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Corona SB-3019 servos FRIED

GhiaMonsterGhiaMonster Club Members Posts: 9
So I've got a 1/6 F-20 turbine and Futaba 14SG "Fasstest" radio. I decided to go S.Bus for the simplicity of wiring. I've installed Futaba S3071HV S.Bus servos for the Elevators and Ailerons. For Flaps, Rudder, Nose Wheel and all the air valves (Gear, Gear doors, Speed Brake and Brakes) I decided I could go cheap and found the Corona SB-3019 S.Bus servos for $18...a steal. Everything's all wired up already ran the turbine and taxied, no first flight yet...luckily.



So I've got the radio powered up and setting up Flaps to mix with a little down elevator and about 2 minutes into the process I smell burning electronics and the servos stop. I powered off and immediately blamed the SmartFly SportReg I'm using for redundant power to the receiver - the heat sink was HOT. Just for laughs I disconnected and connected a standard 6V NiCd pack into the receiver and (according to the telemetry back to the transmitter) only had 3.3V to the receiver! Also the LED on the receiver lit for a couple seconds then shut off. At the same time telemetry on the Tx fell to 0.0V. So now I figured I had a dead receiver...great.



Before going out and buying a new Rx I put a Watts Up between the SportReg and the receiver. Pulled the servos out and powered up. Meter read .20A and clean 6.1V coming from the regulator. Plugged servo lines back in, powered up and this time I got wildly fluctuating Amps - up to 7+! and voltage was all over the place. I moved the ailerons and only the right one worked - sort of. Real jumpy with the voltage fluctuations. Also, the Flap on that side wasn't working...I could move it by hand at will. Then, the Aileron started working normally, Amps and Voltage back to normal. Ok, I've got a possible issue with a Flap servo. So I unplugged just the right wing. and re-power up.



Now I get an immediate spike to 7.5A (the limit of the regulator is 7A) and voltage down to 3.3V, nothing working. So, I pull the left wing out of the picture. Powered up and everything is normal. I move all the servos that are left and Amps never go over 1A. Voltage between 5.8 and 6.09.



I pulled the Flap servo from the right wing expecting to see a pinched/shorted black/red wire but it was fine. Servo however smelled of burned electronics. Haven't pulled the left Flap servo yet, but it's apparently on the same road as the right one.



So after all this history comes the question. Has anyone used these servos and how are they working for you? I find it REALLY odd that BOTH would have internal shorts at about the same time. When the original problem started I wasn't even overdriving the Flaps.



I've already ordered 2 thin Futaba servos to replace these, but now I'm worried about the others (Rudder, Nose, etc.). Given what happens when these (apparently) die, the whole radio system will shut down if another Corona goes tits up. I am however looking into a power expander which will protect against a bad servo. Just wasn't planning on spending this much...probably should have anyways.



I'm just damn lucky a $7,000 aircraft wasn't tooling along at 200MPH when this happened! The failsafe wouldn't have even saved it once all power to the receiver dropped.

Comments

  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    You have a SEVEN THOUSAND DOLLAR GAS TUBINE work of art and you "I decided I could go cheap and found the Corona SB-3019 S.Bus servos for $18...a steal"



    Really??? Come on! I wouldn't put a $18 in ANYTHING with a turbine in it!!! That is one thing I would NEVER scrimp on and only go with equipment from the big boys.



    Sorry to sound harsh, but it is deserved.



    Edit: I don't even use $18 servos is my $200 - $400 helicopters!!!WTWUK2015-02-28 06:24:06
  • swervynswervyn Club Members Posts: 1,313
    There was me thinking the title was an error, ie: 1/6 should of been 1/16, then I saw the $$$$ lol   image





    Edit: photo's please image

    swervyn2015-02-28 11:54:34
  • DaithiDaithi Belfast,IrelandClub Members Posts: 8,708 ✭✭✭
    Have a look here Swervyn
  • __Evan__Evan Club Members Posts: 1,122
    I agree with WTWUK regarding cheap servos in expensive planes ... but we're still talking about a $20 servo here. Not under any sort of load, driven from a Futaba receiver (which will definitely be outputting proper S.Bus signals). And it's happened on two out of eight.



    If I ordered eight HK15178 servos (the cheapest available from HobbyKing) and two were DOA, I'd be disappointed but I'd chalk it up to experience and spend 60c more (per servo) on HXT-900s next time. On $20 servos, it seems reasonable to expect that they've at least been tested for basic functionality during production.



    I'd definitely consign the Corona servos to the scrap bin, and probably replace them with Futaba ones. You could replace them with standard servos (ones that are known to be reliable) and S.Bus decoders, but even things like landing gear doors are fairly essential on such a large model.
  • swervynswervyn Club Members Posts: 1,313
    "Have a look here Swervyn"



    Just watched some youtube vids image



    Think I will stick with my poor man toys lol image
  • GhiaMonsterGhiaMonster Club Members Posts: 9
    I'm sorry for the confusion WTWUK. I neglected to mention the Coronas were for non-critical systems. I've got Futaba High Voltage, High Torque S.Bus servos on all CRITICAL flight surfaces. Flaps and all 5 air valve servos had the Coronas. I say had because I've converted the flaps to Futaba and am waiting for Futaba mini S.Bus servos for the air chores.



    My fear is that in this situation where the Coronas not only burned out (and they DID fry on the inside) but when they did it was like a dead short and took the entire system down with it. I don't think even the Failsafe wouldn't have worked as the Rx even went dark. The freaky thing is that BOTH of the flap servos did it at exactly the same time!



    Thank you for your concern/advice to a potential dim-witted cheapskate image but rest assured, I'm a well seasoned pilot and as this is my first turbine and the plane looks so awesome that I'm leaving NOTHING to chance. That's why it hasn't flown yet.



    Before cockpit/pilot installation:



    image
  • SootySooty Christchurch NZClub Members Posts: 6,110 ✭✭✭
    That is one cool looking model. It is small for a turbine though and will disappear into limits of visual sight very quickly.



    Why not use servos for those "air tasks" with a separate RX and avoid any bad interaction with control surfaces. Jet fliers at my club run redundant systems and even split ailerons and elevators between separate RXs.
  • SawdustSawdust Club Members Posts: 6,763 ✭✭✭
    That thing looks like it's doing Mach 3 just sitting there.

    A lot of the guys at my club also use multiple receivers on their big aerobatic gassers too. I've stood beside one of them when just after takeoff one failed, he managed to land it safely thanks to still having some control with the servos controlled by the other receiver. The problem turned out to be that mid summer here, clear canopy, sun beaming through onto the receivers with it all sitting in the sun they were too hot to touch and one had shut down because of it. A good lesson learnt and many thousands saved by that extra receiver.
  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    Yeah that is a really nice looking jet. Always liked the F-5/F-20 since I was closeup to an RCAF Canadair CF-5 when I was about 7 years old! Actually, I was underneath it (and many many other aircraft) back in the glory days when aircraft did not need to be cordoned off when on static display at air shows!



    It would be a true shame if that model was not fully failsafe and the worst happened. Like that absolutely stunning Hawker Hunter of Al Machinchi that piled in back in 2009 (mind you - that was his fault for not charging the batteries up!!!)
  • GhiaMonsterGhiaMonster Club Members Posts: 9
    Oh, it's got dual batteries and a power regulator that will switch between them. Failsafe fully enabled. If this thing goes in, it'll be 90% sure that it would be pilot error. image



    I worked at Northrop during the 70's and 80's. The F-5 and F-20 were always my favorite. F-18's, too - Really just a Douglas rip off of the F-17 we designed. Now Northrop(-Grumman) builds everything rear of the cockpit.
  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    You could have got a discount on a real F-20 then!!! lol!!!



    image




    And that is even prettier!!! Lovely looking aircraft. And the NASA T-38 was a real stunning looker!!!



    image
  • SootySooty Christchurch NZClub Members Posts: 6,110 ✭✭✭
    From the experience you have already posted dual batteries won't save you from a fried RX when the retract servos short out again after takeoff or gear down heading into landing approach.Sooty2015-03-05 06:17:28
  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    Agreed. Dual RX's is a must I would say. One for the not 'critical' dangly bits, and another one for the flight controls on totally separate power busses. Almost getting into the realms of duplex redundancy of the real thing ... I know I would be with a £7000 model.
  • SootySooty Christchurch NZClub Members Posts: 6,110 ✭✭✭
    Is that a photo of one of the NASA commuter jobs on issue to the Astronaughts to get themselves between home flying field and the Cape?
  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    Probably one of them. I know they have had 30 odd T-38's and use them for chase planes, Astronaught flight taining - particularly when the Shuttle was active as its flight characteristics were similar - and as taxis! Nice way to get to work I must admit!



    imageWTWUK2015-03-05 10:04:58
  • airwaveairwave Club Members Posts: 3,563
    i could be way off base here, but could you not have a board with the small pico fuse that would clear the fault? you would lose the one that shorts but would not take the system out.you could have 2x3 power systems and if a short goes to the main it will take down?be it a $20 or $100 servo it can happen.



    PS great looking plane image airwave2015-03-05 11:50:04
  • GhiaMonsterGhiaMonster Club Members Posts: 9
    Receiver was never the problem, never "fried". The bad servos were sucking the life out of the whole system -



    I was testing program mixes for the flaps/elevator when it first happened. I smelled that lovely burning electronics smell and the servos all stopped working so I shut it all down. I immediately suspected the power regulator, but when I pulled the S.Bus line (all the servos) - and put a Watts Up between the regulator and receiver - the regulator and receiver powered up normally. I plugged in all servos but the wings (ailerons and flaps) and when I fired back up, everything was fine. Amp draw at rest was .2, voltage just about 6.1. I hooked up the right wing and when I put power to it the aileron was acting goofy and the Amps and Voltage were all over the place...until the flap servo finally (apparently) burned out. Then the whole system recovered and worked fine on its own.



    Next test, I left the right wing plugged in and added the left one back in. This time Amps went immediately to 7+ and all servos went dead. I unplugged just the left flap servo and everything powered up nicely.



    So the bad servos literally sucked all the power out of the system, just like a dead short. Drew 7.5A and drove the voltage down to 3.3 for the whole system. Receiver never burned out...I suspect because it's high voltage and designed to handle it.



    I'm not sure even the dual receivers would have saved the day in this case. I've been flying since the late '70s and NEVER saw such a thing. Once the remaining Futabas get here I'm hoping not to see it again!

  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    Each receiver would be on a separate power supply - so the system for flaps, wheels etc. Could not affect the flight controls as it would be electrically independent of the other.

    As you have it, something like a stalled retract servo or gear door servo would suck power if extreme and could cause receiver shutdown.
  • SootySooty Christchurch NZClub Members Posts: 6,110 ✭✭✭
    Have you tested your receiver below 3.3v to see where it stops working? It might not have burned out but did it keep working? It might be a high voltage RX but how low can it go?



    I would not consider flying any turbine model without a 2-3 receiver setup - each with independent power. Split control surfaces between two receivers and manage the U/C and flaps via the 3rd.

    Cut out BECs/regulators completely thus eliminating common fail points and run systems direct from LiFe batteries.
  • SawdustSawdust Club Members Posts: 6,763 ✭✭✭
    Sooty:

    " I would not consider flying any turbine model without a 2-3 receiver setup - each with independent power. Split control surfaces between two receivers and manage the U/C and flaps via the 3rd. "

    Agreed image . The big aerobatic gassers I was talking about using 2 receivers do have strong fast servos but no retractable landing gear or other major complexities. With yours I'm pretty sure I'd be going with 3 receivers. 1 purely for the landing gear plus maybe non critical things like lights or whatever, then one controlling left elevator and aileron and the other controlling the right, take your pick about rudder. Right and left flaps would need to go to the same receiver and all failsafes set to centre. The guys I mentioned use separate LiPos and regulators to control voltages. I'm not keen on that and would prefer to take as many weak links out as possible and use LiFe batteries so there's less connections and less components to fail. I mentioned this to them but they take their competition very seriously and reckon they can notice a difference in servo speed that effects their precision as the voltage drops throughout the flight. Me? I would never notice it at all. Then I don't go in for that sort of stuff, do this followed by that and half way through that do a 45degree twist and rub your belly and pat yourself on the head at the same time. Now practice exactly that same routine a thousand more times, OH NO! that was a 45.3 degree climb and it should have been exactly 45 degrees. Stuff that crap! Flying is about freedom with me and I rarely ever plan what I'm going to do more than a tenth of a second before I do it       image .
  • DaithiDaithi Belfast,IrelandClub Members Posts: 8,708 ✭✭✭
    You mean you time the scream for that last 1/10 second before the latest one does a 3 point landing (spinner and two prop tips) image
  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    My last 1/10th second scream was drawn out to about 5.51sec as the helicopter went into the tree, followed by about 2 minutes of swearing. At myself! lol!!!
  • SawdustSawdust Club Members Posts: 6,763 ✭✭✭
    " followed by about 2 minutes of swearing."

    Ahh yes, the absolutely essential and compulsory swearing at the model, at the wind, the light conditions, the radio and especially yourself. Most things about flying these things require quick precise responses or finesse, the swearing after things go pear shaped is usually the complete opposite and go on for extended periods, often followed by moments of quiet contemplation randomly interrupted by aftershocks of more swearing over the next hour or so image .
  • dart16dart16 Club Members Posts: 77
    So the bad servos literally sucked all the power out of the system, just like a dead short. Drew 7.5A and drove the voltage down to 3.3 for the whole system. Receiver never burned out...I suspect because it's high voltage and designed to handle it.



    the servo dragging 7 odd amps shouldn't put the Rx at risk of 'burning out' as the servo current doesn't go through the receiver.



    Perhaps your 'brown/black out' of the Rx was exacerbated by the fact that you were using an electronic regulator? The reg was passing all the current it could into a near short circuit resulting in the volts dropping to below the Rx operating threshold resulting in a brown out, had you used a LiFe Rx battery it would have delivered upwards of 20 amps into the short circuit servo melting it and it's wires in pretty short order and at the same time probably keeping the terminal volts above the Rx brown out threshold. Just a thought..   image
  • DaithiDaithi Belfast,IrelandClub Members Posts: 8,708 ✭✭✭
    You do know this thread is a year old - don't you?



    It's a safe bet that everything has been fixed by this stage image
  • SawdustSawdust Club Members Posts: 6,763 ✭✭✭
    "the servo dragging 7 odd amps shouldn't put the Rx at risk of 'burning out' as the servo current doesn't go through the receiver."



    And that is also completely wrong. You plug your servos into your receiver, obviously the power does pass through the receiver. 7 amps going through it probably shouldn't be a problem but the fact is it DOES pass through the receiver.Sawdust2016-04-07 06:59:11
  • WTWUKWTWUK CornwallClub Members Posts: 13,190 ✭✭✭
    Steady ... I have two models where the servos only take their signal from the RX. Actual power is taken from an independent bus, so no power for them comed via the RX ... heh heh!
  • SawdustSawdust Club Members Posts: 6,763 ✭✭✭
    Yep, I sometimes do that too WTWUK. 99% of the time though I think people will run all 3 wires that control a servo from the receiver, meaning all that power also runs through the receiver. If someone really wants to keep weight as absolutely low as possible it's the way to go.

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