My Lipo's life with an Eagletree

[jurassic5]

Hi,

Just wondering if it was possible to track the lipo life with an Eagletree ? For example; eagletree one flight in Idleup on the TREX 450 and then look at a specific curve on the eagletree software and if it's straight, lipo is good; when it drops; lipos is close to death

any clues?

cédric

[redgiki]

Yes, it's possible, and I have. Unfortunately, I never backed up my EagleTree data, so when I had a hard-drive crash last year, I lost the history on my Common Sense R/C 15C batteries that lasted over 300 cycles.

What you do is just Eagle Tree the aircraft periodically, and use those as benchmarks for performance. I make sure to do it on the first few flights, and then periodically thereafter. I use permanent marker to number each of my packs, then put clear tape over the number (as it rubs off otherwise), monitor total pack lifespan and starting/ending voltage in a notebook, and every 30-50 flights make sure I check it again.

What you'll see on a sagging pack are:
* Lower starting voltage; whereas it was, say, 12.57v when fresh off the charger when new, it will be 12.4 or so.
* Faster starting-voltage cliff.
* Lower sustained voltage for most of the flight. LiPos are remarkably flat in discharge; basically, 30-60 seconds into your flight (sans governor), your headspeed should remain fairly constant in the rest of the flght until you near the end-of-charge cliff. That flat bit is the portion of the curve you want to check out, because that voltage "cliff" at the start of the flight doesn't tell you a lot; sustained-discharge does.
* Some packs exhibit deeper voltage sags under load when older due to their higher internal resistance. This hasn't been consistent across all my packs, though... some of them just drop the sustained voltage more, and drop the same percentage under load.
* Fewer mAh discharged in flight before reaching the end-of-voltage cliff.
* Fewer mAh returned to the pack for the same duration of flight (the voltage is running lower, so you're using fewer amps as well unless you compensate with a higher throttle curve or larger pinion).

If you use a decent-quality pack with longevity as a goal (so far, I'm really impressed with FlightPower Evo Lites), plan on 100 cycles or so in your T-Rex, then plan on the next hundred or so being in a lower-discharge aircraft. All LiPos sag over time; as long as they are reaching 80% of their stated capacity, they're still good. If the cells are well-matched, your balancer won't work very hard during the charge. Kind of an easy way to tell the quality of the pack assembly process.

[jurassic5]

Thanks,

Theses are my last eagletree shots with different kong power packs

can we get something of this ?

http://www.gamani.org/trex450/trex1.jpg

http://www.gamani.org/trex450/trex2.jpg

http://www.gamani.org/trex450/trex3.jpg

http://www.gamani.org/trex450/trex4.jpg

Cédric

[redgiki]

You have too much start and end time for it to be of much use if we're trying to figure out average watts and flight time. You can set up the Eagle Tree to not record anything until usage rises above a certain amp threshold. That would provide a more useful result.

If I were dead-set on using my Eagle Tree every flight to gather long-term power statistics, I'd want to use an exponential moving average for, say, the first 4 minutes of every flight. That would give you a nice line over time to watch the degradation of your pack.

I don't want to work that hard at watching my lipo lifespan, though. I like to just track voltage start, voltage end, flight time, and overall cycles. Gives me a good idea of when a pack is slowing down. I only EagleTree when I think there is a problem, or when I'm evaluating the power system.

[jurassic5]

For example, on my screenshots; a good idea would be to monitor the first 4 minutes of a flight to see if my lipos handle it well.

[redgiki]

Your packs look totally average for a 15C-20C rating. Up to 35A peaks are very normal on a T-Rex 450.