On Jan 20, 8:14*am, "Michael A. Terrell"
wrote:
...
* *It's simple: Connect a known value capacitor across the coil. *Put a
1K ohm resistor in series with the generator to the hot side and connect
the ground to the other end of the coil. *Then use a scope or AC
voltmeter to look for resonance across the L/C pair.

That's only simple if you have a capacitance meter. Do NOT use an
electrolytic or multilayer ceramic cap. Caps that are physically large
for their value like plastic film ones are more likely to be close to
their nominal value.
http://en.wikipedia.org/wiki/Types_of_capacitor

jsw

Jon Danniken wrote:
Winston wrote:
Bob Engelhardt wrote:
Winston wrote:
The inductance of that coil fell significantly when you lopped
off the 'I' core, yes?

Yes and no, I supposeG. 'Though I did lop it off, I replaced it
with a shorting bar, so it shouldn't be drastically different.

Now's the time to break out your $0.99 inductance bridge.

I haven't tested this but it looks reasonable:

http://www.aronnelson.com/gallery/main.php/v/BinOfBrett/Inductance_meter.jpg.html

http://www.aronnelson.com/gallery/main.php/v/BinOfBrett/Inductance_method.jpg.html


You can also measure inductances of this size using your PC and tone
generating software. Wire up the inductor with a capacitor, apply the tone,
and look for the resonant frequency.

I did this a few years ago with a MOT, testing the difference in inductance
by using different sized paper shims between the "E" and the "I"
laminations.

There's a webpage describing this somewhere out there, but of course I can't
find it right now. I think I made the mistake of saving it instead of
adding it to my bookmarks.

Bob's soundcard software looks promising.
For 29 bucks, it is worth trying IMHO.

http://www.daqarta.com/dw_0ass.htm

--Winston

Winston wrote:
The inductance of that coil fell significantly when you lopped
off the 'I' core, yes?

Can you place a small value sense resistor in series with the
'common' line to your coil? The way I misunderstand magnetic
core saturation is that we expect a 'knee' where current begins
to increase in a nonlinear fashion in relation to applied
voltage. You could set your 'scope up as an X-Y display to
show this nonlinearity very clearly.

Okay, now that caught my attention, as I've been looking for a way to
"notice" saturation when driving the primary of a MOT.

I do know that one can view phase angle with an x-y viewing of current and
voltage, and I guess it makes sense to look at that same waveform for a
change as an indicator of saturation (when phase angle is changed due to an
increase of non-inductive current).

Thanks Winston, I'm gonna have to play around with this.

Jon

Jon Danniken wrote:
Winston wrote:
The inductance of that coil fell significantly when you lopped
off the 'I' core, yes?

Can you place a small value sense resistor in series with the
'common' line to your coil? The way I misunderstand magnetic
core saturation is that we expect a 'knee' where current begins
to increase in a nonlinear fashion in relation to applied
voltage. You could set your 'scope up as an X-Y display to
show this nonlinearity very clearly.

Okay, now that caught my attention, as I've been looking for a way to
"notice" saturation when driving the primary of a MOT.

I do know that one can view phase angle with an x-y viewing of current and
voltage, and I guess it makes sense to look at that same waveform for a
change as an indicator of saturation (when phase angle is changed due to an
increase of non-inductive current).

Thanks Winston, I'm gonna have to play around with this.

Shore.

For A.C. operation, I'd expect that a current transformer
would give you much better isolation and signal - to - noise ratio.

For D.C. (or A.C.) operation, I'd expect that a Hall Effect
Current Sensor would be a better choice, for the same reason.

I've used the Allegro ACS756 in some extremely low impedance
applications where a sense resistor caused power supply
instability.
http://www.allegromicro.com/en/Produ...0756/index.asp

Highly recommended, though you will need to normalize it's
output. (I did that automatically with DAQ gear.)

For seven bucks, it is a great value.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS756&x=0&y=0

--Winston

Winston wrote:
For A.C. operation, I'd expect that a current transformer
would give you much better isolation and signal - to - noise ratio.

For D.C. (or A.C.) operation, I'd expect that a Hall Effect
Current Sensor would be a better choice, for the same reason.

I've used the Allegro ACS756 in some extremely low impedance
applications where a sense resistor caused power supply
instability.
http://www.allegromicro.com/en/Produ...0756/index.asp

Highly recommended, though you will need to normalize it's
output. (I did that automatically with DAQ gear.)

For seven bucks, it is a great value.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS756&x=0&y=0

Ooh, and up to 100 amps, I like that. Curious as to what you mean by
"normalize it's output", though; is this referring to the "typical
application" diagram given in the datasheet (sorry I'm rather dense on some
things).

Jon

Jon Danniken wrote:
Winston wrote:

(...)

I've used the Allegro ACS756 in some extremely low impedance
applications where a sense resistor caused power supply
instability.
http://www.allegromicro.com/en/Produ...0756/index.asp

Highly recommended, though you will need to normalize it's
output. (I did that automatically with DAQ gear.)

For seven bucks, it is a great value.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS756&x=0&y=0

Ooh, and up to 100 amps, I like that. Curious as to what you mean by
"normalize it's output", though; is this referring to the "typical
application" diagram given in the datasheet

Short version: It is a 'single ended' output without a
negative supply. You need to subtract Vcc/2 from the
output and multiply the result by 25 to arrive at
the real reading.

Long version:
Let's say you power it from 5.0000 V DC.
Zero amperes will be represented by a 2.50 V (or Vcc/2)
reading between output and ground.

An output of 2.54 V would thus indicate a current flow
of +1 A and an output of 2.46 V would indicate a current
flow of -1 A.

2.54 V - 2.50000 V = 0.04 V
0.04 V * 25 = 1.0 A

2.46 V - 2.50000 V = (-0.04 V)
(-0.04 V) * 25 = (-1.0 A)

With the data acquisition gear I used, I sensed the
Vcc going to the device and wrote an equation that
automatically did all the arithmetic for every reading.
The log files all showed the current flow in amperes.

It worked a treat!

If you wanted 'cheap and cheerful', you could put a
precision voltage divider between sensor Vcc and
ground to provide your multimeter a 'virtual ground',
then just mentally multiply the reading you see on
the DMM display by 25 to arrive at real amperes.


--Winston

Winston wrote:

Short version: It is a 'single ended' output without a
negative supply. You need to subtract Vcc/2 from the
output and multiply the result by 25 to arrive at
the real reading.

Long version:
Let's say you power it from 5.0000 V DC.
Zero amperes will be represented by a 2.50 V (or Vcc/2)
reading between output and ground.

An output of 2.54 V would thus indicate a current flow
of +1 A and an output of 2.46 V would indicate a current
flow of -1 A.

2.54 V - 2.50000 V = 0.04 V
0.04 V * 25 = 1.0 A

2.46 V - 2.50000 V = (-0.04 V)
(-0.04 V) * 25 = (-1.0 A)

With the data acquisition gear I used, I sensed the
Vcc going to the device and wrote an equation that
automatically did all the arithmetic for every reading.
The log files all showed the current flow in amperes.

It worked a treat!

If you wanted 'cheap and cheerful', you could put a
precision voltage divider between sensor Vcc and
ground to provide your multimeter a 'virtual ground',
then just mentally multiply the reading you see on
the DMM display by 25 to arrive at real amperes.

Ah, I gotcha, thanks. I'd probably put a function in my calculator to
convert it, unless I was doing a lot of measurements.

Jon

Jon Danniken wrote:
Winston wrote:

Short version: It is a 'single ended' output without a
negative supply. You need to subtract Vcc/2 from the
output and multiply the result by 25 to arrive at
the real reading.

Long version:
Let's say you power it from 5.0000 V DC.
Zero amperes will be represented by a 2.50 V (or Vcc/2)
reading between output and ground.

An output of 2.54 V would thus indicate a current flow
of +1 A and an output of 2.46 V would indicate a current
flow of -1 A.

2.54 V - 2.50000 V = 0.04 V
0.04 V * 25 = 1.0 A

2.46 V - 2.50000 V = (-0.04 V)
(-0.04 V) * 25 = (-1.0 A)

With the data acquisition gear I used, I sensed the
Vcc going to the device and wrote an equation that
automatically did all the arithmetic for every reading.
The log files all showed the current flow in amperes.

It worked a treat!

If you wanted 'cheap and cheerful', you could put a
precision voltage divider between sensor Vcc and
ground to provide your multimeter a 'virtual ground',
then just mentally multiply the reading you see on
the DMM display by 25 to arrive at real amperes.

Ah, I gotcha, thanks. I'd probably put a function in my calculator to
convert it, unless I was doing a lot of measurements.

In that case, you can simplify the arithmetic with:
ACS758ECB-200B-PSS-T (Straight Leads) OR
ACS758ECB-200B-PFF-T (Bent Leads)

With your DMM negative lead connected to
the center of a stiff, precision 2:1 voltage
divider and it's positive lead to pin 3 of
the chip, You just multiply the output by 100
to get your reading:

+2.000 V = 200.0 A
+0.153 V = 15.3 A
0 V = 0.0 A
-2.000 V = -200.0 A

Seven smackers each.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS758ECB-200B&x=0&y=0

As a great philosopher once said, "Hell Yeah!"
http://www.youtube.com/watch?v=82dDnv9zeLs

--Winston

Jim Wilkins wrote:

On Jan 20, 8:14 am, "Michael A. Terrell"
wrote:
...
It's simple: Connect a known value capacitor across the coil. Put a
1K ohm resistor in series with the generator to the hot side and connect
the ground to the other end of the coil. Then use a scope or AC
voltmeter to look for resonance across the L/C pair.

That's only simple if you have a capacitance meter. Do NOT use an
electrolytic or multilayer ceramic cap. Caps that are physically large
for their value like plastic film ones are more likely to be close to
their nominal value.
http://en.wikipedia.org/wiki/Types_of_capacitor


I would use the HV capacitor that came from the oven.

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

Winston wrote:

In that case, you can simplify the arithmetic with:
ACS758ECB-200B-PSS-T (Straight Leads) OR
ACS758ECB-200B-PFF-T (Bent Leads)

With your DMM negative lead connected to
the center of a stiff, precision 2:1 voltage
divider and it's positive lead to pin 3 of
the chip, You just multiply the output by 100
to get your reading:

+2.000 V = 200.0 A
+0.153 V = 15.3 A
0 V = 0.0 A
-2.000 V = -200.0 A

Seven smackers each.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS758ECB-200B&x=0&y=0

Even better, thanks Winston.

Jon

Jon Danniken wrote:
Winston wrote:

In that case, you can simplify the arithmetic with:
ACS758ECB-200B-PSS-T (Straight Leads) OR
ACS758ECB-200B-PFF-T (Bent Leads)

With your DMM negative lead connected to
the center of a stiff, precision 2:1 voltage
divider and it's positive lead to pin 3 of
the chip, You just multiply the output by 100
to get your reading:

+2.000 V = 200.0 A
+0.153 V = 15.3 A
0 V = 0.0 A
-2.000 V = -200.0 A

Seven smackers each.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go _button&KeyWords=ACS758ECB-200B&x=0&y=0

Even better, thanks Winston.

Jon

You are welcome, Jon.

--Winston

On Wed, 19 Jan 2011 20:59:16 -0500, "Michael A. Terrell"
wrote:


wrote:

On Wed, 19 Jan 2011 15:06:08 -0500, "Michael A. Terrell"
wrote:


Bob Engelhardt wrote:

wrote:
If I recall correctly when one designs a transformer, you calculate
what the ET product is. ...
snip
So the flux ( B ) depends on the voltage and frequency. And using the
same line frequency and the voltage at 240 volts RMS ( much less than
the usual 2000 volts on the secondary, you should not have to worry
about saturation. ( this assumes you are using AC voltage.).

Thanks, that helps!

I've been thinking about those 2000 volts. If that's the normal voltage
on this coil, it's probably going to take close to that to saturate the
core. I mean, wouldn't they design for the core to be close to
saturation, to minimize the core size needed?


Only at line frequency.

With DC exitation the same flux density will be reached when the
DC reaches the same level as the normal line freqency magnetising
current (i.e the no load current). With DC, the voltage needed to
reach this current will typically be about 5% of the rated line
frequency voltage provided the magnetic circuit is closed (no air
gap)

My interest in saturation is 2 fold: I don't want to run beyond
saturation 'cause of the extra heat, and at saturation is where the
maximum pull will be.

Now, about ACC. To use as an electromagnet, I have full-wave
rectification, unfiltered. Although the coil's inductance will do some
smoothing (I wish my scope was working). My intuition is that the DC
component of the current will be determined by the coil resistance and
that will produce flux proportional to the number of coil turns. So,
the question is whether the DC current will saturate it before 240v. Or
be too high for the coil's wire guage.

Because the rated line frequency full load current is very much
larger than the no load magnetising current, DC excitation will
saturate the core long before rated full load current is reached.

This applies when the magnetic circuit is as fully closed as in
the original transformer. If it is only partially closed with
perhaps inferior iron or small airgap, proportionally
more current will be needed.

But the bottom line is that I'm going to be using 240v max (full wave)
and as long as it isn't saturated then, I'll be getting the maximum pull
available.

240V should be ample.

Jim


None of the text you quote was written by me.


I'm sorry about the error - it was very bad editing on my
part. I hope it has not caused you any difficulty.

With apologies.

Jim

wrote:

On Wed, 19 Jan 2011 20:59:16 -0500, "Michael A. Terrell"
wrote:


wrote:

On Wed, 19 Jan 2011 15:06:08 -0500, "Michael A. Terrell"
wrote:


Bob Engelhardt wrote:

wrote:
If I recall correctly when one designs a transformer, you calculate
what the ET product is. ...
snip
So the flux ( B ) depends on the voltage and frequency. And using the
same line frequency and the voltage at 240 volts RMS ( much less than
the usual 2000 volts on the secondary, you should not have to worry
about saturation. ( this assumes you are using AC voltage.).

Thanks, that helps!

I've been thinking about those 2000 volts. If that's the normal voltage
on this coil, it's probably going to take close to that to saturate the
core. I mean, wouldn't they design for the core to be close to
saturation, to minimize the core size needed?


Only at line frequency.

With DC exitation the same flux density will be reached when the
DC reaches the same level as the normal line freqency magnetising
current (i.e the no load current). With DC, the voltage needed to
reach this current will typically be about 5% of the rated line
frequency voltage provided the magnetic circuit is closed (no air
gap)

My interest in saturation is 2 fold: I don't want to run beyond
saturation 'cause of the extra heat, and at saturation is where the
maximum pull will be.

Now, about ACC. To use as an electromagnet, I have full-wave
rectification, unfiltered. Although the coil's inductance will do some
smoothing (I wish my scope was working). My intuition is that the DC
component of the current will be determined by the coil resistance and
that will produce flux proportional to the number of coil turns. So,
the question is whether the DC current will saturate it before 240v. Or
be too high for the coil's wire guage.

Because the rated line frequency full load current is very much
larger than the no load magnetising current, DC excitation will
saturate the core long before rated full load current is reached.

This applies when the magnetic circuit is as fully closed as in
the original transformer. If it is only partially closed with
perhaps inferior iron or small airgap, proportionally
more current will be needed.

But the bottom line is that I'm going to be using 240v max (full wave)
and as long as it isn't saturated then, I'll be getting the maximum pull
available.

240V should be ample.

Jim


None of the text you quote was written by me.

I'm sorry about the error - it was very bad editing on my
part. I hope it has not caused you any difficulty.


I just wanted to make it clear to those who don't pay attention to
what they read.

I've had more than one character insist I posted something I didn't,
because of this. It's them that I don't want to deal with.

With apologies.


Thank you, and it's accepted.


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

The saga continues. Today's testing:

_COIL HEATING_

I used 160v AC into the bridge. Same as used for the first tests I did
Wednesday.

I assumed a 30% duty cycle (what MagnaBend uses), with 3 seconds on & 7
off. I set up a 555 timer to do this and let it run a half hour. It
probably didn't reach steady state by then, but it's unlikely that I'd
ever use it longer. The temperature rise was 95C (172F). Pretty
modest, given transformer classes are 80, 115, & 150C.

Wondering if the 3 second bend time was realistic, I watched the
MagnaBend video again & measured the time it took to make a bend. It
was about 5 seconds actual bending and 5 seconds or so lining it up. So
I ran another test: 5 seconds on, 10 off (33% duty cycle). I ran this
for 2 minutes (8 cycles). 8 bends being the most I'd ever do at a time.
85C rise.

Then, a balls-to-the-wall test: 250v applied (to the bridge). 5
applications of 4 seconds each & 10 seconds off. 4 or 5 bends is
probably a typical job. I usually only do 1 or 2. A small 39C rise.

_PULL_

My previous pull/grip/force measurements were done with 120v. Looking
for the absolute maximum that I could get, I tried 250v. Knowing that I
couldn't measure the full force, I put 3 equal bars on the magnet and
loaded one of them (the middle one). It lifted 362 lbs, but was heating
up rapidly and as it heated the resistance went up and the current down,
reducing the pull. It let go after a minute or so. I didn't intend to
run a minute's test, it's just that it took me that long to get the load
off the ground. A single bar covering the poles would then exert 3 x
362 = 1086 lbs !!!! Or 290 lbs per inch. The MagnaBend exerts 250 lbs
per inch.

The temperature rise was 120C. The sustained "on" time was the cause.

_SUMMARY_

With 120v applied, the force was 740 lbs (about 200 lbs per in).
Although I didn't measure heating at this voltage, it could probably run
"forever" (100% duty cycle) without overheating.

At 160v, a 30% duty cycle would keep the coil from overheating. Force
was not measured.

At 250v, the force was 1086 lbs (290 lbs per in). A 47% increase from
the 120v force, but with a 108% increase in voltage. Definitely
non-linear. A 30% duty cycle would likely be OK (I didn't test to
steady state), but the "on" period could not be more than 5 - 10
seconds, with a minute's "on" getting the coil very hot.

Were I to actually get around to building a magnetic bender using MOT
electromagnets, I would probably include a variac in the controls. It
would allow the use of 120v when that amount of force would do, without
worrying about heat. But it could be cranked up to 250 when the most
force was needed.

Now, the next step would be to test other MOT electromagnets to see how
much variation there is between them. But that's not going to happen.
I'm going to assume a close-enough between them, but check that the
secondary turns are close. By dividing the cross sectional area by the
wire diameter.

Bob

Joseph Gwinn wrote:

... The fancy hinges are another matter.

In the US, I didn't find any patents assigned to Magnabend, but I bet
there are patents somewhere, starting with Australia. ...

The thread on the Practical Machinist forum about MagnaBends had a reply
from an Australian who had worked with the inventors of the brake and
hinges. He posted this link to the patent:
http://www.google.com/patents/about?id=n3A2AAAAEBAJ

I still don't understand them. Building them would be totally out the
question for me.

But, I've been thinking about it. The hinge does offer the unique
ability to bend at the end of the brake. But the need to make such
bends is pretty limited, for me anyhow. Even the MagnaBend video only
shows one sequence of bends at the end, and many more along the clamp bar.

So, for me, the biggest advantage is the magnetic clamp, which could be
homemade fairly easily. And use traditional pin hinges at the ends.
The bending bar would have to be stiffer without the hinges in the
middle, but that's easy enough.

Bob

In article ,
Bob Engelhardt wrote:

Joseph Gwinn wrote:

... The fancy hinges are another matter.

In the US, I didn't find any patents assigned to Magnabend, but I bet
there are patents somewhere, starting with Australia. ...

The thread on the Practical Machinist forum about MagnaBends had a reply
from an Australian who had worked with the inventors of the brake and
hinges. He posted this link to the patent:
http://www.google.com/patents/about?id=n3A2AAAAEBAJ

Wonderful. I knew there had to be a patent.

Using information from the patent, I've also found some relevant
information in Alan Stuart Bottomley's resume:

http://aaybee.com.au/Resume%20Dec%202010.mht.htm


I still don't understand them.

The patent isn't awfully clear. But the idea cannot be all that
complex. It's probably a beefy variation on the invisible hinges used
on kitchen cabinets.


Building them would be totally out the question for me.

That isn't at all obvious just yet. Some of the later hinge designs look
perfectly practical for a HSM, being two or three orthogonal
pin-in-sleeve hinge joints in mechanical series.


But, I've been thinking about it. The hinge does offer the unique
ability to bend at the end of the brake. But the need to make such
bends is pretty limited, for me anyhow. Even the MagnaBend video only
shows one sequence of bends at the end, and many more along the clamp bar.

So, for me, the biggest advantage is the magnetic clamp, which could be
homemade fairly easily. And use traditional pin hinges at the ends.
The bending bar would have to be stiffer without the hinges in the
middle, but that's easy enough.

Although there has been a thread on using discarded microwave oven power
transformers as the magnet, it isn't obvious that this is necessary.
Given that the excitation current will be DC, laminated steel is not
needed, so one could cobble a magnetic circuit from ordinary mild steel.

Joe Gwinn

In article ,
Joseph Gwinn wrote:

In article ,
Bob Engelhardt wrote:

Joseph Gwinn wrote:

... The fancy hinges are another matter.

In the US, I didn't find any patents assigned to Magnabend, but I bet
there are patents somewhere, starting with Australia. ...

The thread on the Practical Machinist forum about MagnaBends had a reply
from an Australian who had worked with the inventors of the brake and
hinges. He posted this link to the patent:
http://www.google.com/patents/about?id=n3A2AAAAEBAJ

Wonderful. I knew there had to be a patent.

It's US patent 4,513,475 to Fenton.


Using information from the patent, I've also found some relevant
information in Alan Stuart Bottomley's resume:

http://aaybee.com.au/Resume%20Dec%202010.mht.htm

Which led to US patent 4,111,027 (to Bottomley), for the Magnabend
itself. Note that 4,513,475 says that the original hinge design of the
magnabend was not satisfactory, but does not say why.


Joe Gwinn





I still don't understand them.

The patent isn't awfully clear. But the idea cannot be all that
complex. It's probably a beefy variation on the invisible hinges used
on kitchen cabinets.


Building them would be totally out the question for me.

That isn't at all obvious just yet. Some of the later hinge designs look
perfectly practical for a HSM, being two or three orthogonal
pin-in-sleeve hinge joints in mechanical series.


But, I've been thinking about it. The hinge does offer the unique
ability to bend at the end of the brake. But the need to make such
bends is pretty limited, for me anyhow. Even the MagnaBend video only
shows one sequence of bends at the end, and many more along the clamp bar.

So, for me, the biggest advantage is the magnetic clamp, which could be
homemade fairly easily. And use traditional pin hinges at the ends.
The bending bar would have to be stiffer without the hinges in the
middle, but that's easy enough.

Although there has been a thread on using discarded microwave oven power
transformers as the magnet, it isn't obvious that this is necessary.
Given that the excitation current will be DC, laminated steel is not
needed, so one could cobble a magnetic circuit from ordinary mild steel.

Joe Gwinn

Joseph Gwinn wrote:
Bob Engelhardt wrote:
I still don't understand them [hinges].

The patent isn't awfully clear. But the idea cannot be all that
complex. It's probably a beefy variation on the invisible hinges used
on kitchen cabinets.

That was my thought, then I realized that with cabinet hinges the axis
of rotation isn't important. The axis for the MagnaBend hinges has to
be the intersection of the clamp plane and the bending bar plane.

Building them would be totally out the question for me.

That isn't at all obvious just yet. Some of the later hinge designs look
perfectly practical for a HSM, being two or three orthogonal
pin-in-sleeve hinge joints in mechanical series.

Maybe. One thing that troubled me was the patent's description of one
axis of rotation intersecting another axis at yet a third axis.

The thread on the Practical Machinist forum was started by a guy who was
going to make a brake and had made a prototype or mock up of the hinge
that he claimed worked. I could try one in pine, just to get the idea.

....

Although there has been a thread on using discarded microwave oven power
transformers as the magnet, it isn't obvious that this is necessary.
Given that the excitation current will be DC, laminated steel is not
needed, so one could cobble a magnetic circuit from ordinary mild steel.

Yeah, that's a sub-thread in this thread G.

I don't think that I want to do that much coil winding. You'd need a
couple of hundred turns to keep the current at reasonable levels, and
I'd want one at least 24" long.

Bob

In article ,
Bob Engelhardt wrote:

Joseph Gwinn wrote:
Bob Engelhardt wrote:
I still don't understand them [hinges].

The patent isn't awfully clear. But the idea cannot be all that
complex. It's probably a beefy variation on the invisible hinges used
on kitchen cabinets.

That was my thought, then I realized that with cabinet hinges the axis
of rotation isn't important. The axis for the MagnaBend hinges has to
be the intersection of the clamp plane and the bending bar plane.

Building them would be totally out the question for me.

That isn't at all obvious just yet. Some of the later hinge designs look
perfectly practical for a HSM, being two or three orthogonal
pin-in-sleeve hinge joints in mechanical series.

Maybe. One thing that troubled me was the patent's description of one
axis of rotation intersecting another axis at yet a third axis.

I think I figured the fancy hinge out. They don't come out and say it
(in 4,513,475), but they are more-or-less implementing a virtual ball
joint: The center of rotation is the intersection point of the three
hinge axes. In some variants, one of the hinge axes is a goinometer
mechanism (the cylinder-segment bearings). In all cases, the point is to
make the center of rotation be outside of the actual hinge mechanism.

It takes a minimum of two such hinges to define the axis line about
which rotation occurs, just like with ball joints in automobile steering
gear.

The three-pin hinge (figure 20) isn't stiff against side-to-side motion,
so the hinges are provided in pairs, one hinge right-hand the other
hinge left-hand, just like gloves.


The thread on the Practical Machinist forum was started by a guy who was
going to make a brake and had made a prototype or mock up of the hinge
that he claimed worked. I could try one in pine, just to get the idea.

Sounds like a real good idea.


Although there has been a thread on using discarded microwave oven power
transformers as the magnet, it isn't obvious that this is necessary.
Given that the excitation current will be DC, laminated steel is not
needed, so one could cobble a magnetic circuit from ordinary mild steel.

Yeah, that's a sub-thread in this thread G.

I don't think that I want to do that much coil winding. You'd need a
couple of hundred turns to keep the current at reasonable levels, and
I'd want one at least 24" long.

The MagnaBend patent (4,111,027) gives some coil data in Column 5 Lines
5-12:

"A specific construction of the above described tool had a length of 600
mm, a weight of 20 kg. (not including keepers), a coil formed from 22
guage copper wire and weighing 2.4 kg., operated on a 240 volt, single
phase, 50 cycles per second AC supply and consumed, intermittently, 4
amps. That specific construction was able to exert a holding force on
sheet metal of about 4 tonnes. "

Apparently, the Australians used AWG (American Wire Gauge) sizes for
copper back then, and probably have gone over to IEC metric wire sizes.
In any event, #22 AWG wire with single build (thickness) insulation is
1.972 pounds per 1000 feet, and 2.4 Kg is (2.4)(2.2)= 5.28 pounds of
wire, which would be 2,677 feet of #22 wire. The brake is 600mm wide,
which is 600/25.4= 23.62" wide, call it 24" or 2 feet. A turn is
therefore 4 feet, so 2677/4= 669.4 turns, call it 670 turns.

This sounds like a lot, but it is certainly doable by hand, especially
if one cobbles together a simple winding machine out of wood and powered
by hand. One would wind on a wooden form, not on the iron, just as is
done when winding a motor.

From a cross-section drawing in the manual, the winding space is 20 by
28 mm (0.787" by 1.102", 0.868 square inches), which will accommodate
1191 turns of single build, so there is space. In practice, one would
most likely use double build (to better handle the voltage in a single
winding), allowing 1099 turns. There will also be heavy insulation
between the coil and the iron; this will reduce the area available for
winding. But it looks like we have a viable solution. This, for 220
volt systems. Fewer turns of heavier wire will yield the same magnetic
flux in a 120 volt system. Roughly, 335 turns of #19 AWG wire, pulling
8 amps.


The ampere-turns product is (4)(670)= 2,680 amp-turns. This yields a 4
metric tones clamping force in a length of 0.6 meters, or 4000/0.6 =
6,667 kilograms per meter, which is 372.5 pounds per inch.


Joe Gwinn

Joseph Gwinn wrote:
...
Which led to US patent 4,111,027 (to Bottomley), for the Magnabend
itself. Note that 4,513,475 says that the original hinge design of the
magnabend was not satisfactory, but does not say why.

I just read the MagnaBend patent* and found it very straight-forward,
especially compared to the complexity of the hinge. The original hinges
seem like a good idea: they aren't end mounted, so multiples could be
used, and they don't project into the axis of rotation.

I wonder how they were inadequate. The only shortcoming that occurs to
me is that during rotation there is an area near the front edge of the
bed that is opened up, leaving the material unsupported. It's a small
area, but maybe it's enough to allow distortion in the material.

I'd really like to know, 'cause those hinges would be so much simpler to
build.

Bob

* - reading patents is so much easier with 2 monitors. My big one has
the drawings, full screen, and the smaller one the description text. No
scrolling up and down 'tween text & drawings.

Joseph Gwinn wrote:
In article ,
Bob Engelhardt wrote:


Joseph Gwinn wrote:

Bob Engelhardt wrote:

I still don't understand them [hinges].

The patent isn't awfully clear. But the idea cannot be all that
complex. It's probably a beefy variation on the invisible hinges used
on kitchen cabinets.

That was my thought, then I realized that with cabinet hinges the axis
of rotation isn't important. The axis for the MagnaBend hinges has to
be the intersection of the clamp plane and the bending bar plane.


Building them would be totally out the question for me.

That isn't at all obvious just yet. Some of the later hinge designs look
perfectly practical for a HSM, being two or three orthogonal
pin-in-sleeve hinge joints in mechanical series.

Maybe. One thing that troubled me was the patent's description of one
axis of rotation intersecting another axis at yet a third axis.


I think I figured the fancy hinge out. They don't come out and say it
(in 4,513,475), but they are more-or-less implementing a virtual ball
joint: The center of rotation is the intersection point of the three
hinge axes. In some variants, one of the hinge axes is a goinometer
mechanism (the cylinder-segment bearings). In all cases, the point is to
make the center of rotation be outside of the actual hinge mechanism.

It takes a minimum of two such hinges to define the axis line about
which rotation occurs, just like with ball joints in automobile steering
gear.

The three-pin hinge (figure 20) isn't stiff against side-to-side motion,
so the hinges are provided in pairs, one hinge right-hand the other
hinge left-hand, just like gloves.



The thread on the Practical Machinist forum was started by a guy who was
going to make a brake and had made a prototype or mock up of the hinge
that he claimed worked. I could try one in pine, just to get the idea.


Sounds like a real good idea.



Although there has been a thread on using discarded microwave oven power
transformers as the magnet, it isn't obvious that this is necessary.
Given that the excitation current will be DC, laminated steel is not
needed, so one could cobble a magnetic circuit from ordinary mild steel.

Yeah, that's a sub-thread in this thread G.

I don't think that I want to do that much coil winding. You'd need a
couple of hundred turns to keep the current at reasonable levels, and
I'd want one at least 24" long.


The MagnaBend patent (4,111,027) gives some coil data in Column 5 Lines
5-12:

"A specific construction of the above described tool had a length of 600
mm, a weight of 20 kg. (not including keepers), a coil formed from 22
guage copper wire and weighing 2.4 kg., operated on a 240 volt, single
phase, 50 cycles per second AC supply and consumed, intermittently, 4
amps. That specific construction was able to exert a holding force on
sheet metal of about 4 tonnes. "

Apparently, the Australians used AWG (American Wire Gauge) sizes for
copper back then, and probably have gone over to IEC metric wire sizes.
In any event, #22 AWG wire with single build (thickness) insulation is
1.972 pounds per 1000 feet, and 2.4 Kg is (2.4)(2.2)= 5.28 pounds of
wire, which would be 2,677 feet of #22 wire. The brake is 600mm wide,
which is 600/25.4= 23.62" wide, call it 24" or 2 feet. A turn is
therefore 4 feet, so 2677/4= 669.4 turns, call it 670 turns.

Can you be certain the Australians were using AWG and not SWG, it makes
a difference. Their video mentions it bending "16 gauge" and their
specifications mention 16g/1.6mm which would indicate SWG is in use at
least for the metal specs, US metal gauges are thinner for the same number.

This sounds like a lot, but it is certainly doable by hand, especially
if one cobbles together a simple winding machine out of wood and powered
by hand. One would wind on a wooden form, not on the iron, just as is
done when winding a motor.

From a cross-section drawing in the manual, the winding space is 20 by
28 mm (0.787" by 1.102", 0.868 square inches), which will accommodate
1191 turns of single build, so there is space. In practice, one would
most likely use double build (to better handle the voltage in a single
winding), allowing 1099 turns. There will also be heavy insulation
between the coil and the iron; this will reduce the area available for
winding. But it looks like we have a viable solution. This, for 220
volt systems. Fewer turns of heavier wire will yield the same magnetic
flux in a 120 volt system. Roughly, 335 turns of #19 AWG wire, pulling
8 amps.


The ampere-turns product is (4)(670)= 2,680 amp-turns. This yields a 4
metric tones clamping force in a length of 0.6 meters, or 4000/0.6 =
6,667 kilograms per meter, which is 372.5 pounds per inch.


Joe Gwinn

I've been following this thread with interest, but not actually planning on
trying to build this type of machine.
I think that finding a way to get the 51" $375 Craigslist listing unit
delivered would be a worthwhile consideration..but I do understand the
curiousity of potentially being able to make a useful machine from salvaged
parts.

I was thinking that the primary windings may be better than the secondaries,
but you likely know better, and the number of turns on the secondary side is
much greater than the primary.

I haven't looked at a MOT in a long while, but cutting away a primary
winding (or either winding) from the E-core, I think that would leave more
room available for a custom wound bobbin that fills the entire E-core..
making a much stronger electromagnet.. so it would be a determination of
which is the best wire gage to use, and where to get a lot of it, then a
method of carefully winding the bobbin (flat, level layers for the highest
number of windings).
My local motor shop has lent out large spools of magnet wire in the past,
then they weigh the spool when it's returned and charge a very reasonable
fee for how much weight was removed.
If one had a significant number of identical MOTs, doubling either winding
onto the E-core may be possible.

A second aspect is the mating surfaces of the E-core sections of the core to
a separate piece of metal.
I'm thinking that the most effective coupling of the two surfaces would need
to be very precise for the most effective magnetic transfer to the steel
bar.. possibly a very close tolerance smooth/flat surface that a surface
grinder might provide.
Attachment of the E-cores could then be held securely to the steel bar by
tack welding the E-cores in position.

I believe that winding the coil to fit directly on the lower section bar
would be the best solution, for maximum efficiency.

--
WB
..........


"David Billington" wrote in message
...

Can you be certain the Australians were using AWG and not SWG, it makes a
difference. Their video mentions it bending "16 gauge" and their
specifications mention 16g/1.6mm which would indicate SWG is in use at
least for the metal specs, US metal gauges are thinner for the same
number.

On Jan 24, 9:13*am, "Wild_Bill" wrote:


I haven't looked at a MOT in a long while, but cutting away a primary
winding (or either winding) from the E-core, I think that would leave more
room available for a custom wound bobbin that fills the entire E-core..
making a much stronger electromagnet.. so it would be a determination of
which is the best wire gage to use, and where to get a lot of it, then a
method of carefully winding the bobbin (flat, level layers for the highest
number of windings).

MOT's are cheap. Usually available for nothing from Microwave ovens
that have something wrong with them.

So forget winding. Just salvage a HV winding from another MOT, and
slip it on in place of the primary. Connect the two windings in
parallel or series depending what you have for power to energize the
magnet.

Dan

Wild_Bill wrote:
....
I was thinking that the primary windings may be better than the
secondaries, but you likely know better, and the number of turns on the
secondary side is much greater than the primary.

It's basically a volts-amps choice on the supply. High voltage/low amps
using the secondary; low voltage/high amps if the primary. The winding
ratio is about 17:1 (2000:120), so for the same amp-turns, you'd need 17
times the current using the primary as using the secondary.

...
If one had a significant number of identical MOTs, doubling either
winding onto the E-core may be possible.

I did this once to get an isolation transformer: I put 2 primaries on
the same core. It took a long time to find 2 MOTs with the same winding
size. They are very closely fitted, so there is not much margin. I now
have 14 extra MOTs as a result of that search (i.e., the 14 are ones
that didn't match anything).

A second aspect is the mating surfaces of the E-core sections of the
core to a separate piece of metal.
I'm thinking that the most effective coupling of the two surfaces would
need to be very precise for the most effective magnetic transfer to the
steel bar.. possibly a very close tolerance smooth/flat surface that a
surface grinder might provide.
Attachment of the E-cores could then be held securely to the steel bar
by tack welding the E-cores in position.

I agree. But the MOTs are already pretty flat - they don't want to have
air gaps either. I would fasten them in place & then surface grind
(Blanchard would be good enough).

I believe that winding the coil to fit directly on the lower section bar
would be the best solution, for maximum efficiency.

I have wound a couple of windings for customized MOTs and it's not
something that I want to do a lot of.

Bob

I've been thinking: how much better would pure (regulated) DC be? For a
given magnetization, would the current be less? Or would the heating be
less?

A previous Reply said that the DC voltage only has to be about 5% of the
AC voltage to reach the same level of magnetization. In that case the
200v secondary would only need 100v DC. I'm using more than that, but
I'm wondering if it's because the unfiltered DC has so much ripple.

Anyhow, I could build a 100v regulator, but would it be worth it?

Thanks,
Bob

"Bob Engelhardt" wrote in message
...
I've been thinking: how much better would pure (regulated) DC be? For a
given magnetization, would the current be less? Or would the heating be
less?

A previous Reply said that the DC voltage only has to be about 5% of the
AC voltage to reach the same level of magnetization. In that case the
200v secondary would only need 100v DC. I'm using more than that, but
I'm wondering if it's because the unfiltered DC has so much ripple.

Anyhow, I could build a 100v regulator, but would it be worth it?

Thanks,
Bob

I seriously doubt it would be worth it. The MOT is acting as an
inductor in this case and it will be smoothing out the current ripple
as it is. If you have an o'scope add a 1 ohm resistor in series with
a MOT leg and attach the scope across the resistor to monitor the
current. You'll need to float the scope (or isolate the AC source
to the MOT) as both sides of the resistor will be hot. The
waveform will have much less ripple than the excitation voltage
waveform.
Art

Bob Engelhardt wrote:

I've been thinking: how much better would pure (regulated) DC be? For a
given magnetization, would the current be less? Or would the heating be
less?

A previous Reply said that the DC voltage only has to be about 5% of the
AC voltage to reach the same level of magnetization. In that case the
200v secondary would only need 100v DC. I'm using more than that, but
I'm wondering if it's because the unfiltered DC has so much ripple.

Anyhow, I could build a 100v regulator, but would it be worth it?


Why regulate it? A simple filter would make a huge improvement.
Connect the cores in series to drop the DC voltage in half.


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

In article ,
Bob Engelhardt wrote:

Joseph Gwinn wrote:
...
Which led to US patent 4,111,027 (to Bottomley), for the Magnabend
itself. Note that 4,513,475 says that the original hinge design of the
magnabend was not satisfactory, but does not say why.

I just read the MagnaBend patent* and found it very straight-forward,
especially compared to the complexity of the hinge. The original hinges
seem like a good idea: they aren't end mounted, so multiples could be
used, and they don't project into the axis of rotation.

I wonder how they were inadequate. The only shortcoming that occurs to
me is that during rotation there is an area near the front edge of the
bed that is opened up, leaving the material unsupported. It's a small
area, but maybe it's enough to allow distortion in the material.

I'd really like to know, 'cause those hinges would be so much simpler to
build.

Those original hinges looked hard to make, and I wondered if they would
tend to jam, especially if a little dirt got into them. Also, the
cylinder axes would need to be precisely colinear, or they will tear
each other apart. Virtual ball joints will not have this problem.

Bottomley has a web site. I wonder if he will answer questions.


Bob

* - reading patents is so much easier with 2 monitors. My big one has
the drawings, full screen, and the smaller one the description text. No
scrolling up and down 'tween text & drawings.

I have one big display, big enough for side-by-side display, but usually
use the space to make the text big.

Joe Gwinn

In article ,
David Billington wrote:

Joseph Gwinn wrote:

[snip]

The MagnaBend patent (4,111,027) gives some coil data in Column 5 Lines
5-12:

"A specific construction of the above described tool had a length of 600
mm, a weight of 20 kg. (not including keepers), a coil formed from 22
guage copper wire and weighing 2.4 kg., operated on a 240 volt, single
phase, 50 cycles per second AC supply and consumed, intermittently, 4
amps. That specific construction was able to exert a holding force on
sheet metal of about 4 tonnes. "

Apparently, the Australians used AWG (American Wire Gauge) sizes for
copper back then, and probably have gone over to IEC metric wire sizes.
In any event, #22 AWG wire with single build (thickness) insulation is
1.972 pounds per 1000 feet, and 2.4 Kg is (2.4)(2.2)= 5.28 pounds of
wire, which would be 2,677 feet of #22 wire. The brake is 600mm wide,
which is 600/25.4= 23.62" wide, call it 24" or 2 feet. A turn is
therefore 4 feet, so 2677/4= 669.4 turns, call it 670 turns.

Can you be certain the Australians were using AWG and not SWG, it makes
a difference. Their video mentions it bending "16 gauge" and their
specifications mention 16g/1.6mm which would indicate SWG is in use at
least for the metal specs, US metal gauges are thinner for the same number.

SWG is for sheet steel, while AWG is for copper wire.

I did google around a lot, and all indications I found were that they
really did mean American Wire Gauge, although I would have guessed that
they would use BSG (British WG). The difference between AWG and BWG
isn't large. But I feared that AWG really meant Australian WG.
Actually, I was surprised to see wire gauge listed, versus diameter in
millimeters.

If anyone from the Land of OZ is listening, please chime in.

Joe Gwinn

Joseph Gwinn wrote:
Bob Engelhardt wrote:

... those [original] hinges would be so much simpler to build.

Those original hinges looked hard to make, and I wondered if they would
tend to jam, especially if a little dirt got into them. Also, the
cylinder axes would need to be precisely colinear, or they will tear
each other apart. Virtual ball joints will not have this problem.

"Eye of the beholder", I guess.

Bottomley has a web site. I wonder if he will answer questions.

Good idea. I've asked on the Practical Machinist forum. If I don't get
an answer, I'll try Bottomly. Or you could.

Bob

In article ,
Bob Engelhardt wrote:

Joseph Gwinn wrote:
Bob Engelhardt wrote:

... those [original] hinges would be so much simpler to build.

Those original hinges looked hard to make, and I wondered if they would
tend to jam, especially if a little dirt got into them. Also, the
cylinder axes would need to be precisely colinear, or they will tear
each other apart. Virtual ball joints will not have this problem.

"Eye of the beholder", I guess.

I think that the required precision is the issue. They look like a
centerless goinometer mechanism, which requires precision to work well.

http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=860

A bunch of hinges should be easier to make, and that's what MagnaBend
ultimately went to.


Bottomley has a web site. I wonder if he will answer questions.

Good idea. I've asked on the Practical Machinist forum. If I don't get
an answer, I'll try Bottomly. Or you could.

We can work together on the questions to be asked.

Joe Gwinn

Bob Engelhardt wrote:
... I've asked on the Practical Machinist forum. If I don't get
an answer, I'll try Bottomly. ...

I just got the reply on P-M:
"I have spoken to Alan about the hinges and he has brought a box of the
prototype hinges into work today. I think he will write a bit of a story
about the Magnabend development over the next week or so. Geoff is away
on holiday at the moment (far southwest of Tasmania) where there is no
technology, but when he gets back I will see if he want to add something."

Bob

"Jon Danniken" wrote in message
...
I had never heard of these before today, when one of these showed up in the
local Craigslist (no connection to the seller). Found a video on youtube,
and it certainly does look like an interesting tool.

http://www.youtube.com/watch?v=OipSiPSRti8

I don't do enough bending (or have the space) to justify getting one of
these, but this caught my eye. Anyone played with one of these before?

Jon



http://www.magnabend.com/

They are pretty good. We had one at the school shop I attended. They will do
thing you couldn't do with anything else.

In article ,
Bob Engelhardt wrote:

Bob Engelhardt wrote:
... I've asked on the Practical Machinist forum. If I don't get
an answer, I'll try Bottomly. ...

I just got the reply on P-M:
"I have spoken to Alan about the hinges and he has brought a box of the
prototype hinges into work today. I think he will write a bit of a story
about the Magnabend development over the next week or so. Geoff is away
on holiday at the moment (far southwest of Tasmania) where there is no
technology, but when he gets back I will see if he want to add something."

This is excellent news. I wonder if they realized that they have a fan
club.

Joe Gwinn

In article ,
Joseph Gwinn wrote:

In article ,
Bob Engelhardt wrote:

Bob Engelhardt wrote:
... I've asked on the Practical Machinist forum. If I don't get
an answer, I'll try Bottomly. ...

I just got the reply on P-M:
"I have spoken to Alan about the hinges and he has brought a box of the
prototype hinges into work today. I think he will write a bit of a story
about the Magnabend development over the next week or so. Geoff is away
on holiday at the moment (far southwest of Tasmania) where there is no
technology, but when he gets back I will see if he want to add something."

This is excellent news. I wonder if they realized that they have a fan
club.

I may know what the problem with the original hinges is: When bending
at one end, a major claimed benefit of the MagnaBend, the machine frame
will rack a bit, jamming the hinges. Thus the need for a virtual ball
joint hinge.

Joe Gwinn

Joseph Gwinn wrote:
This is excellent news. I wonder if they realized that they have a fan
club.

Joe Gwinn

I'm following this but probably won't be building one. I'm
one of those folks that just likes to absorb interesting
technology :-)
I may even build one or more of the hinges if I can ever]
see some "real" sketches. The (what passes for a) dwg on the
patent doesn't quite make it.
So keep the thread going here or let me know if you take it
elsewhere please.
...Lew...

In article ,
Lewis Hartswick wrote:

Joseph Gwinn wrote:
This is excellent news. I wonder if they realized that they have a fan
club.

Joe Gwinn

I'm following this but probably won't be building one. I'm
one of those folks that just likes to absorb interesting
technology :-)

I was thinking of maybe building a one foot wide unit that clamps to a
bench, mainly to save on storage space. I don't really need to make
that many boxes and pans, so it would be for the joy of building a tool.


I may even build one or more of the hinges if I can ever]
see some "real" sketches. The (what passes for a) dwg on the
patent doesn't quite make it.

A good comparison is a gimbal mechanism, but with the rings reduced to
sectors and half the pivot bearings missing.

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


So keep the thread going here or let me know if you take it
elsewhere please.

No plans to move have been promulgated.

Joe Gwinn

Bob Engelhardt wrote:
Bob Engelhardt wrote:
... I've asked on the Practical Machinist forum. If I don't get an
answer, I'll try Bottomly. ...

I just got the reply on P-M:
"I have spoken to Alan about the hinges and he has brought a box of the
prototype hinges into work today. I think he will write a bit of a story
about the Magnabend development over the next week or so. Geoff is away
on holiday at the moment (far southwest of Tasmania) where there is no
technology, but when he gets back I will see if he want to add something."

Bob

Alan Bottomly (the MagnaBend's inventor) has joined the discussion on
the Practical Machinist forum. As to the original hinges ("cup hinges"
he calls them), he said they tended to jam when being returned from
large-angle bends. Too little engagement after 90 degrees. He also had
comments about wire size used for the magnets, but I'm not going to keep
repeating what's said & recommend that interested RCM'ers join P-M.

Bob

Bob Engelhardt wrote:
Bob Engelhardt wrote:
Bob Engelhardt wrote:
... I've asked on the Practical Machinist forum. If I don't get an
answer, I'll try Bottomly. ...

I just got the reply on P-M:
"I have spoken to Alan about the hinges and he has brought a box of
the prototype hinges into work today. I think he will write a bit of a
story about the Magnabend development over the next week or so. Geoff
is away on holiday at the moment (far southwest of Tasmania) where
there is no technology, but when he gets back I will see if he want to
add something."

Bob

Alan Bottomly (the MagnaBend's inventor) has joined the discussion on
the Practical Machinist forum. As to the original hinges ("cup hinges"
he calls them), he said they tended to jam when being returned from
large-angle bends. Too little engagement after 90 degrees. He also had
comments about wire size used for the magnets, but I'm not going to keep
repeating what's said & recommend that interested RCM'ers join P-M.

Thanks for the P-M cite, Bob. I enjoyed hearing from Alan.

At the risk of turning the 'elegant and beautiful' into the
'byzantine and ugly', what would prevent one from designing
a current-mode PWM controller so that electromagnets with
'too thick' wire could be driven optimally, with just the
proper amount of current for maximum attraction yet not so
high as to cause excessive power dissipation?

I don't understand the conflict with using multiple MOTs as
electromagnets. Every second electromagnet could be driven
with opposite polarity so that no repulsion occurs between
them, yes?


--Winston

Winston wrote:

Bob Engelhardt wrote:
Bob Engelhardt wrote:
Bob Engelhardt wrote:
... I've asked on the Practical Machinist forum. If I don't get an
answer, I'll try Bottomly. ...

I just got the reply on P-M:
"I have spoken to Alan about the hinges and he has brought a box of
the prototype hinges into work today. I think he will write a bit of a
story about the Magnabend development over the next week or so. Geoff
is away on holiday at the moment (far southwest of Tasmania) where
there is no technology, but when he gets back I will see if he want to
add something."

Bob

Alan Bottomly (the MagnaBend's inventor) has joined the discussion on
the Practical Machinist forum. As to the original hinges ("cup hinges"
he calls them), he said they tended to jam when being returned from
large-angle bends. Too little engagement after 90 degrees. He also had
comments about wire size used for the magnets, but I'm not going to keep
repeating what's said & recommend that interested RCM'ers join P-M.

Thanks for the P-M cite, Bob. I enjoyed hearing from Alan.

At the risk of turning the 'elegant and beautiful' into the
'byzantine and ugly', what would prevent one from designing
a current-mode PWM controller so that electromagnets with
'too thick' wire could be driven optimally, with just the
proper amount of current for maximum attraction yet not so
high as to cause excessive power dissipation?

I don't understand the conflict with using multiple MOTs as
electromagnets. Every second electromagnet could be driven
with opposite polarity so that no repulsion occurs between
them, yes?


You could connect the primaries in series.


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