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Thread: A flaw in RTH...

  1. #11
    RTFM aeryck's Avatar
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    I think a combination of both Hucker's and IBCrazy's ideas would give a much better amount of reliability - A backup capacitor to keep the OSD online through a power brownout, and using NVRam/timestamps to only set a new home position if the OSD has been powered off for X amount of time.

    Or even another step - If the plane is in flight, chances are it'll be moving, even if it's falling. On OSD powerup, after GPS gets a lock, wait a few seconds (I know, this may not be the best time to wait), but if the plane is in motion, DO NOT set a new home position. This would also require the home position to be saved in NVRam so it had a value to fall back on in the event the OSD reset mid-flight.
    Far better is it to dare mighty things, even though checkered by failure; than to take rank with those who neither enjoy much or suffer much, because they live in the gray twilight that knows not victory nor defeat.

  2. #12
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    Quote Originally Posted by typicalaimster View Post
    If a catastrophic event happens (Power, Software, Act of God) that both the GPS and flight controller is rebooted. Erasing our true 'home' position.. How do we prevent our true RTH location from being skewed?

    I do not doubt that this is happened before and people have chalked it up to pilot error that resulted in a fly away.
    I thought about this when I briefly had a DOSD setup on a Sky Surfer. This exact scenario crossed my mind and troubled me. I am a software engineer and was trying to think how I would approach the problem. One solution would be:

    1. On bootup/reset/brownout, have the OSD board check for the last good home position recorded. (This would need to be persistent storage between power cycles)
    2. If one exists, load it and use it. If one does not exist, use the latest value from GPS

    Of course some problems come up that we need to solve. One is when you plug the battery in for the first time in a new location, there needs to be some way to bypass using the last stored position and obtain a new position on the spot as the new stored value.

  3. #13
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    Quote Originally Posted by aeryck View Post
    I think a combination of both Hucker's and IBCrazy's ideas would give a much better amount of reliability - A backup capacitor to keep the OSD online through a power brownout, and using NVRam/timestamps to only set a new home position if the OSD has been powered off for X amount of time.

    Or even another step - If the plane is in flight, chances are it'll be moving, even if it's falling. On OSD powerup, after GPS gets a lock, wait a few seconds (I know, this may not be the best time to wait), but if the plane is in motion, DO NOT set a new home position. This would also require the home position to be saved in NVRam so it had a value to fall back on in the event the OSD reset mid-flight.
    Good ideas.

  4. #14
    Navigator BacklashRC's Avatar
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    A flaw in RTH...

    Quote Originally Posted by Hucker View Post
    ..... As I've mentioned above your bigger problem is that your plane almost certainly is not flying straight and level so the AP won't know which way is up unless it was using IR sensors.
    I think this could be solved by having the AP analyze the delta in altitude and GPS coordinates dynamically in the first few seconds after power restoration. Attitude calibration in flight might not be perfect but it would be functional.

  5. #15
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    Quote Originally Posted by aeryck View Post
    I think a combination of both Hucker's and IBCrazy's ideas would give a much better amount of reliability - A backup capacitor to keep the OSD online through a power brownout, and using NVRam/timestamps to only set a new home position if the OSD has been powered off for X amount of time.

    Or even another step - If the plane is in flight, chances are it'll be moving, even if it's falling. On OSD powerup, after GPS gets a lock, wait a few seconds (I know, this may not be the best time to wait), but if the plane is in motion, DO NOT set a new home position. This would also require the home position to be saved in NVRam so it had a value to fall back on in the event the OSD reset mid-flight.
    I guess the question is would a capacitor give us enough surge protection when a jammed servo causes the power sag. Directly on the GPS I would say yes, but on the OSD/Flight controller itself I'd say it wouldn't. I do like the idea of not storing a new home location if the GPS is in motion. The delta between home location and new location may be a good idea as well. I know multicopters usually require you to arm the board in a low throttle position. Sadly this isn't applicable to fixed wing as there's times when the throttle could be down and the sticks jammed into a location.

    Some food for thought.. You could start a RTH arming procedure with a 3 position switch. Start at the top location of the switch and jam the sticks in one direction. Then toggle the switch to middle, throw the sticks in another direction. Then go to bottom and throw them back into the first position. When the RTH is stored you get a ack by the flight controller and you center your sticks. This could be something that could only be entered into when the GPS is not moving.
    Last edited by typicalaimster; 9th January 2013 at 11:41 AM.

  6. #16
    I Like Waffles... SENTRY's Avatar
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    moved to IFR for maximum traction.

    stickied as well.
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  7. #17
    RTFM aeryck's Avatar
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    Quote Originally Posted by typicalaimster View Post
    I guess the question is would a capacitor give us enough surge protection when a jammed servo causes the power sag. Directly on the GPS I would say yes, but on the OSD/Flight controller itself I'd say it wouldn't. I do like the idea of not storing a new home location if the GPS is in motion. The delta between home location and new location may be a good idea as well. I know multicopters usually require you to arm the board in a low throttle position. Sadly this isn't applicable to fixed wing as there's times when the throttle could be down and the sticks jammed into a location.

    Some food for thought.. You could start a RTH arming procedure with a 3 position switch. Start at the top location of the switch and jam the sticks in one direction. Then toggle the switch to middle, throw the sticks in another direction. Then go to bottom and throw them back into the first position. When the RTH is stored you get a ack by the flight controller and you center your sticks. This could be something that could only be entered into when the GPS is not moving.
    Interesting idea on the RTH arming - Essentially what you're saying is using a combination of sticks/switches to "arm" the RTH, which would in turn register the home position. It needn't be too complicated, though - I think the biggest issue with that idea is people forgetting to manually set their home position before launch.

    As far as the capacitor goes, I was thinking more as a hardware change by OSD manufacturers - Add the backup cap to maintain power to the OSD's mcu, nothing more - Keep the memory alive, as it were. A fully functional OSD won't do much good anyway if the camera/vtx browns out; all we really want to do is to make sure that the OSD's memory/home position information is not lost mid-flight. But, as you suggest, a stalled servo can cause a power brownout on the same 5v supply that powers the OSD/rx, so there would need to be some sort of protections in place to keep the capacitor from trying to power the servos and rx as well.

    Of course, I think a simple diode on the capacitor would make sure the capacitor feeds the OSD and doesn't attempt to back-feed the rx. Very rough ASCII schematic, but you get the general idea.

    Code:
                 ↓ Diode
    rx +  ------>|---+---- OSD +
                     |
                    ___  <-- capacitor
                    ___
                     |
    rx -  -----------+---- OSD -
    Far better is it to dare mighty things, even though checkered by failure; than to take rank with those who neither enjoy much or suffer much, because they live in the gray twilight that knows not victory nor defeat.

  8. #18
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    The capacitor is initially what I had in mind as well. The RC Car guys use them to help prevent brownouts as well..

    http://www.horizonhobby.com/products...tector-SPM1600

    I'd just prefer they're not sticking up on the OSD. Something this large runs the risk of having it pulled off during a crash. Almost easier to place it inline like Spectrum suggests.

  9. #19
    RTFM aeryck's Avatar
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    Quote Originally Posted by typicalaimster View Post
    The capacitor is initially what I had in mind as well. The RC Car guys use them to help prevent brownouts as well..

    http://www.horizonhobby.com/products...tector-SPM1600

    I'd just prefer they're not sticking up on the OSD. Something this large runs the risk of having it pulled off during a crash. Almost easier to place it inline like Spectrum suggests.
    Good point; i use a cap on my rc cars too. Inline would make more sense to prevent damage.

    I may try adding a cap to one of my rigs, with a diode to isolate the backup to the osd, and see how long the osd remains powered after i disconnct the battery.
    Far better is it to dare mighty things, even though checkered by failure; than to take rank with those who neither enjoy much or suffer much, because they live in the gray twilight that knows not victory nor defeat.

  10. #20
    GO HAWKS Hucker's Avatar
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    Quote Originally Posted by typicalaimster View Post
    I hard set level in the software so I didn't have to 'level' my plane every bootup. Based on the sensor readings the system can correct itself and then maintain level flight.
    I'm not talking about the accelerometers I'm talking about the gyros.

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