Discussions

Helicopter Avionics Power Supply

Posted by Rob_Lefebvre on February 2, 2013 at 8:10am

I wanted to open up a discussion about how we are powering our avionics, meaning servos and APM, on helicopters as they present a unique challenge in the APM world, and must be treated carefully.  After crashing my Octocopter last weekend because I let the avionics battery drain, this has come front-and-center for me.  I want to make sure it doesn't happen to my helicopter.

Helicopters present a particular problem because we don't have to worry only about the battery dying, but we have to worry about the servos doing something which drags down the APM supply voltage.  While looking into the situation, I found this really interesting thread:

http://www.helifreak.com/showthread.php?t=398142

Long story short here, these guys are using a new Savox servo which is very fast and powerful, and it turns out it can draw a LOT of amps.  A problem occurs when using a BEC powered by the main flight battery as the avionics power supply.  If the servos move too fast, they draw a LOT of amps, it's a spike load, and the switching regulator cannot respond fast enough, and the voltage drops momentarily.  It's not a big problem for the servos, but it is a problem for their FBL controllers.  In some cases it causes a reboot.  

Now, my servos are not that fast or powerful, but it's still a concern.  Something to be aware of and watch out for.

This is one of the reasons I have decided to use HV servos, and power them directly from a battery. It does help the situation, but I think we should all consider using some capacitance in the system to prevent the problem.  That was the solution in the case of these Savox servos.

This weekend I am going to be working on trying to improve the code to be able to monitor a second battery voltage, and also give some warnings about any problems

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Replies

          • Developer
            Philip > Rob_Lefebvre February 27, 2014 at 5:49pm
            Correct, but it leaves you with no redundancy.
            Add the Zener, and you have redundancy.
            • Rob_Lefebvre > Philip February 27, 2014 at 6:04pm

              The problem is, there won't be very many heli uses using 5V on the servo rail anyway.  Most will be using 6V or 7.2V.  Either will eliminate the possibility of redundancy also, since the IDC won't power from the servo rail at that level.

              Now, I have found another option, just working on putting a Pixhawk on my heli now.  So, primary regulator on the PM port.  And then ESC BEC powering the servo rail at 5V, it will power up the Pixhawk.  Then, HV servos on a separate breakout board.  The breakout is likely to happen anyway, just because of the logistics of structuring heli wiring.

              • Developer
                Philip > Rob_Lefebvre February 27, 2014 at 6:38pm
                That's cool, you could have a separate battery on the Bec to the 5v servo rail, as a pure backup. It wouldn't need to be big.
                • Rob_Lefebvre > Philip February 27, 2014 at 6:49pm

                  One thing that some heli guys do, if running the servos at 5V on a BEC, is to install a 4S NiMh pack (4.8V) on the Flybarless Controller.  It charges nicely at 5V, and prevents the controller from going below 4.8V if the servos draw down the BEC.

  • Jim Johnston May 1, 2013 at 9:07am

    Hey Guys,

     

    I am just in the process of setting up my HK600GT FB with APM 2.5 and want to get your OK on my power setup.  I will be using a 6S 5800mAh battery for the motor and plan on powering the APM board with a CC BEC Pro, running off of a 2S 3600mAh pack.  One output of the BEC will power the input side (APM Board) while the second output of the BEC will power the output side (servos).  JP1 will be removed.

     

    Is this correct and do you think that the CC BEC Pro can handle powering both sides of the board at once?  The cyclic servos are JR 8717 and the tail servo is a DS610 (not ideal but I did not have any DS620/650 lying around).  The 600 is FB, as mentioned above.  Or, would I be better powering the Output of the APM with both CC Pro BEC outputs and using a second BEC to power the Input of the APM board from the same 2S battery?

     

    Jim

  • Rob_Lefebvre April 22, 2013 at 2:00pm

    Just a quick update.  I looked at some log data from my 600 heli, using the UCC383 Vreg for the APM, running off the same 2S 2200 20C battery as the HV servos.  Wasn't sure if maybe the batteries could drag down the voltage coming out of the battery faster than the UCC could respond.  Nope, not that I can tell.  The voltage for the entire flight was dithering between 5.096 and 5.120, which I'm guessing is two integer values, so basically as constant as the system can measure.

  • steve March 5, 2013 at 12:09pm

    I'm working on anocto build with the help of Rod's kit and have explored various power methods. What I think I've decided on is this. Any advice is appreciated.

    • Main batteries will be 4 x 33004S. This will only power the 8 motors.
    • Lights will have there own 3S without voltage regulator. That will power the high power side of the IOBoard.
    • Video battery 3S (how many mAh would be good) will be to power gimbal with lontair and hitec servos +500mAh 5.8GHz vTx. I don't see a reason to use a voltage regulator here. The camera is pixim seawolf 12v but works at lower voltages.
    • APM2.5 + uBlox + xBee + minimOSD + IOBoard will be powered by 2 batteries using BatShare. For the APM+ I have some doubts.
    1. How many mAh should I get to give me 1 hour considering I will be using 2 of them?
    2. Is it better to use LiPo or LiFe. 2S or 3S.
    3. Should I go with a lower C rating like what is found in receiver packs? Im sure the draw will be minimal so shouldn't need a high C rating except maybe to facilitate fast charging. How about this one?
    4. http://www.hobbyking.com/hobbyking/store/__14075__ZIPPY_Flightmax_7...
    5. I will use LM1085IT - 5.0. Possibly on the input side of the batshare so I have redundancy on that also.

    Normally I would go with one main flight pack but this being a larger build, and some advice from Rob, I thought to diversify the power system a bit. So that is 4 battery sets. Any and all advice appreciated :)

    Thanks!

  • Developer
    Bill Bonney March 4, 2013 at 8:10pm
    @ray: if you use a 2s it will read fine with no load, under load the voltage would start to fluctuate more at a lower amp draw.

    You mean use the SuperBec on the Ouputs and the APM PM to power the RX and APM?
  • steve February 16, 2013 at 8:24am

    I'm thinking to go for a separate avionics battery as well on my octo. The rest like motors and video tx, LEDs will go on main battery with a reliable linear regulator 12v. I'm using 4S12000. Got some of the regulators Rob suggested so that will make my 12v regulator.

    for the 5V should I use another one of the same regulators or some other way to drop the voltage. Should I go with LiFe or LiPo?

    On the 5V I have no servos but APM2.5, xBee, ioBoard, minimosd.

    I have many 10A castle BECs I could use but they max at 9v and I would prefer 12v for the camera and video tx thought they work at 9v and hopefully lower. I could also use castle for 5v but I'm starting to get worried about BECs though I've never personally had a problem with them. I just want something as reliable as possible and that billion number gave me that warm and fuzzy feeling inside :)

  • Criterion-Industries February 12, 2013 at 12:43pm

    Havent read all the responses here, but coming from the giant scale aircraft world where we run 12-16 super high torque digital servos in one aircraft, we use smart-fly and fromeco regulators, if at all.  Most setups are now 7.4v and run directly off a 2s lipo.  Does not change the fact that if you dont check your battery before you fly you risk stuffing it.

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