Before lift off, my Quad battery indicated 1 green light bar left (which means 5 minutes of fly time left).While elevated into the sky, the LEDS began flashing red, and then it started flying erratically (in place). It seemed like one of more motors or were failing. Unfortunately, it began to fall sporadically from about 100 ft. Seemed like it was fighting to gain stability, but ultimately lost and free fell about 15 ft to ground. Wow- what a mess. I put Humpty Dumty together again, and it still works. Can anyone provide an insight into why the erratic sky dance with 5 minutes of battery left?
Even though the battery indicator showed 5 minutes left, as a general rule you should never take off without a fully charged battery. The indicator is just a reference, not a actual flight time left. Things like load (payload), wind, or even how hard you push the throttle will effect actual battery flight time......hovering takes more power than flying as well as the motors / propellers are not running at the most efficient speed.
I was particularly interested in the erratic behavior. I understand these Lithium batteries have "cells." Does each cell control a specific motor? If all cells work commonly together, wouldn't it slowly lose power and drift to the ground in a stable descent? I thought this model landed itself on low battery. Thank you for your advice!
The entire 12v goes into the main board and then out to the motors at the full voltage - the cells work together since there is just one connection from them to the quad. In general, I would not either fly with less than 15-20% battery....and would not take off without at least 5 minutes or more of flight power. It may be possible to tweak some settings in the DJI software setups to tell the quad to wait a bit longer before it goes into automatic landing modes, but the stock setup should be the best. I learned the hard way when my DJI was far away and I tried RTH - it didn't have enough juice to do so - instead it landed itself right in a grove of trees! I got really luck on that one!
You could of been at a extreme low voltage that the electronics needed to work properly, this could of caused the behavior you saw. Each cell in a LiPo battery is approximately 3.7 volts, a one cell would have 3.7 volts of voltage, two cell would be 7.4 volt, 3 cell 11.1 volts, and so on. A cell is like one battery, they are wired internally in a series connection. Most LiPo's are "safe" down to 3.2 volts per cell, anything lower could destroy the battery (worst case catch fire). and charging a LiPo should not take them higher than 4.2 volts per cell, same thing higher could destroy the battery or make the fire come out. It is better to store a LiPo charged, this will reduce the possibility of the battery being damaged if the per cell voltage goes low.
You have confirmed my suspicions that something more than "low battery" went on. Your auto landing looked a LOT smoother than mine. I did notice a bit of turbulence right before descent into tree.
Not sure about the 2 and 2+, but my old stock Phantom will descend and land at about 11.4 volts, which is about 3.8v per cell. Many NAZA (flight controller) users seem to disable or turn these down, preferring other timers or alarms or the on-screen telemetry to know when to land. It depends on your confidence and experience. No doubt that the automatic modes can sometimes mess you up - but for the larger mass of operators, they are probably good. Here is the DJI wiki on the voltage monitoring: http://wiki.dji.com/en/index.php/Naza-M_Voltage_Monitor
Could be but my machine was very light weight at the time - I think it was Mobius onboard. The 2's are quite heavy due to the large battery. When my stock Phantom is flying my heavier cameras, it acts more like you describe - i.e. drops much quicker. I'm going to try turning the voltage warnings down a little lower and see what happens. I suspect that it will work fine with light loads (slow on the sticks and throttle and less weight), but that it will act up when more loads are pressed upon it.
Directly from battery manufactures, by day I am an engineer and work with these a lot. Panasonic, Sony, and other good manufactures wont sell LiPo's direct to anyone unless they are certified as a battery pack builder and know how the protection circuits work. All properly built LiPo packs will have a low voltage cut off circuit and a high voltage charge cut off circuit built in, some will even have a thermal circuit to cut of the power if the battery is too hot. Cheap LiPo's will skip these circuits to keep costs down, but at the expense of the consumer.....The AMA even posted a fact sheet on LiPo batteries, found here http://www.towerhobbies.com/help/ama_lipo/
I can confirm that the P2+ can act really strange at under 30% battery! This is a result of the intentional programming - it can probably be slightly modified in the DJI Assistant, but doing so may endanger your craft. There is a good reason for the warning and low voltage settings. Today I was up at about 200 feet taking some pics - and the battery was about 30%. I had the sound very low on my phone, so I didn't hear the warning start - but I did know the % and started to bring the quad down. At about 25% battery, the quad started falling FAST - obviously it's internal programming saying it would be wise to get near to the ground. It would not respond well to stick input telling it not to drop quickly. I thought it was crash time - although it was not falling like a rock. It was falling fast enough to hurt it if it contacted the ground. At about 30 feet above ground it stabilized itself and continued toward the ground and actually bounced off the grass - then I was able to get some control although the craft was obviously telling me it wanted to be near the ground. All this is as it probably should be....to some degree...as default settings. But it's certain scary watching it fall quickly.
