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  1. #1

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    Need advice - receiver battery size

    I'm setting up an old ExtremeFllight 68" Yak54 with a YS 1.10; currently I have 4 Hitec 5625MG's, one 5945MG on the rudder, and a standard non-digital Futaba servo on the throttle (I think it's about 50 oz-in of torque).

    Need a suggestion as to the size (maH's ) of the receiver battery. I've already decided on a 6-volt but am unsure as to capacity. I don't plan a lot of heavy 3D use for this airplane; for now it's going to be a practice IMAC plane.

    I may eventually switch to 5645's and a much faster digital servo on the throttle. I haven't been too concerned with the torque of my present servos due to the plane's planned use.

    Thanks for any suggestions about the battery. I was thinking I'd use a NiMH just for simplicity vs a lipo.

  2. #2
    TIA's Avatar
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    RE: Need advice - receiver battery size

    2,000+

    With 2000 I do (6) 10 to 15 minute flights on a similar setup.

    If you want to fly longer up the size to 3,000.

    Having reserve is always a good thing and I don't think I need to go into battery degregation.

  3. #3
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    RE: Need advice - receiver battery size

    I agree with 2000 mah as well. NiMH will be easier as no regulator is needed but you will start off slightly higher then 7V and drop to 6.1V or so towards your last flight. Your servo speed and power will change slightly each flight. If you were to go Li Ion or Li po with a regulator you can set the reg to 6V and have your servos getting 6V all the time. Very difficult to get snaps to stop at the correct position when your servo speed fluxuates.

  4. #4
    Grelker's Avatar
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    RE: Need advice - receiver battery size

    I use about 200 -300 mah per flight depending on the number and type of servos. I'd say 250 for your setup. Determiine your safety factor (mine is 2) and multiply by the number of flights you want to fly between charges. For example, 5 flights x 250 x 2 = 2500 mah. I use a regulator even with nimh since they are over 6 volts for some period of time. Cheap insurance.....
    Jon N.

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    RE: Need advice - receiver battery size

    Thanks for the answers.

    I hadn't thought about the voltage regulator issue-if I didn't mind the changing speed of the servos during the flight, am I going to damage them by putting more than 6v through them initially?

    I had a quick search on RCU about voltage regulators-there's a lot of discussion about switching vs linear regulators. Can you recommend a basic regulator? If I am going to regulate it anyway, I'm happy to use a lipo battery.

    Thanks again.



  6. #6
    Grelker's Avatar
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    RE: Need advice - receiver battery size

    I worry about the receiver getting more than 6 volts. Some of the newer receivers can do fine with over 6, but I have a buddy who lost a receiver continually using 6 volt nimh's with a fresh charge. I've used MPI regulators with good success. check em out: MPI
    Jon N.

  7. #7

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    RE: Need advice - receiver battery size

    I had a quick search on RCU about voltage regulators-there's a lot of discussion about switching vs linear regulators. Can you recommend a basic regulator? If I am going to regulate it anyway, I'm happy to use a lipo battery.
    In general, it's a good idea to stay away from switching regulators if you can find an equivilent linear regulator solution. There are a few benefits with a switcher, but they are really outweighed by the risk of interefering with receivers, even spread spectrum receivers under some conditions. One advantage is that you make more efficient use of the battery capacity as compared to a linear regulator, another is that the switcher runs cooler for a given output level, and it is designed carefully, the switch may be lighter than a linear regulator with similar output levels. That's pretty much the extent of the benefits.

    The main risks with switchers are that with a higher parts count, they are statistically more likely to fail, that they generate and radiate high frequency noise from their circuitry, and that they turn all of your power wiring into antennae to radiate noise into the rest of your onboard electronics. Will a well designed switcher work? Yes, but you need to weigh the potential problems against the small benefits listed.

    If you really look at what happens with even the very best switching regulator, it will still radiate noise through the wiring supplying power INTO it. That is because of the very nature of every switcher, which is that it chops the supply current into on & off at the rate that it is switching at, which causes what would otherwise be a nice, quiet DC supply line into source of noise that is rich in harmonic frequency content, which may extend into the gHz range in some cases. Your power leads become transmitting antennae. There's no getting around that fact. Now, our receivers are pretty well designed and can tolerate a certain amount of crud, but what is the sense in reducing their safety margins if it is not necessary to do so? Keep in mind that even a 2.4 gHz spread spectrum receiver can be interfered with from lower frequency sources, if they are strong enough. They all start with a crystal controlled oscillator, typically 10mHz, which feeds a frequency synthesis circuit that generates the frequencies up into the gHz range. So if you mess with the clean operation of the synthesis circuitry with a strong enough interfering source, then you can affect the normal operation even into the gHz range. Again, the switcher can be used in many cases, but just ask yourself why compromise the situation if you don't need to?

    If you do pick the switcher, do yourself a favor and carefully range check with and without it. If you don't see much noticeable change, then your setup is probably going to work OK. I say probably, because I have seen situations where models have been lost when a sudden, large current demand is placed on the switcher circuit, such as could happen during a snap roll. Large transient load conditions *may* cause some switchers to become unstable. That's bad, so just check it all out well in advance.
    Ed Alt
    Tech-Aero Designs LLC


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