3D-Printed Halbach Motor Part Two: Tuning, Testing

Building your own Halbach-effect brushless DC motor is one thing. Making sure it won’t blow up in your face another matter, and watching how [Christoph Laimer] puts his motor to the test is instructive.

You’ll remember [Christoph]’s giant 3D-printed BLDC motor from a recent post where he gave the motor a quick test spin. That the motor held together under load despite not being balanced is a testament to the quality of his design and the quality of the prints. But not wishing to tempt fate, and having made a few design changes, [Christoph] wisely chose to perform a static balancing of the rotor. He also made some basic but careful measurements of the motor’s parameters, including the velocity constant (Kv) using an electric drill, voltmeter, and tachometer, and the torque using a 3D-printed lever arm and a kitchen scale. All his numbers led him to an overall efficiency of 80%, which is impressive.

[Christoph] is shipping his tested BLDC off to the folks at FliteTest, where he hopes they put it to good use. They probably will — although they might ask for three more for a helicarrier.

8 thoughts on “3D-Printed Halbach Motor Part Two: Tuning, Testing

    1. You’re comparing a (comparatively) soft plastic rotor running at 7000rpm with a strong plastic rotor spinning at 80000rpm. The amount of energy in the rotor is different by orders of magnitude, and even if you did try spinning the printed rotor at higher speeds, it’ll fail much earlier and much less catastrophically.

  1. You’re doing some fantastic work! I also got some early magnetic filament for the grand idea of motor experimentation. It fell to the wayside, so I’ve been very excited to see your project come to fruition!

    Im curious what sort of filtering does your DMM perform for the AC rms measurement? I’m not familiar with agilent DMMs but rather Flukes. I know the Fluke’s will perform LPF for the RMS measure and distort the Kv measurement. A scope, even a simple one is critical IMO for the design envelope your experimenting with.

    A simple scope will give you rpm and voltage simultaneously and produce a consistent Kv parameter. I also find it very insightful for the performance under drive conditions. From the sound of things you’re using a Castle controller? Or equivalent 6 step trap drive?

    Depending on natural BEMF shape, or THD if you will, you may find more efficiency in a sinusoidal drive. While not freely available in the RC market, a flexible drive system that can go from sinusoidal, to SVM to trap is fantastically handy! (And common in industrial apps. TI instaSpin is a great place to start).

    Your balancing techniques and design techniques I 100% agree with. Bearing support and mechanical structure is also great. Those large outrunners are very hard to spin true without a front bearing.

    It will be fun to see what flight test comes up with. I fully believe the 80%+ efficiency #’s and expect that you’ll be able to gain a couple % ontop via controller drive tuning.

    Keep it up! Great project!

  2. Oh, something else. A great sanity check is an Io measurement. Or unloaded current draw at a given voltage. So spin the system up to Max rpm at a given voltage and measure RMS current. Again I feel a scope is crucial to capture the higher order harmonic components that may exist in these systems.
    The Io measurement will tell you the fixed losses involved to spin the motor for a given rpm. – 100% duty cycle of the controller is important to capture this figure.
    Adjust input voltage to gather Io vs Rpm data.

    Also, a scope will show any driver/controller distorion that may arise at high Rpm high pole count systems – commutation rate limits.

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