Minivbar missed channels with spektrum sats.

[Bnito]

I'm askin on behalf my brother.

He flies a logo 690 and he has had now 2 similar crashes where the vbar log shows missed channels and he has lost control of the heli resulting in a crash.

His setup :

Logo 690sx v2
Kontronik Jive 120
Gryphon bec 20A
Mini vbar
BK 7001 and BK 7005 servos
Spektrum sats
DX8

I borrowed a osciloscope from my work (fluke 125) to measure voltage when pitch pump is set to 100 in vbar. I have to say i don't really know how to use the scope that well, but we managed to monitor voltage.

I also bought 4700 uf 16v caps.

We tested with the caps plugged into vbar + and gnd, and without the caps.

What seemed intresting was that without the caps the voltage actually went above 9,5 volts and with the cap it stayed near the bec voltage (8.4v). The lowest dips we saw were 5.xx volts. We also managed to get rail 3.3v error and channel missed in vbar once without the cap plugged in. With the cap plugged in we did not get the rail error.

Could that high voltage be servo reverse current?

i'm referring to this :
http://www.vstabi.info/en/node/1422

When we tested all electric parts were disassembled from the logo frame.

Any advice?

I have the log if needed, all it shows is good health messages from testing and only once rail 3.3v error plus channel missed x 10

[Vinger]

Channel missed warnings are nearly always associatedwith sattelites resetting or losing power, either due to voltage too low or chafed wires.

The mini VBar and the BKS servos you use are a known combination for creating power spikes, either from back EMF or too high a power demand. The capacitors might be a bandaid solution but in the long run it better to use servos that have been designed to not give back EMF.

[tshelby73]

I tried a capacitor on my 450 and it fixed it. I was skeptical at first but it worked. What I did find is i had to use a y-adapter to hook it up and it worked better if I y-ed it off a servo connector and not the esc power coming in. When I had it on the esc power wire it didn't brown out but would see voltage drops. On servo connector no voltage drop.


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[Rabid121]

2 caps (4700each - might help or not, very often it does), but 2 "easy" other/additional things you could do:

1. use R²Buffer (or similar, dont know if available in your country) to stiffen power source for vstabi. such voltage breakdowns are "well known" to produce problems on spektrum sats on vstabi. as a plus it can handle ~45" of power down... by far enough to autorotate.

2. replace the 2 sats by 1 AR7700... this is what i did for all of my birds (one of them a 690SX). the mod is done in 10-15minutes: one sat stays on the bird as before - now just connected to the ar7700's sat port. the ar7700's remote sat port will be connected to the vstabi sat port (cable to buy or solder - it's easy). PLUS one +/- cable for powering up the AR7700. (re)bind the AR7700 & check TX setup in vstabi software (i never had to change a thing).

and you win: original "spektrum sat on spektrum receiver" (a bit less critical on voltage drops - see specs). plus it gives you the additional possibility of using spektrum telemetry. i love to see bec & flight pack voltage, flight log, esc temperature, etc

ciao
Michael