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Old Aug 01, 2012, 10:47 PM
Team Wack-a-Mole
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Originally Posted by Prof100 View Post
The plane has the receiver behind the prop slot and it's embedded into the plane. Moving it would be a PITA. The Guardian standard wiring harness is the constraint unless I transplant the receiver and rewire the plane. I don't want to do so. I just want to add the Guardian with a minimal amount of tearup..
You got it covered then
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Old Aug 01, 2012, 10:55 PM
But often down to earth
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Oklahoma, USA
Joined Sep 2010
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How it works

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

Don't worry about which type of gyro and accelerometer the Guardian uses. The theory is what's important.

Here's what that little postage stamp size board use to look like. Check out how many wires are connected to it. The photo is just the mechanical parts of the system. There are other boxes that have the computer and control system that are also contained on the Guardian board. Amazing. I worked on INS systems in the 70s and the INS box alone weighed about 100 lbs and cost $250,000 each from Litton Industries.

http://en.wikipedia.org/wiki/File:LN...m_MVC-876X.JPG

Steve
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Old Aug 01, 2012, 11:12 PM
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Canton, Michigan USA
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Originally Posted by Melnic View Post
You got it covered then
Guardian mounted and radio programmed. This delta has a big arse rudder so it should be fun to actually have one on the plane.
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Old Aug 02, 2012, 09:35 AM
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Originally Posted by jj604 View Post
Charles, apologies I don't think my point was quite clear.

The Guardian is not a simple rate or heading hold device. Or at least as far as I can tell so far, that's not the simple difference between 2D and 3D mode. It clearly has a more complex algorith for calculating servo outputs based on some combination of gyro displacement and acceleration . 3D mode certainly does not function as a purely 3 dimensional rate gyro and 2D mod acts like but is not the same behaviour as a set of 3 gyros in heading hold mode.

What I was interested in was how the Guardian uses the memory of acceleration and displacement to "know" when it is upside down. After a few turns in an inverted spin this is not a trivial task for a device with no absolute up and down reference like gravity or the sky/ground thermal difference the CoPilot uses. I'm assuming the Guardian is capable of this but it might be a bit more limited and only be able to know when it is back at it's original level position - the inversion was an aerodynamic artefact because the EasyStar is so stable and just won't stay inverted for long.


I don't know was just curious that's all. It works brilliantly in practice.

John
Accelerometers are attracted to and can sense gravity. So the unit always knows which way is down, and since it knows which way is down it can tell which way is up. When you combine this info with gyros that can sense a change in rotation, you then get a more accurate indication of how much tilt you have.

If you hook up your Guardian to a PC and run the software, you'll find an AHI (Artificial Horizon Indicator) depicting the orientation of the guardian. Early adaptation of accelerometers were prone to errors when shaken, and example would be the SK-720 - A flybarless 3d controller

Details of how the software algorithm handles all this is probably proprietary and confidential information.
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Old Aug 02, 2012, 10:15 AM
Team Wack-a-Mole
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Maryland
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Floater,thx for the link but as a person highly interested in gyros, I Indeed care about the brand of chip. I"ll agree that most others won't need to know. Invensense makes it easier on the developer and thus to date, the majority of those boards that pick one of them become highly successful. The BeastX Microbeast was one of the first 3axis heli gyros to use 2 of the earlier ones and the results were very impressive. There are some other chips that are mems but not as developer friendly as the Invensense.
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Old Aug 02, 2012, 02:49 PM
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Quote:
Originally Posted by Floater73 View Post
http://en.wikipedia.org/wiki/Inertial_guidance_system

Don't worry about which type of gyro and accelerometer the Guardian uses. The theory is what's important.

Here's what that little postage stamp size board use to look like. Check out how many wires are connected to it. The photo is just the mechanical parts of the system. There are other boxes that have the computer and control system that are also contained on the Guardian board. Amazing. I worked on INS systems in the 70s and the INS box alone weighed about 100 lbs and cost $250,000 each from Litton Industries.

http://en.wikipedia.org/wiki/File:LN...m_MVC-876X.JPG



Steve
Thread drift: I was always under the impression that the INS was strictly navigation; I.E., the aircraft still used conventional gryo technology back then for the ADI/HSI. The Litton box was a stand alone, independent form of navigation, and had nothing to do with the attitude indicator.
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Old Aug 02, 2012, 04:33 PM
Rick
United States, CA, Santa Clara
Joined Mar 2011
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Originally Posted by Silverexpress View Post
Accelerometers are attracted to and can sense gravity. So the unit always knows which way is down, and since it knows which way is down it can tell which way is up
I'm pretty sure it's not that simple. Gravity as an accelerating force is indistinguishable from other accelerating forces, most notably the centripetal force pushing a body towards the center of a curve. The classic "ball" indicator used for turn coordination is a good example with the ball showing the vector sum of these forces.

The accelerometers are not like a compass that always points down. If a Guardian, or any such device, "woke up" while in a turn the only clues that it's accelerometers were not sensing a direction towards the center of the Earth would be a greater than expected G force and a sense of turning from the Gyros. Actual compasses detecting the magnetic field may be involved also but I think not as they would be more sensitive to motors than we are observing.

In any case there must be a, probably complex, algorithm involved to combine the reading from different sensors to provide a consistent "down/up" reference either in the chip or in the firmware. I'm just glad it works so well.

This lecture you showed us earlier discusses some of this complexity and was very interesting, thank you.
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Sensor Fusion on Android Devices: A Revolution in Motion Processing (46 min 27 sec) Note: Start at 8:40. He begins to talk about Sensors - Accelerometers, Gyros, Compass...etc..., and then how you can use them together to obtain better motion detection. This is a real good presentation. In regards to software, "Sensor Fusion" is one key element that seperates the good from the bad in these stabilization devices we are using.
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Old Aug 02, 2012, 05:26 PM
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Originally Posted by choochoo22 View Post
I'm pretty sure it's not that simple. Gravity as an accelerating force is indistinguishable from other accelerating forces, most notably the centripetal force pushing a body towards the center of a curve. The classic "ball" indicator used for turn coordination is a good example with the ball showing the vector sum of these forces.

The accelerometers are not like a compass that always points down. If a Guardian, or any such device, "woke up" while in a turn the only clues that it's accelerometers were not sensing a direction towards the center of the Earth would be a greater than expected G force and a sense of turning from the Gyros. Actual compasses detecting the magnetic field may be involved also but I think not as they would be more sensitive to motors than we are observing.

In any case there must be a, probably complex, algorithm involved to combine the reading from different sensors to provide a consistent "down/up" reference either in the chip or in the firmware. I'm just glad it works so well.

This lecture you showed us earlier discusses some of this complexity and was very interesting, thank you.
One Example;

http://tutorial.cytron.com.my/2012/0...accelerometer/

Another example and a good easy to understand discussion on Gyro/Accelerometer fusion.
http://arduino.cc/forum/index.php/topic,58048.0.html

There is a good possibility that the function is already a part of the 6 dof chip. if it is the chip that is being used.

http://www.invensense.com/mems/gyro/mpu6050.html

The grand daddy of "Gyro/Accel 101"
http://www.starlino.com/imu_guide.html

I agree that Eagletree has done an awesome job on this Guardian. For $80 we can spend more time enjoying and flying our models than sitting in front of a laptop crunching code.
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Old Aug 02, 2012, 06:23 PM
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Long Island, NY
Joined May 2010
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Originally Posted by jj604 View Post
Was the righting action a fluke or reliably reproducible? That is, the Guardian has no absolute way of knowing which way is up but presumably the accelerometers and gyro and the computer "remember" how they got to where they are and that is precise enough to get the plane back to accurate level flight.

John
Ofcourse it has an ABSOLUTE way of telling which way is up. Gravity. Same as your iPad or iPhone turning the picture right side up. Differential accelerometer sensing. No need to "remember" it senses continuously.
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Old Aug 02, 2012, 06:23 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Quote:
I agree that Eagletree has done an awesome job on this Guardian. For $80 we can spend more time enjoying and flying our models than sitting in front of a laptop crunching code.
Or instead of waiting / wishing the wind would die down enough to be able to fly and enjoy it instead of being afraid of what will happen during that dreaded gusty cross wind landing.
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Old Aug 02, 2012, 06:36 PM
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Guardian Problem

I just test flew my PZ T-28 with my Guardian for the first time after everything checked out fine on the ground. Took off with 3 position mode switch in off & at about 2 mistakes high I switched on 2D; immediately I got very erratic behavior instead of stabilization; so I switched off & recovered level flight; then thinking because I reversed the Mode switch channel to put 2D on top, I switched to 3D & the A/C snapped into a spin! By the time I got the stab unit off, pulled the power & began recovering I was on the ground off the end of my grass runway in some heavy cut hay, resulting in some repairable damage to the nose area. But it was such a shock after everything I've read on this site & after everything seeming to be working as required in both modes while ground checking it - all servos & control surfaces moving right direction & only moderately. I have the pot gains at 50% with the master gain wire unplugged, so 40% default times my 50% set should be about 20% actual gain which seemed right for this A/C.

Is it possible that when switching between off to 2D to off to 3D to off that I may have inadvertently caused the unit to reset level flight & trim again over what I set on the ground? Also do you need to reset level flight & trim before each flight? I read the manual that this wasn't necessary, but I did this setting the day before I actually flew it. Anyway, most distressing & confusing as to what to do now. My confidence in the unit is not nearly as great as before, at least until I can figure out what went wrong. Needless to say the other fellows I was flying with weren't very impressed either.

Jed
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Old Aug 02, 2012, 06:46 PM
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Originally Posted by jedorme View Post
I just test flew my PZ T-28 with my Guardian for the first time after everything checked out fine on the ground. Took off with 3 position mode switch in off & at about 2 mistakes high I switched on 2D; immediately I got very erratic behavior instead of stabilization; so I switched off & recovered level flight; then thinking because I reversed the Mode switch channel to put 2D on top, I switched to 3D & the A/C snapped into a spin! By the time I got the stab unit off, pulled the power & began recovering I was on the ground off the end of my grass runway in some heavy cut hay, resulting in some repairable damage to the nose area. But it was such a shock after everything I've read on this site & after everything seeming to be working as required in both modes while ground checking it - all servos & control surfaces moving right direction & only moderately. I have the pot gains at 50% with the master gain wire unplugged, so 40% default times my 50% set should be about 20% actual gain which seemed right for this A/C.

Is it possible that when switching between off to 2D to off to 3D to off that I may have inadvertently caused the unit to reset level flight & trim again over what I set on the ground? Also do you need to reset level flight & trim before each flight? I read the manual that this wasn't necessary, but I did this setting the day before I actually flew it. Anyway, most distressing & confusing as to what to do now. My confidence in the unit is not nearly as great as before, at least until I can figure out what went wrong. Needless to say the other fellows I was flying with weren't very impressed either.

Jed
It sounds like the unit may have come loose from its mounting or it is also possible that it was not getting enough juice (power).

You have a 15 second window right after the Guardian comes "On" to make changes to 2D level flight, and trims.
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Old Aug 02, 2012, 07:00 PM
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Canton, Michigan USA
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No, you don't need to reset level for each flight.

I would check and see if the control surfaces are correcting in the right direction. I have flown planes with gyros and accidentily reversed their direction. Boy was that a surprise when flying.
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Old Aug 02, 2012, 07:10 PM
Rick
United States, CA, Santa Clara
Joined Mar 2011
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Originally Posted by jedorme View Post
Is it possible that when switching between off to 2D to off to 3D to off that I may have inadvertently caused the unit to reset level flight & trim again over what I set on the ground? Also do you need to reset level flight & trim before each flight?
No and no. Resetting level only works for 15 sec after applying power, this prevents resetting while airborne. Once set properly, you do not have to reset for each flight. It could take some tweaking over a few flights to get level where you want it. It has been suggested that Eagle Tree provide a way to "bump" level by small increments to assist this. In no way, however, would such small deviations cause the behavior you encountered.

Some things to check; Is it mounted flat and facing forward? It's easy to inadvertently mount it backwards. Are you sure the pots are set to apply correction in the same direction as the servos? Which way the pots are turned reverses servo direction which could cause the behavior you saw. Did you make any large trim adjustments after setting level, even in flight? Are you sure you have level set properly (at least close) on the ground?

Try setting the plane on its wheels on a flat surface and setting level. Safest to work on this with prop removed or motor disabled. Turn 2D mode on, the surfaces should stay neutral. Don't touch the transmitter again. Now move the plane carefully on each axis individually and make sure Guardian is correcting each in the proper direction. EG: lift the tail and see if Guardian applies up elevator. Pick the plane up and wave it around to some "unusual" attitude. Now "fly" the plane by manually turning it in the direction each surface is deflected until that surface neutralizes. EG: If you are seeing left aileron, rotate the plane left until the aileron is neutral. Repeat for each axis. The plane should be back in the same level orientation it was when you started.
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Old Aug 02, 2012, 07:15 PM
Electric baptism 1975
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Vernon, BC, Canada
Joined Dec 2000
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Quote:
Originally Posted by jedorme View Post
I just test flew my PZ T-28 with my Guardian for the first time after everything checked out fine on the ground. Took off with 3 position mode switch in off & at about 2 mistakes high I switched on 2D; immediately I got very erratic behavior instead of stabilization; so I switched off & recovered level flight; then thinking because I reversed the Mode switch channel to put 2D on top, I switched to 3D & the A/C snapped into a spin! By the time I got the stab unit off, pulled the power & began recovering I was on the ground off the end of my grass runway in some heavy cut hay, resulting in some repairable damage to the nose area. But it was such a shock after everything I've read on this site & after everything seeming to be working as required in both modes while ground checking it - all servos & control surfaces moving right direction & only moderately. I have the pot gains at 50% with the master gain wire unplugged, so 40% default times my 50% set should be about 20% actual gain which seemed right for this A/C.

Is it possible that when switching between off to 2D to off to 3D to off that I may have inadvertently caused the unit to reset level flight & trim again over what I set on the ground? Also do you need to reset level flight & trim before each flight? I read the manual that this wasn't necessary, but I did this setting the day before I actually flew it. Anyway, most distressing & confusing as to what to do now. My confidence in the unit is not nearly as great as before, at least until I can figure out what went wrong. Needless to say the other fellows I was flying with weren't very impressed either.

Jed
If it were my plane I would suspect that I had reversed 1 of the parameters particularly rudder. I found it difficult to get my head round which way was correct for the rudder, not helped by tightly confined work space.
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