5 ms·

unsprung weight I believe is also a big issue with hub motors esp as you get up to car size at speed

jacquesm 3y ago
It is the issue for in-hub motors. Solve that one and the world will beat a path to your door and shower you with money.
- throwaw33333434 3y ago
  The other issue is that potholes my get quite expensive.
  - jacquesm 3y ago
    Yes, the impact from a pothole can be substantial. Having an upset alignment is one thing, damaging the guts of an in-wheel motor is a totally different picture. But: when properly packaged and lightweight enough I think that is a secondary concern, you can design with that in mind given that it is more or less predictable from which direction and with which magnitude such an impact would happen. But every pound counts and the shocks+spring will have to be matched to the increased weight.
- benj111 3y ago
  Have you got a source. Everyone mentions this, but I've never come across anyone trying and failing. Motor scooters have unsprung motors, the motor is a significant proportion of the mass.
  - jacquesm 3y ago
    Motor scooter motors weigh a fraction of what the equivalent motor for a car would weigh, and it's exactly the problem: The issue is that it scales poorly, unsprung weight is bad enough that on some cars the disc brakes live 'inboard' on the front wheels (older hydraulic suspension cars). Essentially the larger the unsprung mass the bigger the hit every time the road surface irregularities cause the wheels to move relative to the vehicle body. The larger the mass the more energy gets imparted, and the more energy that gets imparted the bigger the impact and all that energy then needs to be absorbed so you'll need a stronger (and heavier) suspension system, roughly half of which is unsprung mass!, and a larger battery to compensate for the losses in the suspension which also adds weight (harder suspension -> bigger range but less comfortable ride). So it feeds back on itself and that's why it scales so poorly.
    - benj111 3y ago
      I can sort of buy this at the upper end. But a small car with 4 relatively small motors with normal tyres v a range rover with run flat tyres and massive disc brakes?
      - jacquesm 3y ago
        In a small car it could work, but you'd be very much limited in power and weight. See upthread links and subsequent updates https://news.ycombinator.com/item?id=38485097 https://news.ycombinator.com/item?id=38485097. Note that more unsprung weight has other effects as well, such as poor handling because the wheel bounces higher and so will be out of contact with the road for a longer time when it encounters an obstacle. If you think of the weight of the wheel as the weight on a pendulum it is easy to see why that would affect the period of the swing.
- Beijinger 3y ago
  You can buy a car powered with in-wheel motors here: We have developed the first production car to use in-wheel hub motors. https://mwmotors.cz/luka-ev/ https://mwmotors.cz/luka-ev/ This car maybe too, as far as I understand it. A Russian UAZ on steroids: https://www.youtube.com/watch?v=RCOf_33C1qc https://www.youtube.com/watch?v=RCOf_33C1qc
  - jacquesm 3y ago
    815 Kg curb weight, aluminum chassis. It makes sense for a vehicle with that form factor (2 seater little sports car) but you can't really compare it with a full sized sedan, and note too that it has a tiny battery pack (22 KWh), range is 'unofficial' 300 Km and likely will be adjusted down based on weight/pack size. The four motors together are less than half the rated power of what you'd find in a more conventional (is there such a thing already?) EV. But with that light total weight it will be a zippy little car anyway (most EVs are over-powered for their weight). Still, very impressive achievement and a nice testbed for this kind of tech, it may also make sense for motorcycles and for vehicles that are not meant for highway use.
    - Beijinger 3y ago
      What is the advantage of in-wheel motors?
      - jacquesm 3y ago
        That you save on a whole bunch of linkage and drive train components, four wheel drive without the associated complexity, that you can integrate the wheels, motors and brakes, cleaner airflow under the car and that the system as a whole can be lighter weight than the same package with motors near the centerline of the car, so you get somewhat better range. It also gives more space for batteries and/or more storage space. That's why manufacturers will keep trying to get this done, if they can get it to work cost effectively and without impacting that unsprung weight too much it will give them an advantage.
        3y ago

It is the issue for in-hub motors. Solve that one and the world will beat a path to your door and shower you with money.

throwaw33333434 3y ago
The other issue is that potholes my get quite expensive.
- jacquesm 3y ago
  Yes, the impact from a pothole can be substantial. Having an upset alignment is one thing, damaging the guts of an in-wheel motor is a totally different picture. But: when properly packaged and lightweight enough I think that is a secondary concern, you can design with that in mind given that it is more or less predictable from which direction and with which magnitude such an impact would happen. But every pound counts and the shocks+spring will have to be matched to the increased weight.
benj111 3y ago
Have you got a source. Everyone mentions this, but I've never come across anyone trying and failing. Motor scooters have unsprung motors, the motor is a significant proportion of the mass.
- jacquesm 3y ago
  Motor scooter motors weigh a fraction of what the equivalent motor for a car would weigh, and it's exactly the problem: The issue is that it scales poorly, unsprung weight is bad enough that on some cars the disc brakes live 'inboard' on the front wheels (older hydraulic suspension cars). Essentially the larger the unsprung mass the bigger the hit every time the road surface irregularities cause the wheels to move relative to the vehicle body. The larger the mass the more energy gets imparted, and the more energy that gets imparted the bigger the impact and all that energy then needs to be absorbed so you'll need a stronger (and heavier) suspension system, roughly half of which is unsprung mass!, and a larger battery to compensate for the losses in the suspension which also adds weight (harder suspension -> bigger range but less comfortable ride). So it feeds back on itself and that's why it scales so poorly.
  - benj111 3y ago
    I can sort of buy this at the upper end. But a small car with 4 relatively small motors with normal tyres v a range rover with run flat tyres and massive disc brakes?
    - jacquesm 3y ago
      In a small car it could work, but you'd be very much limited in power and weight. See upthread links and subsequent updates https://news.ycombinator.com/item?id=38485097 https://news.ycombinator.com/item?id=38485097. Note that more unsprung weight has other effects as well, such as poor handling because the wheel bounces higher and so will be out of contact with the road for a longer time when it encounters an obstacle. If you think of the weight of the wheel as the weight on a pendulum it is easy to see why that would affect the period of the swing.
Beijinger 3y ago
You can buy a car powered with in-wheel motors here: We have developed the first production car to use in-wheel hub motors. https://mwmotors.cz/luka-ev/ https://mwmotors.cz/luka-ev/ This car maybe too, as far as I understand it. A Russian UAZ on steroids: https://www.youtube.com/watch?v=RCOf_33C1qc https://www.youtube.com/watch?v=RCOf_33C1qc
- jacquesm 3y ago
  815 Kg curb weight, aluminum chassis. It makes sense for a vehicle with that form factor (2 seater little sports car) but you can't really compare it with a full sized sedan, and note too that it has a tiny battery pack (22 KWh), range is 'unofficial' 300 Km and likely will be adjusted down based on weight/pack size. The four motors together are less than half the rated power of what you'd find in a more conventional (is there such a thing already?) EV. But with that light total weight it will be a zippy little car anyway (most EVs are over-powered for their weight). Still, very impressive achievement and a nice testbed for this kind of tech, it may also make sense for motorcycles and for vehicles that are not meant for highway use.
  - Beijinger 3y ago
    What is the advantage of in-wheel motors?
    - jacquesm 3y ago
      That you save on a whole bunch of linkage and drive train components, four wheel drive without the associated complexity, that you can integrate the wheels, motors and brakes, cleaner airflow under the car and that the system as a whole can be lighter weight than the same package with motors near the centerline of the car, so you get somewhat better range. It also gives more space for batteries and/or more storage space. That's why manufacturers will keep trying to get this done, if they can get it to work cost effectively and without impacting that unsprung weight too much it will give them an advantage.
      - 3y ago