4 ms·

Surely they wouldn't move the motors into the wheels for actual full-size cars, right? In addition to the poor handling aspects of so much more unsprung weight

Surely they wouldn't move the motors into the wheels for actual full-size cars, right? In addition to the poor handling aspects of so much more unsprung weight, it would have to deal with much more vibration. Seems like a tough sell.

agumonkey 9y ago
I wonder if unsprung weight is a physical dead end or just something that needs a fresh solution. ps: also that design has no absorbing element in the wheel.. I would have done it differently.
- maxxxxx 9y ago
  I think theoretically you could get deal with sprung weight with an active suspension but I am not sure how well that would work.
  - agumonkey 9y ago
    Also you could couple magnetic shock absorbers to the energy storage.
TD-Linux 9y ago
It also requires the motors to be larger because motor size mostly corresponds with torque output, not power output, and there is no gear reduction. However, it also avoids a lot of weight due to the lack of gearbox and axles, and efficiency losses in the gears. It can make sense especially in applications that require lower power output - for example virtually all solar cars use hub motors for efficiency.
dsfyu404ed 9y ago
I don't think handling is of serious concern to the people buying the kinds of cars these will go in.
phkahler 9y ago
>> In addition to the poor handling aspects of so much more unsprung weight, it would have to deal with much more vibration. Seems like a tough sell. I did some work with hub motors a while back. The unsprung mass is still under debate, but moving all that mass to the corners of the vehicle is actually a good thing. I would think putting the inverter in the hub would make for terrible durability problems, but who knows. Anecdote: The hub motors I wrote code for had integrated planetary gear, so they ran 6000rpm at the motor. The rotor was on a rather large bearing and we had all sorts of runout and alignment issues. It's was really hard to package in that space. We had peak power of 40KW per wheel, but you only got that for about 30 seconds before needing to cool off for 5 minutes (it was also water cooled, but not well - packaging again). Because of the heating and alignment issues, nobody could make much progress on doing the software calibration (motor mapping) on it. It was the only motor we had that required my new algorithm to get it up and running. It made light work of the calibration, compensated for the alignment and eccentricity issues, and ran the hell out of that thing. Sometimes I miss working on that stuff ;-)
- 2sk21 9y ago
  Whenever I read car magazines they are always talking about the need to reduce unsprung weight. Supposedly, high unsprung weight causes a harsher ride - so this is not a given?
  - phkahler 9y ago
    Depends. If you hit a bump or a pothole, you need the wheel to move vertically very quickly. But on smooth roads it's not a problem and having the mass at the corners increases the vehicles rotational (pitch, roll, and yaw) stability. I have not formed a personal opinion on it yet, so I listen to both sides. My suspicion is that the unsprung mass is bad and the arguments to the contrary are partly wishful thinking by hub-wheel advocates ;-)
    - abakker 9y ago
      I always wonder whether it is really inspiring weight, or the ratio of sprung va unsprung? In an application I have lots of experience with, mountain biking suspension, the overall sprung weight relative to the frame/rideris so low that even doubling the wheel weight or cassette weight doesn’t really effect suspension performance. (Pedaling rotating mass is a different story) In a car or truck, where the overall mass of the car is very large, adding more unsprung mass might not matter so much. The car still has a lot more inertia than the wheels. You should be able to make up for the heavier wheels with better suspension valving and improved shims. Problem being that most factory standard suspension is really bad.
agitator 9y ago
Yeah, the unsprung weight, handling issue and reliability due to vibration and road impacts are problems. The amount of space it actually saves isn't that large. The Tesla motors essentially fit along the axels. Seems to me like a dead end. Also the hub motors need to spin at the wheel RPM, which might not be in the peak efficiency for motors of that size or dimension, so it becomes a challenging engineering problem to try to match efficiencies with chassis mounted motors, which can be geared to run at their peak efficiency ranges.
- TheSpiceIsLife 9y ago
  See user phkahler's comment about planetary gearing and motor RPM 6000. Still problematic though.
deleted 9y ago
[deleted]

agumonkey 9y ago

I wonder if unsprung weight is a physical dead end or just something that needs a fresh solution. ps: also that design has no absorbing element in the wheel.. I would have done it differently.

maxxxxx 9y ago
I think theoretically you could get deal with sprung weight with an active suspension but I am not sure how well that would work.
- agumonkey 9y ago
  Also you could couple magnetic shock absorbers to the energy storage.

TD-Linux 9y ago

It also requires the motors to be larger because motor size mostly corresponds with torque output, not power output, and there is no gear reduction. However, it also avoids a lot of weight due to the lack of gearbox and axles, and efficiency losses in the gears. It can make sense especially in applications that require lower power output - for example virtually all solar cars use hub motors for efficiency.

dsfyu404ed 9y ago

I don't think handling is of serious concern to the people buying the kinds of cars these will go in.

phkahler 9y ago

>> In addition to the poor handling aspects of so much more unsprung weight, it would have to deal with much more vibration. Seems like a tough sell. I did some work with hub motors a while back. The unsprung mass is still under debate, but moving all that mass to the corners of the vehicle is actually a good thing. I would think putting the inverter in the hub would make for terrible durability problems, but who knows. Anecdote: The hub motors I wrote code for had integrated planetary gear, so they ran 6000rpm at the motor. The rotor was on a rather large bearing and we had all sorts of runout and alignment issues. It's was really hard to package in that space. We had peak power of 40KW per wheel, but you only got that for about 30 seconds before needing to cool off for 5 minutes (it was also water cooled, but not well - packaging again). Because of the heating and alignment issues, nobody could make much progress on doing the software calibration (motor mapping) on it. It was the only motor we had that required my new algorithm to get it up and running. It made light work of the calibration, compensated for the alignment and eccentricity issues, and ran the hell out of that thing. Sometimes I miss working on that stuff ;-)

2sk21 9y ago
Whenever I read car magazines they are always talking about the need to reduce unsprung weight. Supposedly, high unsprung weight causes a harsher ride - so this is not a given?
- phkahler 9y ago
  Depends. If you hit a bump or a pothole, you need the wheel to move vertically very quickly. But on smooth roads it's not a problem and having the mass at the corners increases the vehicles rotational (pitch, roll, and yaw) stability. I have not formed a personal opinion on it yet, so I listen to both sides. My suspicion is that the unsprung mass is bad and the arguments to the contrary are partly wishful thinking by hub-wheel advocates ;-)
  - abakker 9y ago
    I always wonder whether it is really inspiring weight, or the ratio of sprung va unsprung? In an application I have lots of experience with, mountain biking suspension, the overall sprung weight relative to the frame/rideris so low that even doubling the wheel weight or cassette weight doesn’t really effect suspension performance. (Pedaling rotating mass is a different story) In a car or truck, where the overall mass of the car is very large, adding more unsprung mass might not matter so much. The car still has a lot more inertia than the wheels. You should be able to make up for the heavier wheels with better suspension valving and improved shims. Problem being that most factory standard suspension is really bad.

agitator 9y ago

Yeah, the unsprung weight, handling issue and reliability due to vibration and road impacts are problems. The amount of space it actually saves isn't that large. The Tesla motors essentially fit along the axels. Seems to me like a dead end. Also the hub motors need to spin at the wheel RPM, which might not be in the peak efficiency for motors of that size or dimension, so it becomes a challenging engineering problem to try to match efficiencies with chassis mounted motors, which can be geared to run at their peak efficiency ranges.

TheSpiceIsLife 9y ago
See user phkahler's comment about planetary gearing and motor RPM 6000. Still problematic though.

deleted 9y ago

[deleted]