I have a 2250mAh 11.1v 3 cell battery that I'm using for my 450 kit build, motors are 1000Kv motors.
Using a Pixhawk with the PX4v1.3.3 flight stack, loaded via QGC.
And I'm using an Imax B6 charger for the battery. Battery is brand new.
This is the issue; I will plug the battery in, with the props off, as a system check. I can throttle it up all the way, no problem. QGC says batteries are at 100%. External voltage meter says all 12.1, no1 4.03, no2 4.03, no3 4.06.
System check looks good, so I put the props on.
I get the UAV up and within seconds, QGC tells me that the battery has dropped to 33% and the Pixhawk battery alarms go off. The external voltage meter, that is set at 3.6, does not go off.
I keep it up for a few more seconds and the battery level drops to 17% and the alarms go nuts. I set the UAV down, for a flight time of mere seconds.
I will then unplug the UAV from the battery, wait a second, plug it back in and reboot. QGC will say the battery is still at 100%. External voltage meter hasn't changed.
So with the props off I have no issue, but as soon as I put the props on, the battery can't seem to handle it.
What am I doing wrong?
Thanks you for any insight.
Cheers!
_M
Replies
Counterclockwise rotation results from more force from the props that rotate counterclockwise compared to the props that rotate clockwise. Most of the time it comes from an upside down prop, but anything that reduces power from one motor can cause this.
Since you know, without a doubt, that the props are correct, motors all spin in the correct direction, and the motors are all assigned correctly (esc wires are not switched around) THEN you need a bench test.
Without the props installed, arm the drone in stabilize mode and hold it up in the air, run the motors at a slow speed. Tilt the drone, left, right, front, back,You should be able to get some idea if the motors on the lower side of the drone increase in speed as the motors on the higher side slow down. These motors are designed to be run under load, so don't push it, don't run at full speed, and only for a very short period, like, a minute or less.
Some people condone this type of test outdoors with the props installed, so as you hold on to the drone as the props are spinning you can feel the direction the drone is pulling. This may work well but its very dangerous. If you consider it, you should have someone else hold the drone while you operate the controls. I was cut trying this by myself and was very lucky, I will not do it again, however I have a big heavy drone, smaller, lighter, may work without such risk.
The object of the test is to physically see and understand the responses by the drone. Your issue should become apparent.
HAHAHA, I've certainly cursed that same line during my progress through the hobby trying to build my Hexacopter. I can assure you that once you get things working and flying well, especially with the ability to do Autonomous missions, it will be worth it! Hang in there!
mark bellncula said:
I have my props labeled properly, so that I mount them correctly, and I can assure you that the motors are spinning in the correct direction. If there was a miss mounted prop or an incorrect motor spin the quad would flip. It spins flat.
Guess I'll double check everything and recalibrate.
_M
UPDATE
I rebuilt my quad. Some of the solders on the PDB were "weak". I replaced the PDB and upgraded to new 4cell. Happy to say that the power alarm issue is gone.
But now I have a wild counter clockwise spin issue, that I didn't have before. It spins really fast, so fast that trims will not counter. It didn't spin before when I had it up for seconds.
So... one problem solved and another one started.
To all those people who bought DJI's and flew them out of the box... I hate you.
Bringing this back up. I have the latest QGroundcontrol with the new battery calculator on the Power page.
I also have a Power Meter inline on the drone. Here are the numbers I registered:
Battery: 5200mAh, 3S, 11.1V, 15C
454.4 Wp (
28.2 Wh
2.542 Ah (Capacity Drain)
40.32 Ap (Max Current Draw)
11.01 Vm (Minimum Voltage)
Under stock settings, the alarm went off when there was 52% battery left (measured on charger), measuring 3.82V per cell. So with 2.542Ah drained out of a 5.200Ah battery, that is correct.
So if the alarm is going off, I have some parameter wrong. So if I use the new Power Voltage and Amps per Volt calculators what values do I use based on my power meeting readings?
For Voltage Divider: Do I put in Vm, which is 11.01 Volts?
For Amps per Volt: Hmm, what do I use, Max Current Draw, which is 40.32 A in this case?
I am trying to find the forum link that explains this calculator, but haven't found it yet. If anyone has any insight, let me know, thanks!
Derek
I'm not sure if this is the problem, but there's a significant voltage drop on Lipo's when a load is applied. The current drawn while spinning the motors without props is tiny, but with props on the current drawn by brushless motors can be very high.
For example my Hexacopter shows 12.6V sitting on the ground with a fully-charged battery, but as soon as I take off the voltage immediately drops to about 11V and then slowly drops to 10.1V (about 3.4v per cell) when my battery alarm goes off. At hover my copter pulls about 30 Amps on a 3S Battery and I get that large of a drop even with a 5800mAh 35C battery. After the alarm sounds and I land and stop the motors, the resting voltage bounces back to about 11.5V.
Can you try to fly with the voltage meter/alarm attached and see if the low voltage alarm is triggered on that? That should tell you whether the voltage on the battery is actually dropping under the load of the motors or if it's just a calibration issue within QGC that's prematurely setting off the alarm.
Sorry I can't help with QGC as I use Mission Planner for my builds.
Harry & John,
Your analysis seems the most plausible. I can see how "voltage drop" could be the issue. I'm going to look into this, rather than relying on a new build for QGC. Thanks again for your informative replies.
Cheers!
_M
I have a heavy drone (I should have listened to the good advice when I was planning my build)
As such I need big batteries. My battery education has been expensive. One of your priority's needs to be preserving your battery. Its very simple to damage the battery, reducing its capacity, and you may not even know it.
A good article on understanding batteries : http://www.rchelicopterfun.com/rc-lipo-batteries.html
skip down to "Lipo battery ratings."
First never discharge more than 80%. Second, don't allow the current to come close to the C rate.
Most think that as long as the voltage is over 3v/cell everything is ok, but that's not the case. The rule is UNDER FULL LOAD the voltage can never drop to 3v/cell.
Depending on your setup, during flight and under load the voltage drops, sometimes as much as 1.5 volts, after you land and you have no load on the battery, the voltage comes back up, making you think the battery was not used much at all.
The C rating is the maximum discharge current. The closer you are to the C rating, the more the voltage lag will be. As Alasdair stated the C rating is not to be trusted. I now use LIPOs with a high C rating so I will never exceed half of the stated C rating. That seems to work for me now with lass than 0.5v lag most of the time with a calm flight.
Mark,
As for how to proceed, I would get a battery monitor that will plug in between the battery and the drone during flight and will read max / min voltage, AND current. I put a link in the previous post for an inexpensive unit. Watch the min voltage during the flight. Watch the max current during the flight. Record you information, this info holds the answer as to whether your problem is just the settings in your ground control / flight controller, OR, you just need a better battery.
I suspect your in for a new battery, In this case, if you can handle more weight, you can max out the mah, its possible to go to 5000mah, with a C rating double your current battery. (your pic doesn't show a C rating on the current battery). Then monitor your battery, with resolve, to avoid damage.
I have personally destroyed seven large lipos over the past few years, simply by discharging to much capacity, partially due to the large voltage lag caused by drawing more current than the battery was able to handle. These LIPO batteries are delicate, and the rules are rigid, and the consequences are expensive, good monitoring, and constant analysis, are essential. Please keep us informed of your progress.
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