[Moved from Fisker Surf Thread] In-wheel Motor Discussion Thread

RE: Fisker Surf reservations

kabalah70 said:

Doug,
"You really have to appreciate what's possible with a clean, purpose-built motor/inverter package."
You mean like the Protean Electric in-wheel motor package?
http://www.proteanelectric.com/

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Heh... no.

There has been talk about wheel motors for years and I have yet to see anyone do any more than a conversion prototype with them (like the Mini QED, if you remember that). And even then you'll hardly see them do much more than creep along in a straight line.

Lightning originally planned to use PML Flightlink's wheel motors for the Lightning GT, but eventually abandoned them for a more conventional setup. PML Flightlink went bankrupt and then restructured to form Protean (to focus on automotive applications) and another company (I forget the name) to focus on other applications for thin motor technology that were more practical/profitable (like small drive motors and joysticks). Protean, however, is still trying to get some traction (so to speak), but it's not really looking that promising.


So what's wrong with wheel motors? Well one issue is the unsprung weight which gives unfavorable driving dynamics. Another is that you can typically get more power per unit mass by simply designing a larger single motor rather than multiple smaller motors.

Then there are the normal regulatory concerns. This was from back in 2006 when the Tesla Roadster was first unveiled:
http://www.worldchanging.com/archives/005118.html

I also asked whether they thought about using in-wheel motors, since putting a small motor in every wheel instead of having one big motor with a drivetrain connecting it to the four wheels can greatly reduce mechanical complexity and weight, as well as improving reliability. (This is one thing EV's make possible which simply can't be done feasibly with combustion engines.) Interestingly, they did consider it, but [Tesla CTO JB Staubel] said it would have made safety certification extremely difficult. It's perfectly safe, but the certification regulations are written assuming you have one motor and a drivetrain, so there are some certifications (such as the one for Anti-Lock Braking) you can't pass in a car with no drivetrain. These rules would need to be re-written to allow vehicles with in-wheel motors to be certified, which is obviously not going to happen without significant money and time spent lobbying--not a fight a small startup company should take on if it can avoid it.

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So basically no serious manufacturer is considering wheel motors for the near future. I suppose they could help the Surf get more trunk space, but it would be at the expense of performance.

I say what Tesla is doing with their liquid cooled motor and inverter (mated to a single speed diff/transaxel) is the best I've seen so far.

RE: Fisker Surf reservations

kabalah70 said:

Doug,
"You really have to appreciate what's possible with a clean, purpose-built motor/inverter package."
You mean like the Protean Electric in-wheel motor package?
http://www.proteanelectric.com/

Click to expand...

That is pretty cool... where the future is headed!!!

RE: Fisker Surf reservations

doug said:

So what's wrong with wheel motors? Well one issue is the unsprung weight which gives unfavorable driving dynamics. Another is that you can typically get more power per unit mass by simply designing a larger single motor rather than multiple smaller motors.

Then there are the normal regulatory concerns.

so there are some certifications (such as the one for Anti-Lock Braking) you can't pass in a car with no drivetrain. These rules would need to be re-written to allow vehicles with in-wheel motors to be certified, which is obviously not going to happen without significant money and time spent lobbying--not a fight a small startup company should take on if it can avoid it.

So basically no serious manufacturer is considering wheel motors for the near future. I suppose they could help the Surf get more trunk space, but it would be at the expense of performance.

Click to expand...

This is not my area of expertise and I have no reason to disagree with you. I just want to point out that the there are very good technical reasons against using Karma's pure electric drive train also, but Fisker has made it work and there is equal possibility that the issues with the in-hub direct drive systems can also be resolved to make that an option some day. After all, this type of drive system acquitted itself in the harshest possible driving environment in history over 40 years ago:

RE: Fisker Surf reservations

I mentioned unsprung weight above, but here's a so-so Wikipedia article that may help: http://en.wikipedia.org/wiki/Unsprung_mass

This wheel motor discussion is a bit off topic and probably should be moved by a moderator. I think wheel motors are fine for certain applications. But on a performance vehicle, you probably shouldn't take them seriously.

The real point I was trying to make in this thread was that I hope Fisker can rework the packaging of their drivetrain, particularly the inverters so that the Surf can have some trunk space near to what one would expect for that type of car. The Tesla Model S drivetrain shows what is possible.