Pot-Roast of Beginner's Questions

Discussion in 'CineStar FAQ - Tips and Tricks' started by Zach Beggs, Jun 2, 2013.

  1. Zach Beggs

    Zach Beggs Member

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    Will deactivating AH save it? :D I hope so!
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yes! That's why I feel it's so important for me to be able to fly without AH, position hold, FPV, OSD, etc. because one day I just *know* some or all of it's going to fail on my copter....

    I think the hard part (at least for me) is to realize quickly that the automation has failed in time enough to disable it and fly the bird manually.

    Andy.
     
  3. Steve Maller

    Steve Maller UAV Grief Counselor

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    Who needs AH to fail that way? Those three modes pretty much describe my earliest dozen or so flights. Did it all by myself. Fortunately, the airframe, payloads and crew all survived those teachable moments. :eek:
     
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  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I agree, Steve. Those three failure modes come built-in as the intrinsic features set of the Mark I UAV pilot, don't they?

    Andy.
     
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  5. Josh Lambeth

    Josh Lambeth Well-Known Member

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    Funny thing was I was having Failure Mode 3... but now with the new ACC my AH WORKS! :D This is the first time since OCT since I built the HL that my copter has AH. Now Im so used to flying without AH im not even sure how often I'll use it. The main reason was I wasn't sure if my Come Home on radio loss would work if the AH wasn't working. I was worried it would fly back to be but be climbing like a crazy person. The thing literally would climb close to 20-25ft a second at full power! Maybe even faster!

    Josh

    P.S. Zach if your in AH and flying to fast and the copter starts to descend turn of AH immediately and center your sticks. That should save it from AH failure Mode 2. ;)
     
  6. Zach Beggs

    Zach Beggs Member

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    Josh -- I saw that here. Someone was at too steep of an incline while on AH.

    I read on the wiki that the FC2.2 overpowers the frequency of the 2.1 underneath it, however, in the event it 2.2 fails, AH2.1 should still be continuously active. The question is: when AH fails, does it shutdown or go sporadic?
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The new ACC doesn't overpower the frequency Zach -- the new sensor operate at a lower electrical impedance, so it has the effect of making the original, high impedance device, "disappear." The electrons find the path of least "resistance" (impedance is variety of resistance) -- so only the new, low impedance devices "wins."

    I'm not sure what will happen in the new sensor fails....it might stay at low impedance or it might not. Can you cite to the source where it says that the old ACC takes over please? I'm not saying you're wrong, I'm just saying I don't know! :)

    Andy.
     
  8. Zach Beggs

    Zach Beggs Member

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    Hey Andy! I was just speculating after understanding the high impedance of the new AH
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I think we'll have to wait and see what the failure modes are for the new ACC.

    Andy.
     
  10. Zach Beggs

    Zach Beggs Member

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    Mounting Plate: I'm not sure if I screwed the mounting plate incorrectly, but has anyone noticed after screwing in the four bolts around the center hole on the gimbal, you can spin the plate with a slight amount of force?
     
  11. Zach Beggs

    Zach Beggs Member

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    I figured it out :) Thanks guys!

    Solution: there are 8 mounting points for screws from the mounting plate to the pan wheel.
     
  12. Shaun Stanton

    Shaun Stanton Active Member

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    I have the 2.2 but have not had the time to install it. I have a different autopilot on another aircraft that uses it. The only issue with that one is vibration. Edit: Excess vibration can causes the ACC to get erroneous results. These are typically mitigated by the rubber standoffs and should not be an issue. The new accelerometer on the 2.2 is immune from vibration effects so above is not even an issue :p

    In theory the ACC adds another tier of redundancy, because it will force the FC to ignore Barometric gradient shifts in the atmosphere. It has a algorithm that compares the Baro against the ACC. FC says "I see a change in the Baro," then looks at the ACC and says I do not feel any motion in the direction of the Barometric change, so the ACC will vote out the Baro in theory.

    The key is to understand the mechanics of what the accelerometer does. It measures the change in velocity over time or the squared change in position over time squared. By knowing the acceleration over a specific time interval it uses a simple equation based off of two integrals of a t dt and comes up with a solution for the change in position xf = xo +vo t +1/2at2




    What that equations takes into account is the initial position at time t plus the initial velocity which is 0 at constant hover and adds 1/2 the acceleration rate multiplied by time squared. It knows how much shift in position it has done and can compensate accordingly.

    Big thing to understand which it looks like you do, is that the system does not prevent you from over-pitching the aircraft it only modulates motor speeds to the maximum allowable speed to allow for the platform to maneuver and keep a level platform.

    One other thing to keep aware of is that if you use the autopilot to descend in vertical column too fast, or more accurately you do not have enough airspeed, not ground speed it will stall out the rotors. The rotors will stall in their own prop wash as it disrupts the laminar flow and dynamic lift components of the blades. If this happens the autopilot may not provide a quick enough response to counter it and it will start accelerating in a descent. The only way to get out of it is to fly out of it by preferably flying into the wind. This will restore the airflow back to the props and they will start producing efficient lift again. The best procedure when this happens is to immediately disengage AH and advance throttle while flying out of it. You are more vulnerable for this to happen when doing a descent in PH hover with the AH on.

    Those are my few tid-bits. I am glad to see you ask these questions;) .

    Shaun
     
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  13. Zach Beggs

    Zach Beggs Member

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    Shaun you should write a book...

    1.) Power & Pitch: I see another question brewing in the pot roast! You mention the copter will prevent from over-pitching. Are you referring to the copter's degree of pitch preventing it from flipping or the degree of pitch by the total amount of power available meanwhile maintaining altitude (if you have AH on). In effect, you have an excess of 1,000 watts which equals an X degree pitch to maintain X altitude.

    There was a post here a while ago, someone enabled AH while at a far distance and the degree of their pitch start to cause the heli to fall. AH compensates, tries to maintain, only accelerating the fall due to the copter's pitch.

    2.) Airspeed: I just finished 2 flights with a heavy load (5D&24mm). My horizontal airspeed would have been 0 during my landings. I would bring the copter relatively close, descend and land. I didn't notice a rotor stall.

    3.) Wattage: With my current load my hovering wattage is 850-900 watts. There are points during a climb wattages spike to 1200-1800. I try never to peak 2,000 watts. Normally it'll cause you to drop under voltage anyways...

    Safe Flying Wattage Question: What is a safe, high wattage I can judge the degree of demand I am asking of the copter?

    Thanks for your time Shaun.
     
  14. Shaun Stanton

    Shaun Stanton Active Member

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    The degree of pitching to power depends on available power for what ever load you have. I believe the max pitch available is somewhere around 45 degrees cant recall the exact number. It will let you do this regardless if AH is on or not.

    As long as the descent rate is slow for landings that is fine. It is when you try to rapidly bring it out of altitude such as coming out of 300 feet vertically with high rate 5ft/s for example.

    I want to take a moment to clarify something. It is not the ground speed, that's issue it is the airspeed. You may not be aware of the difference. Airspeed is relative to the speed of the wind. So if there is no wind, airspeed equals ground speed. However if there is 10 miles of wind then you could be in a good hover and still have 10 mph airspeed. In other words it is relative to wind velocity. So if you are in a hover and are pitching into the wind like 10 miles, you can descend a little more aggressively in one spot, as far as the aircraft is concerned it is moving through air. Consequently, you could have 10 miles of ground speed but no airspeed, because you are letting the wind carry it in this situation descents in this situation are the same as descending in a no wind situation, straight down. So the trick is to descend while pitching into the wind and not away from it.


    [/quote]

    Yeah if you are forcing the voltage to drop below 14.5 in any situation means you are really pushing the limits of the battery. Its not the wattage so much as the discharge rate of the battery. Power being the actual term watts is its standard unit of measurement using a formula VI. V is potential or Voltage, I is current, measured in amperage. V time I is power. So if you have a 15V battery and you need to hover at 900 watts, the current required is 60 Amps. What happens is that the current required to hover is slightly lower at takeoff because V is higher, probably around 16V with a new battery. As your battery starts to degrade the Voltage drops and therefore the current goes up. Batteries are not ideal so as you pull more current you see more voltage sag.

    The trick is to understand how much your battery can discharge at a burst. Most batteries that we use are 25C. What this means is you battery can discharge 25 times the Amp Hours. In your case an 8000mAh battery is 8Ah Battery, so 25 times 8 is 200. You can continuously discharge at 200A. Keep in mind that number assumes the battery is in the same state that it was statistically in after manufacturing. It is a hard number, but one to stay away from. Which in most cases you should have no problem. The highest discharge current I have seen is around 160 well under the 200A. That is why some people suggest dual batteries. I have never done this. I fly heavy cameras like Sony FS 100's where the extra weight starts to put a toll on my BL's. Is it a bad idea? No it probably is a good idea as long as you are not over grossing the aircraft's mass. Two batteries means if you do a hard climb at 150A lets say, you will theoretically share that current between the batteries. It is a conundrum, two batteries equals less stress on the individual battery, however, it adds mass. You have to experiment and find a happy medium of what works best. If your shots are going to be stable hovers, two batteries may not be what you want. If you are going to be moving it around and keeping air flowing over the ESC's to keep them cool then maybe two batteries might work.

    Just remember, you need to sync charge the batteries and make sure they both are at the same potential.

    Hopefully that helps, I know it is long winded, but I wanted to give the best detail possible.

    Shaun
     
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  15. Zach Beggs

    Zach Beggs Member

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    It makes complete sense. While I was training I would refer to it as "cutting through the air". If you think of the blades of literally cutting into the air, then airspeed makes sense in terms of descent.

    If the air becomes stagnant, things become more difficult. Was that the "vortex" you were talking about a couple days ago?

    Thanks for your time Shaun. I hope to talk to you more soon!

    If you have any reading or links you've found as a good resource, send them my way!
     
  16. Steve Maller

    Steve Maller UAV Grief Counselor

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    Shaun, you rock.
     
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  17. Shaun Stanton

    Shaun Stanton Active Member

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    Exactly! How to imagine it, is a helical ribbon of air that your propellers produce.. If you look at the blades of your copter, you will notice that they have a sharper angle at the hub than they do at the tip. This is because the rotational velocity is the same however the transnational velocity is slower at the hub than it it is at the tips. So the sharper angle keeps the lift component the same at the hub as it does at the tip. So the angle is directly proportional to the Newtonian lift component of an airfoil. Not to sound too nerdy, but the Newtonian component of lift is the component of lift that is caused by air hitting the surface and bouncing off in the opposite direction of the incident angle of the blade at that point. It creates an imaginary "spring" of air that protrudes from the bottom of the blades. At some point that that air dissipates below the copter. The intensity of that air is proportional to what is required to lift the copter. When you fly into this spring of air it wraps around the blades. It starts from the hub at first and moves outward to the rest of the blade as the situation progressively gets worse. The air will start wrapping around the blades in the opposite direction of the forward motion of the prop.

    A way to recognize this is happening is when the copter starts shimmering or wobbling a bit. The blades will start sounding choppy. If recognized early you can get out of it simply by adding the throttle and decreasing the descent. The throttle required to get out of it will not be the same required to continue the descent. You will need more throttle to initially get out of it but then once the wobble stops you can regress the throttle stick a bit and return to a normal descent. Keep in mind this will wreck havoc on your shot if you are shooting long. With the 24mm pancake it will not be too noticeable. but at 50mm or higher it will.

    If it recognized too late it will need more than throttle to get out. You will need to fly out of it. A good way to test and train for this is to take the copter out a 500 feet laterally or so and climb to comfortable altitude like 100 to 150 feet. And descend at different rates while letting the wind carry it. Preferably fly upwind when doing this so the copter is naturally coming back to you. Start lowering the throttle. Once you start seeing it wobble a little you now have flown into its wash and you can try to fly out. It might be a good idea to start with your phantom in ATTI mode and see how it does this. Then try it with the CS cautiously. Keep in mind this phenomenon is harder to get out of the heavier the copter is.

    I have had a few oh-shit moments when I thought I had it under control and have seen my bird loose 50 feet in a second. Had I not been at 150 feet when it happened it could have resulted in a crash. That is why this concept is so important to understand, and has probably been a reason some aircraft have crashed when nothing was wrong. This is where the auto-pilot wont save you at all it will only aggravate the situation. Hopefully with the new ACC this might not be as bad because it should keep the descent rate steadier. But a problem I had once was when a thermal gust pushed the air into my rotors in a descent and that is when the aggressive drop happened. I had a nice stable descent then a burst of wind hit and the thing nearly flew out of the sky. That is why I am trigger fingered to click that AH off and go full throttle if I have to in a controlled manner.

    I have an emergency procedure for this when it is really falling

    Uncommanded Loss of Altitude, AH ON

    1. Altitude Hold - OFF

    2. Throttle - Increase, as required

    The key to flight safety is always to foresee the unexpected and be ready for it at the moment's notice. The unfaithful day if I crash a perfectly flying machine will be because it will be my fault and I was not paying attention.

    Shaun
     
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  18. MIke Magee

    MIke Magee Active Member

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    Sean, I love reading your stuff. Thanks for the explanations. I can visualize the air while I read you.

    My take away and hopefully for other folks, is to arm your finger on the AH switch and throttle at all times. Sub-seconds count when it starts to go bad, and most folks' brains (mine anyway) are in situational denial for a second or two when bad stuff happens.
     
  19. Gary Haynes

    Gary Haynes Administrator
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    Shaun you might want to add a #3 to your recovery list.

    3. Pitch - Left/Right/Back/Forward Drive the copter out of the the downwash.
     
  20. Shaun Stanton

    Shaun Stanton Active Member

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    They sure are. There is a whole study on it in the Air Force. Behavioral scientists and flight physiologists have found through a study that in aviation it can take up to 5 seconds to from recognizing a situation and applying corrective action. They figured out that it takes 2 to 3 seconds to realize to analyze the situation, then another 2 to apply the proper corrective action.

    Obviously 5 seconds is way too long in this thing. I try to keep my on finger near the throttle and the other by the 2 position switch that turns off AH. It has to be accomplished immediately as soon as you see something is not right. I look at flying low altitude, i.e below 100 feet with AH on as one the most critical phase of flight. This is why I like having an OSD for long distant flights I can see if the Baros behavior is being erratic in hopes to catch it first before seeing a rapid descent.

    I have my front nose camera on a front gimbal so I can keep the tilt angle of the camera at the desired angle so I can hopefully also start seeing if the ground is starting to get closer as well. I always hope that I can pull it off, but sometimes we are slaves to our own physiology.
     

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