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ctu-mrs / mrs_uav_system

The entry point to the MRS UAV system.
https://ctu-mrs.github.io/
BSD 3-Clause "New" or "Revised" License
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Flight autonomy of F450 drone #62

Closed fmukwege closed 3 years ago

fmukwege commented 3 years ago

Hello MRS team,

Me and my team have built 4 drone f450 following the configuration on the https://ctu-mrs.github.io/ and following this issue #15 .

We experienced a flight autonomy around 3 min, which is pretty low : The NUC is powered directly from 4S battery (just like @DanHert mentioned in issue #30 ), the same battery which provides voltage to the power distribution board. During flights, whenever the battery is approaching the 12V, the drone lands and the NUC turns off a while after.

We wonder if you have also such short flight time, and if not what did you do to extent the autonomy of your 4S battery-powered drone ? How many minutes can you currently fly with this previous setup #15 ?

Best regards ,

Frank

DanHert commented 3 years ago

Hello, with a 4S 6750mAh battery, we get 10+ minutes of flight, dependant on the mass of the UAV. Can you specify exactly what battery you use, what are the motors and propellers and what is the mass of the UAV?

And by the way, 4S battery should NEVER reach 12V, if it did, it is likely damaged. We set our lipo alarms to 3.5V/cell (14V for the whole pack), and when they go off, we land immediately.

Dan H.

fmukwege commented 3 years ago

Hello @DanHert ,

thank you for the fast reply I forgot to mention that , to power the NUC, we soldered a DC plug at the DC input of the Holybro Power distribution board. This DC plug is connected to the NUC power input.

For a drone of 2.35 kg (everything taken into account) , we use :

Has the alert been setup in QGC or in the px4_config.yaml ?

Best,

Frank

DanHert commented 3 years ago

Hello, the alarm is an external one, like this: download It is plugged to the balance connector and it will beep loudly when the alarm voltage is reached.

Did you charge the battery fully? (to 16.8V). Is the battery new, or old? 2.35 kg is on the limit of the payload capability of this configuration, but you should still get more than 3 mins.

fmukwege commented 3 years ago

Hello,

I am confused : isn't the max voltage for a 4S battery 14.8V ? As it is mentioned on the datasheet ? When we charge, we go up to 14.8V-15V sometimes, but it won't go higher.

The batteries are 6 months old.

DanHert commented 3 years ago

14.8V is the nominal voltage (3.7 V per cell), but at this voltage the cells are less than 50% charged. You need to charge them to 4.2 V per cell for flight, that is fully charged. Learn more here - https://learn.adafruit.com/li-ion-and-lipoly-batteries/voltages

Dan H.

fmukwege commented 3 years ago

Well well,

We made a misunderstanding, we will correct that. Thank you for your answers !

fmukwege commented 3 years ago

Hello again @DanHert ,

I forgot to ask but to make the drone lands automatically when the battery voltage goes below 14V or whatever the threshold, what are the parameters and config files that I need to change ? (like min_voltage in mrs_uav_general/config/px4_config ?

DanHert commented 3 years ago

Hello, you can do this with Pixhawk settings, but you need to properly calibrate its voltage measurement correctly. But I am not sure if this feature will work properly during autonomous offboard flight (we never tested that). We do not use this feature, we simply monitor the flight time and the lipo alarm, and land the drone when the battery is low.

The system will also land the drone automatically when the thrust needed for flight is over 80 percent of the max thrust, which will happen when your battery is dying. But you should never reach this far, as the battery will be damaged.

The battery voltage is also sent from Mavros to the onboard computer, so you can easily program a node that will monitor it and land the drone when the voltage is at a specified level.

Dan H.