Protean 'Inside-Out' Wheel Motor Design: A Company To Watch?

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Starting a company to build electric cars is tough, as Tesla, Fisker, and others have found out.

Building electric motors is tough, too. It's tougher yet if you intend to turn the traditional design inside out, and build big, powerful, slim wheel motors to be used in large sedans, full-size pickup trucks, and other heavy vehicles.

But Protean Electric is doing just that, and today the company announced it has received $84 million in venture funding from GSR Ventures and the New Times Group, a Chinese industrial conglomerate.

Protean's original venture investor, Oak Investment Partners, is also participating in the new round.

590 lb-ft of torque

Protean's wheel motors weigh 68 pounds apiece, and each one puts out 81 kilowatts (110 hp) and a whopping 590 lb-ft of torque.

This makes them particularly well adapted to both heavy load-carrying vehicles and high-performance cars, those weighing 4,000 to 7,500 pounds.

Those vehicles will be the hardest ones to make efficient enough to meet upcoming fuel-economy standards, and Protean sees a big market opening there.

Its motor is designed to fit inside wheels of 18 to 24 inches in diameter, and is said to allow up to 85 percent of the kinetic energy to be recaptured under regenerative braking.

It also integrates a traditional friction disk brake as well.

Protean in-wheel motor - exploded diagram

Protean in-wheel motor - exploded diagram

Enlarge Photo

Depending on the size of the battery pack, Protean says its motors can increase fuel efficiency up to 30 percent when an electric powertrain is added to a conventionally-driven vehicle.

Multiple small motors, inside out

But Protean's "secret sauce" is to turn the electric motor inside out and partition it into a series of sub-motors, arranged in a circle, each with its own power electronics.

The stator is on the inside, mounted to the vehicle's suspension and the rear face of the wheel hub, along with the coils, power electronics, and heat sinks.

Individually wound copper coils are mounted to the heat sink on the stator, each one with its own micro inverter.

The rotor is on the outside, fastened to the wheel and the wheel bearing, resembling nothing so much as an old-fashioned brake drum (albeit depicted in bright green in the diagrams and on some prototypes).

Road shocks are carried through the wheel into the wheel hub and absorbed by the suspension, rather than by the wheel motor.

Protean Electric converted Ford F-150 pickup truck, Detroit, October 2010

Protean Electric converted Ford F-150 pickup truck, Detroit, October 2010

Enlarge Photo

Electric F-150

We first encountered Protean at an October 2010 electric-car conference, where their bright green Ford F-150 full-size pickup truck seemed better suited to promoting an energy drink than demonstrating innovative electric motor technology.

But the F-150 was running solely on plug-in power, and we got a few loops around the same drive course where we'd previously driven "Amp'd Equinox" electric crossover conversion from AMP Electric Vehicles.

The big truck was relatively smooth, for a prototype development vehicle, and somehow the smooth silence of electric drive is eerier when you're in a gigantic pickup truck usually powered by a large V-8 engine that struggles to reach 18 or 20 mpg.

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Comments (17)
  1. Sounds good but, for 2 wheel drive you need two motors and four to get all wheel drive. You need double the amount of motors to do the same as one or two motors mounted in the body. I don't know, I can see what the upsides are but needing two to four motors and the suspension issue I'm just not sure about them. And look at the interior volume in Tesla's Model S, how much more room do we really need.

  2. Comment disabled by moderators.

  3. Oh I have, I even watched the live webcast premiere. The interior volume is incredible and the Model X achieves all wheel drive with two motors whereas a car equipt with hub motors would need four motors. Ferdinand Porsche tried wheel motors back in the late 1890's on the worlds first hybrids or mixed wagons as they were called, you should look them up it's very interesting to read.

  4. The last I heard, these motors, originally called PML Flightlinks, an English company, cost a small fortune ($25,000). Obviously that's changed and hopefully the problems that inwheel motors have had in the past (they fall apart because of their harsh environment). While the concept has its good points, it seems more a solution searching for a problem. The motor in the Model S (and the accompanying diff and axle) could hardly intrude less on the interior space. And we also potentially face the problem of having to synchronize the power to each "axle" wheel when turning. Price and durability while likely determine all, although their main opportunity would seem to be in hybrids.

  5. The hook for in-wheel or hub motors is direct drive and a very low loss of efficiency due to no transmission. Since the vehicle could better use stored electricity it could use a smaller battery and could better deal with the unsprung to sprung weight because of it. Not having a conventional powertrain would free up designers to get 50-50 weight distribution and better than ever crash protection as well.

  6. @Kent, "they fall apart because of their harsh environment". I was actually thinking about this same thing when I first read the article. My area recently was hit by a tropical storm, during the storm my street was flooded with rain and saltwater. The street was still drivable but you had to go slow. But after reading this I started to realize that wheel-hub motors would be partially or completely submerged in severe weather situations. With some caution you can keep water away from the body of the car, but your wheels are going to go through the water no matter what. If I had driven through the water with wheel-hub motors I would have exposed them to saltwater.

  7. No problem, If its like the ...... you just flood it with water. The harsh environment are bumps and potholes. Did anyone ask about changing a tire? Do you need a crain to lift it?

  8. Yah I guess the added mass in the wheel would make potholes a bigger problem. But I don't think changing the tire would be a problem, the wheel is mounted in the same way wheels are normally. Its a normal alloy wheel bolted to the hub. Brake services might be a little harder.

  9. CDspeed, while I see several other quality/performance concerns that will still need to be resolved, water entry into the motor is a relatively easy one to fix with a completely sealed motor. Many motors are already completely sealed and I work for a different motor supplier that sells transmission motors that are actually designed to be submerged in transmission oil for cooling purposes. Not just my company, either, this is pretty common.

    I still think Protean has major hurdles left, but it is an interesting area for development and it would be nice to see this get done for some of the reasons Jim Royston above has noted very well.

  10. Thanks for the helpful info robok2.

  11. Very cool. I was particularly impressed by the inverters being integrated in to the motors.

    As for it being "inside out", well all disk drive motors are built this way, so it is not inside out for me.

  12. These in-wheel motors pop up on the radar periodically, but most players that seem to initially plan to use them end up later deciding against it. Lightning GT comes to mind. I only see them being advantageous in certain specialized applications, like in Nissan's Pivo where the wheels rotate to an extreme angle.

    Looking at this Protean wheel motor, I see many disadvantages and not many advantages.

    Increased unsprung weight.
    Lack of water cooling means continuous power is limited.
    No gearing to provide mechanical advantage.
    Top speed likely limited.
    Motors and integrated drive electronics exposed to harsh environment.

    That said, I wish them success. Depending on price, they might be an easier solution for the conversion market.

  13. Sorry, I take back what I said about continuous power. Looks like they are using liquid cooling.

    Given that they're committed to the in-wheel motor concept, this looks well designed, at least from what is presented on their website.

  14. I have an electric scooter with a wheel motor and its great,completely silent and only one moving part,the wheel.
    We will see this technology in wide use in the years to come it goes hand in hand with electric powered cars.

  15. The implications for fully independent control of 4 wheels speeds (i.e. ESP without braking) are amazing. In the off road 4x4 world this will eventually be capable of tackling terrain that only tracked vehicles can today.

  16. I "get it": There's a separate demountable rim, saving wt in tire changes; it looks quite accessible to replace, saving labor cost if motor's damaged. Wouldn’t mfg. cost less than ICE cars, if scale economies are eventually achieved? Other mfg. cost advantages: no assembly position for rear universal joints, or a differential.

  17. Operationally, each wheel could always offer some effort, no matter what wheel has more traction; where it’s slippery no wheel just slips and spins, leaving the rest idle.
    Today’s mechanical "all"-wheel-drive with mechanical differentials, as in Prius, approximates that, w/ alternate partial braking, from side to side, of a left then right wheel, seeking to encourage the others to keep applying some effort. Lacking such braking friction to overcome in those situations though, wheel motors’ mechanical efficiency would be greater than a body motor’s.
    Giving them high-profile tires should usually keep them above water, but,.... Body mountings may more effectively allow sealing out water.

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