4 ms·

To save others time, "unsprung mass" is the mass of the vehicle not supported by suspension. Lightyear's claim is that putting the motors in the wheels improve

by gnode 7y ago

To save others time, "unsprung mass" is the mass of the vehicle not supported by suspension. Lightyear's claim is that putting the motors in the wheels improves control. Could it be that unsprung mass is reduced by negating the axle?

bkanber 7y ago
I would bet that there's more unsprung mass in this configuration, but it's hard to say without knowing the details of the motors themselves. If each motor is, say, 80 pounds or heavier, then this configuration would likely increase the unsprung mass. Note a distinction between "control" and "handling". Four in-wheel motors will have better control but worse handling. Traction control can be applied to each individual motor, improving control in some cases, but on bumpy or rough roads the car will experience worse handling, as the wheels will "hop" off the surface more. Imagine a car driving over a speed bump a little too fast. In a standard suspension, the wheels are light enough that the suspension pushes them back down to the road surface very quickly at the far end of the bump. If there is more unsprung mass, however, the wheels have more inertia, and so the suspension is not able to push the wheels down to the surface as quickly. Now imagine that same car taking a fast turn on an uneven road surface. If the wheels aren't pressed down to the surface after coming up off a bump, that wheel will lose traction, and traction is required for sticking the turn. In that case, no amount of traction control can make up for the loss of friction.
- gnode 7y ago
  > If each motor is, say, 80 pounds or heavier, then this configuration would likely increase the unsprung mass. Apparently, the motor on the Tesla Model S is 70 lbs ( https://chargedevs.com/newswire/elon-musk-cooling-not-power-to-weight-ratio-is-the-challenge-with-ac-induction-motors/ https://chargedevs.com/newswire/elon-musk-cooling-not-power-... ). With individualized motors, each would likely be less than this. Combined with the battery weight attached to the car's chassis, I would expect this to result in a lower ratio of unsprung mass to sprung, and thus better handling than typical on a non-battery car.
  - solarkraft 7y ago
    > better handling than typical on a non-battery car Is that their main competition, though?
    - gnode 7y ago
      I mean that if it's better than what is typical, then it shouldn't be inadequate, and that helps justify this trade-off in favour of efficiency / range.
- solarkraft 7y ago
  > Traction control can be applied to each individual motor This is not a feature of in-wheel motors, but individual motors. And not even much of that, because you can apply the brakes to shift power through the differential to the other wheel (a technique modern all-wheel drive cars including Teslas use for traction control). Is having a motor for each wheel really a huge improvement over that? Maybe latency can be improved a little?

by gnode 7y ago

bkanber 7y ago

I would bet that there's more unsprung mass in this configuration, but it's hard to say without knowing the details of the motors themselves. If each motor is, say, 80 pounds or heavier, then this configuration would likely increase the unsprung mass. Note a distinction between "control" and "handling". Four in-wheel motors will have better control but worse handling. Traction control can be applied to each individual motor, improving control in some cases, but on bumpy or rough roads the car will experience worse handling, as the wheels will "hop" off the surface more. Imagine a car driving over a speed bump a little too fast. In a standard suspension, the wheels are light enough that the suspension pushes them back down to the road surface very quickly at the far end of the bump. If there is more unsprung mass, however, the wheels have more inertia, and so the suspension is not able to push the wheels down to the surface as quickly. Now imagine that same car taking a fast turn on an uneven road surface. If the wheels aren't pressed down to the surface after coming up off a bump, that wheel will lose traction, and traction is required for sticking the turn. In that case, no amount of traction control can make up for the loss of friction.

gnode 7y ago
> If each motor is, say, 80 pounds or heavier, then this configuration would likely increase the unsprung mass. Apparently, the motor on the Tesla Model S is 70 lbs ( https://chargedevs.com/newswire/elon-musk-cooling-not-power-to-weight-ratio-is-the-challenge-with-ac-induction-motors/ https://chargedevs.com/newswire/elon-musk-cooling-not-power-... ). With individualized motors, each would likely be less than this. Combined with the battery weight attached to the car's chassis, I would expect this to result in a lower ratio of unsprung mass to sprung, and thus better handling than typical on a non-battery car.
- solarkraft 7y ago
  > better handling than typical on a non-battery car Is that their main competition, though?
  - gnode 7y ago
    I mean that if it's better than what is typical, then it shouldn't be inadequate, and that helps justify this trade-off in favour of efficiency / range.
solarkraft 7y ago
> Traction control can be applied to each individual motor This is not a feature of in-wheel motors, but individual motors. And not even much of that, because you can apply the brakes to shift power through the differential to the other wheel (a technique modern all-wheel drive cars including Teslas use for traction control). Is having a motor for each wheel really a huge improvement over that? Maybe latency can be improved a little?