Build-its-inprogress.blogspot.com Website Review

heard about them several years ago, and finally picked up one of the motors to take apart. Here's the weed-wacker.  I just got the head of the tool- they make a base called the drive unit, which holds the battery and The motor's right at the end, direct driving the spool of wire: Removed from the stick.  Three board-mount faston terminals for phase power, and another connector for hall sensors. The motor was a huge pain to take apart, as it is pretty much entirely held together with retaining compound.  With a hammer and some The shaft and front bearing were pushed out of the other half of the housing with a gear puller.  There's a ring of thermal pad on one It's a dual-rotor design, with the PCB stator sandwiched between the two halves of the rotor.  The rotor is held together by even more To pull off half of the rotor, I gripped it in a small lathe chuck and used  a gear puller to pull it off the shaft: First a closer look at the stator.  The board had at least 4 layers, and probably has 4 oz copper - it's very dense feeling.  - Each phase has 4 4-turn coils, and the 3 phases are overlapped.   This is a full-pitch winding. - This winding pattern results in a large area of end-turn, so the actual active area of the stator is unfortunately small - less than half the area of the PCB actually produces torque. - The traces neck down and become thinner within the active area.  Presumably this is to reduce eddy current losses from the magnets swinging over the traces.  - The hall sensors are through-hole halls, surface mounted sideways into cutouts in the PCB, so they add almost no additional thickness. - The empty space around the edges of the board are filled with radial st*ips of copper.  I'm not really sure why.  Maybe for thermal reasons?  The edge of the board is heatsinked to the aluminum housing through a ring of thermal pad. The two rotors have single-piece magnets magnetized with 4 pole-pairs: One of the reasons it's all held together with retaining compound is that the bearing bores in the castings aren't even post-machined.