There are plenty of analogies for torque motors; cars, trains, bicycles, basically everything. For a fixed input, if you add load, the motor/engine/person slows down; you lighten load, it speeds up.

A car with cruise control or a generator with a governor isn't really what I'm looking for; those are both torque-based devices with feedback loops to artificially force them to behave like a speed-based devices. I'm looking for an honest to goodness example of a speed-controlled device "in nature" but I'm starting to think that apart from induction and PM AC motors there are none. These things just aren't natural.

The only thing I can come up with is a wind-up clock, but the example breaks down if I try to expound on it. If you apply load to a clock, hang weights off its arms, I think (not sure, never tried) it will slow down.

 

The question is not very clear.
The word "Speed" generally refers to the velocity of an object,
but Motors are usually measured in RPM and Torque, not velocity.

The word "Speed" is quite often misused in colloquial-English.

There is no "Speed" ( RPM ),
without continuous Torque being applied to overcome inertia, and friction.

The "Speed" that You may be referring to,
is "only" a mathematical-calculation that is derived from the equation ............
Torque X RPM divided by 5250 = Horsepower.

There are similar formulas for use with different units of measure,
but they are all measuring the same thing, which is basically, Force -vs- Time.
.
.
.

 

Speed control in nature?

Sure, using gravitational fields.

1 galactic system rotation.
1 solar rotation.
1 Earth year.
1 lunar cycle.

 

Synchronous motor.

 

There are plenty of analogies for torque motors; cars, trains, bicycles, basically everything. For a fixed input, if you add load, the motor/engine/person slows down; you lighten load, it speeds up.

A car with cruise control or a generator with a governor isn't really what I'm looking for; those are both torque-based devices with feedback loops to artificially force them to behave like a speed-based devices. I'm looking for an honest to goodness example of a speed-controlled device "in nature" but I'm starting to think that apart from induction and PM AC motors there are none. These things just aren't natural.

The only thing I can come up with is a wind-up clock, but the example breaks down if I try to expound on it. If you apply load to a clock, hang weights off its arms, I think (not sure, never tried) it will slow down.

I don't see how your AC motor is any different than the cruise control example. If the motor is loaded and tries to slow down, that results in feedback within the motor that increases the torque in order to speed it back up. Same with when a load is removed. What's unnatural about that? For that matter, how is that not torque-based? In an induction motor, if you increase the load, that will increase the slip and that slip is the error signal that results in greater torque being produced.

 

In an induction motor, if you increase the load, that will increase the slip and that slip is the error signal that results in greater torque being produced.

And in a synchronous motor, an increase in load will cause the angle between the rotating field and the rotor field to increase, which causes the field current (and thus torque/power) to increase sufficiently to maintain the synchronous speed.
If the load becomes too high, then the angle between the two fields will go so high that the motor will suddenly drop out of sync with a significant drop in rotor speed.

 

There are negative feedback systems all around in nature. If a herd of animals expands but the foor supply does not increase then animals die off as things stabilize. As the water supply increases the flow in a river increases to avoid expanding the width of the river.

In an induction motor, as the torque load increases the slip angle becomes larger increasing the torque. So the motor slows a bit but that is compensated some by the torque rise.

Of course the whole question is ambiguouse and does not make sense, any way.

 

Speed control in nature?

Sure, using gravitational fields.

1 galactic system rotation.
1 solar rotation.
1 Earth year.
1 lunar cycle.

I was hoping for something more universally understood than an electric motor. Gravitational fields are sorta going the other direction. Even if I understood them well enough to use the analogy I doubt anyone would understand me.

Synchronous motor.

Synchronous motors are among the motors for which I'm searching for an analogy to.

 

Of course the whole question is ambiguouse and does not make sense, any way.

Was it? Ok let me try again.

In a Synchronous motor, speed is constant. As load increases, torque increases while speed remains unchanged, (until the stall point).

In an induction motor, same story but with a slight sag in RPM as load increases. I am lumping them in with synchronous motors as "constant speed/variable power" machines.

In a series-wound brushed motor, the opposite is true. As load increases, speed decreases as torque increases. It's more of a "variable speed/constant power" machine. There are plenty of universally understood analogies for this: a steam locomotive, a gas engine, you on your bicycle, etc.

But what analogies are there for the constant speed machines?

 

The question is not very clear.
The word "Speed" generally refers to the velocity of an object,
but Motors are usually measured in RPM and Torque, not velocity.

The word "Speed" is quite often misused in colloquial-English.

There is no "Speed" ( RPM ),
without continuous Torque being applied to overcome inertia, and friction.

The "Speed" that You may be referring to,
is "only" a mathematical-calculation that is derived from the equation ............
Torque X RPM divided by 5250 = Horsepower.

There are similar formulas for use with different units of measure,
but they are all measuring the same thing, which is basically, Force -vs- Time.
.
.
.

Do you seriously not know what I mean by "speed?" If so, you're going to be very confused going forward because I'm not going to stop saying it.

 

But what analogies are there for the constant speed machines?

How about the hyperfine transition frequency of electrons in rubidium-87 atoms for an atomic clock.
Can't get much more constant than that.

 

Was it? Ok let me try again.

In a Synchronous motor, speed is constant. As load increases, torque increases while speed remains unchanged, (until the stall point).

In an induction motor, same story but with a slight sag in RPM as load increases. I am lumping them in with synchronous motors as "constant speed/variable power" machines.

In a series-wound brushed motor, the opposite is true. As load increases, speed decreases as torque increases. It's more of a "variable speed/constant power" machine. There are plenty of universally understood analogies for this: a steam locomotive, a gas engine, you on your bicycle, etc.

But what analogies are there for the constant speed machines?

But you just said it yourself -- in an induction motor, as the load increases, the RPM slows. How is that fundamentally any different than in your series-wound brushed motor example? Let alone somehow being "opposite" to it?

In both cases, as the load tries to slow the motor, internal feedback mechanisms result in an increase in torque that attempts to restore the speed to it's no-load value. It's just that the feedback mechanism is more powerful in an induction motor and so there is less speed drop.

The synchronous motor is not really any different, except again with an even more powerful feedback mechanism. You might even say that it has an integral term in it that reduces the steady-state speed error to zero. I think this is probably going to far since you would expect to see the rotation speed up for a bit after the load is removed and I don't think that happens (but I don't know that much about motors, either).

 

I was hoping for something more universally understood than an electric motor. Gravitational fields are sorta going the other direction. Even if I understood them well enough to use the analogy I doubt anyone would understand me.

Well, in nature you need to have action at a distance from a 'force' with some sort of stabilizing free-back in the form of energy/momentum conservation vs inertia.

The basis is much like the electrical characteristics of a LC tank oscillator where we have physical EM properties that determine the 'speed' of energy exchange between reactive elements that can be the electrical length of a conductor or transmission media.

 

But you just said it yourself -- in an induction motor

Ok for the sake of this discussion I will limit the category for which I am searching for an analogy, to synchronous motors.

as the load increases, the RPM slows. How is that fundamentally any different than in your series-wound brushed motor example? Let alone somehow being "opposite" to it?

A synchronous motor (or induction motor, last time I'll mention it, and just for the sake of continuity with your reply) has a certain speed it "wants" to deliver, and will run that speed (or close to it - induction) regardless of load. A series brushed motor has a certain power output that it "wants" to deliver; give it less than rated load and it will spin faster than rated speed to compensate. Give it zero load and it will try its best to spin at the speed of light.

The synchronous motor is not really any different, except again with an even more powerful feedback mechanism.

There is a fundamental functional difference between these two motor technologies. If there wasn't, they wouldn't both need to concurrently exist. If you put them both under a microscope you can make the argument that they both have all the same mechanisms at play but that does not help the guy trying to design something to select the right type of motor. Your current trend of assertions might lead one to believe that it doesn't really matter when it absolutely does. That guy is who this analogy is intended for. A layman who doesn't know the difference between a printer's stepper motor, a fan's shaded pole motor, and a CNC's spindle motor. Very basic, practical stuff. Not a university level physics course.

 

Ok I think I came up with a better way to describe this; just have to start tier higher than the motor. Synchronous and induction motors are better thought of as an extension of the prime mover (generator). You can think of the power lines like an overhead drive shaft spinning 3600RPM, coming from an engine or a turbine or something far off. The motor is like a "coupling" connected to that drive shaft, to transmit mechanical power from the source to mechanical power at the destination, using an electromagnetic medium.

The synchronous motor (not that it would be connected across the line but let's just say it was) is like a rigid coupling, so it is going to spin at exactly the same speed as the prime mover (with some reduction ratio based on pole count) until you apply enough load to break the coupling.

The induction motor is like a slip-clutch coupling. It has some "cushion" which allows it to start across the line but also causes its RPM to sag (just slightly) under load. Like the synchronous motor, if you apply too much torque the coupling will break.

When explained this way it precludes having to address the "unnatural" (IMO) operation of a synchronous motor. The prime mover is just like the locomotive, the bicycle, etc.; put enough load on it and it will slow down. You can see it if you connect a large motor to a small generator and apply a heavy load; the motor will slow down because the generator slows down. We just don't see it in daily life because "the generator" (grid) is functionally infinitely powerful and can't be slowed by our motors.

But then I have to bring the brushed series motor into this analogy and it's a, what? CVT?

 

Synchronous motors are among the motors for which I'm searching for an analogy to.

Leaf growth and fall with the seasons?

 

@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 mean 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.

When you look at the equations governing spin in the case of a motor, you find a relationship between ω and τ (torque) that is limited by P (power). So, if you take any motor and run it unloaded, it will achieve a certain set of values for ω and τ given P. As soon as you load it, in the absence of a change in P, ω and τ must change in relation to each other to deal with the work being done.

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.

 

Ok I think I came up with a better way to describe this; just have to start tier higher than the motor. Synchronous and induction motors are better thought of as an extension of the prime mover (generator). You can think of the power lines like an overhead drive shaft spinning 3600RPM, coming from an engine or a turbine or something far off. The motor is like a "coupling" connected to that drive shaft, to transmit mechanical power from the source to mechanical power at the destination, using an electromagnetic medium.

The synchronous motor (not that it would be connected across the line but let's just say it was) is like a rigid coupling, so it is going to spin at exactly the same speed as the prime mover (with some reduction ratio based on pole count) until you apply enough load to break the coupling.

The induction motor is like a slip-clutch coupling. It has some "cushion" which allows it to start across the line but also causes its RPM to sag (just slightly) under load. Like the synchronous motor, if you apply too much torque the coupling will break.

When explained this way it precludes having to address the "unnatural" (IMO) operation of a synchronous motor. The prime mover is just like the locomotive, the bicycle, etc.; put enough load on it and it will slow down. You can see it if you connect a large motor to a small generator and apply a heavy load; the motor will slow down because the generator slows down. We just don't see it in daily life because "the generator" (grid) is functionally infinitely powerful and can't be slowed by our motors.

But then I have to bring the brushed series motor into this analogy and it's a, what? CVT?

My other post applies here in that when you exceed the available P things suddenly slow down because when you ar within the P limits it is automatically increased or reduced to maintain the relationship between the rotors. I think that maybe a magnetic clutch is the analogy, not the shafts that couple is.

 

OK, there is a fundamental flaw in the statement. There is not some feedback arrangement in those motors at all. What happens is that as the torque required increases, or decreases, the operating point shifts. That is closer to a person walking and coming to a hill, where now they need to apply a different amount of energy to keep moving.

In addition, why spend effort seeking to attach some analogy to a motor??? What benefit would be derived from such a comparison??

 

why spend effort seeking to attach some analogy to a motor??? What benefit would be derived from such a comparison??

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.