@strantor here's something that might seem trivial but is probably important.

The word "speed" has no fixed meaning.

You are talking, I think, about angular frequency* which has the symbol ω and uses rad s⁻¹ (in this case, being the equivalent if Hertz) as units. RPM is a very casual unit and has no SI definition.
*it is also called angular speed and angular rate, but given its rôle in the equations describing the relationship between it, torque, and power the former seems wrong as it confuses things with angular velocity, below.

There is also angular velocity using the symbol ω⃗ and using rad s⁻¹ like ω does meaning the rate of motion rather than of rotation. But the Of course, velocity is a vector and angular frequency is a scalar, but given the general confusion of the meanings of speed and velocity it seems a very good idea to keep them separate.

I have never encountered so much opposition to the word "speed!" It is a well understood word for the target audience who doesn't care if RPM has a SI definition since the definition is in the acronym.

So the only way to can make a motor a "speed device" is by dynamically adjusting P based on the changing load. Whatever analogy you will find is going to have to involve this hidden variable being manipulated, so far as I can see. In nature, the load means work and work means you need P to increase, or the power being used to maintain a certain ω will be moved to dealing with that load and the rotational frequency of the motor will reduce.

If there is an analogy (and I can't think of one at this time) it will require this P adjustment to be structurally included. And that's the trouble, I think.

For a synchronous motor, as torque increases while speed remains constant, P automatically increases. You don't have to do anything to increase it.

 

What benefit do you derive from being on this forum? If you don't have anything constructive and on-topic to say then please move along.

Much of the benefit I get is being able to provide useful answers to questions. There is a good deal of satisfaction in solving a problem for somebody.
In addition, providing others with accurate information is a benefit to humankind.

In addition, the answers to questions that I have posted have included information that I did not have.

 

Much of the benefit I get is being able to provide useful answers to questions. There is a good deal of satisfaction in solving a problem for somebody.
In addition, providing others with accurate information is a benefit to humankind.

That's as I suspected and exactly why I was looking for an analogy. Some people find them helpful in understanding a new topic.

 

For a synchronous motor, as torque increases while speed remains constant, P automatically increases. You don't have to do anything to increase it.

https://www.tutorialspoint.com/effect-of-load-change-on-a-synchronous-motor

"If the load on the motor further increases, then the torque angle (δ) also increases,
i.e., the rotor field poles lag behind the stator field poles by a greater angle (see Figure-2),
but the motor continues to run at synchronous speed."

 

That's as I suspected and exactly why I was looking for an analogy. Some people find them helpful in understanding a new topic.

As you said earlier the problem with analogies is that people don't understand them either. Electrical networks, mechanical systems, hydraulic networks all have basically the same physical laws. If you're lost with one, you will be lost with the others.

Electrician: Electricity is simple, it just like plumbing.
Plumber: Plumbing is simple, it's just like electricity.

 

https://www.tutorialspoint.com/effect-of-load-change-on-a-synchronous-motor

"If the load on the motor further increases, then the torque angle (δ) also increases,
i.e., the rotor field poles lag behind the stator field poles by a greater angle (see Figure-2),
but the motor continues to run at synchronous speed."
View attachment 302559

Thanks but it's not obvious to me what point you're making.

EDIT:
Are you showing that the torque angle increases in order refute an assertion that "nothing changes, the power just goes up?" Because that's not what I meant to imply. When I said "P automatically increases. You don't have to do anything to increase it." What I meant was "you don't have to slap a PID controller on it and force power to go up."

 

As you said earlier the problem with analogies is that people don't understand them either. Electrical networks, mechanical systems, hydraulic networks all have basically the same physical laws. If you're lost with one, you will be lost with the others.

Conficious say "journey of a thousand miles begins with first step (or something)." I think that I failed to make that clear initially; I'm looking for a very elementary training aid; something you might use to introduce the concepts to a child.

Electrician: Electricity is simple, it just like plumbing.
Plumber: Plumbing is simple, it's just like electricity.

strantor: it's just like riding a bike.

I get your point and you're not wrong, but still the process has to start somewhere, and some things are more intuitive and/or more visually demonstrable than others so they lend well to using as analogies. We use the hydraulic analogy for electricity because (while there are nuances when you zoom in) the nature of flow of fluid in a pipe is rather obvious, at least compared to that of electricity. You don't need a PhD in Fluid Dynamics to make the connection.

IMO mechanical power transmission is just barely more complicated than fluid flow, and I think the "power line as a drive shaft" analogy is about as simple as it can be made.

I love analogies. I think of them as a "short cut" to understanding. By associating the subject with concepts already understood, you can skip the "learning to crawl" and proceed directly to "learning to walk." But I perceive that you think an analogy is not the proper tool to use though; if I read that right, then what other tool would you recommend?

 

Conficious say "journey of a thousand miles begins with first step (or something)." I think that I failed to make that clear initially; I'm looking for a very elementary training aid; something you might use to introduce the concepts to a child.

strantor: it's just like riding a bike.

I get your point and you're not wrong, but still the process has to start somewhere, and some things are more intuitive and/or more visually demonstrable than others so they lend well to using as analogies. We use the hydraulic analogy for electricity because (while there are nuances when you zoom in) the nature of flow of fluid in a pipe is rather obvious, at least compared to that of electricity. You don't need a PhD in Fluid Dynamics to make the connection.

IMO mechanical power transmission is just barely more complicated than fluid flow, and I think the "power line as a drive shaft" analogy is about as simple as it can be made.

I love analogies. I think of them as a "short cut" to understanding. By associating the subject with concepts already understood, you can skip the "learning to crawl" and proceed directly to "learning to walk." But I perceive that you think an analogy is not the proper tool to use though; if I read that right, then what other tool would you recommend?

Do like it did with my child.
https://forum.allaboutcircuits.com/...cuum-tube-guitar-amplifier.112582/post-872226
https://youtube.com/shorts/ffIZhntqgwc?si=2eUiHsqNb54A_ATn https://youtube.com/shorts/FnjAH4lk90A?si=VLviImu_9MaTQE8G
Tell them it's a unique thing that they have little or no intuition with other than gravity. Gravity is something most people understand at the effect level because it's vital to survival. Electromagnetism and gravitation are IMO kissing cousins in the electrical analogy realm.
https://forum.allaboutcircuits.com/threads/explaining-the-basics-to-a-15-yo-how.180856/post-1653648

 

It's still not clear to me why you need an analogy for "AC motor speed".
How can that help explain AC motor operation which is basically pretty simple to begin with as in "a rotating magnetic field drags the rotor with it"?

 

Thanks but it's not obvious to me what point you're making.

EDIT:
Are you showing that the torque angle increases in order refute an assertion that "nothing changes, the power just goes up?" Because that's not what I meant to imply. When I said "P automatically increases. You don't have to do anything to increase it." What I meant was "you don't have to slap a PID controller on it and force power to go up."

Just because you don't have to slap an external feedback controller onto it doesn't mean that there isn't feedback -- the feedback mechanism is built into by design.

Think of it as a black box. I've got two motors -- one is a synchronous motor and the other is not, but it has inside the box an electronic feedback controller that makes it behave like a synchronous motor. The person using the motor neither knows nor cares which one they are given. Inside the box, each uses feedback to control its behavior, one is electronic and the other is electromagnetic.

 

Just because you don't have to slap an external feedback controller onto it doesn't mean that there isn't feedback -- the feedback mechanism is built into by design.

Think of it as a black box. I've got two motors -- one is a synchronous motor and the other is not, but it has inside the box an electronic feedback controller that makes it behave like a synchronous motor. The person using the motor neither knows nor cares which one they are given. Inside the box, each uses feedback to control its behavior, one is electronic and the other is electromagnetic.

What is your point? I don't want to be rude but you seem to be willfully ignoring the point of the thread (to simplify the explanation of the differences between motor types, with an analogy) and dragging the discussion in the opposite direction. If someone needed a thumb rule for when to use a Phillips screw driver and when to use a slotted one, would you talk about material dutility and torsional forces, and then summarize with something that sounds to the uninitiated basically like "it actually doesn't matter?"

 

That's as I suspected and exactly why I was looking for an analogy. Some people find them helpful in understanding a new topic.

I predict a post about you throwing stones coming very soon. You just can't disagree with him.

 

I think the desire to learn will always trump any cleverly ( simply ? ) worded "teaching" method.

I was reading Popular-Electronics, Popular-Science, and the McGee-Radio & Electronics-Catalog
when I was ~7-years old, this was because my Dad was perpetually pissed-off at the world
and didn't want to deal with my incessant questions,
so he bought a used set of "World-Book-Encyclopedias" for me, and his answer was always, "look it up".
I learned even more from picking through other peoples trash that was set out by the road for pickup.
At ~15, and with zero-formal-training, I was building top-notch home-stereo-speakers and
working without pay as an Assistant-Engineer at the Local AM-Radio-Station,
and Hot-Rodding my friends Cars.
I made lots of mistakes, and it's amazing that I'm still alive.

Some people have a genuine interest, ( in something, or even many things ),
and others are just "going though the motions" just to get by.
The ones that don't really want to "be-there" will learn nothing,
no matter your sincerity, or how You approach them.
The ones that DO want to be there, will figure it out, and You can't stop them.
.
.
.

 

I think the desire to learn will always trump any cleverly ( simply ? ) worded "teaching" method.

I was reading Popular-Electronics, Popular-Science, and the McGee-Radio & Electronics-Catalog
when I was ~7-years old, this was because my Dad was perpetually pissed-off at the world
and didn't want to deal with my incessant questions,
so he bought a used set of "World-Book-Encyclopedias" for me, and his answer was always, "look it up".
I learned even more from picking through other peoples trash that was set out by the road for pickup.
At ~15, and with zero-formal-training, I was building top-notch home-stereo-speakers and
working without pay as an Assistant-Engineer at the Local AM-Radio-Station,
and Hot-Rodding my friends Cars.
I made lots of mistakes, and it's amazing that I'm still alive.

Some people have a genuine interest, ( in something, or even many things ),
and others are just "going though the motions" just to get by.
The ones that don't really want to "be-there" will learn nothing,
no matter your sincerity, or how You approach them.
The ones that DO want to be there, will figure it out, and You can't stop them.
.
.
.

INDEED!!!! TOTALLY CORRECT!!
And some people do engineering to earn a living, and may even be quite good at it. And some OTHER folks ARE ENGINEERS, 24/7 and it is what they are, more than what they do. I was the kid who took my toys apart to see how they worked, and then put them back together again so they worked again. That was the fun part. Taking things that did not work apart and then assembling them so that they worked again was always educational and often fun, and occasionally profitable.

 

An old busted 5-Tube-Clock-Radio makes a great Christmas-Present !!!
.
.
.

 

I was the kid who took my toys apart to see how they worked, and then put them back together again so they worked again.

At 5 years old my sister was given an expensive 'sleeping doll'. She promptly took it out to our parents workshop and clamped its head in a vice because she was curious as to how the eyes worked. Unfortunately after that the eyes didn't work!