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#1
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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 |
#2
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Heading Hold Gyro.
"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 |
#3
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Heading Hold Gyro.
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 |
#4
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Heading Hold Gyro.
"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 |
#5
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Heading Hold Gyro.
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 |
#6
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Heading Hold Gyro.
"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 |
#7
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Heading Hold Gyro.
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 |
#8
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Heading Hold Gyro.
"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 |
#9
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Heading Hold Gyro.
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 |
#10
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Heading Hold Gyro.
"brian whatcott" wrote in message ... 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 The transmitter frames are about 50Hz but some of the more expensive gyro/servo combinations are able to update the servo a few times between transmitter frames. If I'm not mistaken larger servos don't put a higher drain on the signal lines but they do pull more amps through the power wires, that are often routed through the gyro. It's been years since I looked but I think they have wiring harnesses to deliver servo power more directly through the battery and the signal wire comes through the receiver or gyro, as opposed to the power being routed through the receiver or gyro. Instead of Power switch receiver gyro servo they have Power switch servo and Power switch receiver gyro signal from gyro servo Back maybe 15 years ago I flew with one of the gyro manufacturers and at the time they were using Tokin gyros, and AVR microcontrollers. I think some of the newer gyro sensors have less drift problem than the Tokin did. The drift was at least partially caused by change in gyro output due to change in temperature. When the model heli is setting in the sun, the gyro gets hot, when they start flying around the air flow helps cool it off and it seems to be a good bit of drift during the first few minutes of a flight. They fought this problem using a thermistor and compensating. I know it would be more expensive but I thought it would be interesting to use 2 sensors mounted 180 degrees to each other. That way they should both drift in temperature together, giving nearly 0 differential output but the actual signal from motion should be doubled. RogerN |
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