> If an EV has the power to sustain highway speeds, it'll also have the power to go up a steep hill at a snail's pace.
Most EVs are direct drive from the motor without a gearbox. There absolutely is a minimum speed depending on how the motor is wound. If you imagine, say 12 magnets around the motor driven by 3 phases, the idea is to have one winding attracting the magnets, and this phase is the one the motor is "trying to get to". In this situation, this winding is active until the motor is in the correct position (actually slightly before) when it is depowered and the next phase is powered. The longer the motor stays in that position, the hotter the winding gets for the same current. At the point where the motor stops being able to rotate at all, that winding is receiving 100% duty cycle.
There are strategies that you could try - the simplest is cutting power and letting it cool down, but then the motor will stop where it is, and starting the motor from stationary requires even more power than keeping an already moving motor going. You might apply a reverse polarity to the previous winding for a bit to repel the magnets and then swap back. If the motor has passed the mid point this will be less effective, but still better than nothing.
If you ignore feedback from the axle and just cycle through the windings at the desired speed, then there definitely is a minimum speed. Because when the load is too great and the motor doesn't move and you cycle to the next phase, then next phase won't exert much magnetic field on your magnets and the next phase after that, you're working against the direction you want to go.
It's true that if you gear an EV motor, the torque should be able to be geared down to any speed. But typically pure EVs are direct drive, because usually they have enough torque for the low speeds and adding a gearbox just adds inefficiencies. But for a heavy load, maybe gearboxes are required. As a disclaimer, I don't know if EV trucks have gearboxes or not, but certainly EV cars tend not to have except for hybrids.
Most EVs are direct drive from the motor without a gearbox. There absolutely is a minimum speed depending on how the motor is wound. If you imagine, say 12 magnets around the motor driven by 3 phases, the idea is to have one winding attracting the magnets, and this phase is the one the motor is "trying to get to". In this situation, this winding is active until the motor is in the correct position (actually slightly before) when it is depowered and the next phase is powered. The longer the motor stays in that position, the hotter the winding gets for the same current. At the point where the motor stops being able to rotate at all, that winding is receiving 100% duty cycle.
There are strategies that you could try - the simplest is cutting power and letting it cool down, but then the motor will stop where it is, and starting the motor from stationary requires even more power than keeping an already moving motor going. You might apply a reverse polarity to the previous winding for a bit to repel the magnets and then swap back. If the motor has passed the mid point this will be less effective, but still better than nothing.
If you ignore feedback from the axle and just cycle through the windings at the desired speed, then there definitely is a minimum speed. Because when the load is too great and the motor doesn't move and you cycle to the next phase, then next phase won't exert much magnetic field on your magnets and the next phase after that, you're working against the direction you want to go.
It's true that if you gear an EV motor, the torque should be able to be geared down to any speed. But typically pure EVs are direct drive, because usually they have enough torque for the low speeds and adding a gearbox just adds inefficiencies. But for a heavy load, maybe gearboxes are required. As a disclaimer, I don't know if EV trucks have gearboxes or not, but certainly EV cars tend not to have except for hybrids.