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Feb 07, 2017, 09:18 AM
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Discussion

Issue with FrSky and Freewing Mig21, Need Help


This is by no means intended to cast doubt on Freewing or FrSky but I'm trying to figure this out. Have owned several Freewing planes and consider them to be of very good quality, same goes for FrSky. Have about exhausted my knowledge and looking for input.

Situation:

Have an out of box stock Freewing Mig21, and FrSky radio system that I am getting a continuous receiver lock out condition that will not reestablish link with radio unless power to receiver is cycled. Have been able to repeat this condition many times using both FrSky Horus with OpenTx N362 FW and a brand new stock FrSky QX7 with stock FW. I have tested two receivers with same results a S6R and X6R. Both which came from other airplanes with zero issues for either of them. Batteries used are Zippy 4000mah 6S 40C and Turnigy 4500mah 6S 30C. Also have current and voltage telemetry. Any mix of these will cause this condition.
Was very lucky the first time this happened. After powering up the Horus and plane I taxied around the runway for around 30 seconds to get a feel for the steering control. After all looked good I lined up at the end of the runway and advanced to full throttle. About 2-3 seconds into the take off and just before I pulled elevator the motor stopped and I realized I had no control. Figured something had unplugged or esc blow up but red light on receiver was slow flashing, indicating signal loss. The servos with failsafe set where powered up and locked into their failsafe position. The link would not reestablish unless the power to the receiver was cycled. Cycling power on transmitter will not reestablish the link only cycling receiver power. I have repeated this condition at least 20 times.

Things I know for sure:

1. After receiver locks out and failsafe kicks in the receiver still has power. I know this because servos where failsafe is set to hold or a known position have power to servos keeping them in that position. Also the ESC will drop to idle when lock out and fail safe happens if failsafe is set for the throttle channel. If failsafe is not set on throttle channel motor will still run at last commanded position for approximately 2-3 seconds until esc failsafe kicks in due to the absent of PWM signal, this I have tested. Have not test actual voltage at the receiver but telemetry shows a high of 5.4volts and a low of 5.1 volts. The red light on receiver is slow flashing indicating a signal loss condition.

2. If I force a failsafe with either an extended range test or getting transmitter antenna too close to the receiver the link will reestablish the moment I stop that condition, like taking radio out of range mode or separating the receiver and radio. So it’s not that the system can’t reestablish a link after a failsafe but it does not after the condition listed above.

Things I think I know:

1. It is not an issue exclusively to the Horus or OpenTx FW I installed since the Out of box stock QX7 does the same thing. When testing the QX7 I created a new model in the radio and did not transfer the model program from the Horus, if that is even possible.

2. It is not a problem that is exclusive to either the S6R or the X6R since I can reproduce the same condition on either.

3. The battery needs to be fully charged and the lock out usually happens after a full throttle or near full throttle run of 2-3 seconds. If battery voltage is below around 22 volts the lockout has happened but rarely.

4. After testing in my garage using up three fully charged batteries I could not get it to lockout. The RSSI running up and down the runway is around 60-80, in my garage at a close range it is 95-100. This seems to make a difference.

5. Have not had this condition in the hundreds of other flights where I used the FrSky system. At one time I was flying a 10k jet with a X9E so I have confidence in FrSky .

6. Do feel this is related to an ESC/BEC but if I’m having this issue there may be others. Regardless whether there is a voltage issue with the Freewing ESC/BEC which causes the receiver to lock out once voltage returns there is no reason that I know of that the link does not reestablish. Again voltage from telemetry records a high of 5.4 a low of 5.1 and an average of 5.2.

Next I need to test with a separate receiver battery to see if isolating the esc will prevent this condition. My hunch is that it will but that doesn’t explain why and what it is happing. Without knowing what the problem is I will just worry about every other plane that I put in the air.
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Feb 07, 2017, 09:32 AM
Registered User
Sound like a BEC issue. Try another esc / bec and all should be fine.
Feb 07, 2017, 09:38 AM
S.A.D. member
ivanc's Avatar
I wouldn't use a BEC with more than 4S packs - anything using 5S and more uses a separate 2S LiFe for the receiver and servos.

Ivan
Feb 07, 2017, 09:41 AM
Registered User
Thread OP
Replacing the ESC does not tell me why the link does not reestablish. Will this happen to other planes? Even if I know the BEC is causing the receiver to lockout, great, but that doesn't explain why the receiver does not reestablish a link with the radio when power is present. On a small foamy big deal, on my 45 pound jet very big deal.
Feb 07, 2017, 09:47 AM
Registered User
Thread OP
Ivanc,
About everyone that buys the hundreds of Freewing, Taft, Etc EDFs are not using separate BEC or separate receiver battery. The current BEC can handle 6s quit easily. CC makes them that handle 12s quite easily.

I'm not questioning whether I think I should replace BEC, I know the answer there. The issue I have is why the receiver is not reestablishing a link with the radio when voltage is clearly present.

EDIT:Sorry, did not mean for that to sound curt.
Feb 07, 2017, 09:59 AM
Registered User
The bec can switch to a low voltage maybe, to low to let the receiver work. If the bec is generating a very unstable voltage the receiver might also not reconnect. You need to measure the voltage when the receiver is not re-connecting, that is when it is important to know.

Also, try to re-connect the receiver only and leave the esc / bec on to see if that helps. Try without any servo also.
Feb 07, 2017, 10:02 AM
FJH
FJH
Registered User
Horus and QX7 both are running OTx 2.2.0 version. Don't misunderstand, I am not saying that this is what causes your trouble. Anyway if I were you, i would crossckeck behaviour with a Taranis and OTx 2.1.x.
Feb 07, 2017, 10:09 AM
Registered User
FrSky RF had nothing to do with OpenTX version.......
Feb 07, 2017, 10:09 AM
Registered User
Thread OP
Tadango, I have cycled power using both the main battery connector and by just unplugging the receiver bec line. Both resulted in a quick relink. I can say with confidence that after whatever event happens to cause the receiver to lockout the voltage is stable enough to power up the receiver and relink.

FJH, Good point about 2.2 but I don't have Taranis 2.1 to test with. Will try to find one if nothing else identifies the problem.

I've emailed FrSky as well.
Feb 07, 2017, 10:11 AM
Registered User
Quote:
Originally Posted by yellowbird2800
Tadango, I have cycled power using both the main battery connector and by just unplugging the receiver bec line. Both resulted in a quick relink. I can say with confidence that after whatever event happens to cause the receiver to lockout the voltage is stable enough to power up the receiver and relink.

FJH, Good point about 2.2 but I don't have Taranis 2.1 to test with. Will try to find one if nothing else identifies the problem.

I've emailed FrSky as well.
Try without servos. Maybe a servo is causing an issue?
Feb 07, 2017, 10:21 AM
Registered User
Thread OP
The power system in the Mig has power coming from the BEC to receiver and then power is pulled from the receiver to power the board that delivers power to the servos and gear. Can't really taxi it around with no servo for steering. I've tried to recreate this in my garage with the set up exactly like it is at the field but it won't lock out. Only way I can make it lockout is to taxi around with full throttle bursts, it has locked at lower throttle setting but usually full throttle does it. Can try to test at house in range mode to see if it happens.
Feb 07, 2017, 10:21 AM
FJH
FJH
Registered User
Quote:
Originally Posted by Tadango
FrSky RF had nothing to do with OpenTX version.......
Ofcourse OTx communicates with the RF module and who knows for sure, OTx2.2.0 is still being worked on. Thus on both Tx is still a pre-release OTx version.
And I did not say that this is the cause of trouble, I just pointed out the common feature of both Tx, nothing more.
Feb 07, 2017, 10:24 AM
Registered User
Thread OP
I remember when Spektrum would not link up to a model with an ESC/BEC unless it had a ferrite ring on the esc lead. Is it possible excessive noise from the ESC/BEC is throwing the receiver for a loop? That is not an educated guess just a guess. I spoke with Motion RC and they have not had any reports of this problem.
Feb 07, 2017, 10:26 AM
Registered User
Quote:
Originally Posted by FJH
Ofcourse OTx communicates with the RF module and who knows for sure, OTx2.2.0 is still being worked on. Thus on both Tx is still a pre-release OTx version.
And I did not say that this is the cause of trouble, I just pointed out the common feature of both Tx, nothing more.
True but OpenTX 2.2.0 is mainly not finished due to companion issues for Horus. Radio firmware is hardly worked on and is very stable. Nothing beta about the critical features. Since both receivers work fine in another plane something in the plane is the issue.
Feb 07, 2017, 10:28 AM
Registered User
Quote:
Originally Posted by yellowbird2800
I remember when Spektrum would not link up to a model with an ESC/BEC unless it had a ferrite ring on the esc lead. Is it possible excessive noise from the ESC/BEC is throwing the receiver for a loop? That is not an educated guess just a guess. I spoke with Motion RC and they have not had any reports of this problem.
That is what i suspect, maybe even due to a bad servo also. Adding a low esr cap on the receiver could fix that also (and was sold / advised for Spektrum also).

When you unplug the esc lead to the RX you also reset the servo's that is why i would like to see if the problem also exists without any servo connected.


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