On Thursday, May 1, 2014 9:12:52 AM UTC-7, Tim Wescott wrote:
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

Problem restatement: get a rotation indication using a Hall sensor.
So, put the magnet on the fuselage, the Hall sensor between the magnet
and the backplate, and drill/tap the spinning part for a small
ferrous screw. When the screw nears the field, it will cause
a spike in the magnetic field (as it becomes magnetized). Works
with a seek coil, too.

Loctite will hold the threaded part.

On Fri, 02 May 2014 20:56:45 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

John B. fired this volley in
:

That is not necessarally true when it comes to model airplanes. I once
saw a "speed job" a small controll line model designed to go fast,
that used a single bladed prop, with a conterweight with an engine
speed in excess of 10,000 rpm.

What kind of chugging hunk of a model airplane engine goes 10K? (except at
a high idle?) There are lots of them out there that consistently tach
29Krpm.

Lloyd

I was being conservative as I saw the plane in, probably the mid
1950's, and I really have no recollection of actual RPM as we just
tuned them by ear and flew them :-)

--
Cheers,

John B.
(invalid to gmail)

On Fri, 02 May 2014 20:59:10 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Larry Jaques fired this volley in
:
Vibe tach? Nevahoiduvit. Are they available?


All day long. They're almost a commodity item. Anything with a reliably
repeatable cyclic vibration is a candidate for the method.

Interesting! More research is in the offing.

They even sell sub-$20 elapsed-time meters for gasoline engines that are
only activated when vibrated by the running motor.

Yeah, $13.98 for a vibration hour meter for ATV/cycle/etc. on eBay.

--
If government were a product,
selling it would be illegal.
--P.J. O'Rourke

On Sat, 03 May 2014 08:46:55 -0700, Larry Jaques
wrote:

On Fri, 02 May 2014 20:59:10 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Larry Jaques fired this volley in
m:
Vibe tach? Nevahoiduvit. Are they available?


All day long. They're almost a commodity item. Anything with a reliably
repeatable cyclic vibration is a candidate for the method.

Interesting! More research is in the offing.

They even sell sub-$20 elapsed-time meters for gasoline engines that are
only activated when vibrated by the running motor.

Yeah, $13.98 for a vibration hour meter for ATV/cycle/etc. on eBay.
Hour meter and tach are totally different tech togh. The hour meter
just counts time when it is buzzing. No speed info involved.

On Fri, 2 May 2014 23:26:14 -0700 (PDT), whit3rd
wrote:

On Thursday, May 1, 2014 9:12:52 AM UTC-7, Tim Wescott wrote:
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

Problem restatement: get a rotation indication using a Hall sensor.
So, put the magnet on the fuselage, the Hall sensor between the magnet
and the backplate, and drill/tap the spinning part for a small
ferrous screw. When the screw nears the field, it will cause
a spike in the magnetic field (as it becomes magnetized). Works
with a seek coil, too.

Loctite will hold the threaded part.
Much simpler to use variable reactance sensor - fine coil around a
magnet, makes signal when ferous screw passes by.

On Sat, 03 May 2014 15:54:10 -0400, wrote:

On Fri, 2 May 2014 23:26:14 -0700 (PDT), whit3rd
wrote:

On Thursday, May 1, 2014 9:12:52 AM UTC-7, Tim Wescott wrote:
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

Problem restatement: get a rotation indication using a Hall sensor.
So, put the magnet on the fuselage, the Hall sensor between the magnet
and the backplate, and drill/tap the spinning part for a small
ferrous screw. When the screw nears the field, it will cause
a spike in the magnetic field (as it becomes magnetized). Works
with a seek coil, too.

Loctite will hold the threaded part.
Much simpler to use variable reactance sensor - fine coil around a
magnet, makes signal when ferous screw passes by.
Male that variable "reluctance"

fired this volley in
:

Hour meter and tach are totally different tech togh. The hour meter
just counts time when it is buzzing. No speed info involved.

Clare, Clare... (sigh) One can make a tach from a transducer as simple
as a 75-cent electret microphone. Some AGC, peak detection, and a little
band-pass filtering, then simply square up the signal and count it.

And all those features are available on a single analog chip. But done in
DSP, it can be done on a $4.00 Cortex.

Think about it. "Technology"? Yeah, 1970s technology.

Lloyd

On Sat, 03 May 2014 15:52:20 -0400, wrote:

On Sat, 03 May 2014 08:46:55 -0700, Larry Jaques
wrote:

On Fri, 02 May 2014 20:59:10 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

Larry Jaques fired this volley in
:
Vibe tach? Nevahoiduvit. Are they available?


All day long. They're almost a commodity item. Anything with a reliably
repeatable cyclic vibration is a candidate for the method.

Interesting! More research is in the offing.

They even sell sub-$20 elapsed-time meters for gasoline engines that are
only activated when vibrated by the running motor.

Yeah, $13.98 for a vibration hour meter for ATV/cycle/etc. on eBay.
Hour meter and tach are totally different tech togh. The hour meter
just counts time when it is buzzing. No speed info involved.

Right, but you see that I replied under the reference to hour meters
vs. the reference to cyclic vibration. I only LOOK dumb, clare.

--
If government were a product,
selling it would be illegal.
--P.J. O'Rourke

On Sat, 03 May 2014 17:10:17 -0400, wrote:

On Sat, 03 May 2014 15:54:10 -0400, wrote:

On Fri, 2 May 2014 23:26:14 -0700 (PDT), whit3rd
wrote:

On Thursday, May 1, 2014 9:12:52 AM UTC-7, Tim Wescott wrote:
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

Problem restatement: get a rotation indication using a Hall sensor.
So, put the magnet on the fuselage, the Hall sensor between the magnet
and the backplate, and drill/tap the spinning part for a small
ferrous screw. When the screw nears the field, it will cause
a spike in the magnetic field (as it becomes magnetized). Works
with a seek coil, too.

Loctite will hold the threaded part.
Much simpler to use variable reactance sensor - fine coil around a
magnet, makes signal when ferous screw passes by.
Male that variable "reluctance"

Step away from the bar, sir. Spelling's a ferris wheel ride, wot?


--
If government were a product,
selling it would be illegal.
--P.J. O'Rourke

On Sat, 03 May 2014 17:17:02 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

Hour meter and tach are totally different tech togh. The hour meter
just counts time when it is buzzing. No speed info involved.

Clare, Clare... (sigh) One can make a tach from a transducer as simple
as a 75-cent electret microphone. Some AGC, peak detection, and a little
band-pass filtering, then simply square up the signal and count it.

And all those features are available on a single analog chip. But done in
DSP, it can be done on a $4.00 Cortex.

Think about it. "Technology"? Yeah, 1970s technology.

Lloyd
Yes, both can be done with very simple technology - but the hour meter
can be even simpler. Not meaning any less expensive, however. Just a
missed pulse detector - can be as simple as a 555 with a trip and
reset. As long as there is a signal to reset before the timing period
expires, it keeps the clock running. (that's mid-seventies tech)

On Sat, 03 May 2014 17:44:26 -0700, Larry Jaques
wrote:

On Sat, 03 May 2014 17:10:17 -0400, wrote:

On Sat, 03 May 2014 15:54:10 -0400, wrote:

On Fri, 2 May 2014 23:26:14 -0700 (PDT), whit3rd
wrote:

On Thursday, May 1, 2014 9:12:52 AM UTC-7, Tim Wescott wrote:
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

Problem restatement: get a rotation indication using a Hall sensor.
So, put the magnet on the fuselage, the Hall sensor between the magnet
and the backplate, and drill/tap the spinning part for a small
ferrous screw. When the screw nears the field, it will cause
a spike in the magnetic field (as it becomes magnetized). Works
with a seek coil, too.

Loctite will hold the threaded part.
Much simpler to use variable reactance sensor - fine coil around a
magnet, makes signal when ferous screw passes by.
Male that variable "reluctance"

Step away from the bar, sir. Spelling's a ferris wheel ride, wot?
It was more than spelling though - both reactance and reluctance are
real and spelled properly -----

fired this volley in
:

Yes, both can be done with very simple technology - but the hour meter
can be even simpler. Not meaning any less expensive, however. Just a
missed pulse detector - can be as simple as a 555 with a trip and
reset. As long as there is a signal to reset before the timing period
expires, it keeps the clock running. (that's mid-seventies tech)


Are you someone who enjoys deliberately diverting a subject just to ruin
a conversation, or are you so thick you don't know you're off-track?

WE were talking about implementing a tach. The reason I mentioned ET
meters was that they often use the same acoustic transducers as vibration
tachs to trigger them. And you know that's why it came up.

You're getting as bad as that 'CNC expert' asshole who's always trying to
wreck other people's threads. Get back on the subject - if you know
anything about it.

Lloyd

On Thu, 1 May 2014 09:28:19 -0700, "Bob La Londe"
wrote:

"Tim Wescott" wrote in message
m...
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

The thing needs to work with a model airplane engine, so it's going to be
a high vibration environment.

The easy to get magnets (which is what I have) are nickel plated, so
they're slippery as hell. They're also not machined to super-tight
tolerances, and NdFeB is brittle as hell (it's optimized for magnetic
hardness, not physical strength!).

The best I can think of is to drill the hole to a slip fit and then
epoxy. I have visions of actually achieving a press fit, then watching
magnet after magnet crumble into clinging dust trying to press them in.

Suggestions?

In the alarm industry rare earth magnets are often used for problem or
difficult installation situations. Perhaps a magnet like this with a screw
mounting hole might be of some use to you.

http://grisk.com/recessed/mighty_mag.html

I would think even using epoxy and a light interference fit with the resin
squeezing up through the hole, or the use of a screw would work fairly well.
To be fair, we do not typically use these in a high vibration environment in
the alarm industry, but magnetic reed switches and magnets are often used on
machinery where abrasive grit will work into most other types of switches
and destroy them. I would expect there is some vibration in those
environments.

Anyway, the rare earth magnets pictured on that page might give you other
options.

Drop me a line if you like.

alarm(underscore)wizard
dfkgjs-to-confuse-email-harvesters-asljdprhrtph
(at)hotmail(dot)com

I have found when using a raw bare metal rare earth magnet they will not
hold up to more than the lightest interference fit. In practice we often
get them already glued into a plastic sleeve which will take a rather firm
interference fit, and is how they are typically installed such as the
magnets on this page.

http://grisk.com/recessed/20rs.html

I would point out that a rare earth magnet may have to wide of a magnetic
field for optimum detection by your sensor. As it spins past it will be
detected for a wider range of travel. Depending on the sensing speed of
your sensor, its reset time, and the distance from the axis of rotation you
may wind up with a continuous or nearly continuous activation.

Well stated.











--

"
I was once told by a “gun safety” advocate back in the Nineties
that he favored total civilian firearms confiscation.
Only the military and police should have weapons he averred and what did I think about that?

I began to give him a reasoned answer and he
cut me off with an abrupt, “Give me the short answer.”

I thought for a moment and said, “If you try to take our firearms we will kill you.”"

On Sat, 03 May 2014 23:21:07 -0400, wrote:

On Sat, 03 May 2014 17:44:26 -0700, Larry Jaques
wrote:

On Sat, 03 May 2014 17:10:17 -0400, wrote:

On Sat, 03 May 2014 15:54:10 -0400, wrote:

On Fri, 2 May 2014 23:26:14 -0700 (PDT), whit3rd
wrote:

On Thursday, May 1, 2014 9:12:52 AM UTC-7, Tim Wescott wrote:
Problem statement:

Mount a small (nominally 3.2 x 1.6mm) NdFeB magnet in an aluminum model
airplane spinner backplate (for a tachometer).

Problem restatement: get a rotation indication using a Hall sensor.
So, put the magnet on the fuselage, the Hall sensor between the magnet
and the backplate, and drill/tap the spinning part for a small
ferrous screw. When the screw nears the field, it will cause
a spike in the magnetic field (as it becomes magnetized). Works
with a seek coil, too.

Loctite will hold the threaded part.
Much simpler to use variable reactance sensor - fine coil around a
magnet, makes signal when ferous screw passes by.
Male that variable "reluctance"

Step away from the bar, sir. Spelling's a ferris wheel ride, wot?
It was more than spelling though - both reactance and reluctance are
real and spelled properly -----

Reference: ferous. 'Nuff said?

--
If government were a product,
selling it would be illegal.
--P.J. O'Rourke

On Sat, 03 May 2014 22:32:15 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

Yes, both can be done with very simple technology - but the hour meter
can be even simpler. Not meaning any less expensive, however. Just a
missed pulse detector - can be as simple as a 555 with a trip and
reset. As long as there is a signal to reset before the timing period
expires, it keeps the clock running. (that's mid-seventies tech)


Are you someone who enjoys deliberately diverting a subject just to ruin
a conversation, or are you so thick you don't know you're off-track?

Nope. I believe it was YOU who brought up the hour meter

WE were talking about implementing a tach. The reason I mentioned ET
meters was that they often use the same acoustic transducers as vibration
tachs to trigger them. And you know that's why it came up.
And I just pointed out they are not necessarily the same - and to get
an accurate ET meter is a different and less complex challenge than
getting an accurate tach reading.

You're getting as bad as that 'CNC expert' asshole who's always trying to
wreck other people's threads. Get back on the subject - if you know
anything about it.

Lloyd
I've run a few "audio" tachometer applications on PC and
smartphone.Dead accurate on one engine, and way off on another
virtually identical engine (with different exhaust), and not even
close on another engine. If sensing (non audio) vibrations the same
thing can happen - a different engine mount stiffness, and the tach is
way off. Getting them tuned can be a challenge

I used to use a piezo tach and timing light on deisel engines a couple
decades ago - which did work very well.(clamped the sensor onto an
injection line - read the pressure pulse as the line expanded ever so
lttle under the several thousand PSI injection pulse)

I've had the same problem with photo-tachs, where for some reason the
tach would cycle from dead on, to 2x, 3x and even 4x speed when
reading off the prop at certain speeds - don't know if it had to do
with a resonance in the drive, or what. Again, this was a few years
back, and the capability of "simple" electronic circuits has increased
with leaps and bounds in the intervening years - but there are also a
lot more "cheap" solutions out there that are just plane poorly
engineered and implemented - always someone willing to make something
cheaper than it should be.

fired this volley in
:

I've run a few "audio" tachometer applications on PC and
smartphone.Dead accurate on one engine, and way off on another
virtually identical engine (with different exhaust), and not even
close on another engine. If sensing (non audio) vibrations the same
thing can happen - a different engine mount stiffness, and the tach is
way off. Getting them tuned can be a challenge


Pffft! We're talking about a one-lung model airplane engine with a
straight pipe! Even if it were a twin or a radial, it would represent
the same sort of vibration profile, which is almost always power-stroke
induced. Just more of them per rev.

I've used a lot of vibration tachs, too, and never had one misrepresent
the correct RPM on a single-cylinder engine.

Lloyd

On Sun, 04 May 2014 14:19:28 -0500, "Lloyd E. Sponenburgh"
lloydspinsidemindspring.com wrote:

fired this volley in
:

I've run a few "audio" tachometer applications on PC and
smartphone.Dead accurate on one engine, and way off on another
virtually identical engine (with different exhaust), and not even
close on another engine. If sensing (non audio) vibrations the same
thing can happen - a different engine mount stiffness, and the tach is
way off. Getting them tuned can be a challenge


Pffft! We're talking about a one-lung model airplane engine with a
straight pipe! Even if it were a twin or a radial, it would represent
the same sort of vibration profile, which is almost always power-stroke
induced. Just more of them per rev.

I've used a lot of vibration tachs, too, and never had one misrepresent
the correct RPM on a single-cylinder engine.

Lloyd
"model aircraft" engines run the gamut from 2 stroke compression
ignition mosquitos to 4 stroke spark ignition singles and twins, to 3
and 5 cyl rotary and radial 4 strokes, and wankels.

Our local RC club flies them all. Twin engines too (and even a 4
engine monster) Vib tachs don't work very well to sync twin engines.

And they go nuts when an (2 stroke) engine starts "4 stroking". If a
spark ignition 2 stroke doesn't 4 stroke coming off load, it's running
too lean.. Don't know (or pretend to know) about a glow engine but I
know my old enya 4 stroked unloaded when it was running properly.(WAY
too many years ago)

fired this volley in
:

And they go nuts when an (2 stroke) engine starts "4 stroking". If a
spark ignition 2 stroke doesn't 4 stroke coming off load, it's running
too lean.. Don't know (or pretend to know) about a glow engine but I
know my old enya 4 stroked unloaded when it was running properly.(WAY
too many years ago)


And you also know that anyone interested in tach-ing a model isn't
interested in performance outside the flight power envelope.

And no, I doubt they'd be very interested in the RPMs running all the
'exotics' like Wankels, either. (got a few thousands of hours RC'ing
myself).

I'm betting his is a performance model like a pylon racer or a ducted-fan
job. There's not much other cause to need to know the speed of the
engine. Just for the record, the high-performance engines NEVER 4-stroke
unless they're broken. They pretty-much run full-load and full RPM all
the time except when coasting. And most of that class are single-
cylinder. (mass has its costs)

You'll bring up ANY minor point you can to prove your own personal
argument, won't you? It seems you'll do that even if it doesn't match
the general subject or the specifics of what's being discussed.

Engineers work on the problems at hand, Clare, and they only bring up
spurious side-bar crap when they think it might affect the actual goal.
You never ASKED what sort of engine, and had absolutely no insight into
why someone might want to know the RPMs of an RC engine (right there,
tells me that you're only spouting crap from a catalog, and not from
actual RC-ing)

B.S. salesmen are the ones who raise all the issues not related to the
project. 'Guess you were a technology salesman.

Lloyd

On 5/2/2014 2:45 PM, Tim Wescott wrote:
On Fri, 02 May 2014 14:54:05 -0300, Mike Spencer wrote:

Tim Wescott writes:

On Thu, 01 May 2014 23:55:27 -0300, Mike Spencer wrote:

[snip]

Take apart an old (computer) mouse and get the LED and sensor. Should
be far more responsive than a reed switch. (But I'm only guessing.
Electronics weenies to the bridge, please. Is there such a thing as a
high-speed, solid state magnetic switch?)

Yes there is -- they're called Hall switches, or Hall sensors (they
work by the Hall effect. You get one guess as to the last name of the
guy who wrote it up first.)

Ah, tnx for that. Heard of "Hall effect", didn't know that commonplace
articles implemented it. Where would I look in old junk to find one?

Crank position sensors (they'll have a hall sensor and a magnet).

Laptops and flip-phones often use them to sense that the thing is closed.

Be warned that the laptop and flip-phone ones achieve very low power
consumption by only turning on about ten times a second -- at all other
times they pretty much ignore the world. Also be warned that this is the
biggest market share by far -- finding a Hall sensor that'll work on a
12000 RPM engine takes some digging (I've got part numbers, if you want
to order some from DigiKey).


Any 8 cylinder automotive electronic distributor. 8 cylinders firing
once every 2 revolutions at 6,000 rpm equals 8 times 6,000 divided by 2.

24,000 trigger events per minute. should work. Just adapt the
mechanicals, reduce, whatever, but the electronics in a distributor are
VERY robust.

On 2014-05-02, Mike Spencer wrote:

Tim Wescott writes:

[ ... ]

Ah, tnx for that. Heard of "Hall effect", didn't know that commonplace
articles implemented it. Where would I look in old junk to find one?

Hmm ... near where moving magnets are sensed -- if you can find
"old junk" which is new enough. :-)

I just don't feel that doing this optically will be robust.

Someone gave me a DecWriter II in 1990, when it was at
archaeological-artifact stage of life, which I played with for a
while. The opto-mechanical unit for spacing eventually failed and I
was never able to get it working again. I suppose the similar little
wheels in a mouse would have the same potential for refractory
NFG-ness, which is why I thought of but didn't try that for my (real)
mouse tach.

The problem with the DecWriter-II is that the chopper was a thin
metal disc stuck to a hub with double-sided tape. When the temperature
gets too hot, it can shift off-center and stop being sensed properly.
(The head will bang into the stops at one end of travel or the other.)
(Ask Me How I Know This. :-)

So -- the problem there was not with the robustness of optical
sensing, but with the robustness of the mounting of the chopper wheel.
A very different matter. If you drill a number of holes through the
spinner, and put the sensor inside (assuming that you want this to be
sensing during flight, instead of just on a test bench) it should be
well enough protected, and the spinner will certainly stay put. It is
not mounted by glue, I hope. :-)

Enjoy,
DoN.

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