How to Succeed in Motor Control: Olaus Magnus, Donald Rumsfeld, and YouTube

Jason SachsDecember 12, 2016

Almost four years ago, I had this insight — we were doing it wrong! Most of the application notes on motor control were about the core algorithms: various six-step or field-oriented control methods, with Park and Clarke transforms, sensorless estimators, and whatnot. It was kind of like a driving school would be, if they taught you how the accelerator and brake pedal worked, and how the four-stroke Otto cycle works in internal combustion engines, and handed you a written step-by-step procedure for parallel parking… and then they told you, OK, now go drive! A whole bunch of stuff missing. Maybe not the best analogy, but the industry seemed to be really fixating on field-oriented control and estimators. Yes, you have to understand what the d- and q-axes are in FOC, in order to use it well and understand what’s going on, but there are other much more mundane issues, like how to analyze how much voltage you need to run a motor at a certain torque and speed, or how to test an FOC system since you can’t directly measure the d- and q-axis currents. What I wanted to do was teach a class at Microchip’s MASTERs Conference.

I’ll jump ahead — the result is something that was released recently to YouTube:

If you want to know the technical content, watch the video! I won’t be talking much about the technical details here — my policy is to keep the motor control stuff at my day job — but I thought I’d share some of the “behind the scenes” moments.

This article is available in PDF format for easy printing

MASTERs is a “contrived acronym” that stands for Microchip’s Annual Summer Technical Exchange Review; it’s a technical conference that Microchip hosts in north Phoenix in summertime, when it’s really hot and the Sonoran desert is just about the last place you’d want to visit. But there are a lot of classes on everything from touch sensing to USB to switched-mode power supplies and motor control, and hundreds of people descend on this conference each summer to learn and to network and to see the latest offerings in chips and development tools. As I’ve stated in a previous article, I’m an applications engineer at Microchip Technology (standard disclaimer: the statements and opinions herein are solely those of my own, and do not represent those of my employer), and we are encouraged — sometimes requested — to teach classes at MASTERs. It is a lengthy and time-consuming process to prepare a class. You commit to teaching a class by signing up in February. It is a serious commitment, with checkpoints every month or so to develop classes from abstract to draft slides to dry-run rehearsals, and grievous harm may befall you if you miss any of those commitments. Nobody wants to have to tell MASTERs attendees that, “Hey, um… you know that class you signed up for and traveled 5,000 miles to see? We had to cancel it because the guy who was supposed to teach it skipped town and went skiing in Colorado for a week because he didn’t have his slides done in time, and just couldn’t take the stress anymore.”

Anyway, in January 2013 I was all gung-ho to teach a class that coming August — originally titled “How to Succeed in Motor Control Without Really Trying” (H2S for short) — and prepared an outline to discuss with my manager. He said he’d support me if I wanted to teach it, but he cautioned me about the time commitment, and after discussing the other tasks on my plate for the coming months, we agreed to put it off that year.

That summer I don’t remember much of 2013 MASTERs, other than the usual energizing effect it has on me — and I thought ahead to 2014. In November 2013 we had a training session we conducted over a conference call with some of our European Field Application Engineers, and I decided to cover two short (30-45 minute) presentations, one on Zero-Sequence Modulation — which eventually led to the online Zero Sequence Modulation Tutorial — and the other titled “HIC SVNT DRACONES (HERE BE DRAGONS): What to Expect (And Worry About) on Your Next Voyage into the Land of Motor Control”, which was a sampling of some of the topics I’d intended to use in the H2S class, just to test the waters, so to speak. It’s always hard to tell how something is received over a phone call, but the feedback I got was generally positive.

February 2014 came and went; I had a full plate for 2014 so gave up on teaching H2S that summer — our group taught a lab class on FOC — but I taught the same two short presentations at our North American Motor Control FAE seminar, along with an impromptu session about phasors and calculating terminal voltage requirements of permanent magnet synchronous motors, and got a lot of enthusiastic feedback.

2015 MASTERs was again a busy year, and we reworked the 2014 FOC class as a lecture format to keep our workload manageable. Lab classes are generally a pain; they’re right for some topics, but you really have to be careful — all classes have a tight schedule, so when participants get stuck or something doesn’t work in the middle of a lab class, then they miss out.

When January 2016 came around, things were busy as ever, but I talked to my manager and said I would lose my mind if I put H2S off another year, I’d make sure it would happen even if it meant I had to put in some extra hours. So I took some content from the Here Be Dragons presentation and just started working on PowerPoint slides. For the most part it went really smoothly; I know this stuff backwards and forwards, and most of the time I put into it was on getting the content and images to look nice and polished.

The equations are done in MathJax (cut + pasted from screenshots of a web browser into the crippled world of PowerPoint), the diagrams in TikZ for the most part. I’m very particular about the way stuff looks.

The first section and the transition slides draw from the Carta Marina shown on the James Ford Bell Library website — this is a beautiful 1539 map drawn by Olaus Magnus. He was kind of an eccentric guy who tramped all over Scandinavia in the 1520s working for the Catholic Church and studying various aspects of Scandinavian folklore. Just a few years earlier, in 1517, this other guy in Germany named Martin Luther just happened to kick off a little spat against the Pope in Rome. Yes, that Martin Luther. Ninety-five theses nailed on a church door, and all that. Six years later, King Gustav I ascended the throne, and due to a disagreement with the Pope, Sweden broke all ties with Rome and Lutheranism was introduced. Olaus Magnus was exiled and his assets in Sweden seized. He lived the rest of his life outside Scandinavia — in Poland and later in Rome — but had this obsession with Scandinavian folklore, writing a book on the subject and publishing the Carta Marina.

Including these and some of the other images required getting permission from various places. For the most part, everyone I wrote to (James Ford Bell Library, the British Library, Kollmorgen, Sensor Developments, and PEM UK) was very kind and provided me with permission to reproduce their images in my presentation. I had one figure from an IEEE paper; they are really strict when it comes to copyright, and although they streamline the process by letting you purchase reprint rights in an online form, it’s essentially single-use, and there’s no way to purchase the right to use a figure in an unbounded series of presentations; you have to tell them the dates of your presentation and how many people you estimate will attend and so forth. I purchased reprint rights for 2016 MASTERs but couldn’t work out a general agreement, so for the YouTube video I had to substitute an alternate figure on FOC.

The second section, “Field-Oriented Control in Fifteen Minutes” was really tough for me to put together. This is content that is mathematically intense, and I didn’t want to get bogged down too much in equations, but they’re unavoidable. I had professors in college who would spend a whole lecture writing equations on the blackboard to derive some key result in electrodynamics or quantum physics or whatever, and I really hated it, because I don’t think equations by themselves lead to understanding. I did state that a prerequisite for the course was some knowledge of FOC, so I hope that the attendees respected that, and that my course material wasn’t new to them. It was intended as a refresher, so I aimed for a kind of a “drive-by” coverage of each of the equations, and for each one, to really point out the essence of what it meant. I hope it was useful.

The section on “Hazards” derives from experiences I have had over my whole career — some rather painful, where I have been part of teams tackling motor control projects even though we were not fully prepared to do so. At the beginning, I didn’t know enough to be concerned, but over the years I’ve learned to recognized the signs, although I have not often been able to convince project leads that there were real problems lying ahead. It’s really hard to warn people; sometimes they think that just because they understand the fundamental concepts, they should be able to put everything into practice successfully. Unless you can point to specific hazards, it’s hard to get people to accept that creating a motor drive with a digital field-oriented controller is, in fact, a difficult task if you don’t have prior experience working on one.

I have written about one kind of hazard in the context of design margin, where I cite the Nassim Nicholas Taleb book The Black Swan, which explores the probability and psychology of seemingly improbable events — usually negative ones. I considered bringing this up in the context of my motor control class… but this isn’t really the type of event that I would warn against. Black swan events are more like… let’s say you’re working on a product with a motor drive, where the motor drive development is in the critical path to getting the product done on time. You are halfway through the product, and the manufacturer of your DSP controller decides to put it on end-of-life status, forcing you to redesign your hardware around another device, with small but uncertain differences, and one of your team members leaves for a competitor, and another one comes down sick with the shingles for three weeks. You’re late. Very late. Product success at risk. Oops. There’s no way anyone could have anticipated any of those events happening; perhaps you could have put some padding in the schedule for unknown contingencies, but nature abhors a schedule vacuum and it’s hard to justify telling your boss you need several weeks for unknown factors. The type of “unknown” I mention in H2S is Donald Rumsfeld’s “unknown unknowns” quote — in the engineering context, some technical problem was necessary to solve make your motor drive successful, and you might have known to look for it if you had experience from working on motor drives before… but you don’t. I am still somewhat uncomfortable referring to Rumsfeld and his involvement in the US wars in Iraq and Afghanistan, but I wasn’t able to find another alternative that I felt was as memorable.

A few weeks before MASTERs, I got an email message mentioning that our Marketing Communications (Marcom) department was interested in filming some of the classes so they could be offered to a wider audience, and would I like to give a presentation of it for videotaping? I agreed, and one of their staff members named Kurt scheduled a session in a conference room. I had one other colleague show up in the audience (thanks Han!!!) which made it much easier than talking to an empty room. Somehow I managed to deliver my lecture nonstop, without making any major blunders, although at the end, my lower back was killing me.

MASTERs itself went well — crazy busy as usual!— and I had one session teaching H2S that was nearly full (27 people out of a capacity of 30, if I remember correctly), along with two sessions of another class I taught with a colleague. My evaluations were overall positive, although unfortunately as presenters we rarely get detailed feedback.

Toward the end of October, Marcom contacted me and said that Kurt was done editing. I reviewed the video and shortly thereafter it went up on YouTube!

If you watch it and have technical comments, or have certain sections that you really like or dislike, please post on the Microchip forum (not here!) so I or another Microchip staff member can respond in an official capacity.

I hope it helps some of you in your projects; thanks for watching!


© 2016 Jason M. Sachs, all rights reserved.


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