5 ms·

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 signif

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.

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.