401 in extreem cold

[flyinfool]

I went flying today just because it is Saturday and I finished building my Stinger 90 kit last night.
The temp was -11*F in the morning and got all the way up to -1 by 3:00 when I quit and went home to thaw my bones.
My last flight was my longest since it had "warmed" up.
About 3 minute into the flight the heli started to piro in the middle of a rolling tail slide. some how I managed to save it ( don't ask how, I had my eyes closed) and get it back level and into a climbing piro when suddenly the tail locked back in. I made a bee line back for a landing but the tail let go again, this time from forward flight in a slow turn and kept going in a slow piro. I hit hold and did a pirouetting auto to a safe landing on the ice.

I could not tell you if it was pirouetting to the left or right in either case, I was to busy to notice.

My question is, has anyone else flown a 401/9254 in sub zero F temps?

[DavidH]

The temperature operating range in the instructions states

-10C to +45 C
In Farenheit that is
14 degs F to 113 deg F

So I would say you operating the gyro in temperatures well below the range listed in the instructions. This is not the first time I have heard of problems with gyros that are being used in extreme cold below the recommended temp operating range in the instructions.

David

[z11355]

one of the key advantages of the SMM type sensor is that the onboard temperature correction
is built directly into the sensor (since it's a microchip anyway, measuring temperature is easy
since silicon structures are affected by temp).

so you may be outside the sensor's ability to accurately measure temp and correct for it.

my hunch however, would be more toward the physical side and lay most of the blame on
the servo not behaving optimally in the cold since it has moving parts and tight tolerances.

[flyinfool]

I tried it again today, the temp was up to 20*F and same thing, after a couple of minutes the piros started. This time I was hovering at about a foot waiting for it.
I think something is just dieing of old age and abuse. This 401/9254 has been through about 12 cases of fuel and 2 crashes.
None of the other 401/9254's or 601 or 611 at the field today were bothered by the temp.
I'll try a new servo first and then a new gyro. One or both of them is flaky.

[SteveL]

Did you get a kick of the tail before this happened?
Sound like a typical 9254 that is about 1 yr old.

When you land after this happens do you have rudder control?

If so, offer a little resistance to the servo and see if it gives up. If it does you need a new servo.

I just lost my airtronics I put in place of my 9254. I am seriously thinking of trying JR. Futaba has some serious issues with the 9254 and they will not recognize it. If they still made the 9253 I would go that route they las a lot longer.

[flyinfool]

Putting resistance on the servo has a nomal responce.
On the ground all is good.
I was thinking of trying a Hitec 6965 with the 401.
I am running LiOn with a 5.3V reg so the 6965 is at .09 speed and 100 torque. vs the 9254 with .06 speed and 47 oz torque.

[SteveL]

Mine both did really funkey things when they went bad.
The first one just signed out.
The second one I landed adn wiggled the rudder and it seemed to work.
I reached down and put pressure on the rudder servo and it acually ran away from the pressure. Straagest thin I have ever seen... Was like one of thos cars you had as a kid that would hit something and go the other way.
I don't know the frame rate of the hitec digitals...You may have to turn off the DS switch on the 401.

The speed should be fine because as you pointed out the torque is much higher so they will run close to the same speed under a slight load.

[Ivan]

It seems to me that several of the owners of older 401's had similar problems. They had attributed it to the gyro resetting in flight, causing the center position to be established in a different place, and the heli acting like you gave it a full deflection command on the stick and held it there. I was under the impression that the newer 401's had this fixed though.

Personally, I don't think I will buy another 401, mine has never been all that great. The difference between it and my 502 is like night and day, the 502 is much better. With the 401, you coudl spend considerably less and get a JR 410T which seems to hold better than the 401, but doesn't have in flight gain setting, which I rarely use on the 401 anyway. I don't think the 502 was all that much more expensive than the 401 either, so I think it would be worth the extra dollars to get that.

[flyinfool]

I own and use the 401, 502 and 601.
The performance is obvious between them.
The 502 is priced close to the 601/611.

I did finally figure out my problem.
It was not electrical in nature, unless you count the electrical pulses (or lack thereof) between the ears.

What happened was that we have an enclosed pit area for winter that is a little warmer than outside.
I had adjusted the belt tension in the pit area not thinking that when I went from 30*F to -10*f outside that the belt will be loose again. It was.

While I was changing the servo i noticed that there were a few teeth missing from the belt, well maybe more than a few.

The worst part is that I know better than to not check the belt tension at outside temp.

I feel so silly now.

[svein]

Can we add this thread as a standard place to point the NEXT guy that tells us how the boom doesn't contract in the winter?

//Svein

[Ivan]

That makes a lot of sense, now that you say it.

It is amazing how much the belt will tension and loosen in the winter, just form going inside to out side.

Glad you found the problem.

[flyinfool]

What snuck up on me was that I did tighten it in the clubhouse at 30*F and never even thought to check it again outside at 10 below zero.
I am one of those that is always preaching about how the boom shrinks in the cold.
The boom contracted enough for the belt to slip and rip the teeth off of the belt.
The first time it let go was in a rolling tail slide so there was plenty of load on the belt.

[DavidH]

Glad you figured it out Jeff. Also be aware that the same can happen in warm weather also. Model been sitting in cool house a while. Belt is adjusted in the cool house. It is not tight but just right. <G> Then take the model outside in 95 deg plus temps. Belt is so tight you can play it like a guitar string. <G> It won't skip a tooth, but it does put some pressure on the bearings.

David

[flyinfool]

I here ya. :cool: