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12-01-2015, 06:08 AM | #1 |
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72MHZ and Digital Servo's
I still use a 72MHZ radio and have a question. Why would I have an issue running all digital servo's in some of my planes. My Showtime 90 is fine with all digital's except for one on the throttle. I put 4 digital's in a plane and I got a chatter and movement on my rudder. I swapped out the digital's on my Rudder and Elevator for standard servo's and the problem went away. I'm using standard servo wire on my extensions. I use steel push rods. Its a 40 sized 3D plane so my extensions are 12". I had a friend that had the same trouble years ago and hooked up his 2.4 Radio and the problem went away. I've tried different RX's and even different servo's and extensions. Anyone have a clue as to what's going on. Cheers floyd
Last edited by floyd; 12-01-2015 at 12:11 PM. |
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12-01-2015, 06:34 AM | #2 |
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Re: 72MHZ and Digital Servo's
Your servo leads on 72mhz systems could be acting as antenna's. This is problematic with long servo leads. On 72mhz systems, we had to use chokes on the servo leads to cut off any radio signals that were picked by the servo from reaching the reciever.
With 2.4G, the servo leads do not affect the reciever in the same way they did 72mhz, so the problem with long servo leads no longer presents a problem on 2.4G
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12-01-2015, 07:51 AM | #3 |
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Re: 72MHZ and Digital Servo's
Are you powering the the Rx from the BEC on the ESC? If so, it would be worth a quick test with an external BEC or Rx battery to see if it makes a difference.
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12-01-2015, 08:05 AM | #4 |
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Re: 72MHZ and Digital Servo's
Its a glow engine. I have tried both 4.8 and 6 volt packs. My Showtime 90 has the longest extensions of any of my planes and its fine. Cheers floyd
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12-01-2015, 10:26 AM | #5 | |
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Re: 72MHZ and Digital Servo's
Quote:
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12-01-2015, 12:09 PM | #6 |
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Re: 72MHZ and Digital Servo's
stegl, I've answered some of your questions in my original thread. I've seen this problem before, but I've never had it happen to me. The servo's are from HobbyKing. But I have another 20cc plane with HobbyKing digital's in it with no problems at all. And the servo extensions are longer. That's why I posed the question so I could try to figure out why one plane is fine but the other isn't.
Cheers floyd |
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12-01-2015, 02:42 PM | #7 |
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Re: 72MHZ and Digital Servo's
Are the HK digital servos all the same model or different models ? Have you tried changing out the digital servos with the same model of digital ( not make but same model) servo and problem cured ? I guess when I was asking about servo wire I should have asked what gauge of wire ? the "standard" servo wire can be pretty thin when running into longer leads with more voltage loss to the servos if mounted in the tail. Since digital servos do take more power ; probably better to run larger gauge like 20 or 22 as " standard servo wire leads " can be anywhere from 24 to 26 gauge depending where bought.
Thing with some digitals especially lower quality ones is that they minimise the circuitry to keep the cost down but then from servo to servo there can be issues. If using long metal pushrods they can act as a reflective antenna. Sometimes plastic pushrods like Sullivan golden rods may minimise that. Are you running ignition gas motors with the problems stated or glow fuel ? Many years ago with 72 MHz I had a radio that had issues with metal to metal contact interference causing some servos to jitter. found out it was a metal fuel filter rubbing on another metal part causing induced electro static interference that was picked up by longer servo leads and cheap servos. Changed out the cheap servos and never had that issue again. Since then always stayed with quality radios , receivers and servos and never had the problem again. If using gas and ignition engines ; have heard that interference can be caused by incorrect grounding of components or ignition module issues. That is why we should be using IC ( Industry Canada) approved radio systems as they have been approved to minimise creating and accepting any outside interference. That is the problem today with allowing non approved radio systems into North America that are not approved and nothing has been done to prevent their use except possibly at a club level. It is hit or miss. Sorry , I may have strayed here a little off topic but still radio systems concerns Last edited by stegl; 12-01-2015 at 03:09 PM. Reason: spelling |
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12-01-2015, 04:18 PM | #8 |
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Re: 72MHZ and Digital Servo's
Floyd I had the same problem with a Funtana X100 and hitec 5645MG servos with
PPM receiver I switched to a PPM receiver and the problem went away I have about 30 flights on it now no problems |
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12-01-2015, 06:17 PM | #10 |
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Re: 72MHZ and Digital Servo's
Are you running your battery packs through a switch, or direct to the Rx?
Asking as digitals are power hogs by design and most stock flight system switches are only rated at 4A. Max brought up a good point in that 72MHz receivers are sometimes more sensitive to stray signals feeding back over long extensions. As you did not mention which 72 MHz system, taking a guess at how problematic that may be. I do know some JR and Futaba receivers were excellent at filtering out noise on the antenna signal and I imagine better as feedback along the servo signal leads, as well. On that subject, how far is your antenna routed from any extensions, steel rods and power system leads? Have you tried reorienting it to see if the problem is mitigated at all? This was also a problem with our electric helis as everything was in close proximity, especially to higher power ESC setups. This was one reason there was a carbon choke ring on the ESC to receiver lead as close to the Rx plug as possible. You may be experiencing feedback into the Rx from external sources or even a jittery power control in one or more servos feeding back though the signal lead. Also, you don't specify the gauge wire used in your "standard" extensions. 24g may be too small for longer runs, and any connection is another possible resistance point introduced into the system. I have been making my own 22g extensions for quite a while now and always use twisted leads as they seem to be better at this than straight. In all the years before switching to 2.4 recently very rarely have I seen any problems not caused by other issues, (too close with the Tx, power problems, bad connectors, etc.). NOTE: One solution I have used before is to isolate the flight system power from the Rx, running the servos and other systems on one larger source, while the Rx is off a much smaller 4 cell NiMH. Only the negatives are common.
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