, it’s easy to understand why 3D printing makes a difference - remember, this technology is on it’s way to your living...

Christoph is at it AGAIN!

What can we say but INCREDIBLE and AMAZING!  Check out the latest 3D printable projects by makeSEA Chief Designer Christoph Laimer - click here to see more


At makeSEA we're all about innovation. Through the process of change, alteration, transformation and metamorphosis, using new methods and creativity, that new or improved products can evolve from...

What time is it?!? - Time for the Oct O'Clock!

YES - it's that time again - Christoph's latest amazing creation is the Oct O'Clock - scope it out and start building yours today!

Halbach Motor Build Kits Are Finally In!

Have you been waiting for the Halback Motor Build Kits to become avaialble?  So have we - they are In Stock Now - Get yours today HERE .

A viable, efficient 3D printed motor? Yes we can.

              This was actually a dream of ours: to design a 3D-printable motor that can be printed on most basic 3D printer models...

Exploring magnetic PLA and other 3d printer filaments

  Question of the day: Can the reduced magnetism of 3D-printable magnetic PLA from Proto Pasta actually resolve efficiency issues by reducing eddy currents in a 3D printed motor?...

Burning up

Heat is an important consideration when working with 3D printable ABS and PTEG materials.

The devil is in the details

When Christoph designed, printed and load tested version 1 (the second version) of the makeSEA brushless motor, he had some concerns about how many RPMs the rotor could sustain without breaking apart.

Why 3D printing will change the world: reason 13

3D printing is unleashing conceptual designs from the minds of students, amatuers, professional 3D designers and engineers worldwide. And that is a good thing. It allows for trial and error and...