DeepDrive’s novel dual-rotor radial-flux motor may be just the solution to range anxiety we’ve been waiting for
If there’s one thing the last five years of testing battery-powered vehicles has taught me, it’s that, contrary to much of the marketing that surrounds electric vehicles, there’s really not much difference in efficiency between different brands of electric motors. Oh, to be sure, electric motors, in general, are more efficient than the internal-combustion engines they seek to supplant. Phenomenally so, in fact. And, the range of EVs does indeed vary greatly according to battery size.
But, unlike the bad old days of pistons and spark plugs, there’s really not much difference in efficiency between the types — or brands — of electric motors driving the wheels.
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I won’t reminisce about the good old days of internal-combustion — mainly because the boredom of driving a cruise-controlled speed down the same boring piece of highway over and over again is not at all relieved by what’s under the hood. But the one thing that really stands out is how much more of a difference there was in the fuel efficiency of different types of ICE. Turbocharged fours could be at times a little more fuel-efficient than V6s. Atkinson- or Miller- cycled fours and small sixes were more efficient still, and, no surprise — especially to a Volkswagen TDI owner — a diesel would wipe the floor with anything fuelled with gasoline.
And one more difference stood out: the faster you went, the greater the difference between types of ICEs. In one memorable test, a 2.0-litre EcoBoost four (powering a Ford Fusion, if I remember correctly) and a TDI’d Volkswagen (a Passat, if memory serves) had roughly the same highway fuel economy at 80 kilometres an hour, but by the time we reached 120 kilometres an hour, the gas-powered Ford was consuming 50% more dino-juice than the oil-burning Veedub. What I’m trying to say — in an admittedly long-winded reminisce — is that there were tangible, often very significant differences in fuel economy depending on what was powering your pistons.
Not so much with electric motors. Indeed, if my experience bears any truth, once you factor in size, shape, and battery capacity, there really isn’t all that much difference in range and efficiency between various electric powertrains. Indeed, when you plot a graph of the 20 or so vehicles I have subjected to Range Finder testing, they make a surprisingly straight curve that depends almost entirely on their size and aerodynamic slipperiness. In other words, two similarly-sized and -shaped EVs, regardless of brand, are much more alike in energy efficiency than ICE-powered vehicles, the difference mostly in the pen of the marketer.
And thanks to there now being two rotors, DeepDrive says the new design is 30% more powerful than an equivalent single-rotor machine, yet still compact enough to be used as a hub motor. (It can, also, says DeepDrive, be scaled as a single motor powering the entire vehicle.)
Ender’s DeepDrive has both, and what seems to make the DeepDrive motor so efficient — and remember, this is coming from an engineer who switched his major from electrical to mechanical because of third-year electromagnetics — is that it seems to combine the energy density of a radial motor with the twin rotors common to axial-flux versions. As well, the larger diameter of the dual-rotor design increases the torque — “quadratically,” says Ender — resulting in as much as 1,770 pound-feet.
One of DeepDrive’s big selling points is the motors’ relatively light weight, an important criteria when the motor is the wheel hub. Heavier hubs mean more unsprung weight, a common bug-a-boo of hub motors that hurts suspension performance and ride.
Crowning the achievement — if, of course, all this promise proves true — is Ender’s claim that, because his twin-rotor design uses less electrical steel and rare-earth minerals, it is as much as 50% cheaper than comparable electric motors.
Which brings us ’round to perhaps the most impressive achievement this new electric motor may bring: if the boast of 20% more efficiency and cheaper construction proves true, Ender’s DeepDrive could prove a decidedly cheaper way to improve range than building 20% bigger batteries. Price parity with ICEs — still but a twinkle in electrical engineers’ eyes — might yet be a reality.
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