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Old Jan 03, 2013, 08:14 AM
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TX, RX, ESC, BEC, where is my problem?

I am having an issue with my model airplane. I keep loosing signal randomly and am wondering which component to start with. Here is my system and problem.

The system: I have a scratch built Polaris seaplane park flyer with a turnigy 2826-6 2200kv motor, 6x4e prop, turnigy trust 45a esc with internal 3amp sbec. I am running 3 dynam 7gm servos for aileron, rudder and elevator. My battery is the zippy compact 2200 mah 25c and the compact 1800 mah 25c packs. I have this problem with both so I think I can rule out the battery. I am pulling 23 amps static at WOT. My radio is the airtronics rd8000 with the original Frsky diy 2.4 module and the full range frsky v8fr-II rx

The problem: I flew this airplane for over 8 trouble free flights and then the esc started to get stuck between half and full throttle, it would not shut down. The esc and battery got very hot very quickly as I tried to unplug the battery. I threw that esc away and got another one of the same model. This esc seamed to work very well for the first 4 flights. Then after flying around for about 3/4 of the battery, I lost signal to the airplane, I regained it a couple seconds later and was able to land the plane. Everything seemed to work alright so I thought that maybe my battery was just a little low, it wasn't. I flew the next day and lost control about 3/4 of the way through a different battery. this time the plane came straight down and crashed. I pugged everthing in after the crash and had full control of everthing. I rebuilt the plane and flew another 4 uneventfull flights and then yesterday, I was flying and after about 3/4 of the way through the flight, I lost signal again. The plane went down on the other side of the house and when I ran over there I had full signal. There was no damage to the structure so I proceeded to take of and land another 7 times over a save area with no problems. The plane in two cases was within 40 yards and in the other at about 120 yards all line of sight. It seems like in all the incidences that the plane lost signal after about the same duration of flight and after about the same type of flying, (1/2 to 3/4 thottle during most of the flight)

Problem?: So after a very long post and explanation, what component would be the first to be replaced if it was your plane? I am thinking that I could check the amp drawn on the system with the servos under load to see if the servoes are getting to the bec limits. I have a 3 amp ubec that I could hook up and bypass the built in bec of the esc. I also have another rx I could plug in and use for a while. I also have another esc of a different brand that I could install with a little more difficulty.
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Old Jan 03, 2013, 08:31 AM
Dude, I do fly all day long!
rcalldaylong's Avatar
San Jose, California
Joined Dec 2007
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Quote:
Originally Posted by flybyjohn View Post
I am having an issue with my model airplane. I keep loosing signal randomly and am wondering which component to start with. Here is my system and problem.
Problem?: So after a very long post and explanation, what component would be the first to be replaced if it was your plane? I am thinking that I could check the amp drawn on the system with the servos under load to see if the servoes are getting to the bec limits. I have a 3 amp ubec that I could hook up and bypass the built in bec of the esc. I also have another rx I could plug in and use for a while. I also have another esc of a different brand that I could install with a little more difficulty.
I'm a spektrum flyer, and on a spektrum when you run into low voltage (brownout), the rx flashes. Check to see if there's anything like that on yours.

You didn't mention so I assume you don't have another plane to test with. Anyhow, I'd vote to swap out the Tx and rx. I had the same weird issue happen to me on the DX7. It would be fine, then wham lose all control. When I go pick up the plane, I have full control. It happened to multiple planes over a period of a few weeks. I finally sent in the Tx to horizon to repair. They swapped out the RF deck and I haven't had a single failure in over a year now.
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Old Jan 03, 2013, 09:06 AM
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dedStik's Avatar
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You also failed to mention if you did proper range checks prior to flying.
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Old Jan 03, 2013, 09:14 AM
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Its is not spectrum, it is Frsky, which has a really good track record. And that is correct, I did not do a preflight correct range check but to rule that out as a problem, I did during the 7 minutes prior to loosing signal in all instances, fly out to a distance to where I could hardly see the airplane ( approx.200+ yards) with full control. With the first esc, before it went bad, I did not have any problems with the sbec. I even had full control of the control surfaces when the motor cut off or got stuck on half to full throttle. The problems were first noticed after 3-5? (don't really remember) flights with the second esc, but only sparaticaly. This has happened in two different locations 4 miles apart from each other.

Just a few more details: The esc is inside of a foam sealed fuse, with the cooling fins sticking out of the top of the plane. I am flying in sub freezing weather, (below 32F) but using warm batteries and the batteries are warm when removed from plane. ESC is very cold with the cooling fins exposed to the outside air. Overheating is not a problem. Could rf noise at certain motor rpm cause the rx to reboot?
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Old Jan 03, 2013, 12:17 PM
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The one area that you seem to have passed by ... Battery connection to ESC ...

What connection do you have ? Deans, XT60, APP ????

Deans are known to have a connection problem after a while if not cared for ... the spring tab bends and initially all seems fine, but vibration / manouevres can cause the Deans to lose contact ... you go to model and all seems fine ...

You can also have intermittent motor problems from this as voltage drop across faulty connector is enough to cause motor problems but radio gear appear normal.

I only post above as examples of what can happen with a used / worn connector. I have had all you have had due to faulty intermittent ESC, and / or faulty battery to ESC connectors ...

The indicator to me is the battery packs as you say are still good capacity and you fly again ...

Could be wrong ........ only way I found out was to swap a part - fly, if not cured - swap another part ... fly ... carry on till all fine.

Nigel
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Old Jan 03, 2013, 02:27 PM
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Originally Posted by solentlife View Post
The one area that you seem to have passed by ... Battery connection to ESC ...

What connection do you have ? Deans, XT60, APP ????

Nigel
Yes, I did forget that. I am using the XT60 connectors and they are extreamly hard to get apart, so I think that the connection to the esc from the battery is solid. The motor also keeps running when I loose signal, so the esc is still getting power as is the motor.

I do not have the fail safe set up on the rx so when it looses signal, the servos just freeze in the last position they were in when the signal failed. This would also be the case if the rx lost power. I believe I have it narrowed down to the problem of loosing rx/tx connection, or intermittently loosing power to the rx by failure of the sbec. As said previously, it seems to happen after a duration of flight time (right about 7 minutes into the flight), but the battery has always had over 11.5 volts (3s) still in it when it happened. It has never happened at the beginning of the flight. The control is always regained on its own post crash or before it hits the ground. It doesn't happen every flight, just every now and then.
I am going to put another esc into it tonight and see if I have any problems. That will eliminate the esc and bec. If I still have problems, then it will leave me with the rx.
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Old Jan 03, 2013, 03:16 PM
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You are overheating the integral bec.

Try flying at reduced throttle, or with improved ESC cooling, or with a separate ubec.
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Old Jan 03, 2013, 03:22 PM
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Canada, ON, Ottawa
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Quote:
Originally Posted by flybyjohn View Post
Yes, I did forget that. I am using the XT60 connectors and they are extreamly hard to get apart, so I think that the connection to the esc from the battery is solid. The motor also keeps running when I loose signal, so the esc is still getting power as is the motor.

I do not have the fail safe set up on the rx so when it looses signal, the servos just freeze in the last position they were in when the signal failed. This would also be the case if the rx lost power. I believe I have it narrowed down to the problem of loosing rx/tx connection, or intermittently loosing power to the rx by failure of the sbec. As said previously, it seems to happen after a duration of flight time (right about 7 minutes into the flight), but the battery has always had over 11.5 volts (3s) still in it when it happened. It has never happened at the beginning of the flight. The control is always regained on its own post crash or before it hits the ground. It doesn't happen every flight, just every now and then.
I am going to put another esc into it tonight and see if I have any problems. That will eliminate the esc and bec. If I still have problems, then it will leave me with the rx.
Sounds like you're going about it the right way. Install a different ESC to eliminate that possibility. Take a good look at the receiver, as on FrSky the antennas are plugged in and I have heard of cases where the connector came apart (I had one that wasn't connected when I got it). For sure do a range test to establish that the transmitter module is putting out. I presume you have the antennas set up appropriately, well spaced and roughly at right angles, not directly on CF, not under the battery, etc.

I would suggest setting failsafe ASAP. I generally set it to low throttle and a little up elevator. The latter may not save the model, but it does produce a characteristic pitch-up to tell you what's happening (I've had it happen with another system, never FrSky).

By the way, when using FrSky I typically fly Polaris with either a D6FR or V8R4. Both have been 100% reliable.

This kind of intermittent problem is excruciatingly frustrating. About the only thing you can do is to keep changing things. Next step, different receiver.
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Old Jan 03, 2013, 03:38 PM
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Originally Posted by peterangus View Post
You are overheating the integral bec.

Try flying at reduced throttle, or with improved ESC cooling, or with a separate ubec.
I may be overloading the internal bec but it is definently not overheating. The entire esc unit is freezing cold when I get done flying. With the cooling fins outside the plane and the cold temperatures, the esc stays stone cold. The only time that the problems have occured are at reduced throttle settings. When flying full throttle and fast I haven't had a problem yet.

I would really like to find the exact problem by switching one component at a time, but on the other hand I do have an extra esc and rx that I could put in together. By changing both units, I probably won't know exactly what the problem was but if I only change one unit at a time, I might not have a Polaris before I find the problem.

Daedalus66, The antennas are 90 deg apart and the tips are about 6 inches apart and 1.5 inches back from the leading edge of the wing. The esc is hanging above and to the side of the rx in the fuse.
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Old Jan 03, 2013, 03:45 PM
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Just a thought but flying slow would reduce airflow over cooling fins, and the controls would have to move farther to control the airplane. Could possibly cause a bec overloading/heating problem. I will have to check the current draw of the servoes and rx under heavy load.
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Old Jan 03, 2013, 06:09 PM
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I checked the amp draw for the servos and rx and the most I could muster up is 0.5 amps with all the servos stalling out and motor running. So I think that if the bec is rated for 3 amps, I should not be overloading it. Could however still be faulty. I am hooking up the other esc and will give it a test tomorrow afternoon.
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