3 ms·

you ought to get into the habit of looking at a spectral analysis of the sound in your home. modern power supplies and motors rely on the ever more powerful and

by bronz 9y ago

you ought to get into the habit of looking at a spectral analysis of the sound in your home. modern power supplies and motors rely on the ever more powerful and cheap power transistors that we have these days -- they are able to switch power on and off at very high frequencies and thus reduce the size of the rest of the circuitry needed to raise or lower voltage. but this often results in extremely high pitched sound coming from parts that, for whatever reason, physically move or expand in response to current or voltage changes. in cheap electronics, this effect is not accounted for and controlled with vibration dampening materials applied to the vibrating parts, and the result is a maddening high pitched squeal. even if humans arent able to hear it, there could be devices in your house that make some kinds of pets uncomfortable. ive been meaning to buy something that will let me detect ultrasonic sound so that i can smash those devices with a hammer. ive always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. i think it would be great because, as long as they were induction based motors, you could run one and leave the other off with no interference from the one that is turned off. it would be like having a transmission without any of the energy loss or maintenance problems. you could also distribute power however you want among the two motors, and in a way have something like an infinitely variable transmission. that would be really cool.

Animats 9y ago
I've always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. Traction motors for locomotives and transit vehicles used to be built with multiple windings and switching. The windings were switched from series to parallel as speed increased. Locomotives once had manual "transition controllers" for this.[1] Here's the more automatic mechanism from a PCC streetcar of the late 1940s.[2] The operator just has an accelerator pedal, and all that control gear takes care of the complexity of operating the motors. [1] http://cs.trains.com/trn/f/741/p/249329/2783262.aspx http://cs.trains.com/trn/f/741/p/249329/2783262.aspx [2] https://www.youtube.com/watch?v=pgSWuTxQh6s https://www.youtube.com/watch?v=pgSWuTxQh6s
pbasista 9y ago
I've always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. The dual motor versions (D) of Tesla electric vehicles (models S and X at least) use this principle. As far as I know, they have induction motors. However, I am not sure to which extent one of the motors is used primarily for high torque and the other for high speed.
- vvanders 9y ago
  Yup, the front motor is the cruising motor and the rear one is the accelerating one(since weight distribution means that the rear wheels get a bit more traction). They shut the rear motor down at highway speeds giving the Dual Motor cars slightly better range.
  - MBCook 9y ago
    Do the single motorcars only have one of those two? If so which? Or do they have a third kind of motor which is wound to be a better balance?
    - vvanders 9y ago
      My understanding is that there's 3 configurations Single motor, non-P: 1 large motor in the rear. Dual motor, non-P: 2 small motors in front/rear with front motor geared for cruising, rear for accel. Dual motor, Performance: 1 small motor in front geared for cruising, one large motor in the rear. There's really no reason to have a front motor only. It's done in ICE cars to save cost/complexity since the engine is up front. With how the center of gravity shifts during accel you want the drive wheels to be on the rear since they have better traction. Same reason in reverse you have large disk brakes on the front wheels and drum in the rear.
      - ars 9y ago
        > you want the drive wheels to be on the rear since they have better traction. But you need a powerful motor to act as the brake (you want to avoid friction braking as much as possible). And that needs to be in the front.
hwillis 9y ago
>modern power supplies and motors rely on the ever more powerful and cheap power transistors that we have these days -- they are able to switch power on and off at very high frequencies and thus reduce the size of the rest of the circuitry needed to raise or lower voltage. but this often results in extremely high pitched sound coming from parts that, for whatever reason, physically move or expand in response to current or voltage changes. in cheap electronics, this effect is not accounted for and controlled with vibration dampening materials applied to the vibrating parts, and the result is a maddening high pitched squeal. Battery-powered motors almost always operate in the range of 80 to several hundred kHz, which is basically unavoidable. Those make up a minority of motors in your home. Wall-plugged motors use AC, in which case they have no high-frequency harmonics, or they are DC in which case the ultrasonic noise comes from the brushes scraping and arcing on the commutator. This is the source of noise in vacuums and the one you're most likely to hear but it's basically static at a very high frequency. Supposedly this is one of the reasons pets hate vacuums, because it's a loud noise of a rarely-heard pitch. Vacuums will be much louder than almost any other motor in your house. The difference between cheap an expensive power supplies is often down to the use of fully integrated PSUs. The expensive ones operate in the MHz, which lets them use very small capacitors that are built into the chip. Cheaper supplies operate at closer to audible frequency, but they aren't actually louder despite using larger components. The efficiency is relatively close to a more expensive supply so the amount of energy loss is also similar. >ive been meaning to buy something that will let me detect ultrasonic sound so that i can smash those devices with a hammer. It's actually very easy to make one! Cheap (<50 cents) electret microphones can hear up to 100 kHz and are pretty common in DIY bat detecting microphones[1]. Note that you can't use normal ultrasonic sensors like those used in rangefinders (about 1 cm wide, black plastic cylinders). Those are heavily tuned to resonate at 40 kHz and can't pick up sound outside that range at all. >ive always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. That's exactly why 4wd Tesla models have a longer EPA rated range, or at least speculated to be why, anyway. The EPA range test is done at a set speed and Tesla optimized on that by having one motor for lower speed and one for higher speed. It's also useful for vectoring torque to the front/back for braking/acceleration. You can't use it like a variable transmission though, since there's very limited benefit to splitting the power up. The benefit in practice is pretty unclear since you won't be driving the exact speed it's optimized for and the difference in efficiency is only a few percent anyway. [1]: http://www.wildlife-sound.org/equipment/technote/micdesigns/index.html http://www.wildlife-sound.org/equipment/technote/micdesigns/...
gnicholas 9y ago
The first time I sat in a Prius, I heard an annoying high-pitched noise like this. I don't hear them in current models, but it's possible that this is just because I'm 15 years older now and my high-frequency hearing is not as good.
- hwillis 9y ago
  That phenomenon is known as cogging[1]. Improved motor controls (Direct Torque Control) and motor designs (trapezoidal magnetization) have indeed eliminated it from all but the cheapest designs. Induction motors like those in the Tesla model S and X (but not the upcoming 3) don't have any cogging at all. [1]: https://en.wikipedia.org/wiki/Cogging_torque https://en.wikipedia.org/wiki/Cogging_torque

by bronz 9y ago

Animats 9y ago

I've always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. Traction motors for locomotives and transit vehicles used to be built with multiple windings and switching. The windings were switched from series to parallel as speed increased. Locomotives once had manual "transition controllers" for this.[1] Here's the more automatic mechanism from a PCC streetcar of the late 1940s.[2] The operator just has an accelerator pedal, and all that control gear takes care of the complexity of operating the motors. [1] http://cs.trains.com/trn/f/741/p/249329/2783262.aspx http://cs.trains.com/trn/f/741/p/249329/2783262.aspx [2] https://www.youtube.com/watch?v=pgSWuTxQh6s https://www.youtube.com/watch?v=pgSWuTxQh6s

pbasista 9y ago

I've always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. The dual motor versions (D) of Tesla electric vehicles (models S and X at least) use this principle. As far as I know, they have induction motors. However, I am not sure to which extent one of the motors is used primarily for high torque and the other for high speed.

vvanders 9y ago
Yup, the front motor is the cruising motor and the rear one is the accelerating one(since weight distribution means that the rear wheels get a bit more traction). They shut the rear motor down at highway speeds giving the Dual Motor cars slightly better range.
- MBCook 9y ago
  Do the single motorcars only have one of those two? If so which? Or do they have a third kind of motor which is wound to be a better balance?
  - vvanders 9y ago
    My understanding is that there's 3 configurations Single motor, non-P: 1 large motor in the rear. Dual motor, non-P: 2 small motors in front/rear with front motor geared for cruising, rear for accel. Dual motor, Performance: 1 small motor in front geared for cruising, one large motor in the rear. There's really no reason to have a front motor only. It's done in ICE cars to save cost/complexity since the engine is up front. With how the center of gravity shifts during accel you want the drive wheels to be on the rear since they have better traction. Same reason in reverse you have large disk brakes on the front wheels and drum in the rear.
    - ars 9y ago
      > you want the drive wheels to be on the rear since they have better traction. But you need a powerful motor to act as the brake (you want to avoid friction braking as much as possible). And that needs to be in the front.

hwillis 9y ago

>modern power supplies and motors rely on the ever more powerful and cheap power transistors that we have these days -- they are able to switch power on and off at very high frequencies and thus reduce the size of the rest of the circuitry needed to raise or lower voltage. but this often results in extremely high pitched sound coming from parts that, for whatever reason, physically move or expand in response to current or voltage changes. in cheap electronics, this effect is not accounted for and controlled with vibration dampening materials applied to the vibrating parts, and the result is a maddening high pitched squeal. Battery-powered motors almost always operate in the range of 80 to several hundred kHz, which is basically unavoidable. Those make up a minority of motors in your home. Wall-plugged motors use AC, in which case they have no high-frequency harmonics, or they are DC in which case the ultrasonic noise comes from the brushes scraping and arcing on the commutator. This is the source of noise in vacuums and the one you're most likely to hear but it's basically static at a very high frequency. Supposedly this is one of the reasons pets hate vacuums, because it's a loud noise of a rarely-heard pitch. Vacuums will be much louder than almost any other motor in your house. The difference between cheap an expensive power supplies is often down to the use of fully integrated PSUs. The expensive ones operate in the MHz, which lets them use very small capacitors that are built into the chip. Cheaper supplies operate at closer to audible frequency, but they aren't actually louder despite using larger components. The efficiency is relatively close to a more expensive supply so the amount of energy loss is also similar. >ive been meaning to buy something that will let me detect ultrasonic sound so that i can smash those devices with a hammer. It's actually very easy to make one! Cheap (<50 cents) electret microphones can hear up to 100 kHz and are pretty common in DIY bat detecting microphones[1]. Note that you can't use normal ultrasonic sensors like those used in rangefinders (about 1 cm wide, black plastic cylinders). Those are heavily tuned to resonate at 40 kHz and can't pick up sound outside that range at all. >ive always wondered what it would be like if you used a dual motor system in a car, where one motor is wound and sized for very high torque and the other motor is wound and sized for very high speed. That's exactly why 4wd Tesla models have a longer EPA rated range, or at least speculated to be why, anyway. The EPA range test is done at a set speed and Tesla optimized on that by having one motor for lower speed and one for higher speed. It's also useful for vectoring torque to the front/back for braking/acceleration. You can't use it like a variable transmission though, since there's very limited benefit to splitting the power up. The benefit in practice is pretty unclear since you won't be driving the exact speed it's optimized for and the difference in efficiency is only a few percent anyway. [1]: http://www.wildlife-sound.org/equipment/technote/micdesigns/index.html http://www.wildlife-sound.org/equipment/technote/micdesigns/...

gnicholas 9y ago

The first time I sat in a Prius, I heard an annoying high-pitched noise like this. I don't hear them in current models, but it's possible that this is just because I'm 15 years older now and my high-frequency hearing is not as good.

hwillis 9y ago
That phenomenon is known as cogging[1]. Improved motor controls (Direct Torque Control) and motor designs (trapezoidal magnetization) have indeed eliminated it from all but the cheapest designs. Induction motors like those in the Tesla model S and X (but not the upcoming 3) don't have any cogging at all. [1]: https://en.wikipedia.org/wiki/Cogging_torque https://en.wikipedia.org/wiki/Cogging_torque