CSM SL720 and cold weather

[steveru]

I've been using a 720 gyro on my Trex 600N for most of the year with great results until last weekend. My helis were transported the few miles from the warmth of my dinning room (very understanding wife ) to our clubs field. On arrival the snow was swept from the table and the helis placed apon it and fuelled up. After about a 20 minute acclimatisation period I connected a fresh 2S lipo, switched on the regulator and waited for the gyro to set. I waited and waited but it didn't set. I power cycled the reg and again waited for the gyro to set, but it didn't.
Thinking that the problem was probably due to the cold I grasped the gyro to warm it up and after a few minutes I switched on the reg and was glad to see the gyro set.
After an enjoyable 10 minute flight I landed, switched off and refuelled for my second flight. I was very surprised and concerned that when I switched on the reg the gyro failed to set and required warming before it would set again.
I recieved a very prompt reply from CSM Tech Support who explained that their gyro's are tested down to -15C and that it shouldn't of been affected by the -2C at the weekend. They reckon that the problem could of been caused by low voltage due to the cold temperatures. I find this hard to believe as I use a 5.8v Align regulator which was showing all green lights.

Any ideas??

Has anybody else had problems with their gyro's (720 or other) in cold temperatures?

If gyros are affected by cold temperatures what are the chances of it failing during flight?

Regards,
Steve

[tonystevens]

im using a 720 and it worked fine this weekend,cant say the same for my lipos though

[debrooker]

had the raptor out in the snow on Sun, also using 720 with no issues.

[daren]

It was -4 at our field the weekend, 720 worked fine on mine...sorry i can't help

[Rotorhead]

Weird they would say its probably low voltage, like you say a reg will kick out what ever its supposed to aslong as its supply is high enough, and in the cold lipo's voltages go up a bit.

[Ashley Davis]

I've flown my 720s for the past 5 years in extreme cold and never had an issue, in fact one session it was so cold the rx wouldn't work let alone the gyro.......you know it's time to pack up when that happens.

and in the cold lipo's voltages go up a bit.

down a bit you mean, that's why electric heli performance is shit in the cold.

[Mike W]

Was flying in -2 and my 720 was fine as well ... prolly down to lipo by the sounds of it

[Tolly]

Had very similar thing at the weekend, not with a gyro but with a csm cyclock, got to the field on Sunday and went to fly with my 600 and the cyclic and pitch where total dead. when I got home I checked things out and everything was working fine. I also put this down to the cold weather. I have removed the cyclock and setup the normal swashmix in my tx just to be safe.

Cheers
John

[moyesboy]

All my 720s have been out in very cold weather quite regularly with no issues.
The lights on the 2in1 mean that there was no lipo issue.
I've also been using the 2in1 in the cold with no problems.
The evidence that warming the 720 made it work suggests it really is the gyro, but CSM say it is spec'd to run down to -15c.
There could be some other cold effected problem with a connection between rx and gyro. Check it out and try replacing the leads perhaps?
If you can't find aproblem outside the gyro send it to CSM for a check out. Ask them to check it in the cold- its probably about -10c at Colin Mills farm in Glossop right now!

I would be very reluctant to fly when the gyro only started working after you warmed it with your hand.

I assume that all the other channels were working and the problem wasn't the rx failing to bind? (ie like happened to Ash).

[trvo]

I've been using CSM gyros for quite a few years now, even flown in 1ft deep snow whilst still snowing (T-Rex 700e) and not had an issue with the cold. It's more likely for the rest of your electronics to fail first.

Trev

[Rotorhead]

down a bit you mean, that's why electric heli performance is shit in the cold.

Nope, voltage goes up, capacity goes down.

[Ashley Davis]

sorry still wrong.

Cold slows the chemical reactivity of lithium polymer cells. So in the cold the ability of the chemistry to release ions reduces. This equates in our simplistic view as a voltage drop but in reality it is a slowing of the packs chemical reactions and an inability to release charge (ion flow). If you measured the voltage using a meter it wouldn't have changed, under load it will DROP as the pack cannot deliver the demanded discharge. The pack will generate heat internally whilst it operates, in effect warming itself and increasing it's ability to release ions. In very cold conditions we often see this as a very sluggish powerless heli in the first 30 seconds of a flight and then it all seems to improve (ie. the pack got warmer internally from delivering the high current demand).

Lithium polymer delivers it's best ion flow at around 60C this is why on discharge charts you very often see a drop in voltage at high discharge currents followed by a gain in voltage, the drop in voltage is the pack failing to deliver the required amps but this generates a lot of heat, which increases the packs ability to deliver charge and so the voltage then increases again.

Capacity is a separate but related issue, at 0 degrees a lithium pack has a reduced deliverable capacity of 90%, this drops exponentially as you go below zero degrees. At around -20 you only have about 40% capacity. This is only 'delivery' capacity, ie. how much charge it can deliver at that temperature. This is why you MUST reduce flight times in cold weather as the pack will not be able to deliver it's full normal capacity of charge.

Charging in the cold is another issue, once cold the pack gives a false reading on it's capacity. So it will say it's 40% charged but in fact it's full charged (at -20C). The charger will continue to deliver charge to the pack until it reads 100% (or more likely explodes). This is why cellpro chargers have cold charge protection, they reduce the amount of charge (capacity) they put into the pack at low temps.

[Rotorhead]

I am only talking about the case that the OP probably would have had, charging in the warm, then taking the pack into the cold, doing that will cause the voltage to rise.

Which would make the claim of a low voltage situation unlikely, and since we are on about pre-flight, no real servo loads, there isnt going to be much of a voltage drop from a load, and since its a 600N then its not going to have any load from a motor.

If you re-read the opening post, he said he took the heli from a warm room out into the cold and had trouble, if anything the idea that it would have been low voltage is dubious at best.

Anyway, I've just been out flying with two helis with 720's on each of them, no problems.

[robgt]

The voltage won't rise...

Cheers,
Rob

[Rotorhead]

Just done a quick and dirty test, I have a Kokam 3200mAh 2S pack that has been in the warm at a voltage of 8.09, took it outside its only been out ten minutes and its voltage is already up to 8.26v.

I think I'll stick to what I can see

It doesnt seem like I'm alone in this either....http://www.rcheliaddict.co.uk/main-d...ld-li-pos.html....http://www.rcheliaddict.co.uk/batter...o-storage.html