Novice question about high and low speed motors
Why some low speed electrical drives employ a high-speed motor and some form of mechanical speed reduction rather than direct drive motor. Is it because of size?
motor
New contributor
add a comment |
Why some low speed electrical drives employ a high-speed motor and some form of mechanical speed reduction rather than direct drive motor. Is it because of size?
motor
New contributor
2
Because you will find it difficult to get either an AC or DC motor capable of rotating at very low speeds (less than 30rpm for example) and still produce high levels of torque.
– David777
10 hours ago
@David777 And the question is why it is difficult.
– Harry Svensson
9 hours ago
Put another way from how @David777 put it: for a given basic motor design (induction, DC field wound, DC permanent magnet with a given magnet material, etc.), the torque you can get out of the motor is roughly proportional to the amount of power dissipated in the motor. The power you can get out of the motor at a given torque is proportional to how fast you can turn it. So it's usually most economical to turn the motors as fast as the bearings will let you, and gear it down.
– TimWescott
8 hours ago
1
@HarrySvensson Sorry Harry, I thought I did answer why, by saying that electric motors are generally high speed rotating machines and torque is greatly reduced by lowering their rotational speed, as Tim and DaveTweed also said. But please feel free to expand on my answer if you want as we are supposed to be helping the OP.
– David777
7 hours ago
@David777 Yes, you explained the first level of why (which doesn't answer much on its own), and Dave Tweed went to the second level of why, which was why of your why (which is what OP is actually asking about). I don't know if it was due to my comment, or if Dave is just that good. My money is on Dave being that good. - So far you haven't given an answer David, you've made two comments.
– Harry Svensson
7 hours ago
add a comment |
Why some low speed electrical drives employ a high-speed motor and some form of mechanical speed reduction rather than direct drive motor. Is it because of size?
motor
New contributor
Why some low speed electrical drives employ a high-speed motor and some form of mechanical speed reduction rather than direct drive motor. Is it because of size?
motor
motor
New contributor
New contributor
New contributor
asked 12 hours ago
ArtyomShep
82
82
New contributor
New contributor
2
Because you will find it difficult to get either an AC or DC motor capable of rotating at very low speeds (less than 30rpm for example) and still produce high levels of torque.
– David777
10 hours ago
@David777 And the question is why it is difficult.
– Harry Svensson
9 hours ago
Put another way from how @David777 put it: for a given basic motor design (induction, DC field wound, DC permanent magnet with a given magnet material, etc.), the torque you can get out of the motor is roughly proportional to the amount of power dissipated in the motor. The power you can get out of the motor at a given torque is proportional to how fast you can turn it. So it's usually most economical to turn the motors as fast as the bearings will let you, and gear it down.
– TimWescott
8 hours ago
1
@HarrySvensson Sorry Harry, I thought I did answer why, by saying that electric motors are generally high speed rotating machines and torque is greatly reduced by lowering their rotational speed, as Tim and DaveTweed also said. But please feel free to expand on my answer if you want as we are supposed to be helping the OP.
– David777
7 hours ago
@David777 Yes, you explained the first level of why (which doesn't answer much on its own), and Dave Tweed went to the second level of why, which was why of your why (which is what OP is actually asking about). I don't know if it was due to my comment, or if Dave is just that good. My money is on Dave being that good. - So far you haven't given an answer David, you've made two comments.
– Harry Svensson
7 hours ago
add a comment |
2
Because you will find it difficult to get either an AC or DC motor capable of rotating at very low speeds (less than 30rpm for example) and still produce high levels of torque.
– David777
10 hours ago
@David777 And the question is why it is difficult.
– Harry Svensson
9 hours ago
Put another way from how @David777 put it: for a given basic motor design (induction, DC field wound, DC permanent magnet with a given magnet material, etc.), the torque you can get out of the motor is roughly proportional to the amount of power dissipated in the motor. The power you can get out of the motor at a given torque is proportional to how fast you can turn it. So it's usually most economical to turn the motors as fast as the bearings will let you, and gear it down.
– TimWescott
8 hours ago
1
@HarrySvensson Sorry Harry, I thought I did answer why, by saying that electric motors are generally high speed rotating machines and torque is greatly reduced by lowering their rotational speed, as Tim and DaveTweed also said. But please feel free to expand on my answer if you want as we are supposed to be helping the OP.
– David777
7 hours ago
@David777 Yes, you explained the first level of why (which doesn't answer much on its own), and Dave Tweed went to the second level of why, which was why of your why (which is what OP is actually asking about). I don't know if it was due to my comment, or if Dave is just that good. My money is on Dave being that good. - So far you haven't given an answer David, you've made two comments.
– Harry Svensson
7 hours ago
2
2
Because you will find it difficult to get either an AC or DC motor capable of rotating at very low speeds (less than 30rpm for example) and still produce high levels of torque.
– David777
10 hours ago
Because you will find it difficult to get either an AC or DC motor capable of rotating at very low speeds (less than 30rpm for example) and still produce high levels of torque.
– David777
10 hours ago
@David777 And the question is why it is difficult.
– Harry Svensson
9 hours ago
@David777 And the question is why it is difficult.
– Harry Svensson
9 hours ago
Put another way from how @David777 put it: for a given basic motor design (induction, DC field wound, DC permanent magnet with a given magnet material, etc.), the torque you can get out of the motor is roughly proportional to the amount of power dissipated in the motor. The power you can get out of the motor at a given torque is proportional to how fast you can turn it. So it's usually most economical to turn the motors as fast as the bearings will let you, and gear it down.
– TimWescott
8 hours ago
Put another way from how @David777 put it: for a given basic motor design (induction, DC field wound, DC permanent magnet with a given magnet material, etc.), the torque you can get out of the motor is roughly proportional to the amount of power dissipated in the motor. The power you can get out of the motor at a given torque is proportional to how fast you can turn it. So it's usually most economical to turn the motors as fast as the bearings will let you, and gear it down.
– TimWescott
8 hours ago
1
1
@HarrySvensson Sorry Harry, I thought I did answer why, by saying that electric motors are generally high speed rotating machines and torque is greatly reduced by lowering their rotational speed, as Tim and DaveTweed also said. But please feel free to expand on my answer if you want as we are supposed to be helping the OP.
– David777
7 hours ago
@HarrySvensson Sorry Harry, I thought I did answer why, by saying that electric motors are generally high speed rotating machines and torque is greatly reduced by lowering their rotational speed, as Tim and DaveTweed also said. But please feel free to expand on my answer if you want as we are supposed to be helping the OP.
– David777
7 hours ago
@David777 Yes, you explained the first level of why (which doesn't answer much on its own), and Dave Tweed went to the second level of why, which was why of your why (which is what OP is actually asking about). I don't know if it was due to my comment, or if Dave is just that good. My money is on Dave being that good. - So far you haven't given an answer David, you've made two comments.
– Harry Svensson
7 hours ago
@David777 Yes, you explained the first level of why (which doesn't answer much on its own), and Dave Tweed went to the second level of why, which was why of your why (which is what OP is actually asking about). I don't know if it was due to my comment, or if Dave is just that good. My money is on Dave being that good. - So far you haven't given an answer David, you've made two comments.
– Harry Svensson
7 hours ago
add a comment |
1 Answer
1
active
oldest
votes
Power is the product of torque and speed. If you want high power at low speed, then you need high torque.
In an electric motor, the torque is basically a function of the radius of the rotor, its surface area, and the magnetic field intensity between the rotor and the stator.
You can play with all three of these variables, but there are definite limits on how much field intensity you can get with reasonable materials. Therefore, you end up needing either a long motor or a large-diameter motor, both of which require lots of extra (expensive) material to produce.
This is why it usually works out best to go back to the first equation and raise the speed of the motor by means of a gearbox. This gives you the required output speed and torque while allowing the motor speed to be higher and its torque to be lower in order to get the required power.
"but there are definite limits on how much field intensity you can get with reasonable materials", I assume you're talking about magnetic saturation here?
– Harry Svensson
7 hours ago
2
@HarrySvensson: Actually, no. There is an air gap between the stator and the rotor that largely prevents saturation. But this gap has a minimum width that is mostly determined by the practicalities of manufacturing the motor -- things like basic machine tolerances, bearing runout, thermal expansion, vibration, etc. The width of this gap puts a limit on how intense (or effective) the field can be.
– Dave Tweed♦
4 hours ago
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["\$", "\$"]]);
});
});
}, "mathjax-editing");
StackExchange.ifUsing("editor", function () {
return StackExchange.using("schematics", function () {
StackExchange.schematics.init();
});
}, "cicuitlab");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "135"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
ArtyomShep is a new contributor. Be nice, and check out our Code of Conduct.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2felectronics.stackexchange.com%2fquestions%2f414583%2fnovice-question-about-high-and-low-speed-motors%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Power is the product of torque and speed. If you want high power at low speed, then you need high torque.
In an electric motor, the torque is basically a function of the radius of the rotor, its surface area, and the magnetic field intensity between the rotor and the stator.
You can play with all three of these variables, but there are definite limits on how much field intensity you can get with reasonable materials. Therefore, you end up needing either a long motor or a large-diameter motor, both of which require lots of extra (expensive) material to produce.
This is why it usually works out best to go back to the first equation and raise the speed of the motor by means of a gearbox. This gives you the required output speed and torque while allowing the motor speed to be higher and its torque to be lower in order to get the required power.
"but there are definite limits on how much field intensity you can get with reasonable materials", I assume you're talking about magnetic saturation here?
– Harry Svensson
7 hours ago
2
@HarrySvensson: Actually, no. There is an air gap between the stator and the rotor that largely prevents saturation. But this gap has a minimum width that is mostly determined by the practicalities of manufacturing the motor -- things like basic machine tolerances, bearing runout, thermal expansion, vibration, etc. The width of this gap puts a limit on how intense (or effective) the field can be.
– Dave Tweed♦
4 hours ago
add a comment |
Power is the product of torque and speed. If you want high power at low speed, then you need high torque.
In an electric motor, the torque is basically a function of the radius of the rotor, its surface area, and the magnetic field intensity between the rotor and the stator.
You can play with all three of these variables, but there are definite limits on how much field intensity you can get with reasonable materials. Therefore, you end up needing either a long motor or a large-diameter motor, both of which require lots of extra (expensive) material to produce.
This is why it usually works out best to go back to the first equation and raise the speed of the motor by means of a gearbox. This gives you the required output speed and torque while allowing the motor speed to be higher and its torque to be lower in order to get the required power.
"but there are definite limits on how much field intensity you can get with reasonable materials", I assume you're talking about magnetic saturation here?
– Harry Svensson
7 hours ago
2
@HarrySvensson: Actually, no. There is an air gap between the stator and the rotor that largely prevents saturation. But this gap has a minimum width that is mostly determined by the practicalities of manufacturing the motor -- things like basic machine tolerances, bearing runout, thermal expansion, vibration, etc. The width of this gap puts a limit on how intense (or effective) the field can be.
– Dave Tweed♦
4 hours ago
add a comment |
Power is the product of torque and speed. If you want high power at low speed, then you need high torque.
In an electric motor, the torque is basically a function of the radius of the rotor, its surface area, and the magnetic field intensity between the rotor and the stator.
You can play with all three of these variables, but there are definite limits on how much field intensity you can get with reasonable materials. Therefore, you end up needing either a long motor or a large-diameter motor, both of which require lots of extra (expensive) material to produce.
This is why it usually works out best to go back to the first equation and raise the speed of the motor by means of a gearbox. This gives you the required output speed and torque while allowing the motor speed to be higher and its torque to be lower in order to get the required power.
Power is the product of torque and speed. If you want high power at low speed, then you need high torque.
In an electric motor, the torque is basically a function of the radius of the rotor, its surface area, and the magnetic field intensity between the rotor and the stator.
You can play with all three of these variables, but there are definite limits on how much field intensity you can get with reasonable materials. Therefore, you end up needing either a long motor or a large-diameter motor, both of which require lots of extra (expensive) material to produce.
This is why it usually works out best to go back to the first equation and raise the speed of the motor by means of a gearbox. This gives you the required output speed and torque while allowing the motor speed to be higher and its torque to be lower in order to get the required power.
answered 8 hours ago
Dave Tweed♦
117k9144256
117k9144256
"but there are definite limits on how much field intensity you can get with reasonable materials", I assume you're talking about magnetic saturation here?
– Harry Svensson
7 hours ago
2
@HarrySvensson: Actually, no. There is an air gap between the stator and the rotor that largely prevents saturation. But this gap has a minimum width that is mostly determined by the practicalities of manufacturing the motor -- things like basic machine tolerances, bearing runout, thermal expansion, vibration, etc. The width of this gap puts a limit on how intense (or effective) the field can be.
– Dave Tweed♦
4 hours ago
add a comment |
"but there are definite limits on how much field intensity you can get with reasonable materials", I assume you're talking about magnetic saturation here?
– Harry Svensson
7 hours ago
2
@HarrySvensson: Actually, no. There is an air gap between the stator and the rotor that largely prevents saturation. But this gap has a minimum width that is mostly determined by the practicalities of manufacturing the motor -- things like basic machine tolerances, bearing runout, thermal expansion, vibration, etc. The width of this gap puts a limit on how intense (or effective) the field can be.
– Dave Tweed♦
4 hours ago
"but there are definite limits on how much field intensity you can get with reasonable materials", I assume you're talking about magnetic saturation here?
– Harry Svensson
7 hours ago
"but there are definite limits on how much field intensity you can get with reasonable materials", I assume you're talking about magnetic saturation here?
– Harry Svensson
7 hours ago
2
2
@HarrySvensson: Actually, no. There is an air gap between the stator and the rotor that largely prevents saturation. But this gap has a minimum width that is mostly determined by the practicalities of manufacturing the motor -- things like basic machine tolerances, bearing runout, thermal expansion, vibration, etc. The width of this gap puts a limit on how intense (or effective) the field can be.
– Dave Tweed♦
4 hours ago
@HarrySvensson: Actually, no. There is an air gap between the stator and the rotor that largely prevents saturation. But this gap has a minimum width that is mostly determined by the practicalities of manufacturing the motor -- things like basic machine tolerances, bearing runout, thermal expansion, vibration, etc. The width of this gap puts a limit on how intense (or effective) the field can be.
– Dave Tweed♦
4 hours ago
add a comment |
ArtyomShep is a new contributor. Be nice, and check out our Code of Conduct.
ArtyomShep is a new contributor. Be nice, and check out our Code of Conduct.
ArtyomShep is a new contributor. Be nice, and check out our Code of Conduct.
ArtyomShep is a new contributor. Be nice, and check out our Code of Conduct.
Thanks for contributing an answer to Electrical Engineering Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2felectronics.stackexchange.com%2fquestions%2f414583%2fnovice-question-about-high-and-low-speed-motors%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
Because you will find it difficult to get either an AC or DC motor capable of rotating at very low speeds (less than 30rpm for example) and still produce high levels of torque.
– David777
10 hours ago
@David777 And the question is why it is difficult.
– Harry Svensson
9 hours ago
Put another way from how @David777 put it: for a given basic motor design (induction, DC field wound, DC permanent magnet with a given magnet material, etc.), the torque you can get out of the motor is roughly proportional to the amount of power dissipated in the motor. The power you can get out of the motor at a given torque is proportional to how fast you can turn it. So it's usually most economical to turn the motors as fast as the bearings will let you, and gear it down.
– TimWescott
8 hours ago
1
@HarrySvensson Sorry Harry, I thought I did answer why, by saying that electric motors are generally high speed rotating machines and torque is greatly reduced by lowering their rotational speed, as Tim and DaveTweed also said. But please feel free to expand on my answer if you want as we are supposed to be helping the OP.
– David777
7 hours ago
@David777 Yes, you explained the first level of why (which doesn't answer much on its own), and Dave Tweed went to the second level of why, which was why of your why (which is what OP is actually asking about). I don't know if it was due to my comment, or if Dave is just that good. My money is on Dave being that good. - So far you haven't given an answer David, you've made two comments.
– Harry Svensson
7 hours ago