Spektrum DX6 Transmitter Voltage Drop

[Pipistrelli]

I had not flown my Trex 450x for a while owing to a bump that pulled the feathering spindle apart (without breaking my 315 Pro blades!) and lost all the dampers and spacers.

I ventured to Inwoods on NYE to get the bits, went home early fixed the heli and there was enough time to test it before it was time to party. I hadn't flown for a while, so I turned on the DX6 Transmitter to check the voltage....................9 volts and holding, so good enough for a quick test.

I engaged Throt Hold, connected up the heli, disengaged TH and tentatively started flying. I just wanted to make sure everything was as it should be. Hovering ok, then after about 3-4 minutes, the heli lost control, smacked into the ground, onto its side and shredded my favourite Pro blades. Hitting TH switch had no effect, the motor started screaming because it had stripped the main gear, so I quickly had to disconnect the heli battery. I was seriously not happy!

When I checked the TX, the LCD screen was blank so I turned it off then back on again briefly, the screen came to life for a moment and the alarm started to sound for the first time before the screen went blank again . The Tx voltage had dropped so quickly the alarm DID NOT sound . The 1st thing I knew about it was when I had lost all control! I recharged the Tx pack and it took 1498mA (rated at 1500)!

Still, these Rex's are tough, after all that thrashing around all I had broken was a set of Pro blades, stripped main gear and broken a ball off one plastic flybar mixing arm!

Has anyone else had a similar incident of Tx voltage dropping so quickly that the low voltage alarm didn't sound? I know I hadn't used it for a while, but to drop from 9 volts over a few minutes was really not expected!

[pchristy]

It is a characteristic of both NiCAD and NiMH cells that they hold a pretty constant voltage right up to the point where they go flat, and then drop very quickly. The better matched the cells are, the quicker the drop will be, as all the cells will go together.

The fact that your battery took 1498mAH on recharge indicates that it was stone flat! Any voltage that you were reading was residual, and clearly wasn't an indication of the state of charge that it held.

I don't know how many cells the DX6 has, but if its an 8 cell pack, like the DX7, then the nominal voltage should be 9.6 volts (that .6 is important!). Anything less than 9.6 should be treated with great caution!

NiMH cells don't hold their charge as well as NiCADS when left idle. They tend to self discharge, though modern cells are much better in this respect.

The moral is: Always make sure you cells really are charged before you attempt to fly!

--
Pete

[moyesboy]

ALSO
you checked the tx and it had 9v in the warm of your house
then you went outside and flew the heli
The batteries would also reduce in output as the cooled!

9v is pretty darn flat at initial switch on.
When fully charged it gets up near 11v

[David Drew]

Did that with my Raptor once - way back & learnt my lesson.

I always keep the Tx fully cahrged and would never risk it again.

[Pipistrelli]

Thanks guys,

The DX6 is an 8 cell stick pack and I assume it is NiMH because of the 1500mAh capacity.

I usually fly right up to the low voltage warning tones (at 8 volts), then swap for a fully charged spare pack, that way both packs get cycled regularly (with my FF9), but because this Tx is only used on my 'Rex. It doesn't see as much day-to-day use and I did think it might be flat, but was surprised when the voltage was as good as 9v.

I was wary about this and only intended to test fly the heli for a few minutes. However, I was shocked that I didn't get a LV warning alarm and just lost control. I know its all my fault, but just really surprised how quickly the voltage decayed! It won't happen again!

[David Drew]

Don't you just cus when you do something stupid. I now take a big 12v batt & charger with me just to top up Tx & Rx packs. Better safe than sorry.

David

[pchristy]

Pip,

8v is way too low! You need to stop flying when it gets down to 9, if not earlier. As soon as the pack drops below 9.6, it is getting on the steep part of the discharge curve - you are in the danger zone!

This is especially true if the cells are well matched, as they will all drop off together! The better the pack is, the more suddenly it will drop!

--
Pete

[Pipistrelli]

Pip,

8v is way too low! You need to stop flying when it gets down to 9, if not earlier. As soon as the pack drops below 9.6, it is getting on the steep part of the discharge curve - you are in the danger zone!

This is especially true if the cells are well matched, as they will all drop off together! The better the pack is, the more suddenly it will drop!

--
Pete

Pete,

Thanks, noted and I will act on this as of now. Although I thought nickel based cells were classified as fully discharged at 0.9 volts, so an 8 cell pack would theoretically be totally flat at 7.2 volts.

My concern was that the alarm didn't sound to warn me of low voltage though!

[pchristy]

Pip,

from the information you've provided, the pack was almost exhausted. It probably went so quickly that the alarm did not have chance to sound!

NiCAD / NiMHs shouldn't be discharged below 1.1 volts per cell in an ideal world. By the time they get that low, the discharge curve is almost vertical!

--
Pete