Heading Hold Gyro.

I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately,
you have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the
tail rotor pitch. The device takes over when a rotate ("pirouette')
command stops, and stops the tail dead on that heading - fast, and holds
it against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add
another $40 on it.

Think of the possibilities for a heading stabilize function in a homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super
cheap altitude hold/augment?)

Brian W

"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately, you
have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the tail
rotor pitch. The device takes over when a rotate ("pirouette') command
stops, and stops the tail dead on that heading - fast, and holds it
against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add another
$40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super cheap
altitude hold/augment?)

Brian W

One of the avionics makers, Bendix IIRC, had a system available about 25 or
so years ago that used an air stream across a pair of resistance elements,
or two pairs of resistance elements for a two axis autopilot. Basically,
each pair of elements was an uninsulated resistor on each side of the
airstream for heading hold and top and bottom for pitch hold--not really the
same thing as altitude hold but possibly usefull in smooth VFR conditions.
AFAIK, the system worked because the resistance of each element (for most
materials) tends to increase with rising temperature and decrease with
falling temperature--so that the system can work by comparing the
resistances with little regard for the actual resistance values. My best
recollection is that the device could also maintain a standard rate turn.

I only vaguely recall that there may have been an article in one of the
homebuilding magazines--possibly in the early 1980s.

Peter

Peter Dohm wrote:
"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately, you
have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the tail
rotor pitch. The device takes over when a rotate ("pirouette') command
stops, and stops the tail dead on that heading - fast, and holds it
against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add another
$40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super cheap
altitude hold/augment?)

Brian W

One of the avionics makers, Bendix IIRC, had a system available about 25 or
so years ago that used an air stream across a pair of resistance elements,
or two pairs of resistance elements for a two axis autopilot. Basically,
each pair of elements was an uninsulated resistor on each side of the
airstream for heading hold and top and bottom for pitch hold--not really the
same thing as altitude hold but possibly usefull in smooth VFR conditions.
AFAIK, the system worked because the resistance of each element (for most
materials) tends to increase with rising temperature and decrease with
falling temperature--so that the system can work by comparing the
resistances with little regard for the actual resistance values. My best
recollection is that the device could also maintain a standard rate turn.

I only vaguely recall that there may have been an article in one of the
homebuilding magazines--possibly in the early 1980s.

Peter




Electro-Fluidic Autopilot.
Sport Aviation -


May '78
Preliminary Report-Development of a Poor Man's VFR Autopilot/Don Hewes

March '79
Update On The Poorman's Autopilot... by Donald E. Hewes

February '80
Autopilot System For Homebuilt Airplanes... by Don Hewes

August '80
Fine Tuning The Electro-Fluidic Autopilot.. . by Doug Garner

April '81
Muscle For Your Homebuilt Autopilot... by Don Hewes

November '81
A Magnetic Heading Reference For The Electro Fluidic Autopilot,Part I
by Doug Garner

December '81
Magnetic Heading Performance For The Electro Fluidic Autopilot
Part 11 . . , by Doug Garner

--

Richard Lamb

Peter Dohm wrote:
"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately, you
have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the tail
rotor pitch. The device takes over when a rotate ("pirouette') command
stops, and stops the tail dead on that heading - fast, and holds it
against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add another
$40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super cheap
altitude hold/augment?)

Brian W

One of the avionics makers, Bendix IIRC, had a system available about 25 or
so years ago that used an air stream across a pair of resistance elements,
or two pairs of resistance elements for a two axis autopilot. Basically,
each pair of elements was an uninsulated resistor on each side of the
airstream for heading hold and top and bottom for pitch hold--not really the
same thing as altitude hold but possibly usefull in smooth VFR conditions.
AFAIK, the system worked because the resistance of each element (for most
materials) tends to increase with rising temperature and decrease with
falling temperature--so that the system can work by comparing the
resistances with little regard for the actual resistance values. My best
recollection is that the device could also maintain a standard rate turn.

I only vaguely recall that there may have been an article in one of the
homebuilding magazines--possibly in the early 1980s.

Peter



I remember this project well, it was the brainchild of a research
engineer at one of the NASA labs - NASA Ames, if I remember.
I was so intrigued, I called him up to talk about it.
A few people scratch built the device, the "gyros" were four thermistors
on a circle, with a little tube blowing air into the center of the
circle. Rotation in either axis shielded one from the air jet, and
ventilated the other, of each pair. Thermistors generate a little heat,
and their resistance varies dramatically with temperature. Each pair fed
an operational amplifier as differential inputs.
A weakness of the design was the little motor and fan involved.
These days, a two axis (piezo) gyro is more stable, more sensitive and
more reliable, not to mention using much less power. And you can buy it
off the shelf!

Regards

Brian W

"cavelamb" wrote in message
m...
Peter Dohm wrote:
"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately,
you have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the
tail rotor pitch. The device takes over when a rotate ("pirouette')
command stops, and stops the tail dead on that heading - fast, and holds
it against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add
another $40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super
cheap altitude hold/augment?)

Brian W

One of the avionics makers, Bendix IIRC, had a system available about 25
or so years ago that used an air stream across a pair of resistance
elements, or two pairs of resistance elements for a two axis autopilot.
Basically, each pair of elements was an uninsulated resistor on each side
of the airstream for heading hold and top and bottom for pitch hold--not
really the same thing as altitude hold but possibly usefull in smooth VFR
conditions. AFAIK, the system worked because the resistance of each
element (for most materials) tends to increase with rising temperature
and decrease with falling temperature--so that the system can work by
comparing the resistances with little regard for the actual resistance
values. My best recollection is that the device could also maintain a
standard rate turn.

I only vaguely recall that there may have been an article in one of the
homebuilding magazines--possibly in the early 1980s.

Peter




Electro-Fluidic Autopilot.
Sport Aviation -


May '78
Preliminary Report-Development of a Poor Man's VFR Autopilot/Don Hewes

March '79
Update On The Poorman's Autopilot... by Donald E. Hewes

February '80
Autopilot System For Homebuilt Airplanes... by Don Hewes

August '80
Fine Tuning The Electro-Fluidic Autopilot.. . by Doug Garner

April '81
Muscle For Your Homebuilt Autopilot... by Don Hewes

November '81
A Magnetic Heading Reference For The Electro Fluidic Autopilot,Part I
by Doug Garner

December '81
Magnetic Heading Performance For The Electro Fluidic Autopilot
Part 11 . . , by Doug Garner

--

Richard Lamb



Thanks, Richard, I had forgotten where I saw it--and completely forgotten
that there were really a series of articles!

Peter

"brian whatcott" wrote in message
...
Peter Dohm wrote:
"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately,
you have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the
tail rotor pitch. The device takes over when a rotate ("pirouette')
command stops, and stops the tail dead on that heading - fast, and holds
it against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add
another $40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super
cheap altitude hold/augment?)

Brian W

One of the avionics makers, Bendix IIRC, had a system available about 25
or so years ago that used an air stream across a pair of resistance
elements, or two pairs of resistance elements for a two axis autopilot.
Basically, each pair of elements was an uninsulated resistor on each side
of the airstream for heading hold and top and bottom for pitch hold--not
really the same thing as altitude hold but possibly usefull in smooth VFR
conditions. AFAIK, the system worked because the resistance of each
element (for most materials) tends to increase with rising temperature
and decrease with falling temperature--so that the system can work by
comparing the resistances with little regard for the actual resistance
values. My best recollection is that the device could also maintain a
standard rate turn.

I only vaguely recall that there may have been an article in one of the
homebuilding magazines--possibly in the early 1980s.

Peter



I remember this project well, it was the brainchild of a research engineer
at one of the NASA labs - NASA Ames, if I remember.
I was so intrigued, I called him up to talk about it.
A few people scratch built the device, the "gyros" were four thermistors
on a circle, with a little tube blowing air into the center of the circle.
Rotation in either axis shielded one from the air jet, and ventilated the
other, of each pair. Thermistors generate a little heat,
and their resistance varies dramatically with temperature. Each pair fed
an operational amplifier as differential inputs.
A weakness of the design was the little motor and fan involved.
These days, a two axis (piezo) gyro is more stable, more sensitive and
more reliable, not to mention using much less power. And you can buy it
off the shelf!

Regards

Brian W

Some very good points there, especially regarding the advances in some of
the components that are now available, which also remind me of a problem
that could be either general or local in nature.

Most of the sources that I used to know about have dissappeared from the
local business landscape--so I not not sure were one would buy solid state
gyros, abolute pressure sensors, mass flow sensors, thermistors, or any of
the resistors and SSI and LSI components that used to be so common.

Peter

Peter Dohm wrote:
...regarding the advances in some of
the components that are now available, which also remind me of a problem
that could be either general or local in nature.

Most of the sources that I used to know about have dissappeared from the
local business landscape--so I not not sure were one would buy solid state
gyros, abolute pressure sensors, mass flow sensors, thermistors, or any of
the resistors and SSI and LSI components that used to be so common.

Peter




Sad but true. The source these days is the Internet via Google, and
originating usually in China or Taiwan.

Brian W

"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately, you
have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the tail
rotor pitch. The device takes over when a rotate ("pirouette') command
stops, and stops the tail dead on that heading - fast, and holds it
against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add another
$40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super cheap
altitude hold/augment?)

Brian W

The heading hold gyros are rate gyros and use a microcontroller integrate
the error. They hold heading real well but drift over time. Most of the
time we can trim out the drift well enough to not be a problem but remember
most model helicopter flights last no more than 15 minutes and if a constant
heading was held for an entire 5 minutes it would be a long and boring time
for the pilot.

But gyros in model helicopters do make a world of difference. When I
started trying to learn to fly model helicopters (1981) gyros weren't very
common. I tried for years and was never able to hover out a tank of fuel
before a crash. After purchasing a simple mechanical rate gyro, I flew some
70 full tanks of fuel before crashing, and that crash was a result of
getting too far away and losing orientation (the heli turned black in the
bright sky!).

On my larger model helicopters I have gyro's that once sold for nearly $400
and a servo that sells for $130, I bought most of my stuff used and
sometimes crashed. By that time I had so much experience rebuilding crashes
that I would buy heli's needing work for a fraction of the new cost. I have
my own home machine shop and make most of the shafts simply by cutting drill
rod to length and cross drilling the holes for the bolts, a $20 main shaft
costs me about $2 + 10 minutes.

RogerN

RogerN wrote:
/snip/
Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super cheap
altitude hold/augment?)

Brian W

The heading hold gyros are rate gyros and use a microcontroller to integrate
the error. They hold heading real well but drift over time. Most of the
time we can trim out the drift well enough to not be a problem but remember
most model helicopter flights last no more than 15 minutes and if a constant
heading was held for an entire 5 minutes it would be a long and boring time
for the pilot. /snip/
RogerN


Good thought. Gyros drift.
When I consider my personal heading hold, cross country, I drift way
more than any gyro I could buy, I reckon :-)

Moreover (as I find to my cost) a mini rate gyro won't drive a torquey
servo, unless I beef up the output signal.
It's pretty to watch a little scrap of gyro stretching and shrinking a
1.5 millisecond pulse repeated at 50Hz when I rotate the gyro.
I needed to slap together a pretend receive signal which pulses at 1.5
ms per 20 ms with a pot to vary the pulse from 1 ms to 2 ms to provide a
command signal. That's one 556 chip and a few Rs and Cs. Next step is
a heading hold - which I should have bought initially, and some mini
servos that can use this mini rate servo.

Brian W

"RogerN" wrote in message
m...

"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately, you
have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the
tail rotor pitch. The device takes over when a rotate ("pirouette')
command stops, and stops the tail dead on that heading - fast, and holds
it against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add
another $40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super cheap
altitude hold/augment?)

Brian W

The heading hold gyros are rate gyros and use a microcontroller integrate
the error. They hold heading real well but drift over time. Most of the
time we can trim out the drift well enough to not be a problem but
remember most model helicopter flights last no more than 15 minutes and if
a constant heading was held for an entire 5 minutes it would be a long and
boring time for the pilot.

But gyros in model helicopters do make a world of difference. When I
started trying to learn to fly model helicopters (1981) gyros weren't very
common. I tried for years and was never able to hover out a tank of fuel
before a crash. After purchasing a simple mechanical rate gyro, I flew
some 70 full tanks of fuel before crashing, and that crash was a result of
getting too far away and losing orientation (the heli turned black in the
bright sky!).

On my larger model helicopters I have gyro's that once sold for nearly
$400 and a servo that sells for $130, I bought most of my stuff used and
sometimes crashed. By that time I had so much experience rebuilding
crashes that I would buy heli's needing work for a fraction of the new
cost. I have my own home machine shop and make most of the shafts simply
by cutting drill rod to length and cross drilling the holes for the bolts,
a $20 main shaft costs me about $2 + 10 minutes.

RogerN


As a matter of fact, I really allowed myself to get way off track early on
in this thread--along with nearly everyone else.

Basically IIRC the rate gyro systems are traditionally called wing levelers,
while a real heading gyro is just that--and frequentle slaved to a flux
gate--so that an autopilot on heading hold will really continue to follow
the same magnetic heading. The rate gyro allows the autopilot to intersept
a new course or heading without commanding an acrobatic maneuver to
accomplish it.

Peter