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This is very interesting. And it is very good news that companies are finding higher efficiencies in mass produce-able electric motors. It means that electric c

This is very interesting. And it is very good news that companies are finding higher efficiencies in mass produce-able electric motors. It means that electric cars will become more affordable and practical quicker. But I do hope they do not proceed with the in wheel concept. In wheel motors make the ride not only bumpier but more dangerous. This is because the wheel with more un-sprung weight bounces more and tends to lose contact with the road more, which in turn makes the car more likely to spin out of control, miss a turn, etc. Electric cars, being still relatively new, cannot afford to get a reputation for danger.

hinkley 7y ago
Might work out if it’s paired with active suspension. The idea with motors at the wheel seems to be that the moving parts are all concentrated there. No mechanical distribution. Compartmentalization. But that is not incompatible with active suspension systems.
- adrianmonk 7y ago
  What would be the advantage of doing it that way instead of just putting the motor on the car frame and connecting it to the wheel with a CV axle? From what I could dig up, mechanical losses in a CV axle are on the order of 1%. An active suspension requires power, too. And a heavier wheel would presumably require a more power-hungry active suspension than a lighter wheel, so you're not getting something for nothing in terms of efficiency. I guess it is a matter of numbers, though. A CV axle also gives a wheel inertia, as it has mass and moves when the wheel does (partially). If you can make an insanely light motor, maybe you could make it so light that it's actually contributes less inertia than a CV axle would, in which case go ahead.
  - davidgould 7y ago
    The small diameter of the CV axle makes the inertia small compared to the rest of the wheel, tire, brake assembly.
- b0rsuk 7y ago
  Doesn't active suspension need to be powered itself? I skimmed the article, and the main advantage they cite is more efficient energy use. That may be gone if you have to spend extra energy elsewhere.
- agumonkey 7y ago
  maybe motor-wheels are bad for normal cars but maybe it's still a neat devices for simple setups, carts, or whatever rover that doesn't go super fast.
analognoise 7y ago
"Electric cars, being still relatively new, cannot afford to get a reputation for danger." The Lohner-Porsche was a hit at the World's Fair in 1900 and was in development before that. I mean I guess a concept 120 years old is still new enough to get a bad reputation...
aidenn0 7y ago
If their numbers bear out then 120kW would only add 8kg of unsprung weight. (160hp 18lbs)
- jacquesm 7y ago
  That's not an 'only'. Unsprung weight is very precious.
  - JDEW 7y ago
    I remember this being mentioned in car related articles once in a while, would love to learn more. Any sources you can recommend?
  - usrusr 7y ago
    There is obviously a threshold, that where the unsprung part of the transmission is heavier than the motor itself. That's why brakes are in the wheel and not inboard working through the axle (which would have to be massively beefed up to handle the enormous braking power). Do they reach that threshold? Probably not, but it's worth noting that they are getting closer and that as a consequence application-specific preference shifts.
    - leoedin 7y ago
      Off topic, but there are a few cars with inboard brakes. The Hummer H1 is one.
      - dsfyu404ed 7y ago
        Because it has portals at the knuckle and finding a way to put brakes on that without massive rims would result in some janky packaging compromise. Also with the vehicle weight, wheel and tire size they run having the brakes benefit from the portal reduction sure doesn't hurt.
    - drewbt 7y ago
      Perhaps the an in hub motor could be integrated with braking and a KERS system.
newnewpdro 7y ago
Electric cars are pretty heavy thanks to the batteries, so it's not like having a bit more weight in the wheels is going to drastically change the unsprung:sprung weight ratio for the worse. In a light vehicle, it's very important to minimize unsprung weight for the reasons you've listed. Not so much with a heavy vehicle.
coryrc 7y ago
Don't worry, hub motors are so completely bad in highway-capable vehicles that even the most oblivious person would notice while on a test drive. They won't get a chance to sell.
- ncmncm 7y ago
  Hub motors make excellent sense in indoor forklifts, which are often electric anyway. The reduced weight is not so important there, because the forklift body needs to weigh enough, but moving to the wheels means there is more room for batteries. Size matters, in forklifts, which need to maneuver in tight spaces. Trucks and trains are often not sprung, and can benefit from lighter, smaller,more efficient hub motors. Cooling is easier when the whole motor is moving through the air.
  - lightedman 7y ago
    "The reduced weight is not so important there, because the forklift body needs to weigh enough" More than the body needs to weigh enough, you need a proper center of gravity via weight distribution or you're simply going to tilt the thing over and wreck everything when you lift an object (source: have multiple sit/stand/clamp lift certifications.) "Size matters, in forklifts, which need to maneuver in tight spaces." That's why we made the reach forklift, which is operated while standing up. Half the footprint of a traditional forklift with the ability to reach out across a shelf to pick up a pallet. Where this will make even more sense is for driving conveyor belts on assembly lines. You'll save more power there in a manufacturing warehouse environment than you typically will switching your entire forklift fleet over to these new motors.
  - 91aintprime 7y ago
    This is a very good comment
- theincredulousk 7y ago
  While an expensive option, if the advantages of an in-wheel motor were sufficient for a given application, active/magnetorheological suspension could largely compensate for it. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.678.7884&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.678... https://www.clearmotion.com/ https://www.clearmotion.com/ https://en.wikipedia.org/wiki/MagneRide https://en.wikipedia.org/wiki/MagneRide https://www.youtube.com/watch?v=hiaMpG4Y640 https://www.youtube.com/watch?v=hiaMpG4Y640 Further, on newer vehicles with the trend of 20inch+ rims, that is already 60-90+lbs (27-40+kg) of unsprung weight per wheel with tire. There is certainly room there for improvement to offset at least some of the motor weight. Would have to know how much their in-wheel models would actually weigh though to determine beyond speculation if it could be reasonably compensated for in a highway vehicle.
elihu 7y ago
If they're right that it's much lighter than an equivalent motor, maybe in-hub motors wouldn't be all that bad. Watching the video that was linked in another thread, it made me think that maybe the hub could be stationary, and the tire just spins around the outside. That could cut down a lot on wind resistance.
pkulak 7y ago
I got the impression that the wheel motors were just for testing. They'll leave the car making to someone else for sure.
Tade0 7y ago
They said they've achieved 15kW/kg, so a powertrain of 120kW(~160BHP) would add around 2kg to each wheel - that's as much as two different rims can differ in weight.
dsfyu404ed 7y ago
>But I do hope they do not proceed with the in wheel concept. In wheel motors make the ride not only bumpier but more dangerous. This is because the wheel with more un-sprung weight bounces more and tends to lose contact with the road more, which in turn makes the car more likely to spin out of control, miss a turn, etc. >Electric cars, being still relatively new, cannot afford to get a reputation for danger. I'm really sick of this "anything that measurably effects handling in a negative way is a non-starter because safety" attitude that's become increasingly pervasive. The fact of the matter is that there is a range of handling that is "acceptable" and anything in it is fair game. Nobody is expecting a Dodge Journey or a Spark EV to handle like a Porsche. At 15kwh/kg these motors will be fine for vehicles with average power to weight ratios that do not place a massive emphasis on performance (i.e all the "appliance" vehicles that purists hate). For low power levels these motors may weigh on the same order as the parts you need to transmit power to the wheels in a conventional applications so there might not even be any net gain in some applications.

hinkley 7y ago

Might work out if it’s paired with active suspension. The idea with motors at the wheel seems to be that the moving parts are all concentrated there. No mechanical distribution. Compartmentalization. But that is not incompatible with active suspension systems.

adrianmonk 7y ago
What would be the advantage of doing it that way instead of just putting the motor on the car frame and connecting it to the wheel with a CV axle? From what I could dig up, mechanical losses in a CV axle are on the order of 1%. An active suspension requires power, too. And a heavier wheel would presumably require a more power-hungry active suspension than a lighter wheel, so you're not getting something for nothing in terms of efficiency. I guess it is a matter of numbers, though. A CV axle also gives a wheel inertia, as it has mass and moves when the wheel does (partially). If you can make an insanely light motor, maybe you could make it so light that it's actually contributes less inertia than a CV axle would, in which case go ahead.
- davidgould 7y ago
  The small diameter of the CV axle makes the inertia small compared to the rest of the wheel, tire, brake assembly.
b0rsuk 7y ago
Doesn't active suspension need to be powered itself? I skimmed the article, and the main advantage they cite is more efficient energy use. That may be gone if you have to spend extra energy elsewhere.
agumonkey 7y ago
maybe motor-wheels are bad for normal cars but maybe it's still a neat devices for simple setups, carts, or whatever rover that doesn't go super fast.

analognoise 7y ago

"Electric cars, being still relatively new, cannot afford to get a reputation for danger." The Lohner-Porsche was a hit at the World's Fair in 1900 and was in development before that. I mean I guess a concept 120 years old is still new enough to get a bad reputation...

aidenn0 7y ago

If their numbers bear out then 120kW would only add 8kg of unsprung weight. (160hp 18lbs)

jacquesm 7y ago
That's not an 'only'. Unsprung weight is very precious.
- JDEW 7y ago
  I remember this being mentioned in car related articles once in a while, would love to learn more. Any sources you can recommend?
- usrusr 7y ago
  There is obviously a threshold, that where the unsprung part of the transmission is heavier than the motor itself. That's why brakes are in the wheel and not inboard working through the axle (which would have to be massively beefed up to handle the enormous braking power). Do they reach that threshold? Probably not, but it's worth noting that they are getting closer and that as a consequence application-specific preference shifts.
  - leoedin 7y ago
    Off topic, but there are a few cars with inboard brakes. The Hummer H1 is one.
    - dsfyu404ed 7y ago
      Because it has portals at the knuckle and finding a way to put brakes on that without massive rims would result in some janky packaging compromise. Also with the vehicle weight, wheel and tire size they run having the brakes benefit from the portal reduction sure doesn't hurt.
  - drewbt 7y ago
    Perhaps the an in hub motor could be integrated with braking and a KERS system.

newnewpdro 7y ago

Electric cars are pretty heavy thanks to the batteries, so it's not like having a bit more weight in the wheels is going to drastically change the unsprung:sprung weight ratio for the worse. In a light vehicle, it's very important to minimize unsprung weight for the reasons you've listed. Not so much with a heavy vehicle.

coryrc 7y ago

Don't worry, hub motors are so completely bad in highway-capable vehicles that even the most oblivious person would notice while on a test drive. They won't get a chance to sell.

ncmncm 7y ago
Hub motors make excellent sense in indoor forklifts, which are often electric anyway. The reduced weight is not so important there, because the forklift body needs to weigh enough, but moving to the wheels means there is more room for batteries. Size matters, in forklifts, which need to maneuver in tight spaces. Trucks and trains are often not sprung, and can benefit from lighter, smaller,more efficient hub motors. Cooling is easier when the whole motor is moving through the air.
- lightedman 7y ago
  "The reduced weight is not so important there, because the forklift body needs to weigh enough" More than the body needs to weigh enough, you need a proper center of gravity via weight distribution or you're simply going to tilt the thing over and wreck everything when you lift an object (source: have multiple sit/stand/clamp lift certifications.) "Size matters, in forklifts, which need to maneuver in tight spaces." That's why we made the reach forklift, which is operated while standing up. Half the footprint of a traditional forklift with the ability to reach out across a shelf to pick up a pallet. Where this will make even more sense is for driving conveyor belts on assembly lines. You'll save more power there in a manufacturing warehouse environment than you typically will switching your entire forklift fleet over to these new motors.
- 91aintprime 7y ago
  This is a very good comment
theincredulousk 7y ago
While an expensive option, if the advantages of an in-wheel motor were sufficient for a given application, active/magnetorheological suspension could largely compensate for it. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.678.7884&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.678... https://www.clearmotion.com/ https://www.clearmotion.com/ https://en.wikipedia.org/wiki/MagneRide https://en.wikipedia.org/wiki/MagneRide https://www.youtube.com/watch?v=hiaMpG4Y640 https://www.youtube.com/watch?v=hiaMpG4Y640 Further, on newer vehicles with the trend of 20inch+ rims, that is already 60-90+lbs (27-40+kg) of unsprung weight per wheel with tire. There is certainly room there for improvement to offset at least some of the motor weight. Would have to know how much their in-wheel models would actually weigh though to determine beyond speculation if it could be reasonably compensated for in a highway vehicle.

elihu 7y ago

If they're right that it's much lighter than an equivalent motor, maybe in-hub motors wouldn't be all that bad. Watching the video that was linked in another thread, it made me think that maybe the hub could be stationary, and the tire just spins around the outside. That could cut down a lot on wind resistance.

pkulak 7y ago

I got the impression that the wheel motors were just for testing. They'll leave the car making to someone else for sure.

Tade0 7y ago

They said they've achieved 15kW/kg, so a powertrain of 120kW(~160BHP) would add around 2kg to each wheel - that's as much as two different rims can differ in weight.

dsfyu404ed 7y ago

>But I do hope they do not proceed with the in wheel concept. In wheel motors make the ride not only bumpier but more dangerous. This is because the wheel with more un-sprung weight bounces more and tends to lose contact with the road more, which in turn makes the car more likely to spin out of control, miss a turn, etc. >Electric cars, being still relatively new, cannot afford to get a reputation for danger. I'm really sick of this "anything that measurably effects handling in a negative way is a non-starter because safety" attitude that's become increasingly pervasive. The fact of the matter is that there is a range of handling that is "acceptable" and anything in it is fair game. Nobody is expecting a Dodge Journey or a Spark EV to handle like a Porsche. At 15kwh/kg these motors will be fine for vehicles with average power to weight ratios that do not place a massive emphasis on performance (i.e all the "appliance" vehicles that purists hate). For low power levels these motors may weigh on the same order as the parts you need to transmit power to the wheels in a conventional applications so there might not even be any net gain in some applications.