Bavarian Demon Temperature Question

[tvoth3]

Hey All,
I posted a question regarding odd behavior I had this weekend with my Gasser in the BD topics area and haven't gotten any responses so thought I'd try here as I know a number of folks use the 3SX on gassers (https://www.helifreak.com/showthread.php?t=742416).

Basically, had odd tail behavior where the tail wouldn't stop a piro after commanded to do so. Had been flying very nicely up until that point. As I landed the heli began to pitch forward and backward. Cut the throttle and got it on the ground with only bent gear.

I understand that the BD 3SX can be effected by temperatures and think that might be a long shot but wondering what others have seen that can be attributed to high temperature effects on heli behavior. I should note that I was running with the canopy off and the unit didn't seem hot (to the touch) and outside temperatures were about 70F or slightly less. How hot does the unit have to get to have issues and what do these issues look like?

Thanks in advance for any insight here.
Tom

[rbort]

Heat doesn't cause anything like that. If the demon gets too hot, it will continue to work, but if you go to power cycle it again, if its too hot it won't initialize.

You never get it to cause spinning tails or loss of control, no matter how hot it gets. I've been there with it being hot, never was a danger to the heli.

You must have some other issue, power, bad servo, chafed wire, etc.

-=>Raja.

[fastflyer20]

+1

Plus the Goblin is very effective at keeping the FBL cool. I had BD overheat on some other gassers but never on the Goblins.

What are the details on your RX power setup? Do you have a genny or other backup RX power?

[tvoth3]

Ok. Search continues then.

Running hv servos (align 815 and 855) off 2s lipo. No backup power or generator. Setup included 2 full receivers through an XPS X10+ unit. Transmitter is taranis and receivers are x8r. The x10+ monitors low voltage condition and did not indicate that on landing though one of the receivers had its (sbus) connection to the x10+ come loose. Still had one good receiver connection tho and xps says that would be sufficient to keep control. Also telemetry never indicated signal strength issue.

I think the setup is too complicated and I'm going to drop the x10 and second receiver and see if that solves the problem.

Note that I spun the thing up on the ground (no blades) afterwards and it was rock solid. No twitching at all. Amazing considering the vibes from the engine.

Thanks for the input
Tom

EDIT: I should note the servos arnt from the bad batch. I'm aware of that issue.

[rbort]

Can you switch to something else? Might be worth it before a crazy pointless crash. The point of the matter is, don't fly it again until you change something, nothing worse than flying the same setup again and have it suddenly jump into the ground on you. At least if you change something you have a chance to fix it than just roll the dice again.

New demons work really well now, I used to put the demon outside on my whiplash like on the Goblin now, in the rear, but with the new demon sensors that came out last, that is not needed any more. I moved it back inside the canopy in the front and there is no issue any more even being warmer there than outside on the tail boom plate.

-=>Raja.

[tvoth3]

Raja. Yeah I'm going to simplify the setup. That said I wish I had a real lead on the failure. I'm not eager to have another experience like that.

Is it safe to run the engine in the heli without blades for an extended period so I can watch for strange behavior? Would that damage the engine?

[rbort]

Never go beyond 1/4 throttle or let the governor engage.

-=>Raja.

[rhodesengr]

a couple of years ago I did observe a temperature issue with the 3SX but it was nothing like you describe. What I had was some vertical pitch jumps (not huge) and some the tail would wobble around some in a hover. Wobble is the wrong word. It was more like some random, small excursion tail motion. As you would expect for a thermal issue, it would come on after five minutes or so. I moved my 3SX out from under the canopy and have never had any more such problems.

I believe Raja has posted that the thermal issue was only with the older sensors that became unavailable. Captron went to new sensor (about two years ago I think) and he says these new sensors don't have the thermal sensitivity.

The 3SX will alarm if it actually overheats. I think the LED code is 6 blinks but I saw thermal symptoms well below that point.

I think what's odd about your situation is that is that you describe both tail and cyclic. If it was just the tail, I would say it was a bad position sensor in the servo or a bad connection. I had an MKS servo that became intermittent from a bad internal pot. The tail would jump in large, random jumps.

Seems odd that you would have two servos go bad at the same time.

Maybe its the old Sats only thing? Are you using a full RX or just Sats?

[tvoth3]

Rhodes
Yeah the behavior wasn't what you describe for temperature issue. The setup didn't use sats but did use two receivers through a unit that picks the best sbus signal and uses that. The 3sx got power through the appropriate wire and the receivers got power through sbus (see above about x10+).

I'm thinking I need to simplify the setup and use single Rx in the traditional mode with power to Rx and 3sx and wire loom between the two ( as described in ldlohrs sticky).

Two servos going out at same time would be my luck!

Raja - OK. Thanks for the warning.

Thanks for your input
Tom

[rhodesengr]

I was going to say, try just one RX. I think 99.9% just use one RX.

[fastflyer20]

Make sure you have two connectors carrying power from the battery into the FBL, not the RX.

[in2deep]

Off subject a bit...

No help with the Demon, but glad to hear your using OpenTX with the gasser. When the Horus is released this year Ill be making the switch. (and probably PMing you for advice on setup lol)

[KSHeli]

Were any of the servos hot? Bench test your servos, I had a set of Align HV servos on my Goblin and 2 of them would get hot just bench testing. They eventually brownedout the system.

[tvoth3]

Originally Posted by in2deep

Off subject a bit...

No help with the Demon, but glad to hear your using OpenTX with the gasser. When the Horus is released this year Ill be making the switch. (and probably PMing you for advice on setup lol)

Not sure I'm the best source for OpenTX but I'd be glad to tell you what I've got. I followed Arch's "simple" setup advice and have added a bit for govenor etc. Amazingly powerful but also difficult to navigate. All in all I really like it. I've been using it on my 450 for about 2 months now and works a charm.

[tvoth3]

Originally Posted by fastflyer20

Make sure you have two connectors carrying power from the battery into the FBL, not the RX.

I had one to the BD and one to the receiver with the loom providing power back to the BD as the secondary source. Is that not sufficient?

[tvoth3]

Originally Posted by KSHeli

Were any of the servos hot? Bench test your servos, I had a set of Align HV servos on my Goblin and 2 of them would get hot just bench testing. They eventually brownedout the system.

KS, I haven't noticed them getting hot. Do you know if your servos were from the "bad" lot? I know there were issues with the early release of the 855 and/or 815 but that has been resolved. You can tell if you've got a good lot as it has a number etched into it.

[tvoth3]

Originally Posted by rhodesengr

I was going to say, try just one RX. I think 99.9% just use one RX.

Yeah, definitely going to do that.

[FrankFuss]

Originally Posted by tvoth3

I had one to the BD and one to the receiver with the loom providing power back to the BD as the secondary source. Is that not sufficient?

This creates a ground loop. There are some that suspect a ground loop causing issues. It is probably best to avoid it and run power directly to the FBL, since the FBL buss directly powers the servos, and then from FBL to receiver. It may not be a factor in the odd behavior you noticed, but why take the chance?

[tvoth3]

Originally Posted by FrankFuss

This creates a ground loop. There are some that suspect a ground loop causing issues. It is probably best to avoid it and run power directly to the FBL, since the FBL buss directly powers the servos, and then from FBL to receiver.

Frank,
I used this setup based on the sticky:
https://www.helifreak.com/showthread.php?t=618417
using the illustration at the top of the first post (full RX) and replacing ESC/BEC with the 2s lipo. Is that incorrect?
Thanks,
Tom

[FrankFuss]

Originally Posted by tvoth3

Frank,
I used this setup based on the sticky:
https://www.helifreak.com/showthread.php?t=618417
using the illustration at the top of the first post (full RX) and replacing ESC/BEC with the 2s lipo. Is that incorrect?
Thanks,
Tom

That diagram is perfectly fine, but creates a ground loop. Now, it may only be an urban legend, but there are some that swear that they have had issues because of a ground loop. It may be superstition, but I would only directly power the FBL. If you don't have a spare port on the FBL to provide a second power connection, you can use a Y-cable to power one of the ports connected to a servo. Others can comment about this, and you can go with the majority oppinion. Maybe just simplifying your wiring will be all that is needed.