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PostPosted: Wed 20. Mar 2019 22:34:59 
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It's my flying buddies heli, it's a Trex 450LM (belt drive tail). Standard Align 'Super Combo' except for Hobbywing 50A V3 ESC. Spirit pro, spektrum SPM4649T Rx and DSMX satellite. DX8 G2 Tx which works faultlessly on his other helis

He has suffered a couple of crashes due to control loss and two other control loss incidents during spoolup. Briefly: the symptom is that there is a sudden and total loss of control but the failsafe does not kick in, the heli remains powered but unresponsive to any control, including throttle hold. Failsafe is correctly set.

First time it happened after the crash we did a BEC test, which failed. We upgraded the ESC to the HW and fitted a 'brownout capacitor'. BEC test then passed fine and we thought we had fixed it. Heli was good for a a few months.

Three weeks ago during spoolup all control was lost. The heli just kept running at full power on the ground until the battery went down to low voltage, my buddy had no control at all and throttle hold didn't stop it. Receiver and satellite LED lights remained lit.

So we checked the heli over, took the blades off and tested it, all fine. Put the blades back on, spooled up and the same thing happened :cry: .. again receiver and satellite lights were lit, hwli just sat there running at full power until low voltage kicked in.

So he stripped it all down, re-wired it, checked it out, test spooled up without and with blades, all was fine. Today he went for a re-maiden and a couple of minutes into the flight he got a twitch. He was coming back to land when all control was lost and the heli went nuts. Again neither throttle hold or rescue had any effect. Heli went down some distance away and motor kept running after crashing (throttle hold active the whole time). By the time he found the heli the battery was again over discharged and the motor had eventually stopped. Receiver and sat LEDs were lit when he found it

Spirit log attached. I'm reading this that the Spirit re-started and calibrated mid-flight (for reasons unknown) but after it re-started it did not pick up receiver input? The log from the last spoolup incident is identical (attachment #2). The low voltage at the end of the first log is i think just caused when the battery went flat.

So why does the Spirit re-start? And why doesnt it either pick up the receiver signal, or go into failsafe? Could this be a static hit?

Attachment:
File comment: Today's flight and crash
image1.png
image1.png [ 407.17 KiB | Viewed 245 times ]


Attachment:
File comment: Spool-up incident from 3 weeks ago
image2.png
image2.png [ 357.23 KiB | Viewed 245 times ]


Any suggestions greatly appreciated cos my buddy is pretty frustrated right now and the intermittent nature of the fault makes it very hard to nail down. As i mentioned earlier, I'm now suspecting static mainly because i cant think of anything else.


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PostPosted: Wed 20. Mar 2019 23:40:52 
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Joined: Thu 06. Sep 2018 0:21:37
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Possibly static discharge as it has a belt drive.


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PostPosted: Thu 21. Mar 2019 8:26:52 
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Joined: Sat 24. Oct 2015 19:06:03
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denis747 wrote:
Possibly static discharge as it has a belt drive.


Thanks, yes, that's what i was thinking but i was hoping that someone (Tomas maybe?) had seen a flight log that looked the same and so knew with some certainty what the cause was. It's proving quite frustrating for us both that we havent been able to pin this one down. The intermittent nature of the fault makes it really hard to know for sure if fixed or not.

If it was static i wonder why the loss of control lasts for the whole battery?.. And why isn't failsafe kicking in when signal from receivers is lost?

It's got me baffled I have to admit.


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PostPosted: Thu 21. Mar 2019 8:42:24 
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Hello,

I recommend to try to spool up the model without main blades to try to reproduce the issue.
It is likely that the problem is really due to static discharge since these are the most intense during spoolup, hard maneuvers and landing - whenever the belt could touch the boom.

Also it is very important how the cables and receivers are placed. If they are near the boom then it could cause the issues.

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PostPosted: Thu 21. Mar 2019 8:55:51 
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Joined: Sat 24. Oct 2015 19:06:03
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Thank you Tomas,

Would static cause the failsafe to not activate? I did think that maybe the belt could have been a little slack and rubbing in the boom causing an increase in Static. The belt snapped in the last crash though so impossible to prove.

He did re-wire the heli and the receiver placement is good (not on boom). He also did spoolup without blades but could not reproduce the fault, then a couple of minuted into the flight it happened again :cry: Next steps I think are to check that the belt is good and tight, maybe add a little silicon lube to the belt, and add a grounding wire between boom and motor mount. Than test again as much as possible before trying to fly again.

Any other suggestions are welcome.


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PostPosted: Thu 21. Mar 2019 10:49:49 
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Unfortunately static discharges are very bad for the electronics since it can cause a random unexpected behavior. It is similar as a lightning bolt, not good at all.
So the unit, servos, ESC might not operate well at all and could reboot or freeze.

Yes, please test at the bench as much as possible. Of course in the air conditions are different as the model is not touching anything.

After each test please open the flight log and check for any warning or error. This could help.

The belt should never touch the boom if it is tightened properly.

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PostPosted: Fri 22. Mar 2019 3:06:14 
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Hello all...
This is so sad, and I have lived this problem myself as well, but not as bad as described here. For a year or more I occasionally got hit with static issues, where heli would crash with no control input. It also was a belt heli that was a similar heli. So frustrating and could happen anytime. I am sure I have resolved my issues and hope this will help.

Here's what has completely fixed my TREX 500 heli static issues, that may help you and anyone else having similar problems:
1). Spray the tail belt down with silicone spray, each time you go to fly for the day. (BTW Wal-Mart sells a spray silicone that works great) This really helps the static problem. When you change the belt entirely, spray silicone in a baggie and let the belt soak overnight.
2). Spray some silicon spray on on a cloth or cotton ball and coat the left and right sides of the carbon mainframes before each flying session.
3). Also coat and spray the large main gear teeth with silicone, you can wet a Q Tip and apply the silicon spray in all the teeth. Again, spray some silicone spray in plastic baggie and you can use Q-Tips to dip in and wet the Q-Tip and apply to the part.
4). If the above does not help resolve static completely, as in my case, I also added a 12,000 uF 35V capacitor in parallel across the main BEC / power leads to the RX. You can get these cheap on eBay or local electronics shop.
5). Be sure to coat the tail drive smaller gear with silicone spray before each flying session.
6). Hopefully doing all this will help solve the issues with static.
7). If not resolved, then the next step would be to add static arrest wires using a small wire to arrest the electrical static problems. This would be done by using small ring wire crimp or solder connectors so that you can add wire to each of the major sections of the heli, tail drive box, tail boom, carbon frames both sides, then to the motor mount screw as well, to connect them all together and this gets rid of the static build up.
8). If your heli manufacturer offers a metal tail block like the company I2RC (May be out of business now) used to carry for the TREX 500 that works awesome, this will definitely help the static issue. That was the last thing I had to do to totally get rid of the static issues once and for all. This last step has assured me that this static problem is gone for good for over a year.

I know this is a lot of work as I have lived this problem, thinking I knew I did not crash the heli as it was flying great and then went in all of a sudden with no control inputs. Doing the above resolved the static issues for me.

Hope this helps,
Dave


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PostPosted: Sat 23. Mar 2019 9:33:46 
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Joined: Mon 16. Apr 2018 7:19:02
Posts: 140
Hi, in some previous posts you can find my experience on similar problems. I write these things because I messed up and problems with I was also caused by the Fake Sat receivers of Spektrum, in practice I found myself without any control of my heli trex 250, then I eliminated the electrostatic discharge but I had a problem with the esc, I never passed the test, there was a high absorption by the servos, and I had to use a new esc with at least a continuous internal 5 amp bec, from 25 amps, I discovered that I also had to update the control unit boot loader, because even that gives problems, I don't speak of the firmware, but of the boot loader.
My advice besides silicone spray and copper wire bridge to ground the frame, pay attention to the receivers (spektrum false) and the boot loader of the control unit,
and make sure that the test of the bec passes on the control unit


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