<story><title>Why car wheels are so flat these days</title><url>https://www.theautopian.com/heres-why-car-wheels-are-so-flat-these-days-and-no-its-not-just-aerodynamics-and-styling/</url></story><parent_chain><item><author>extrapickles</author><text>That is easy to accommodate as you can design the electronics such that when there is no power they cause maximum braking force and dump energy into the braking resistors. This can be done completely with power taken from the motor itself and if it’s not turning to generate power, then I would expect the parking brake system to engage, eg: a spring defaults it to “On” and power is used to keep it disengaged.</text></item><item><author>sbradford26</author><text>So a big reason why this probably wouldn&amp;#x27;t fly is that it has a common mode failure which is loss of power. Most EVs don&amp;#x27;t use permanent magnetic motors so it needs power to be able to use the motors for regen. So lets say the relay fails from the main battery pack suddenly you have no power, and no way to energize the coils in the motors to use them to regen. This could be mitigated by using permanent magnet motors but you still have the issue if control power is lost the vehicle cannot stop. The beauty of hydraulic brakes is that they work really well with power, but still function without it.</text></item><item><author>londons_explore</author><text>One day, I believe car design regulations will be amended to allow fully electric braking (ie. no hydraulics, drums, rotors, or pads).   At that point, the motor can be moved into the wheel (unsprung mass = bad, but weight savings from not needing an axle or gearbox will outweigh this).  Suspension and steering design is then far easier, because there is no axle to need to keep straight.&lt;p&gt;Braking redundancy will be achieved by having motors&amp;#x2F;brakes on all four wheels, and within each motor 3 independant phase coils with independant controllers, such that there are effectively 12 brakes on a car.   Normally the controllers work together for smooth braking, traction control, software differential, etc.  But even after 3+ failures braking performance should still be satisfactory for an emergency stop.&lt;p&gt;Obviously braking energy needs to go somewhere.  In the happy case, it&amp;#x27;s regen&amp;#x27;ed into a battery.  If the battery can&amp;#x27;t accept it, it gets dumped into dump resistors.  If the dump resistors fail, it gets dumped into motor coils (of which there are 12 remember).  Obviously the motor coils will heat up very fast, so this is probably a one-use-only failsafe, like airbags.&lt;p&gt;So the whole system (except the pedal itself) is 12 way redundant.</text></item></parent_chain><comment><author>sbradford26</author><text>This can only be done with permanent magnetic motors which is not the norm for EVs for many reasons. In a non permanent magnetic motor on loss of power there is no energy to dump into braking resistors since the motor is not causing any resistance because the coils have been de-energized.</text></comment>
<story><title>Why car wheels are so flat these days</title><url>https://www.theautopian.com/heres-why-car-wheels-are-so-flat-these-days-and-no-its-not-just-aerodynamics-and-styling/</url></story><parent_chain><item><author>extrapickles</author><text>That is easy to accommodate as you can design the electronics such that when there is no power they cause maximum braking force and dump energy into the braking resistors. This can be done completely with power taken from the motor itself and if it’s not turning to generate power, then I would expect the parking brake system to engage, eg: a spring defaults it to “On” and power is used to keep it disengaged.</text></item><item><author>sbradford26</author><text>So a big reason why this probably wouldn&amp;#x27;t fly is that it has a common mode failure which is loss of power. Most EVs don&amp;#x27;t use permanent magnetic motors so it needs power to be able to use the motors for regen. So lets say the relay fails from the main battery pack suddenly you have no power, and no way to energize the coils in the motors to use them to regen. This could be mitigated by using permanent magnet motors but you still have the issue if control power is lost the vehicle cannot stop. The beauty of hydraulic brakes is that they work really well with power, but still function without it.</text></item><item><author>londons_explore</author><text>One day, I believe car design regulations will be amended to allow fully electric braking (ie. no hydraulics, drums, rotors, or pads).   At that point, the motor can be moved into the wheel (unsprung mass = bad, but weight savings from not needing an axle or gearbox will outweigh this).  Suspension and steering design is then far easier, because there is no axle to need to keep straight.&lt;p&gt;Braking redundancy will be achieved by having motors&amp;#x2F;brakes on all four wheels, and within each motor 3 independant phase coils with independant controllers, such that there are effectively 12 brakes on a car.   Normally the controllers work together for smooth braking, traction control, software differential, etc.  But even after 3+ failures braking performance should still be satisfactory for an emergency stop.&lt;p&gt;Obviously braking energy needs to go somewhere.  In the happy case, it&amp;#x27;s regen&amp;#x27;ed into a battery.  If the battery can&amp;#x27;t accept it, it gets dumped into dump resistors.  If the dump resistors fail, it gets dumped into motor coils (of which there are 12 remember).  Obviously the motor coils will heat up very fast, so this is probably a one-use-only failsafe, like airbags.&lt;p&gt;So the whole system (except the pedal itself) is 12 way redundant.</text></item></parent_chain><comment><author>SketchySeaBeast</author><text>So rather than coasting to the shoulder when you run out of gas your tires immediately slam full on coming to a screeching, uncontrolled stop in the middle of the highway?</text></comment>