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> I get the impression that electric motors are hard on transmissions. Rather, electric motors don't need transmissions. Transmissions are a workaround for the

> I get the impression that electric motors are hard on transmissions. Rather, electric motors don't need transmissions. Transmissions are a workaround for the failings of the internal combustion engine.

gameswithgo 6y ago
They do if you want a car that performs optimally at a wide enough speed range, like a supercar. But that is an edge case, and eventually even that might not require one.
dharmab 6y ago
* at any speed you would want to drive on a public road.
leetcrew 6y ago
they don't need a clutch because they can't stall. but, like ICEs, they cannot make peak power at 0 RPM. unless the vehicle is already traction limited (quite possible), it could accelerate faster with a shorter first gear. my guess is in reality it's usually cheaper to just overbuild the motors than to add lower gears to hit your desired 0-60 time, but this isn't a law of nature.
- mrfusion 6y ago
  I wonder what torque looks like at 0 rpm. I thought that was peak? But If it’s bad maybe a torque converter would be useful?
  - Cerium 6y ago
    Peak torque is at zero, but peak power is not.
  - mywittyname 6y ago
    Electric motors "torque ripple" at low RPMs (well, at all RPMs, but it is most noticeable at lower RPMs), which can cause motor "cogging". Cogging is either a complete stall, or really jerky behavior that feels pretty close to what an ICE is like at very low RPMs. * There are different motor designs out there that alter power delivery for situations where very low-RPM torque is required. As with most design decisions, there are trade-offs involved. And yeah, I'm sure a torque converter would be helpful in that situation. But I think that generally, passenger cars don't need to go very fast, so most EVs can get away with short enough gearing that cogging isn't an issue, at the expense of top seed. * hold some low-power electric motor in your hands, turn it on then gradually clap the output with your fingers. You'll eventually feel the power output go to nothing and the motor will wind. That's cogging. Also, the whole "peak torque at 0 RPMs" thing is really a side effect of the fact that electric motors produce consistent power across the rev band (except at really low, and really high RPMs). And the formula for power is power = torque * RPM. Since power is essentially fixed with an electric motor, you rearrange that equation to be torque = power / RPM, and peak torque is at the limit as RPM goes to 0. In real world applications, torque output is limited by physics and current delivery, so peak torque is truncated at low RPMs.
    - deleted 6y ago
      [deleted]
    - rcxdude 6y ago
      Cogging is only really a problem if you either have a particular motor design or not very sophisticated control. EVs are not generally going to suffer from it.
- mixmastamyk 6y ago
  What about those new gear boxes that are gradual instead of stepped?
  - elihu 6y ago
    You mean continuously variable transmissions? Those could work in an EV I suppose. I don't know much about CVTs but I think the general complaints against them are that they tend to have a narrower highest-to-lowest gear ratio range than a traditional geared transmission, and it's hard to build them to handle large amounts of power.
- red369 6y ago
  I'm sure you're right about increasing motor power being cheaper than adding gears, but just thought I'd add that my understanding is that you might then also need to increase battery capacity because the rate at which Li-ion batteries can discharge is another limiting factor. As an example, I think there is a Honda 2 motor hybrid system which can accelerate faster (generate more power on the motor driving the wheels) if using power generated from the petrol engine as well as battery power.
- saberdancer 6y ago
  Another reason is that any type of gearbox or clutch increases losses. EV cars are all about minimizing losses of energy as their power source is not energy dense as petrol.
throwaway0a5e 6y ago
My electric drill begs to differ. Well so long as I don't want to let the magic smoke out it does. Your commuter car can get away with a simple single gear reduction drive system. Electric work vehicles are going to need at least a couple gears for the same reason modern truck transmissions have stupid low 1st gears and 4x4s have low range.
mlindner 6y ago
That's not true. All EVs have transmissions. But most use a single speed transmission. It's still a transmission if there's only a single gear ratio. It's called a fixed-ratio transmission.

gameswithgo 6y ago

They do if you want a car that performs optimally at a wide enough speed range, like a supercar. But that is an edge case, and eventually even that might not require one.

dharmab 6y ago

* at any speed you would want to drive on a public road.

leetcrew 6y ago

they don't need a clutch because they can't stall. but, like ICEs, they cannot make peak power at 0 RPM. unless the vehicle is already traction limited (quite possible), it could accelerate faster with a shorter first gear. my guess is in reality it's usually cheaper to just overbuild the motors than to add lower gears to hit your desired 0-60 time, but this isn't a law of nature.

mrfusion 6y ago
I wonder what torque looks like at 0 rpm. I thought that was peak? But If it’s bad maybe a torque converter would be useful?
- Cerium 6y ago
  Peak torque is at zero, but peak power is not.
- mywittyname 6y ago
  Electric motors "torque ripple" at low RPMs (well, at all RPMs, but it is most noticeable at lower RPMs), which can cause motor "cogging". Cogging is either a complete stall, or really jerky behavior that feels pretty close to what an ICE is like at very low RPMs. * There are different motor designs out there that alter power delivery for situations where very low-RPM torque is required. As with most design decisions, there are trade-offs involved. And yeah, I'm sure a torque converter would be helpful in that situation. But I think that generally, passenger cars don't need to go very fast, so most EVs can get away with short enough gearing that cogging isn't an issue, at the expense of top seed. * hold some low-power electric motor in your hands, turn it on then gradually clap the output with your fingers. You'll eventually feel the power output go to nothing and the motor will wind. That's cogging. Also, the whole "peak torque at 0 RPMs" thing is really a side effect of the fact that electric motors produce consistent power across the rev band (except at really low, and really high RPMs). And the formula for power is power = torque * RPM. Since power is essentially fixed with an electric motor, you rearrange that equation to be torque = power / RPM, and peak torque is at the limit as RPM goes to 0. In real world applications, torque output is limited by physics and current delivery, so peak torque is truncated at low RPMs.
  - deleted 6y ago
    [deleted]
  - rcxdude 6y ago
    Cogging is only really a problem if you either have a particular motor design or not very sophisticated control. EVs are not generally going to suffer from it.
mixmastamyk 6y ago
What about those new gear boxes that are gradual instead of stepped?
- elihu 6y ago
  You mean continuously variable transmissions? Those could work in an EV I suppose. I don't know much about CVTs but I think the general complaints against them are that they tend to have a narrower highest-to-lowest gear ratio range than a traditional geared transmission, and it's hard to build them to handle large amounts of power.
red369 6y ago
I'm sure you're right about increasing motor power being cheaper than adding gears, but just thought I'd add that my understanding is that you might then also need to increase battery capacity because the rate at which Li-ion batteries can discharge is another limiting factor. As an example, I think there is a Honda 2 motor hybrid system which can accelerate faster (generate more power on the motor driving the wheels) if using power generated from the petrol engine as well as battery power.
saberdancer 6y ago
Another reason is that any type of gearbox or clutch increases losses. EV cars are all about minimizing losses of energy as their power source is not energy dense as petrol.

throwaway0a5e 6y ago

My electric drill begs to differ. Well so long as I don't want to let the magic smoke out it does. Your commuter car can get away with a simple single gear reduction drive system. Electric work vehicles are going to need at least a couple gears for the same reason modern truck transmissions have stupid low 1st gears and 4x4s have low range.

mlindner 6y ago

That's not true. All EVs have transmissions. But most use a single speed transmission. It's still a transmission if there's only a single gear ratio. It's called a fixed-ratio transmission.