Some ideas are real head-scratchers from a design standpoint: Why in the world would you do it that way? For many of us, answering that question often requires a teardown, which is what [Ben Katz] did when this PCB motor-powered weed whacker came across his bench. The results are instructive on what it takes to succeed in the marketplace, or in this case, how to fail.
The unit in question comes from an outfit called CORE Outdoor Power. The line trimmer was powered by a big lithium-ion battery pack, but [Ben] concentrated on the unique motor for his teardown. After a problematic entry into the very sturdy case at the far end of the trimmer’s shaft, he found what looks like a souped-up version of [Carl Bugeja]’s PCB brushless motors. The rotors, each with eight large magnets embedded, are sandwiched on either side of a very thick four-layer PCB with intricately etched heavy copper traces. The PCB forms the stator, with four flat coils. The designer pulled a neat trick with the Hall-effect sensors needed for feedback; rather than go with surface-mount sensors, which would add to the thickness of the board, they used through-hole packages soldered to surface pads, with the body of the sensor nestled in a hole in the board. The whole design is very innovative, but sadly, [Ben]’s analysis shows that it has poor performance for its size and weight.
Google around a bit and you’ll see that CORE was purchased some years back by MTD, a big player in the internal combustion engine outdoor power market. They don’t appear to be a going concern anymore, and it looks as though [Ben] has discovered why.
[Jozef] tipped us off to this one. Thanks!
3.5″ floppy drives have used traces on PCB for motor coils. Nothing really new.
Really? I only ever saw the PCB be used as a carrier for flatwound coils. Never saw actual traces being used in place of coils.
People were designing PCB based motors since the early 2000s at the latest. Here is a thread in 2011 showcasing some work: https://endless-sphere.com/forums/viewtopic.php?t=21127&start=225
https://imgur.com/2de33cv
“Innovative Designs Sometimes Fail” so what failed?
All that was said was “The whole design is very innovative, but sadly, [Ben]’s analysis shows that it has poor performance for its size and weight.” What are we supposed to take Ben’s word for it.
+1
Read the source material, it got some details, but newer draws any conclusion/verdict that its a “fail”. Also Ben probably compares to high end brushless motors, thats what he usually deals with. I definatley trust him when it comes to motor analysis, he have done some very impressive work.
“- 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 strips 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 copper on the edges could be for ease of manufacturing. PCBs consist of glued together layers of copper clad substrate. Areas without copper need to be filled with glue in order to make up the overall board thickness. This generally works out OK for basic circuit boards, but with heavy (thick) copper, you need a lot of glue to fill in areas without copper. On the edge of a board in particular, you need enough copper to prevent undesired warping or voids from forming.
The motor was most likely optimized for low production cost rather then high efficiency. Also i see no evidence that this motor design had anything to do with the fate of the company, if they got bought up, many would consider it a sucess?
” if they got bought up, many would consider it a sucess”
And that is a great part of what is wrong with the world.
Instead of stable, long-term companies providing careers we have sociopaths looking to make a buck by killing the next golden goose.
Except.. this one might not have been so golden anyway.
Also if you do google around you will find:
“MTD Products says it has recently acquired two companies that will help keep it on the cutting edge of innovation,……”
“MTD recently acquired CORE Outdoor Power, a Montana-based company that powers lawn equipment with gasless motor technology that produces higher torque and increased efficiencies.”
So the only thing that failed was this article?
Um, no. I looked around a bit for any trace of CORE Outdoor Power, and not only could I not find the company as a going concern – like I said, it was bought my MTD a few years ago – I couldn’t find the brand anywhere in MTD’s offerings, nor any trace of the technology in any of their products. Granted, I didn’t do an exhaustive search, but it sure looks like the company didn’t succeed in the marketplace.
They may have succeeded in coming up with an innovative design, but it just smacks of innovation for innovation’s sake. I’m going to stand by my assessment of this as a marketplace failure.
https://www.cubcadet.com/equipment/cubcadet/string-trimmer-cct400
Looks a bit familiar, not saying that it has the same motor, but CORE is mentioned in the product detail, and the top casing looks very familiar.
Or, competition bought out off the market. They probably have patents for this, so now the new company has the patents and nobody else can make these things. This is what happens to innovative designs: the inventors have a good idea, but it takes years to monetize it and turn up a profit. Things get boring, business is risky, and everybody gets bored of making weedwhackers – they’re hackers, they want to do innovating instead of bean counting.
So someone offers them a 10 million dollar handshake and buries the IP for 20 years, or at least long enough until the market is saturated with their existing products and demand drops, at which point it’s time to whip out this “new innovation” and replace them.
Also, why use thin wires: limit stall current with a measured amount of distributed resistance.
I don’t understand why someone took this and went “a perfect application for this is a weed whacker” but I would actually like to see some performance numbers
I’m not expecting this to be as powerful as an iron core motor with proper windings but I don’t see how this was a “fail” and would like to see it composed to an equally weighted outdoor use motor
In this case I guess the whack-to-weight ratio is pretty nice, considering the inertia of the rotating disks I imagine it would be pretty efficient as a whacker in that range would only be able to whack grass and herbs anyway
If I compare it to an electric whacker of the same range with full-blown iron cored brushed motor, I can tell you which one makes your arms sad at the end of the day…
I can also imagine the thinner traces are for less back-emf current when hitting rocks or wood
I purchased the troy bilt TB4200 40v (rather 36V) trimmer in 2017, lowes had several units discounted deeply i believe regular price was around $250 per which came w/ 40v li-ion batt. charger & trimmer discounted down to $100 per unit. These trimmers were new not returns or reman. Thought there must have been some issues and lowes is discontinuing the Core line however, $100 per unit with 5 year limited warranty sold me I purchased 2 trimmers and the TB core 40v hedger. The core powered trimmer has been phenomenal i have debated with my pro landscape buddies about the power resembling gas trimmers ive let these fellas zip arround the field with 1 they were amazed as well. When the trimmer goes from common grass to thicket the core motor auto adjusts torque without pressing the boost button when boost engages this trimmer shows the power.
Ive concluded Core didnt cut corners with power plant nor li-ion battery they did it with plastic housing battery port at the end gives balance for this huge battery but the plastic screw bosses securing case to shaft have broken twice from tapping trim line housing releasing more by tapping the housing at opposite end paired w/ the weight of 40v li-ion batt. shows exactly where Core shaved cost. The 40v hedger is opposite not impressed, i only purchased hedger for the 40v battery & charger this hedger was deeply discounted down to $100 as well new w/ warranty. I am now repurposing battery & charger for an ebike project ive been working on i can still us my trimmer once housing is repaired again
I’m not normally so negative, but this article is full of unsubstantiated click-bait and is irresponsible. Somehow, from Ben’s technical assessment (which may well be correct) that “Over all it’s not a particularly high performance motor for it’s size or weight. There’s a lot of dead space, and a very heavy, high-inertia rotor,” the author has made the crazy leap that this led to the company’s demise. As was already pointed out, Ben and the manufacturer may have different criteria for evaluating the performance of the motor. Maybe cheap and high inertia is a perfect impedance match for this application. But regardless, companies fail for a million reasons beyond “their motor wasn’t high performance.” And there is no evidence that this company even failed. It was evidently acquired, and maybe its IP was wrapped into something else. Or maybe there were other business reasons why the parent company took it off the market. Anyways this reads like a fifth grade essay, trying to make a point and still in search of any facts. Or am I missing something?
Well said.
At the very least, the author should have included some of the key points as to why it was such a failure…
+1
I was reading some reviews and I’ve got a bit of speculation, but I understand that most of the reviews were not written by technically minded people and such this is to be taken with a grain of salt: The general consensus seems to be mostly battery failure issues. I’ve seen a couple of reviews referring to motor failure and with that some mentioned a lack of availability for replacement parts.
I’m thinking, grab the motor and see if it will be a good generator for a small wind turbine say for camping/bushwalking.
High speed and high inertia are what you want in a string trimmer. The inertia keeps it from bogging down as the filament slashes through the grass and its the speed that makes it able to cut. This application doesn’t need to be capable of super fast RPM changes nor does it need a wide power band.
That makes sense.
The motor is coreless for the speed. Iron core motors have high flux density, which is great for torque and good power density, but makes high frequency commutation inefficient. This design is obviously aimed for better cost efficiency through simplicity, and low manufacturing cost. The only downside is the bad power density, but that doesn’t seem to be important in this application.
Does this inefficient high-frequency commutation really matter at speeds in the 8,000 to 10,000 RPM range in which those weed whackers work? Typical RC-Motors in the 500W-Range have efficiencies greater than 80%.
That is depending on the configuration of the motor, the materials used, etc. Your BLDC may be 90% efficient at medium speed, but put out excessive heat at high.
Maybe they aimed for higher than usual speeds with this product, idk. I didn’t find the datasheet for the trimmer.
Or the PCB coils were used mainly for low cost rather than high speed. Seems cheaper.
I own one of these and i must say, the things a BEAST!
I agree with Chris S.
I’ve owned one for a long time and still going strong.
I think the design was/is better & purchased to remove it from the market just for that reason.
I never bought a second battery and now can’t get one. Modding up an Lipo. Do you think 6S would be ok? Or stick with 5S like the original Battery?