Hi,
I have a strange issue. I can fly my apm 3.1.15 quadcopter perfectly when i'm using my 5000mah Zippy 20C 3S battery. However when i put in the 1600mah zippy 20C 3S battery i can't take off without flipping the quadcopter and landing on it's back. I've tried three 1600mah batteries with the same result. but as soon as i put in the 5000mah all is good. I took a quick glance at the pids but they seem to be on default values. The only theory i could come up with in my head is that weight of the 5000mah battery was some how balancing the copter.
Bear in mind, i've ran the compass calibration, got respectible values, and i've also done compassmot and got very respectible values. i'm not too sure whats wrong. Any help would be appreciated.
Replies
Thats just pure logic Steve. Good idea, i'll give that a go over the weekend.
Simple test: put a weight on top of the 1600 battery so that the total weight is the same as 5000, if it doesn't work you can rule out all possible inertia related explanations and concentrate on the current drawn.
EDIT: too slow :)
CG on a quad is not a real issue unless it is a) way off b) your motors are already running near max c) very bad weather.
I've hung a 2L bottle of water off the end of an arm on my hex and it "just works". Struggles - sure - but it manages.
All an out-of-whack CG will do is cause some motors to work harder than others in a hover. With bad wind or certain maneuvers then those motors might not have enough grunt to correct the attitude and you'll have a crash but for something as simple as this - I can't see it being a problem unless.... you're mounting the 5Ah battery at the end of an arm which is actually balancing out everything and the smaller battery centered. Still, it won't flip but rather just struggle to sustain level hover.
Check the current draw - your smaller battery does not have enough juice (as per maths) and the APM or ESCs are browning out / shutting down due to low voltage.
I hope he's disabled all four ESC LVC's at the very least. I set them to NiCd if there is not a 'disabled' choice.
This may be a silly question but, when you swap in the 1600mAh battery, are you re-checking your CG? The weight difference between a 5AH and 1.6AH LiPo is considerable and unless you are re-positioning the smaller battery to compensate, the shift in CG could easily topple your copter on takeoff.
Unless all your batteries are physically identical and are always mounted in the exact same location, you'll need to re-check your CG balance fore-aft and left-right each time you swap in a different battery.
Hi Brian, If you're getting a perfect balance when you lift the airframe at its center points with the 1.6AH then it's time to review your log files. I would add the CTUN option and then try to lift off. If it flips over again then you can review the control loop data as well as the power curves/voltages of your motors to see what's happening.
If you think the 1.6AH batteries may not be supplying enough current you could try making a Y-cable and run 2 of the batteries together in parallel. That would double the available current to 3.2AH and provide a pack closer in weight to your 5AH battery. I actually have a pair of 40C 2.6AH LiPos that I run this way without any issues — held together with Velcro.
How can I tell how much current is being used?
Assuming you have a power module and that it's calibrated, your APM/Pixhawk will record battery voltage and current. Playing back the logs, you will be able to see see voltage and current in the graph like this:
If you have telemetry, you can view your voltage and current live in Mission Planner in the bottom left of the HUD:
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