"drunk" 450 Pro DFC?

[Bronek]

What do you do when your heli behaves like "slightly drunk"? The heli in question is Trex 450 Pro DFC with AR7200BX (i.e. BeastX). And by "slightly drunk" I mean : acting in accordance with "general direction" of Tx commands, but as if the setup/servos/motor were off, by large amount.

Here is the story: I put my Trex 450 on a shelf after nice and uneventful flying, picked it up few days later and it performed terribly. The air temperature about 5 Celsius, the battery not the best I have. Checks before start good - general directions of cyclics and rudder OK, battery fully charged even though not very well balanced, Tx range good. However after start the cyclics were slow to react, main rotor bogging down on pitch ~ 8 degrees or even smaller. Very difficult to maintain altitude in ground effect zone, difficult to change attitude. Finally when landing I switched TH at the height between 0.5m - 1m (hard to see the height since it wasn't close to me, I felt it might be dangerous to bring it close), hoping to at least land it nicely. However the heli developed suicidal tendency and just rammed into the ground breaking more than few bits. Broken main blades, bent main shaft and boom, mangled DFC head, broken gears in two cyclics servos AND one horn, torn one DFC link. All fixed now apart from head, so not much problem (I keep range of spares, including gears for my servos etc.).

My suspicion is on DFC links, but there might be other reasons. The main question is: what should I do next time when my heli develops such "drunken behaviour"? I suppose I should have landed it right after noticing it does not fly well, but what next? Disassemble head and redo the setup? Replace DFC links (trouble is, hard to see whether they are good or bad)? Something else?

I'm not keen on replacing everything in the heli just because in the first few seconds of flight the "general feel" is bad or close to unusable, but what do more experienced folk do?

[Obi Wan]

Hi Bronek,

Could it be the lipo + Cold weather. I have a few oldish lipos and if cold they perform really bad. Could the "drunken behaviour" be due to a low head speed due to poorly performing lipos in the cold?
Happened to me last week when a mate of mine tried to fly my 450 Pro DFC with cold lipos. Flew the same lipos today, but made sure they were kept away from the cold and they performed better.

Just a thought.

Paul

[milly0812]

"drunk" 450 Pro DFC?

Make sure your trim tabs are centred, the beast x will see any trim as a command. Also try a new mounting pad and you could try strapping the unit too. Did you move the heli before it initialised ?

[cjcj1949]

You might have low volts due to the lipo and cold weather. You can monitor this with a cheap programmable alarm that plugs into the balance connector. The sensor could be affected by the cold as well. Does the heli react correctly when just moved by hand (in the cold) with the motor disabled? The sensors should be ok in general, but some will probably fail in the cold. Perhaps a wooly jumper would work?

[Bronek]

Re: "drunk" 450 Pro DFC?

I use voltage monitor attached to balance lead. It's set to sound alarm at 3.6V which, under load, should be high enough I think. The alarm sounded some 4mins into the flight (which is not ideal, but acceptable) and then I landed, or perhaps crashed.

I also check trims everytime before start, they were zero.

[Stevec]

Cold lipo gets my vote. The dfc will be set up for a higher head speed than the older models so low head speed will probably manifest as a nod while hovering. The lower head speed from a cold battery will also make the tail less authoritative.

try bringing the lipos indoors before flying. Some people in cold climates use a chemical hand warmer in a cool box to keep everything up at 20 degrees or so.

theoretically if you charge a lipo In Really cold weather you could damage it, because the cold cells will accept more charge, and then the warm up under load and the voltage rises with the temperature and you end up with an over charged battery.

You dont mention how old the batteries are or what capacity and make they are..

good luck tracking it down.

/Steve

[jmackenzie]

Try adjusting the cyclic gain (dial 1) on your AR7200BX, if its to high it will feel soft and oscillate on the elevator axis, to low and it will be softer, slower and less direct.

[maddog7]

What Stevec says +1 :-)
D

[cjcj1949]

Cold lipo gets my vote. The dfc will be set up for a higher head speed than the older models so low head speed will probably manifest as a nod while hovering. The lower head speed from a cold battery will also make the tail less authoritative.

try bringing the lipos indoors before flying. Some people in cold climates use a chemical hand warmer in a cool box to keep everything up at 20 degrees or so.

theoretically if you charge a lipo In Really cold weather you could damage it, because the cold cells will accept more charge, and then the warm up under load and the voltage rises with the temperature and you end up with an over charged battery.

You dont mention how old the batteries are or what capacity and make they are..

good luck tracking it down.

/Steve

Do you have a source for that theory? I've measured volts on a lipo and it doesn't change by more than a mv going from 5 to 20 Centigrade. The max voltage that we charge lipos to is an arbitrary figure based on how many cycles we want. 4.3v gives a lot less cycles than 4.1V or even 3.9V, 4.2V is a compromise, not written in stone.

Only one charger manufacturer limits charge voltage to a lower temperature, and they use the temperature of the charger, which sometimes is the same as the battery.
Voltage drop with current does change a lot with temperature and it is easy to get the volts on load below 3V in the cold.

Cold weather charging may have to be at a lower current or to a lower voltage than warm charging, but I haven't seen any evidence on this. A lot of our rules date back to old lipos and lack of knowledge and may not apply to 25C+ discharge lipos, like the 1C charge limit.

To OP, does the heli work in the cold, just moving it by hand? It could be as simple as a dry joint or other faulty component. Heating the lipos is easy to do, but if they stay above 3.6V they should be ok, as they are providing enough volts. The electronics should work down to 3V a cell.

[Stevec]

[QUOTE=cjcj1949;943144]Do you have a source for that theory? I've measured volts on a lipo and it doesn't change by more than a mv going from 5 to 20 Centigrade. The max voltage that we charge lipos to is an arbitrary figure based on how many cycles we want. 4.3v gives a lot less cycles than 4.1V or even 3.9V, 4.2V is a compromise, not written in stone.

/QUOTE]

no I don't have anything written, but I am sure it was a topic Lucien Miller talked about on the all things that fly podcast a couple of weeks back. They were talking about squeezing some extra capacity into a lipo by charging in a colder environment, I am pretty sure the answer was something like what I said.


i am not a lipo expert but the way I understand lipos is they can be seen as a balloon and the temperature can be seen as how far under water you push that balloon.

if you inflate it at the surface you can submerge it and it just gets smaller(as it gets colder) but if you fill the balloon up 30m under water and then bring it back up to the surface (warm it up)it will over inflate and pop.

But as you say maybe this view only works on the older original lipo chemistry.
seeing as they are quite easy to overcharge I just thought I'd point out that if it is cold, you could actually overcharge it without the charger doing anything wrong. Whether that takes 3 cycles or 100 cycles off the lifespan we will probably never find out.

/Steve

[barney]

Check that the swash and links are smooth with no resistance. Electrics 'dry out' since there not getting an oil bath every flight. The small servo's have little reserve for any binding. Best to check whilst the model is cold in the environment you wish to fly in as the links may be going tight due to the cold.

Brian

[cjcj1949]

You can usually get more capacity out of a battery by charging slowly. Lipos don't behave like most batteries though. There isn't a chemical reaction during charge but an intercalation. They seem able to absorb more charge until they pop as well, so full charge is a compromise on safety and cycle length. There are many different chemical mixes as well and many manufacturer's claims. I used to think the manufacturer's were hiding information, but having read some of the research work, it seems we are at the limit of understanding on a very complex problem. More than 1C charging was considered dangerous a few years ago as it would make cells overheat. I tried it (at 2C) and found the cells got cooler. Giant Cod said that was nonsense and commercial suicide until someone else confirmed my findings. We still don't know the effect of charge rate and temperature on cycle length and we don't know if high C lipos last longer than lower C lipos. I would like to know if charging cold lipos is good or bad. I'd rather not charge them in the house. We know that discharging cold lipos is a bad idea.