Do you limit your flight time by Volts or Amps

Discussion in 'Cinestar Misc' started by Tyler Olson, May 8, 2013.

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Do you watch the volts amps or both to limit your flying time

  1. Volts Primarily

    84.2%
  2. Amps Mainly

    0 vote(s)
    0.0%
  3. Whichever shows 20% first

    15.8%
  1. Tyler Olson

    Tyler Olson Member

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    Do you watch the volts or amps more closely when you are flying. Which do you look at to say your time is up? Volts, Amps or which ever one shows 20% left first?
     
  2. Gary Haynes

    Gary Haynes Administrator
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    All of the above. I fly primarily by time based on data from recharging after flights. I do have the voltage alarm set for 14.4v but as a reminder only.
     
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I have Fraulein Graupner speaking voltage to me every 15 seconds. I keep an occasionally eye on the current, but the voltage is a good proxy for the current. Certainly if the voltage goes too low then the bird's going to go down.....
    I also set the voltage threshold to 14.4v. If I'm 400 meters away that gives me ample time to come up unless I'm fighting a headwind, and even then, it's usually close to the landing area at 14.2 so I have a little time to loiter if there's a need.

    Andy.
     
  4. MIke Magee

    MIke Magee Active Member

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    Same here Andy.
    -m
     
  5. Shaun Stanton

    Shaun Stanton Active Member

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    All of the above. I use the amps used on my OSD to get an idea of how much time I have coupled with how much voltage down-lash I have at takeoff. I usually expect to see a voltage dip of around 15.8 in a climb than settle. If I see less than that I take that into account in how much available usable amperage that I have. When I start seeing about 14.5 Volts I figure that I have about another 1000mAh available to get it into a low hover about 20 feet. Then once my voltage alarm on my controller goes off I start bringing it in for a landing. My voltage alarm in my DX8 is set .2V higher than the aircrafts systems. If I do it right I get it on the ground right as the aircraft starts blinking and chiming.
     
  6. Tyler Olson

    Tyler Olson Member

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    Is there a loaded voltage minimum? Before you answer, yes, obviously, my question is as follows - Resting voltage should be 3.75V per cell - when flying, loaded voltage drops well below that. To figure out what loaded voltage will result in a resting voltage of 3.75V is it just trial and error. Will I damage my batteries if my loaded voltage goes below X volts, even if the resting voltage is still about 3.75V?

    Landing with a 14.2V reading, that must be loaded voltage then.. and 3.55V per cell while flying... do I understand that correct?
     
  7. Shaun Stanton

    Shaun Stanton Active Member

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    To quanitfy it 3.3V per cell is the suggested minimum which for a 4S equates to 13.2V.

    Its a non linear relation ship for the first 20 seconds or so based off of experimental data. Typically you can expect the voltage to immediately drop 1 volt under load of 60A which equates to .28Ohms of load. Then shortly after the voltage will continue to drop some more non linearly until it stabilizes. This is because the internal resistance is finally at a maximum which is the result of the Exothermic properties of the battery. Based off of data that I looked at by one of our resident experts;) Hmm Andy! The battery reaches its maximum internal resistance in about 20 seconds. Once the load is off the battery immediately rises in voltage and then the rise will continue and taper off in a logarithmic fashion as the battery cools. Based off of the analysis of such data the resting voltage should return to a nominal safe state for the battery.

    3.3V is not a number to strive for. I would consider that Emergency Fuel once the battery goes below that threshold its discharge rate significantly is reduced. Its not an exact science all the time, its TLAR, that looks about right. I personally strive to be on deck before the load voltage drops below 14.0 giving me some time to maneuver if necessary, or abort a landing due to an unknown circumstance such as an unexpected gust of wind. The thing to keep in track of is how quick your Vload drops to a nominal number based off of how much current is used. If you start seeing the number taper down with the same weights, that maybe an indication that the battery is tappering off in its flyability.
     
  8. Gary Kaplan

    Gary Kaplan New Member

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    Guys,

    I really need to step in here and give some much needed correct information regarding LiPo's and basic EE 101 in order to help so many in this forum who either are misinformed or just flat out have things totally wrong. If you montitor voltage to determine your flight time you will eventually crash because of it. If you montior current (its not called "amps") to determine yourflight time you will eventually crash because of it. BOTH need to monitored because they are interrelated. They are just as interrelated as voltage, discharge rating (C-rating) and capacity are related. I'm not going to write a huge dissertation like I did in a previous thread because it just takes too much time to put down all the info and I don't really think people read it, understand it and then apply it properly.

    Simply put, you must monitor a data log (in chart form) in order to fully understand what your rig (and its batteries, and motors) are doing while it is in the air and then use that information to 1.) maximize safe flight time, and 2.) know when its time to change replace batteries.

    Please see the chart below. It was taken following a high speed flight with my 150MPH+ airplane. I download the data from my ESC after every flight. Why? Because I don't want to lose my expensive airplane due to component failure. The chart tells me EVERYTHING I need to know about the system performance during flight.

    Flight Data Log Graph Example.png

    What does this tell me? My plane (and the same principle applies to my helicopter logs) prop reached a maximum 18,036 RPM, the motor put out 2,043W of power, consumed 125.8A, and battery "sagged" down to 14.3V while doing it under load! Is that good , bad, or OK? That depends on the capabilities of the battery, motor and prop. That's it. In this case this is dangerous. The battery is fine, its a 5S 65C/130C battery. That means it can continuously source 65A without a sweat and burst to 130A for short durations (15sec or less). The prop is fine. My APC 8x8 prop can safely spin up to 25,000RPM (with tip speed faster than the speed of sound!). However, my motor is rated at only 1100W. You can see I did two high speed passes. If I had kept it up the motor would definitely have burnt out. So what did I learn? The Hacker 8-pole high kV helicopter motor on a 5S battery (as told by Hacker) cannot drive a 8x8 prop. Based on what RPM I expected to get close to (based on the formula: kV x battery voltage = RPM) 24,050RPM (1300kV x 18.5V). But it only hit 18,000RPM. Why? The motor tried to reach 24,000RPM but it couldn't because it didn't have the torque required to get there. 8-poles is not enough to turn that size prop. After maxing out at 18,000 every amp of current driven by every volt from the battery went into HEAT in the motor. Too much heat and you get burnt out motor. Efficiency went threw the floor. Current shot up while the battery tried to hold its voltage but it could not and the battery "sagged" under the load of the prop down to 14.3V.

    So, I knew I had to change props (or install a larger motor that could handle 2000W but that wouldn't get me any more speed...ie additional prop speed). I went DOWN to a 7x6 APC prop (properly balanced) and what do you know. Just as I expected to see, the RPM went UP to 22,000RPM (it will never hit the theoretical maximum of 24,050 because the motor, or any motor for that matter, is 100% efficient), the current DROPPED to 66A and the battery "sag" went away (at just 0.3V).

    A good battery will keep its voltage without (too much) sag until the capacity of the battery is gone (in otherwords almost zero current left to provide). So if you are watching just voltage how will you know when its time to land? You won't. Your heli will drop out of the sky when the motors stop turning. On a collective pitch heli that isn't necessarily deadly because you can autorotate and land. In a fixed pitch muti-rotor is if fatal. If you are just watching current you are also putting your heli at risk because you can't tell what the voltage is doing while its sourcing the current and you could not only damage your battery but you can be cutting your flight time prematurely.

    The moral of the story is.... use high C rating batteries (at least 45/90 spec., but since you are flying an expensive heli don't pinch pennies and get 65/130's. Come down with at least 1/3 of the capacity left in the battery (get a battery monitor), don't ever drag the individual cell voltage of the battery to 3.2V or below (3.5V is safer, but I fly down to 3.7V just to have a little extra margin of safety and your batteries will last much longer), don't overheat the batteries (get a cheap infrared temp guage from HobbyKing) or motor. Start at a low flight time of a few minutes and measure everything, then fly again for a little longer and come down and repeat until to find the sweet spot of maximum flight time while making sure you don't do any of the no-no's above. As your battery ages you will notice more and more voltage "sag" during the flight or you might see one or more cells come back with lower voltage than the others. This is telling you its time to use a new battery. ALWAYS use a balancing charger to charge the batteries. Never fly with one or more cells with voltage lower (or high for that matter) than the others. If you do you are a disaster waiting to happen.

    Good luck.

    Gary
     
  9. Zach Beggs

    Zach Beggs Member

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    I was listening to MK voice trigger relay voltages...

    "input voltage: 15.6 volts"
    "input voltage: 0.0 volts"
    "input voltage: 15.6 volts"

    Wait what?!?

    I checked the GPX files -- no "0.0 volts" but what a scare!
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah. Fraulein Graupner does that just to see if you're paying attention. In the software business this is known as a "feechur." Everyone else calls it a mistake.

    Andy.
     
    Fredrik Eriksson likes this.
  11. Colin Snow

    Colin Snow Active Member

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    I am new to MX20 and have a a couple of questions after reading the manual and attempting to making adjustments (oh boy and I thought SAP over engineered software...)

    1. Is the only way to get a low voltage warning to set MK "Under Voltage" on Misc tab or is there a way to set a warning on the TX itself?

    My reference is a DX8 where you can set a warning for low voltage on the TX for the main pack and when violated the transmitter shakes and beeps. Same thing with the timer. I realize that MX20 doesn't have shake, but what I want is some sort of signal to bring it home at 14.4v - not necessarily create an Error code that ends up in my GPX file.

    2. How exactly do you get repeating audible of flight pack voltage while in flight? Can some take a photo of their set up screen and post?

    Appreciate the help

    Colin
     
  12. Gary Haynes

    Gary Haynes Administrator
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    1. If you have the voice files installed you will get a voice warning if you have an earphone.
    2. Search MX-20 on the MK Wiki. You will find a complete description of setting up the MX-20 setup to get voice.
     
  13. Colin Snow

    Colin Snow Active Member

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    1. Voice files installed. Have earphone. Need answer to the question I asked, not the one I didn't.
    2. Been there. Done that. The answer i'm sure is there, but for me it's lost in translation - hence my request.
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Colin:
    Check out page 222 of the MX-20 manual and then this thread: http://forum.freeflysystems.com/ind...-20-to-give-me-voice-warnings-and-status.621/

    The mental model you need is:

    1. You need two switches: one to trigger the voice response, and the other to cause it to repeat every N seconds.
    2. So you set up these two switches and associate them with the voice response/repeat functions.

    These two steps are covered on page 222 of the manual.

    Hope this helps -- post again if you're stuck.
    Andy.
     
  15. Colin Snow

    Colin Snow Active Member

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    Thanks Andy. That thread and your Occam's Razor explination for switches helped. Can I assume the answer to #1 is only by setting the MK value in the Misc tab or should I keep digging?
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Colin:
    No. The voice response is purely an MX20 thing. Mikrokopter's firmware works with the MX20 without any changes done by MK Tool.

    Note: The integration of the MK software and the MX-20 requires that you use version 4.1 HoTT software and you put the custom MK voice file on to the MX20. The relevant Wiki page for that, with step by step instructions and the links to the Graupner Web site for the downloads and procedures is at http://www.mikrokopter.de/ucwiki/en/HottUpdate

    Work your way through page 222 to get the switches set up.
    Then go through sections 6, 7, and 8 of the Mikrokopter wiki page that Gary cited to: http://www.mikrokopter.de/ucwiki/en/MX-20

    Some of what you'll read on the Wiki page is duplicative of page 222 of the manual, but a lot is new and speaks to how to set up the MX-20.

    Getting it all set up right is a multi-step procedure so it demands patience:

    1. Update the MX20 (http://www.mikrokopter.de/ucwiki/en/HottUpdate)
    2. Update the Graupner receiver. (as above).
    3. Install the MK Voice file via the microSD card in the MX-20.
    4. Configure the switches.

    None of it is particularly hard, but it will feel like a secret society's series of initiation rites at times...(fortunately no need for ritual sacrifices of goats etc. ;) )

    Andy.
     
  17. Colin Snow

    Colin Snow Active Member

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    Thanks Andy. I’ve been typing here under the assumption that I am a member of the secret society by default.

    As far I can tell all of this was already done by QC. I say that because I saw nothing in the wiki or instructions that led me to believe otherwise. For example, when I power up the kopter I hear Fraulein Graupner say “MikroKopter”. The telemetry settings and data view is the same as on the wiki. I see www.Mirkrokopter.de at the bottom of the screen. My MX20 is at Firmware 1.126 and MK Version: FC HW:2.2 SW:0.90h + NC HW:2.0 SW:0.30h.

    That said, I get MK telemetry in the TX and have set the parameters that I want for audible – altitude, sensor 2 temp, and input voltage. I now can get Ms Graupner to repeat voltage (thank you). I hear “input voltage NN.N Volts” every N secs.

    Sorry if I am being unclear, but my question remains:“ Is the only way to get a low voltage warning to set MK "Under Voltage" on Misc tab or is there a way to set a warning on the TX itself?”

    Right now my MK “Under Voltage” value is set for 13.8. I intentionally ran a bad battery pack and got an audible warning when the input voltage went below that value. The error shows up in the GPX file.

    What I want is some sort of warning to bring it home at 14.4v but not create an “Under Voltage” Error code that ends up in my GPX file.

    Is that possible or am I stuck with either setting the value at 14.4 (and get the error) or constant monitoring because it is set at 13.8 (which IMHO is too low for bring home)?


     
  18. Gary Haynes

    Gary Haynes Administrator
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    Colin the only way to have the TX get direct data is to add one of the Graupner data modules. You would get data but I'm not sure what type of warning it would give. I haven't tried their modules but I don't believe that there is any voice type announcement.

    If you want a warning prior to the low voltage unfortunately the MK only has the one low voltage warning. That's why I use the countdown timer on the Graupner. From experience I know that with the FF 9000 packs I reliably get a safe 7 minutes. With the countdown set to that number it starts giving an increasing number of tones starting 30 seconds before that. I still have the MK setup for 14.4 volts but don't like the distraction of the repeated voice messages.

    Other added benefit of using the timers is that the Graupner also has a logging function which might be helpful on a fly away since it records the GPS position data that is coming from the MK.
     
  19. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Colin: Gary's got a more ingenious system than what I use -- I simply have the MK Tool threshold set for 14.4 volts. The audio voltage I have set for 15 seconds repeat and is always on when I fly. I use a Smart On Screen Display and FPV that allows me to monitor the descending voltage as I fly so I can plan my flights.

    The only thing I don't like about using the MX-20's timers is that they start based on an increasing throttle setting but you have to remember to press the ESC button (left-hand side), to stop the timers. I'm sure there's a reason for that, but.....

    I'm not bothered by the voltage being announced every 15 seconds as it means I can visually focus on other aspects of the flight.

    I'm just curious, why don't you want the Low Bat status showing up in the GPX files?

    Andy.
     
  20. Colin Snow

    Colin Snow Active Member

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    Gary & Andy. Thanks for your replies.

    Gary - I used a timer (without voltage warning) before and stopped doing that when my kopter went into 'min gas' mode and commenced a very abrupt landing on a hard surface (read 'replacement parts required'). What I found was the pack had started to go bad depleting at a rapid rate, but my 8 min countdown timer was not at sync with that rate. So, I vowed never to do that again and use voltage as the primary indicator.

    Andy - I also use a Smart-OSD On Screen Display and FPV that allows me to monitor the descending voltage as I fly so I can plan flights. I am guilty of stretching it at times to get that last good shot (why do they always come at the end?). But, again, in the case of deteriorating battery pack, an audible / warning / alarm seems like the best early detection device.

    I don't want the Low Bat status showing up in the GPX files because I fear that in the case of crash lawsuit claim this data would be used against me to implicate negligence on my part - even though I would be using it as a safety measure. Perhaps I am being overly paranoid.

    Since this seems to be the only way to get a warning I've decided to set it at 14.4v and work with it. When the lawyer asks me about this practice I'll just say: "Well, Andy does it"...

    Cheers

    Colin
     

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