Back to school

Posted on September 17, 2008

4


I realized it is almost impossible for a family man with a full-time job to pull this project together in useful time, especially when trying to develop a crucial and complex component such as the hub motor.

So I’m changing my life in order to accommodate the project. 🙂

I’ve enrolled in a Master of Science degree in Electrotechnical Engineering with the goal of getting some dedicated time for the project, as well as the added benefits of having access to electro and mechanical workshops and rubbing elbows with the people who actually know something about electric motors. 😉

To start off my education, I’ve bought a very nice book on the subject of permanent magnet motors. I had been scared off by it’s price (165 USD or 163 EUR – I guess the conversion rates don’t apply when it comes to foreign books in Europe), but after John Bass told me it was good, I went ahead and ordered it.

I’ve only had time to read half a chapter, but I’ve already found the answer to a long-standing question my web readings left me with: what the hell is the difference between a “Brushless DC” motor (BLDC) and a “Permanent Magnet Synchronous” AC motor (PMSM)? The answer, just like I suspected from my readings, is: almost none. The motor design itself does not have to have any fundamental differences. The differences reside almost entirely in the electronics that control the motor. But if you were fighting for extremely high efficiency, you might introduce some magnetic optimization tricks to take advantage of the higher harmonics content of the BLDC technique. So, ultimately, you can control the very same motor with BLDC (“six-step” or “trapezoidal” waves) or PMSM (“sine” waves) electronics – you’ll just get different efficiencies, maximum torque, and torque ripple. It’s a good reading, this book. Well balanced between the theoretical maths and the textual and graphic conceptual introduction.

Having said this, my next goal is to go back to work on my motor simulation scripts and make them a lot more realistic by introducing the missing constraints (such as back-EMF and AC/harmonics). Only after that I will have enough realistic info to decide on an actual prototype design. Oh, if only I had tons of money, the damn things would be built already… what the heck, I’ll just have more geek fun then. 8)

Speaking of scripts, if you would like to experiment with them and change them to suit your needs, feel free to do so – that’s why they are open source. 🙂 My main focus is the radial flux design and the framework itself, which means my axial flux design is pretty much abandoned and in need of a maintainer. There is so much interest in axial flux these days, it would be nice if some one else picked it up and developed it. It would feel very good to develop a real extensible and flexible framework for motor simulation, and these two directions feel just right to start with. So if you’re up to the challenge, step up. I won’t bite.  😉

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