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| Electronics Discuss radios, chargers, etc... |
Topic Review (Newest First)
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| 07-04-2016 11:08 AM | |
| ishmatt |
Re: RX power redundancy pack Thanks for all this Andrew; I lost a scratch built PT19 because or Rx failure ;( |
| 06-27-2016 09:50 AM | |
| kcaldwel |
Re: RX power redundancy pack I don't have any experience with retract systems, but it sounds like having them on a separate power supply is a good idea. You can easily set the Taranis up to log the voltage and RSSI telemetry at least. That really helps with any analysis. There are some good tests of various BECs on RCGroups. As with most RC electronics, there are good ones and bad ones, and price isn't necessarily much of an indication what percentage of their specs they will actually deliver. I usually expect about 50% of the spec'd amp capability. http://www.rcgroups.com/forums/showthread.php?t=1277428 Kevin |
| 06-26-2016 04:01 PM | |
| Scerbina |
Re: RX power redundancy pack Great info Kevin. My last 2 crashes were both (at least I believe), due to a retract landing gear failure. One was on Freewind Su-35. It seems my Taranis radio played the message - "Telemetry lost", right after the take off, when I retracted LG. Destroyed the plane. The second crash, only 2 weeks ago, on my PZ FockeWulf. The e-flite retracts were in the mid-retracted position when I lost control. Also on X8R receiver. These 2 crashes inspired me to come up with some kind of solution to significantly reduce the probability of the equipment failure. First thing I did was put the retracts on a separate BEC. Now, my BECs in these planes were also pretty good. How could the retracts pull so many amps to brownout the X8R receivers in both cases? That is why now I am a bit skeptical. But it is good to know that a typical servo would pull 1A (1.6A max). P.S. The servo may get jammed with a direct short, pulling as many amps as the wires will handle. But I guess these failures are less likely to occur. Also, I agree with you, that these types of failures (servo jams) are much less likely to occur, than loosing the ESC/BEC or the main pack. |
| 06-26-2016 03:43 PM | |
| kcaldwel |
Re: RX power redundancy pack I just checked all the servos in the Servormances data base, and at a quick glance through, the highest stall current I can see is 1.6A. Most servos have a stall current of less than 1A according to their testing, which I trust more than any manufacturer's number. A 1A load is unlikely to bring down my 10A BEC that has been tested to supply over 5A reliably. Perhaps there are very large servos that will draw more, but likely the space and weight of a larger back-up system wouldn't be an issue for those type of airplanes. From the only failure analysis I have seen, failure of the main battery has the highest probability by an order of magnitude. That agrees with my personal experience. Covering off that failure mode, as well as the failure of the outboard BEC and wiring, reduces the probability of power system failure by several hundred times. Now if I could reduce the probability of a flying skill failure by a similar amount, my airplanes would all have very long lives! Kevin |
| 06-26-2016 12:23 PM | |
| Scerbina |
Re: RX power redundancy pack Well, my 1S 160mah (actual capacity is below 100, since it is an old battery) works surprisingly very well on my Yak with all digital servos. But it only offers half of the protection of this circuit. Your 650mah 1S probably as well. Though it will not drop the voltage as fast as my small 1S battery. I would have to test and see. In the case of a servo jam, if the system starts pulling large current, and your main BEC drops the voltage to the brownout level, the 1S battery may not be of much help, while the 2S through a good BEC, would have a higher voltage and would be able to supply way more amps while sharing the load with the struggling main BEC, before dropping the voltage to a brownout level. So it seems. When I have time, I would like to do some tests. |
| 06-25-2016 03:00 PM | |
| davidmc36 |
Re: RX power redundancy pack Reading with interest. Graupner Rx operates to 3.6V so will make good testing bed to see which servos will function and to what voltage. Two upcoming gliders could benefit from this. |
| 06-25-2016 10:41 AM | |
| kcaldwel |
Re: RX power redundancy pack I've never tried anything smaller than a 650mAh HK round cell, about 15g I think. A 160 is testing new ground! The 1S set-up makes a nice small and light back-up solution (and cheap!), with a good telemetry warning. I have sat and moved the controls rather frenetically on my airplanes running on 1S for more than 30 minutes, trying to get the voltage to come down for the low voltage test. I've always had to put the cell on discharge on my charger to drop the voltage. I am convinced that, with the telemetry warning, I have far more reserve than I will need to gently land an airplane from the 1S set-up. I usually plug my back-up battery in first, to make sure I get a low Rx battery warning, but not a critical warning. The FrSky voltage telemetry won't read voltages below 3.5V for some reason. I have a receiver battery alarm at 4.4V to tell me I have lost the main power supply (5.5V - 0.4V = 5.1V normal voltage), and a critical arm at 3.5V. There have been other reports as well: http://www.rcgroups.com/forums/showp...9&postcount=18 I guess the motor stopping will be a good clue on power airplanes, but not so good in a sailplane. I see from my notes I actually tested my 4 Airtronics and 2 MKV digital servos, FrSky X4R SBus system down to 2.8V (about 3.2V on the cell). The servos were slow at that point, but everything still worked even waving the sticks around and loading up the servos. It is remarkable how low the voltage can be, at least for FrSky systems. Many other brands are used with a 1S primary power supply in DLGs as well. Kevin |
| 06-25-2016 12:27 AM | |
| Scerbina |
Re: RX power redundancy pack Here, also connected a nice switch for the secondary RX pack. Installed in the plane. I suggest you to program your radio if it ever detects the voltage under 3.4V to inform you to charge the RX pack. This way you never really need to go there and check the battery. Beautiful solution! Loving it. So extremely simple to do and so effective. |
| 06-24-2016 11:33 PM | |
| Scerbina |
Re: RX power redundancy pack Kevin, The timing of your post couldn't have been better. I have just bought a new plane, and I was kind off reluctant to put in a 2S + BEC secondary power supply, since this is a 3D aerobatic plane, and I don't really want to add any more weight. And an even bigger issue was that the main BEC (onboard of the ECS) only supplies 5.32V. I needed the voltage difference for the diode to use the main bec and not discharge the small battery pack. 1S with its ~ 4V supply provides that difference. So, I do not have to add 2 BECs. All I added for redundancy is my cable (with diode) and an extra small 1S battery. See pics attached. I have just tested a very small 1S battery from my Ultra Micro plane. And indeed, it has no problem powering my X8R receiver along with all of the digital servos on my E-Flite Yak Carbon Z. The voltage is 4.8V on main power source, and 3.5V on secondary power source. I programmed my radio to warn me accordingly, if the voltage drops below 4.4V Off to flying today worry free! 
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| 06-24-2016 05:25 PM | |
| kcaldwel |
Re: RX power redundancy pack Yes, 1S will be personal preference, and should be tested for a particular system. The FrSky stuff has been pretty thoroughly tested by the DLG community for use with 1S set-ups, and many of the Rx work down to 2.7V. Here is a test of the X4R: https://www.youtube.com/watch?v=IXL9...ature=youtu.be I fly FrSky, and all my FrSky stuff works down to the 3.3V I have personally tested to. It is generally the servos that quit first, but all mine have worked down to the 3.3V also. I've tested a variety of brands, all digital: JR, Airtronics, Graupner, MKS, Hyperion. I have tested my D8, V series, X4R and X8R receivers, and they don't have any issues down to 3.3V on an actual 1S cell, not a power supply. I don't really have space for another BEC and a 2S battery in most of my sailplanes, or need the weight. Light sailplanes are expensive! Kevin |
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