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#1
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Heading Hold Gyro.
RogerN wrote:
Moreover (as I find to my cost) a mini rate gyro won't drive a torquey servo, unless I beef up the output signal. Brian W /snip/ 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 /snip/ RogerN I tried driving a Futaba S3010 with a GWS PG-03 rate sensor. From a 6 volt cad stack. The servo drives well with my dummy receiver signal - but just sits there with the PG-03 in line. But a scope demonstrates the GW-03 is reshaping the pulse with angular rate.... So I ordered a Futaba 251 HH... Brian W |
#2
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Heading Hold Gyro.
"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 |
#3
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Heading Hold Gyro.
"Peter Dohm" wrote in message ... "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 The problem with sensing magnetic heading in model helicopters is that they want them to hold the heading relative to the model. For example if you were heading north and did a loop you would be heading south at the top of the loop, that would be interesting if it tried to auto correct magnetic heading during a loop or other aerobatics. But for stabilizing an aircraft that wasn't performing aerobatics perhaps a rate gyro, magnetic heading, and perhaps an accelerometer might be able to do the job. RogerN |
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