The Trials Of Working With Brushless DC Motors For The First Time.

We’ve all worked with DC motors at some point. Even if you aren’t a big hardware person, you’ve probably at least picked up a motor as a kid and touched a battery to the leads causing it to whir to life. These are usually standard DC motors and not their brushless relatives. Brushless motors require a bit more work since you are manually controlling things that are normally taken care of with the brushes. This article won’t teach you how, rather it will show you the mistakes one person made in his inaugural effort to use them. It is mildly amusing, but the project summary that he’s using them for seems even more interesting.

The job that’s been paying my bills and keeping me away from artsy-fartsy circuits for the past six months involves making a set of these enormous robot doors for a Certain Very Fancy Person’s house. Each door is 13 feet tall, around 7 feet wide, and weighs 1500 pounds. There are 66 of them in said house, and more in the servant quarters(!?!). The circuits on board each door have to handle running an onboard air compressor (which regulates a pneumatic weatherseal) as well as keeping track of temperature to linearize the pressure sensors when the weather gets cold. They also have to charge and maintain sealed lead acid batteries. They have commutated power rails. They have to communicate over said power rails, and do so using an capacitively-coupled data slicer and a proprietary protocol I wrote. This protocol has to be robust enough to bootload the processor over. It’s a proper embedded systems job.


[via Adafruit]

9 thoughts on “The Trials Of Working With Brushless DC Motors For The First Time.

  1. I’m halfway wondering if he’s working on the Star Trek (would be neat if it wasn’t the 2009 version) themed fantasy hotel I read about a few months back. :p

    Although his comment certainly gives me an idea of a cool way to make a whoosh door.

  2. It’s a shame they didn’t have a more appropriate ‘scope to use for the task at hand. For those that don’t know, the Tek 2467 has a microchannel plate behind the phosphor screen. That gives the scope amazing brightness (you can see a single sweep at 10 ns/div in a normally-illuminated lab), but it’s total overkill for something like this (notice the horizontal is set to 1 ms/div). Unfortunately, the MC plate has a limited life: There is a maximum total charge that can pass through any given channel before the amplification of that channel begins to fall. Usually, the readout areas go first, followed by any part of the screen where a constant waveform was allowed to sit for a long time. There’s a built-in timer designed to limit the worst of that kind of damage, but it can be over-ridden with a button the front panel.

    1. that’s a pretty good paraphrasing of what I shouted out loud when I saw the pic – “F*ck me! Check out the scope!” I’d be using my old Avo for a job like that, turning it slowly by hand and probing the Halls. 3 rpm and DC-300millihHertz or so.

      Screw up driving these big-ass motors and bus-bars glow cherry-red and sag, from bitter experience :)

  3. I realize a job that a) lets you work with cool stuff and b) pays money is something to be cherished, but this Very Fancy Person with his 66 1,200 pound automated doors in his house can go to hell.

    In my opinion, if you’re able to afford a house with 66 1,200 pound doors and to wanted to automate them, you should be doing it yourself instead of just paying someone else to do it for you.

    1. They’re actually 1500 pound doors. I thought I’d give you that fact in case it makes a difference to your opinion :)
      It’s probably the US President or someone similar. Or maybe someone even more influential like Rupert Murdoch or Joey Deacon. The “weatherseals” sound more like hermetic sealing for nerve agent attack than keeping fart smells contained.

    2. Chances are the person wanting this can’t do it himself. This is why we have people with specialised skills to do jobs like this and probably why he hired our guy.

      I don’t see how rich he is or how outlandish the desires are have any influence on the job at hand. You quote on a job and get employed, who cares what the person who hired you wants the job doing for. As long as he pays on time and doesn’t fuck with you all is good.

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