Hacker News Reader

Comment by throwawaycanada | Hacker News Reader

Electric motors are already well over 90% efficient. I don't see what they could do to improve this. Maybe weight/power ratio? Even then, Tesla pretty much nailed it with his three phase "squirrel cage" motor. That's why even today that is what a Tesla car uses and it's what quadricopters use.

View on HN

If you go distillate the actual claims from the fluff, the article is saying it has a larger torque to weight, smoother operation at low speeds, and larger efficiency at very high speeds.

And well, three is much to improve on the last two, so I'm willing to believe they got something for those, while I do expect the first claim to get completely lost once they actually produce the motor.

Cogging (non-smooth operation at low speeds) is pretty much a solved problem already. You simply program the cogging torques into the controller as a function of shaft angle, and tell it to compensate.

Final result: motor that behaves as if it had no cogging.

In the Fully Charged episode[1] linked in a recent thread here about some guy in Amsterdam making electric cars and boats, the guy mentions that the motors have brushes. I was mildly surprised as I just assumed they'd be brushless DC motors.

Are they just efficient enough that the cost/simplicity outweighs going brusless? Or are there other advantages to using brushed motors for electric vehicles?

[1]: https://www.youtube.com/watch?v=7zz3H0pSQ4Q

Brushed motors are readily available in the appropriate sizes in small quantities and used. Brushless motors not so much yet. Then you also have to use the OEM inverter which will take some reverse engineering or bring your own inverter. People are doing this with car conversions, but it's early days and anyone can wire up a brushed motor.

Perhaps it’s simpler and more efficient speed control circuitry. For a DC motor you just need to step down the DC voltage from the batteries. For a brushless motor you basically need a variable frequency inverter that’s necessarily going to be more complex and possibly less efficient.

Yep, mainly. You still need basically the same circuitry, but 3x simpler- you only need one phase instead of three. However you still need the same PWM-type controller to do it. The single phase can operate at several times lower speed though, which makes the output devices and gate drive much cheaper.

Reply on news.ycombinator.com