The following does NOT contain paid promotional content. I just find the topic interesting.
Motors, motors everywhere
A Texas startup, Linear Labs, has made rounds on the usual automotive and technology websites over the past weeks with claims to a new Electric Vehicle (EV) targeted motor design. I’m normally skeptical of a startup’s claims about a rosy future, given the PR department’s obvious motivations. But this one is interesting enough to have picked up $4.5 million in seed funding despite using verbal gimcrackery in its promo materials (“Electric Turbine” wut?), so let’s take it for a quick spin.
Linear’s claim to fame is a novel take on the brushless multi-phase motor. That may not sound like any usual English spoken at the Tech Report, so here is the connection: there is a long-running TR forum thread right now which began life as a debate on leasing or buying an EV. It has since evolved into a catch-all discussion for electric vehicles, with Tesla Motors appearing frequently. Meanwhile the latest EV designs, including the Tesla Model 3, are using brushless motor technologies.
Ergo, any commercially viable advances in brushless motor design will demonstrate the unique property of drawing stacked cash directly out of investors’ pockets, and Linear wants a piece of it. Here is their lead video:
There’s also a bit more technical discussion on the “Why our motor” page of their website.
We won’t go deep into electric motor design here, partly because I don’t have the chops. Summarily, an electric motor has two key parts: a rotor, and a stator. One turns, the other does not. To remember which is which, just think “ROTATE-tor” and STAY-tor”. In a brushed design, there are electromagnet coils in the rotor assembly, requiring some means to transfer electricity from not-moving power supply terminals to always-moving contacts on the rotor shaft. These are the “brushes” we speak of in motor circles.
In a brushless design, all the electromagnet bits are located on the fixed stator, and the rotor carries permanent magnets. Brushless motor design has become more practical since the development of powerful and lightweight rare-earth magnets in the 1970s and 1980s. Brushless motors live everywhere these days. Did you, our loyal reader, buy one of those fancy new washing machines that advertised “direct drive” in the promotional brochure? Then you probably have a large brushless motor assembly sitting in your laundry room. The guts of it might look like this:
One possible layout of a brushless appliance motor’s stator assembly.
(Image Credit: Samsung)
Here’s another common form that’s probably spinning in at least one of your computers or set-top electronic components right now:
Typical computer fan, with clear-plastic hub showing four stator poles.
That one’s trickier to spot because we expect our motors to have a fixed stator in the outside shell while the rotor turns inside. In a computer fan, the fixed stator and its electric bits are located inside the rotor’s magnet assembly, which is carried around on the fan hub. If that gets you wound up, I found a two-part presentation on YouTube that covers brushless motor basics with animated visuals and only minimal jargon: Part 1 here, and Part 2 here. The YT channel host doesn’t seem to be the original content owner, but the original owner’s domain (DIY Inventor) appears to be inactive or hijacked.
And what of Linear Labs?
In our two previous examples, the stator windings are designed to target a rotor that either lives inside the stator (the Samsung washing machine motor) or outside the stator (the computer fan), but not both at once.
What Linear Labs claims to have spun out is a toroidal-wound stator that produces a uniform magnetic pole on each segment. Purportedly, that allows permanent magnets to be mounted on a rotor assembly that turns both inside and outside of the stator windings. Scroll down to the “Electronic Transmission” section on the “Why our motor” page at Linear’s site and they show an animation. The arrangement requires a more complex rotor but produces much higher torque, permitting the motor to operate with both high torque and high rotational speeds. Previous designs would be optimized more for one or the other. The Linear Labs design also optimizes the magnetic field at a given rotational speed (“field weakening”) by actively mis-aligning end-cap magnet arrays on either end of the rotor as required, which supposedly produces fewer losses compared to how previous designs achieved that effect.
One more trick: According to reporting by CNet, the efficiency gains from the Linear Labs design are high enough that rare-earth magnets are not required. It can make do with cheaper iron-based materials, which are not subject to the higher average cost and wide price fluctuations of rare-earth minerals.
The result is claimed to be a smaller, lighter, cheaper, and more efficient brushless motor for a given amount of electrical input. In theory, that would permit EV designs that are either faster and have longer range than current designs at the same weight or have the same performance and range as current designs but with less weight and cost. We would prefer a bit more technical data, but the company’s current website is obviously targeting investors more than engineers, so it is what it is. For a bit more history on the company and their proof-of-concept demos, here’s another YT link. Legal-eyed types might find more information from reading Linear’s recent patent history. One of which seems to include detailed technical drawings of the new motor design.
Currently, Tesla’s Model 3 contains some of the best-regarded brushless motor technology in the EV industry, so if Linear’s design has merit, we would expect one of the legacy manufacturers to snap up the IP in order to gain a much-needed competitive advantage. Ford recently did something like that with Rivian, so there’s certainly precedent.
I can’t speak to Linear Lab’s technical claims. What I do expect is that the toroidal winding of the stator may be more labor intensive that conventional designs, something that has bedeviled the manufacture of toroidal-core transformers for years. That could have implications on mass production. Then again, EV makers are doing amazing things with automated manufacturing these days, so who knows? If anyone out there has experience with motors or motor drives, please do speak up in the comments section, and help us understand this better.