water analogy- a simple calculator

[Rich Grise]

George Herold wrote:

On Jan 11, 4:55 pm, John Larkin

The holy grail of automotive design is the continuously-variable
transmission. The electronic equivalent is easy. Eat your hearts out,
MEs!

Did you ever see the variable Vee Belt drive on a snowmobile?

No, but I've seen one on a drill press. Fascinating!

I wonder how hard it is to design the cone-shaped pulley halves to maintain
proper belt tension throughout its range?

Cheers!
Rich

 

[F. Bertolazzi]

Rich Grise:

George Herold wrote:

Did you ever see the variable Vee Belt drive on a snowmobile?

No, but I've seen one on a drill press. Fascinating!

I wonder how hard it is to design the cone-shaped pulley halves to maintain
proper belt tension throughout its range?

In Italy the best selling mopeds in the '70s and '80s where the Bravo and
Ciao, both equipped with V belt "variatore". I think that modern scooters'
transmission is still made that way, but I never "opened" one.

 

[John Larkin]

On Wed, 12 Jan 2011 18:04:19 -0600, "krw@att.bizzzzzzzzzzzz"
<krw@att.bizzzzzzzzzzzz> wrote:

On Wed, 12 Jan 2011 13:31:45 GMT, N0Spam@daqarta.com (Bob Masta) wrote:

On Tue, 11 Jan 2011 13:41:39 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Jan 2011 13:51:52 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

Agreed in principle, but there can be serious debate over
the proper analogy even in this basic RLC case. Consider
that with a series connection, current is analogous to force
in that it is identical in all elements, while the voltage
drop across each element is analogous to relative velocity.
That doesn't fit well with the voltage-as-pressure concept.


Mechanical engineers use different analogies as needed, and
can make the math work out even when there isn't much
intuitive connection (to this poor EE, at least!).


Why do MEs need analogies? They can see and feel their stuff!


They need analogies so they know what equations to borrow
from the EEs!

When I started working for IBM in '74 I was surprised to see the heat transfer
folks down the hall were using "our" circuit simulators to do their work.

Ther was one thermal simulator, called Sauna, that was based on
connecting an array of dots in 3-space with (thermal) resistors in a
cubic matrix, and caps to ground, and then running a Spice-like sim.

I've used Spice to simulate thermal systems. This works pretty well:


ELECTRICAL THERMAL

1 amp 1 watt
1 farad 1 gram aluminum
1 volt 1 degree C
1 second 1 second
1 ohm 1 degC/watt

John

 

[krw@att.bizzzzzzzzzzzz]

On Wed, 12 Jan 2011 17:59:13 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Jan 2011 18:04:19 -0600, "krw@att.bizzzzzzzzzzzz"
krw@att.bizzzzzzzzzzzz> wrote:

On Wed, 12 Jan 2011 13:31:45 GMT, N0Spam@daqarta.com (Bob Masta) wrote:

On Tue, 11 Jan 2011 13:41:39 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Jan 2011 13:51:52 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

Agreed in principle, but there can be serious debate over
the proper analogy even in this basic RLC case. Consider
that with a series connection, current is analogous to force
in that it is identical in all elements, while the voltage
drop across each element is analogous to relative velocity.
That doesn't fit well with the voltage-as-pressure concept.


Mechanical engineers use different analogies as needed, and
can make the math work out even when there isn't much
intuitive connection (to this poor EE, at least!).


Why do MEs need analogies? They can see and feel their stuff!


They need analogies so they know what equations to borrow
from the EEs!

When I started working for IBM in '74 I was surprised to see the heat transfer
folks down the hall were using "our" circuit simulators to do their work.

Ther was one thermal simulator, called Sauna, that was based on
connecting an array of dots in 3-space with (thermal) resistors in a
cubic matrix, and caps to ground, and then running a Spice-like sim.

I've used Spice to simulate thermal systems. This works pretty well:

They were doing some pretty sophisticated thermal analysis on 100-chip, 1kW
and higher, packages.

ELECTRICAL THERMAL

1 amp 1 watt
1 farad 1 gram aluminum
1 volt 1 degree C
1 second 1 second
1 ohm 1 degC/watt
1 henry 1 ????

;-)

 

[George Herold]

On Jan 12, 5:15 pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:

George Herold wrote:
On Jan 12, 3:27 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net>  wrote:
George Herold wrote:
On Jan 12, 7:16 am, John Fields<jfie...@austininstruments.com>    wrote:
On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin

jjlar...@highNOTlandTHIStechnologyPART.com>    wrote:

Right. I can't think of an electrical analogy to friction.

---
Why would you think that resistance isn't analogous to friction?

---
JF

Did you look at the plots I posted John?  Friction causes a linear
decrease in amplitude, not exponential.

George H.

Cute demo.

I'm not really persuaded by the v**0 argument for frictional damping.
Long years of painstaking research in the field of yo-yo tricks has
convinced me that when you have a string sliding on a roller, once you
break it loose there's very little friction.

I suspect that if you put a load cell on the string, you'd find that the
actual retarding force was concentrated in narrow pulses near the peak
of each oscillation.  The work required to break the string loose is
pretty well constant, so you'd lose a fixed amount of energy per half
cycle.  The total energy is

The data is a lot better than the 'scope shots.  The static friction
acts only for an 'instant' when the rotor turns around.  I never
really looked closely, but there are no 'big' steps at the ends. If I
record some data I could try and fit the envelope... it should be
possible to determine the static amplitude loss at the turn around
points and constant loss through the rest of the motion.

There are actually two strings pressing on opposite sides of the
rotor.  And we can load them with differernt weights and change the
frictional force.

        I omega**2    k*theta**2
E =   ---------- + ------------
            2            2

where omega = d/dt(theta).  The average energy loss would be linear in
time, so

  ** It's the amplitude loss that is linear in time! **

I get to that point later.  Right now I'm doing the reciprocating yo-yo
case.  (Patience, Grasshopper.)







dE
--  = Qdot = I omega d(omega)/dt + k*theta*d(theta)/dt.
dt

At the extremes of motion, omega = 0, so if dE/dt over one cycle is some
constant B, then

As above amplitude loss for one cycle is constant. Not energy loss.

d(theta)/dt =  B/(k*theta)

so theta = (2B/k)*sqrt(t0-t),

where t0 is the time where the motion stops.  That's the case for car
brakes--you have to lighten up on the pedal as you slow down, to avoid
jerking to a stop.

Doesn't your car behave like that?  All the ones I've driven do.

Yeah sure that's how I drive a car.... If my car went back and forth
and I wanted to stop it, I'd apply the brakes at the turn around point
where the velocity is zero.... I guess I'm just saying I don't get the
(hic) analogy.

Now we get to the coefficient-of-friction case, which is what your web
page assumes.







With the usual coefficient-of-friction approximation, i.e. your v**0
approach, the power consumed by the rotor in overcoming friction is

dE/dt =  omega Gamma,

where Gamma is the frictional torque.

At the peak velocity, theta = 0, so

d(omega)/dt = -Gamma/I,

and you get a linear decrease in the amplitude, as you say.

A colleague has worked out the math in detail.  I'd be happy to send
you the appropriate section of the manual.

If those were the whole story, I'd expect to see the envelope be convex,
i.e. with a linear slope at high amplitudes where the sliding friction
dominates, and a steeper slope at low amplitude where it's the stiction
that matters most.

I think the only point where static friction matters is right when it
stops.  At that point there is not enough torque in the spring to over
come the static friction and it stops.  And stops at a non-equilibrium
position.

But it stops twice per cycle, which is the point I was trying to make
above. Doesn't it?

Sure. If there was energy loss (from say the thread sticking?) right
at the turn around point wouldn't the amplitude have to undergo some
sort of 'step' change in amplitude? The energies all in the spring at
that point. I'm not sure what the thread is at one point we were
using 'spider' wire. (use for fishing.) It's rubbing against an 1"
diameter Al rod, There are two strings each touching for maybe 45
degrees of the circle. We first tried a complete wrap of string and
that was much to much friction. I think there's ~100 grams hanging on
each string.

Your plot's envelope is slightly concave, which looks like you have some
exponential behaviour in there someplace.

Yeah there is a little bit of 'concavity' to it.  I can't really say
if this is some velocity dependent damping... or perhaps something to
do with the friction.

The coefficient of friction approximation isn't that good, but it
certainly leads to a decay that's a lot closer to linear than to
exponential.

I was looking at some other data today. The amplitude looks a lot
more linear.

(And for the viscosity fans, viscous drag goes like velocity squared, so
it isn't like resistance either.  
We 'attempt' to do that too. I've never tried fitting the data, but

at least it's different than exponential. We put two ~2 foot long
1/4"diam. aluminum tubes through the rotor with paddles one the
ends. ... I was just thinking one way to test the v**2 depenedence
would be to drive it and look at the response.

If you take a boat with a displacement
hull, i.e. one that doesn't plane like a speedboat, then for any initial
velocity, its displacement goes like log(initial velocity * time).)

Interesting, anyway.

Say if you like Yo-yo's my son has a new model with a built in
clutch... (Or anti clutch... it grabs on when the angular velocity is
small.)  Making it 'sleep' is a piece of cake!

Progress can only be made against a resisting medium.

Yeah, feel free to 'resist' me any time.

Thanks,
grasshopper.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

 

[George Herold]

On Jan 12, 3:37 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Jan 2011 09:48:45 -0800 (PST), George Herold





ggher...@gmail.com> wrote:
On Jan 11, 4:55 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 11 Jan 2011 06:11:41 +0100, "F. Bertolazzi"

TOGLIe...@MAIUSCOLEtdd.it> wrote:
Michael A. Terrell:

John Larkin wrote:

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

A transformer: High flow at low pressure is transformed into low
flow at high pressure.

Humm. Maybe John is right.

HA!

A transformer could be a water-powered motor driving a pump. For
non-steady-state, a driven piston pushing another piston of a
different size.

Oh the piston thing works nicely for me as a transformer. Thanks.

It's easier to just explain the electricity. That way, you don't have
to explain two systems, when you're trying to teach one.

One interesting analogy is a synchronous buck switcher to a pair of
gears. That sort of works. You can apply conservation of energy in
both ideal cases and predict behavior without having to go into gory
detail.

The holy grail of automotive design is the continuously-variable
transmission. The electronic equivalent is easy. Eat your hearts out,
MEs!

 Did you ever see the variable Vee Belt drive on a snowmobile?
George H.

John

Yeah, and that's been used in some cars. I think it tends to be
unreliable at high horsepowers.

I can think of a mechanical equivalent to a synchronous switcher,
using clutches and torsion springs and flywheels and such. It would be
noisy and not very reliable.

My Audi has a 6-speed tranny with two parallel gear trains, 3 speeds
each, odd and even gears used sequentially, two clutches, no torque
converter. It's very efficient and shifts in something silly like 80
milliseconds. It's the equivalent of a tap-switched transformer.

John- Hide quoted text -

- Show quoted text -

My car is a 2002 Corolla. But I do have a cool little ride'm lawn
mover. You have two levers, that connect to the back wheels. The
front wheels are like those on shopping carts and free turn where they
want. The levers are like those on a tank. The clutch mechanism is
''tangentail' spheres. (I certainly can't describe it.) But it's a
dang fast way to cut grass in summer. (My son's been driving it since
before I'm free to mention.)

We've finally got a bit of snow here. Two feet up the east coast and
we only get six inches, sigh.

George H.

 

[George Herold]

On Jan 12, 5:43 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Jan 2011 12:22:25 -0800, John Larkin





jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 12 Jan 2011 10:38:47 -0800 (PST), George Herold
ggher...@gmail.com> wrote:

On Jan 11, 9:49 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:
John Larkin:

On Wed, 12 Jan 2011 01:46:59 +0100, "F. Bertolazzi"
TOGLIe...@MAIUSCOLEtdd.it> wrote:

John Larkin:

Right. I can't think of an electrical analogy to friction.

Uh?

Uh? Can you?

Yes, I can. But I understand that somebody that cites non-laminar flows in
example pipes just to demonstrate that he is right no matter what, will
surely pull my "chain" with static and dynamic friction.

Wait until I get to retirement age and you'll see. ;-)

Friction is different than a resistor.  (Did you look at the plots I
posted?)  With friction you get a decay in amplitude that is linear in
time.  As long as the oscillator is moving it's losing amplitude at a
constant rate.  For a damping term that depends on velocity you get an
exponential decay.  Like an RCL circuit.

With electricity the electrons start moving even with the smallest
electric field.

I've been racking my brains for a friction analogy in electronics and
can think of nothing.  Now I'm wondering if you could make some circit
that would look "friction like".  (An oscillator that decays
linearly.)

An LC tank paralleled by current-limiting devices, like jfets maybe.
That will produce linear decay at high amplitudes, but will go
exponential at low level when the jfets get resistive. It certainly
won't go into static friction mode at the end.

John- Hide quoted text -

- Show quoted text -

Yeah, I was thinking about zeners (which I think John F mentioned) if
they are low voltage so it's kinda the same in both directions.. then
at high voltage there's 'always' a zener+diode drop which looks like
my requested constant amplitude decrease.

Does that work? (I've got a growing list of 'fun' useful measurements
to do... )

George H.

 

[Phil Hobbs]

George Herold wrote:

On Jan 12, 5:15 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
George Herold wrote:
On Jan 12, 3:27 pm, Phil Hobbs
pcdhSpamMeSensel...@electrooptical.net> wrote:
George Herold wrote:
On Jan 12, 7:16 am, John Fields<jfie...@austininstruments.com> wrote:
On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin

jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

Right. I can't think of an electrical analogy to friction.

---
Why would you think that resistance isn't analogous to friction?

---
JF

Did you look at the plots I posted John? Friction causes a linear
decrease in amplitude, not exponential.

George H.

Cute demo.

I'm not really persuaded by the v**0 argument for frictional damping.
Long years of painstaking research in the field of yo-yo tricks has
convinced me that when you have a string sliding on a roller, once you
break it loose there's very little friction.

I suspect that if you put a load cell on the string, you'd find that the
actual retarding force was concentrated in narrow pulses near the peak
of each oscillation. The work required to break the string loose is
pretty well constant, so you'd lose a fixed amount of energy per half
cycle. The total energy is

The data is a lot better than the 'scope shots. The static friction
acts only for an 'instant' when the rotor turns around. I never
really looked closely, but there are no 'big' steps at the ends. If I
record some data I could try and fit the envelope... it should be
possible to determine the static amplitude loss at the turn around
points and constant loss through the rest of the motion.

There are actually two strings pressing on opposite sides of the
rotor. And we can load them with differernt weights and change the
frictional force.

I omega**2 k*theta**2
E = ---------- + ------------
2 2

where omega = d/dt(theta). The average energy loss would be linear in
time, so

** It's the amplitude loss that is linear in time! **

I get to that point later. Right now I'm doing the reciprocating yo-yo
case. (Patience, Grasshopper.)







dE
-- = Qdot = I omega d(omega)/dt + k*theta*d(theta)/dt.
dt

At the extremes of motion, omega = 0, so if dE/dt over one cycle is some
constant B, then

As above amplitude loss for one cycle is constant. Not energy loss.

d(theta)/dt = B/(k*theta)

so theta = (2B/k)*sqrt(t0-t),

where t0 is the time where the motion stops. That's the case for car
brakes--you have to lighten up on the pedal as you slow down, to avoid
jerking to a stop.

Doesn't your car behave like that? All the ones I've driven do.

Yeah sure that's how I drive a car.... If my car went back and forth
and I wanted to stop it, I'd apply the brakes at the turn around point
where the velocity is zero.... I guess I'm just saying I don't get the
(hic) analogy.

Deceleration of a braking car is due to sliding friction, but for a
given normal force on the brake pads, the deceleration isn't constant.
I'm not sure why that is, but it clearly shows that the coefficient of
friction model isn't always adequate as the speed goes to zero.

Now we get to the coefficient-of-friction case, which is what your web
page assumes.







With the usual coefficient-of-friction approximation, i.e. your v**0
approach, the power consumed by the rotor in overcoming friction is

dE/dt = omega Gamma,

where Gamma is the frictional torque.

At the peak velocity, theta = 0, so

d(omega)/dt = -Gamma/I,

and you get a linear decrease in the amplitude, as you say.

A colleague has worked out the math in detail. I'd be happy to send
you the appropriate section of the manual.

If those were the whole story, I'd expect to see the envelope be convex,
i.e. with a linear slope at high amplitudes where the sliding friction
dominates, and a steeper slope at low amplitude where it's the stiction
that matters most.

I think the only point where static friction matters is right when it
stops. At that point there is not enough torque in the spring to over
come the static friction and it stops. And stops at a non-equilibrium
position.

But it stops twice per cycle, which is the point I was trying to make
above. Doesn't it?

Sure. If there was energy loss (from say the thread sticking?) right
at the turn around point wouldn't the amplitude have to undergo some
sort of 'step' change in amplitude? The energies all in the spring at
that point. I'm not sure what the thread is at one point we were
using 'spider' wire. (use for fishing.) It's rubbing against an 1"
diameter Al rod, There are two strings each touching for maybe 45
degrees of the circle. We first tried a complete wrap of string and
that was much to much friction. I think there's ~100 grams hanging on
each string.

You wouldn't get a noticeable discontinuity on each start because when
the stiction lets go, the rotor accelerates smoothly from 0. There
might be something visible when it stops each time--another of those
square-root decelerations.

Your plot's envelope is slightly concave, which looks like you have some
exponential behaviour in there someplace.

Yeah there is a little bit of 'concavity' to it. I can't really say
if this is some velocity dependent damping... or perhaps something to
do with the friction.

The coefficient of friction approximation isn't that good, but it
certainly leads to a decay that's a lot closer to linear than to
exponential.

I was looking at some other data today. The amplitude looks a lot
more linear.

Cool. As I said, it's a great demo. Nothing like a bit of data to
discourage pontification.

(And for the viscosity fans, viscous drag goes like velocity squared, so
it isn't like resistance either.
We 'attempt' to do that too. I've never tried fitting the data, but
at least it's different than exponential. We put two ~2 foot long
1/4"diam. aluminum tubes through the rotor with paddles one the
ends. ... I was just thinking one way to test the v**2 depenedence
would be to drive it and look at the response.
If you take a boat with a displacement
hull, i.e. one that doesn't plane like a speedboat, then for any initial
velocity, its displacement goes like log(initial velocity * time).)

Interesting, anyway.

Say if you like Yo-yo's my son has a new model with a built in
clutch... (Or anti clutch... it grabs on when the angular velocity is
small.) Making it 'sleep' is a piece of cake!

Progress can only be made against a resisting medium.

Yeah, feel free to 'resist' me any time.

Thanks,
grasshopper.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

 

[George Herold]

On Jan 12, 7:12 pm, "F. Bertolazzi" <TOGLIe...@MAIUSCOLEtdd.it> wrote:

George Herold:

Friction is different than a resistor.  (Did you look at the plots I
posted?)

No. Where? If it's some binary NG I can't see it.

Ahh it's nothing but shameless advertizing.

http://www.teachspin.com/instruments/tho/experiments.shtml
You've got to scroll down till almost the end, Look for Damping.

With friction you get a decay in amplitude that is linear in
time.  As long as the oscillator is moving it's losing amplitude at a
constant rate.  For a damping term that depends on velocity you get an
exponential decay.  Like an RCL circuit.

Or like drag, that varies with the square of speed.

I've been racking my brains for a friction analogy in electronics and
can think of nothing.

As I said, I'm not retired yet, so I must rake my brain to earn a decent
living, not to perfect an introductory analogy that is already perfect for
that scope.

Hmm, this all looks like 'work' to me. Mind you I mostly enjoy going
to work.
Do you do electronics for a living?

Now I'm wondering if you could make some circit
that would look "friction like".  (An oscillator that decays
linearly.)

Easy. Take a controller with a D/A that ouputs variable m

for(m = 0, i = 10; i > 0; i++)
  if(i % 1) m -= i;
  else m += i;

Digital sure.

George h.

 

[George Herold]

On Jan 12, 7:18 pm, Rich Grise <ri...@example.net.invalid> wrote:

George Herold wrote:
On Jan 11, 4:55 pm, John Larkin
The holy grail of automotive design is the continuously-variable
transmission. The electronic equivalent is easy. Eat your hearts out,
MEs!

  Did you ever see the variable Vee Belt drive on a snowmobile?

No, but I've seen one on a drill press. Fascinating!  

I wonder how hard it is to design the cone-shaped pulley halves to maintain
proper belt tension throughout its range?

Cheers!
Rich

Ya, I have no idea how to make it all work.

George H.

 

[George Herold]

On Jan 12, 8:59 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Jan 2011 18:04:19 -0600, "k...@att.bizzzzzzzzzzzz"





k...@att.bizzzzzzzzzzzz> wrote:
On Wed, 12 Jan 2011 13:31:45 GMT, N0S...@daqarta.com (Bob Masta) wrote:

On Tue, 11 Jan 2011 13:41:39 -0800, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Jan 2011 13:51:52 GMT, N0S...@daqarta.com (Bob Masta)
wrote:

Agreed in principle, but there can be serious debate over
the proper analogy even in this basic RLC case.  Consider
that with a series connection, current is analogous to force
in that it is identical in all elements, while the voltage
drop across each element is analogous to relative velocity.
That doesn't fit well with the voltage-as-pressure concept.

Mechanical engineers use different analogies as needed, and
can make the math work out even when there isn't much
intuitive connection (to this poor EE, at least!).

Why do MEs need analogies? They can see and feel their stuff!

They need analogies so they know what equations to borrow
from the EEs!

When I started working for IBM in '74 I was surprised to see the heat transfer
folks down the hall were using "our" circuit simulators to do their work..

Ther was one thermal simulator, called Sauna, that was based on
connecting an array of dots in 3-space with (thermal) resistors in a
cubic matrix, and caps to ground, and then running a Spice-like sim.

I've used Spice to simulate thermal systems. This works pretty well:

      ELECTRICAL       THERMAL

       1 amp            1 watt
       1 farad          1 gram aluminum
       1 volt           1 degree C
       1 second         1 second
       1 ohm            1 degC/watt

John- Hide quoted text -

- Show quoted text -

Yeah I do it with one resistor and one cap.. (Well I usually break the
resistor in half.)

When I have to explain thermal circuits to people I love to use the
'electronic' analogy.
(I'm not sure it helps them, but it's how I understand it.) Of course
capacitors don't have phase changes.

Oh the Farad is equivalent to the heat capacity. Joules/deg K. (I
think that's right. RC is time, seconds in both 'units')

George H.

 

[John Larkin]

On Wed, 12 Jan 2011 20:05:30 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

On Jan 12, 8:59 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 12 Jan 2011 18:04:19 -0600, "k...@att.bizzzzzzzzzzzz"





k...@att.bizzzzzzzzzzzz> wrote:
On Wed, 12 Jan 2011 13:31:45 GMT, N0S...@daqarta.com (Bob Masta) wrote:

On Tue, 11 Jan 2011 13:41:39 -0800, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 11 Jan 2011 13:51:52 GMT, N0S...@daqarta.com (Bob Masta)
wrote:

Agreed in principle, but there can be serious debate over
the proper analogy even in this basic RLC case.  Consider
that with a series connection, current is analogous to force
in that it is identical in all elements, while the voltage
drop across each element is analogous to relative velocity.
That doesn't fit well with the voltage-as-pressure concept.

Mechanical engineers use different analogies as needed, and
can make the math work out even when there isn't much
intuitive connection (to this poor EE, at least!).

Why do MEs need analogies? They can see and feel their stuff!

They need analogies so they know what equations to borrow
from the EEs!

When I started working for IBM in '74 I was surprised to see the heat transfer
folks down the hall were using "our" circuit simulators to do their work.

Ther was one thermal simulator, called Sauna, that was based on
connecting an array of dots in 3-space with (thermal) resistors in a
cubic matrix, and caps to ground, and then running a Spice-like sim.

I've used Spice to simulate thermal systems. This works pretty well:

      ELECTRICAL       THERMAL

       1 amp            1 watt
       1 farad          1 gram aluminum
       1 volt           1 degree C
       1 second         1 second
       1 ohm            1 degC/watt

John- Hide quoted text -

- Show quoted text -

Yeah I do it with one resistor and one cap.. (Well I usually break the
resistor in half.)

When I have to explain thermal circuits to people I love to use the
'electronic' analogy.
(I'm not sure it helps them, but it's how I understand it.) Of course
capacitors don't have phase changes.

Oh the Farad is equivalent to the heat capacity. Joules/deg K. (I
think that's right. RC is time, seconds in both 'units')

George H.

Unfortunately, most useful thermal systems are diffusive, unlike
lumped electrical circuits. And the diffusion is usually among nasty
3D shapes. So the modeling is ugly finite-element stuff, basically a
many-element 3D hairball of resistors and capacitors.

Interestingly, there is no thermal equivalent of an inductor. So
thermal systems don't ring or oscillate, unless you sneak in some
nonlinear mechanical or transport phenomenon.

I wish I had some nice little thermal resistance calculator, even a 2D
one.

John

 

[John Larkin]

On Wed, 12 Jan 2011 18:40:42 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

On Jan 12, 3:37 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Wed, 12 Jan 2011 09:48:45 -0800 (PST), George Herold





ggher...@gmail.com> wrote:
On Jan 11, 4:55 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Tue, 11 Jan 2011 06:11:41 +0100, "F. Bertolazzi"

TOGLIe...@MAIUSCOLEtdd.it> wrote:
Michael A. Terrell:

John Larkin wrote:

OK, what's the electrical equivalent of the finger-on-the-hose thing?
Schematic, please.

A transformer: High flow at low pressure is transformed into low
flow at high pressure.

Humm. Maybe John is right.

HA!

A transformer could be a water-powered motor driving a pump. For
non-steady-state, a driven piston pushing another piston of a
different size.

Oh the piston thing works nicely for me as a transformer. Thanks.

It's easier to just explain the electricity. That way, you don't have
to explain two systems, when you're trying to teach one.

One interesting analogy is a synchronous buck switcher to a pair of
gears. That sort of works. You can apply conservation of energy in
both ideal cases and predict behavior without having to go into gory
detail.

The holy grail of automotive design is the continuously-variable
transmission. The electronic equivalent is easy. Eat your hearts out,
MEs!

 Did you ever see the variable Vee Belt drive on a snowmobile?
George H.

John

Yeah, and that's been used in some cars. I think it tends to be
unreliable at high horsepowers.

I can think of a mechanical equivalent to a synchronous switcher,
using clutches and torsion springs and flywheels and such. It would be
noisy and not very reliable.

My Audi has a 6-speed tranny with two parallel gear trains, 3 speeds
each, odd and even gears used sequentially, two clutches, no torque
converter. It's very efficient and shifts in something silly like 80
milliseconds. It's the equivalent of a tap-switched transformer.

John- Hide quoted text -

- Show quoted text -

My car is a 2002 Corolla. But I do have a cool little ride'm lawn
mover. You have two levers, that connect to the back wheels. The
front wheels are like those on shopping carts and free turn where they
want. The levers are like those on a tank. The clutch mechanism is
''tangentail' spheres. (I certainly can't describe it.) But it's a
dang fast way to cut grass in summer. (My son's been driving it since
before I'm free to mention.)

We don't have grass. I hate grass.

We've finally got a bit of snow here. Two feet up the east coast and
we only get six inches, sigh.

There's only, officially, 48" of snow on the ground in Truckee. But
some of the mounds tossed up by the snow plows are easily 12' high.
And the year is young!

John

 

[Rich Grise]

George Herold wrote:

Oh the Farad is equivalent to the heat capacity. Joules/deg K. (I
think that's right. RC is time, seconds in both 'units')

Well, the Farad is the unit of capacity, which we geeks call

capacitance. ;-)

Cheers!
Rich

 

[Jasen Betts]

On 2011-01-12, Bob Masta <N0Spam@daqarta.com> wrote:

On Tue, 11 Jan 2011 17:35:43 -0800, Rich Grise
richg@example.net.invalid> wrote:

The only analog to an inductor I can think of would be
a positive-displacement turbine (like a gear pump) and a flywheel.

How about a big coiled garden hose? Not only looks like an
inductor, but the mass of the water in it will give it
inductor properties: Hard to get current to start flowing,
and once it's flowing, hard to stop or change directions.

apart from the fact that it's elastic and behave more like a long
straight wire with lots of parasit capacitance it's a good analogy,
you can even make a boost converter based on it.

http://en.wikipedia.org/wiki/Hydraulic_ram

--
⚂⚃ 100% natural

 

[F. Bertolazzi]

George Herold:

http://www.teachspin.com/instruments/tho/experiments.shtml
You've got to scroll down till almost the end, Look for Damping.

Why scroll?

Hmm, this all looks like 'work' to me.

I guess so.

Mind you I mostly enjoy going to work.

I don't even go. I live in it.

Do you do electronics for a living?

Just power and interface for my embedded contraptions.

Digital sure.

That's how I know to do it. I wish I was able to do it in a more elegant
way, but my knowledge and "time to market" don't allow for better
solutions.

 

[Michael A. Terrell]

"krw@att.bizzzzzzzzzzzz" wrote:

1 henry 1 ford

;-)


--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

 

[F. Bertolazzi]

Rich Grise:

Michael A. Terrell wrote:

No 'Mutual Inductance' though.

Hmm. Yeah, that's be a fairly hard thing to analogize with the water
pipe model

Someone proposed, for inductance, a turbine with a flywheel. What about a
second turbine in the "inducted" pipe?

Coupled crosstalk is easier, since a higher pressure in one hose will
expand it, so that it will squeeze the other one, that runs parallel to it.

 

[F. Bertolazzi]

John Larkin:

I can think of a mechanical equivalent to a synchronous switcher,
using clutches and torsion springs and flywheels and such. It would be
noisy and not very reliable.

The hydraulic analogy is also useful with switchers, to show that it is
possible to divide the content of one bucket in two buckets, so it is
possible to make a divide-by-two buck converter with two capacitors, a few
switches and no inductors. But the efficiency, given the fact that we
lowered the top half of one bucket to ground, wasting most of the energy,
would be lousy.

 

[John Fields]

On Wed, 12 Jan 2011 14:45:40 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Jan 2011 15:53:48 -0600, John Fields
jfields@austininstruments.com> wrote:

On Wed, 12 Jan 2011 09:04:52 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 12 Jan 2011 13:25:14 +0100, "F. Bertolazzi"
TOGLIeset@MAIUSCOLEtdd.it> wrote:

John Fields:

On Tue, 11 Jan 2011 13:47:18 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

Right. I can't think of an electrical analogy to friction.

---
Why would you think that resistance isn't analogous to friction?

Because he does not want to. ;-)

I don't want to because the behaviors are very different. You'd have
to actually understand friction behavior to see why.

---
Typical Larkinese intimidation attempt, to wit: "I'm betting that he
doesn't understand friction, so I'll intimate that he doesn't, and
I'll add the "actually" as a fillip (since I've puffed myself up as an
authority) to get him to shut the fuck up."
---

Neither static friction nor sliding friction behave like electrical resistance.

---
Nonsense.

"Stiction" is like a Zener and Teflon on Teflon is like charge flowing
through silver.


In that case, alligators are like transformers.

---
That's like saying that you don't understand analogy.

---
JF