U-NAV RTL module malfunction

[Disciple4123]

I have a problem that is likely my fault, but wanted to hear if others may have had a similar issue. I run the RTL and the ALT3 on a common trainer 40 w/aileron type plane. The RTL is hooked with a Y to the AIL and RUD. When I got the RTL about a year ago, I opened it trying to place the GPS unit on a wing, I never cut any wires, and sealed it back up with black heatshrink.

Today the unit was in the hot sun prior to startup, and the rud/ail moved to limit on startup and became limp, It did this several times. I can get it to work better inside (cool) after changing to a white covering and scrapping the hot black wrapper. I can also get it to work better with just the RUD connected, and disconnecting the AIL. When it initializes like this, it never works at all, continues limp control surfaces, when it initializes OK, it doesn't seem to give out later.

Anyone had a similar problem? If I had not wrapped it in black, the overheating would not be as much of a consideration. I also am running a JR 4131 on the RUD and JR DS811 on the ail. The control surfaces are satisfactory, but probably not as friction free as can be (cheap trainer 40 plane). The unit is getting 5.97 volts consistently.

I have gotten about 20 good flights on 2 airframes with this system during the winter, the only difference about today was that it is the first 90 degree day it has been used (that I can recall).

Thanks,

[Disciple4123]

I have changed the aileron servo, and re-did testing. My conclusions are as follows:

1) Heat, gently applied by hairdryer or by sun, when paired with the 811 + 4131 servo combo, will act up. When the heat is not present, it was not failing to initialize as much.

2) When the symptom came about, voltage read 5.9 to 6.0 volts at a servo at the end of this circuit, so a voltage drop or open circuit was not involved in this.

3) When the DS811 was changed for a 537 (analog) on the AIL, the problem went away completely.

4) All involved servos have been tested, they were not faulty upon operational examination.

5) The 900MHZ downlink located 20 inches from the UNAV unit, was taken out of servise to diagnose, it had no effect on initializations.

I have flown a lot this afternoon in similar heat, and intialized several times, no further problems.

Perhaps when an analog and a digital are paired on a Y connector strange things happen, perhaps this is an anomoly of the UNAV system, either way I am glad it is resolved.

[lvspark]

It would interesting to compare the current consumption vales on the whole set-up with each servo in place. Also would be interesting to get the unit to fail on the bench, then apply component cooler and see what one was the culprit.

[Disciple4123]

You are right that such tests would be meaningful. I will say that I believe theat with both servo's being kind of high load, and aged it was to be expected. The UNAV uses light wires, the UNAV tests the travel range initially, it was twitching to one side then dying by dropping signal only. I suspect that the UNAV drops signal when load is excessive, the manual even says to provide a volt source after the module when running heavy loads.

The tests were provoked by heating the UNAV, it was a bit clear that the UNAV was the temp sensitive source, and that is OK. I'd rather it do this than die, the RTL is a good little piece of equipment, very well made.

I am going to transfer all the goodies over to a mini telemaster (single rudder HS85 type servo plane) within 10 days, so for now I have switched both servos to analogs on the trainer 40, and then the load will probably be 1/3 as much. Since all my camera work is done with the helicopter, and this unit is relegated only to FPV flight, I feel that a mini telemaster at 2LBS is a better choice than the current 6LB 40 trainer.

Thanks,

[Disciple4123]

Well problems came back again. Outside it would not intialize at all, after 1/2 hour indoors (cool, no sun) it began to initializa, and do so reliably.

It seems that a sensitive thermal factor is at play. It is wrapped in thin white electrical tape, on the top of the aircraft now, so it should not be "overheating"

I will add, that when it fails to initialize, it also does not do the red light flash (no automatic attempt to locate base taking place). I hope this critter is alright, I really liked it.

Below is a photo of the install, with the y connector in view. forgive the appearance of the plane, it is just a prototype airframe, kind of taped up I know.

http://www.aerialphotographyservices.com/P7143722

[lvspark]

Unav should be able to help you with this. Sounds like a vreg overheating? If they can repair it, that would be my first choice, otherwise open the case, get it to fault, then use component cooler to locate the thermally sensitive part.
http://www.radioshack.com/sm-component-cooler--pi-2102648.html

[Disciple4123]

Thanks, I am in contact with them. I added a picture of the install in the prev. post.

[Disciple4123]

Well I had the chance to speak to Mark on the phone about my unit after it was checked. He indicated that a resonator is likely bad, and he will replace it.

Some recommendations from UNAV:

1) It is preferred to mount the RTL unit in a fuselage recess, with a cover of white Monokote to allow a smooth fuselage appearance and block the sun heat.

2) Use caution storing the RTL in a hot car under sun, shade it.

3) Don't dissassemble units :rolleyes:

It seems that heat was involved in my failure, and he will have it working for me in short order.

Thanks.