For most people running electric vehicles, it has always been assumed that the motor(s) will always use far more power than the flight controller and associated control systems.
However, for those people running internal combustion engines (or gliders, balloons, etc) for long duration flights the question of power consumption of the flight controller becomes a much more important question.
I spent some time measuring the power requirements of a Pixhawk flight controller and thought I'd share the results with the community.
I cut up a USB cable in order to run it through my multimeter. The same was done for another cable with an XT60 connector. This would allow current readings over both USB and battery power.
Over USB power a standard Pixhawk setup (Pixhawk running APM:Plane 3.3.0, GPS/Compass modules, safety switch, buzzer, 433 MHz telemetry radio) a total of 280mA current is drawn. Breaking this down by component gives the following plot:
Of note in the above pie chart is the GPS module uses almost 1/5 of the total current requirements. The Pixhawk itself uses the vast majority of the power, as expected (with its comparatively high-powered CPU and many diagnostic LED's).
There was very little difference with the APM:Copter and APMRover2 software running in both armed and disarmed states. All 3 APM branches are consistent with their power usage.
Moving on to the other 2 power supply inputs (Pixhawk power module, ESC into servo rail), it was noticed that the main LED on the Pixhawk is very high powered - on the order of a 1/2 Watt.
In comparing the different power supplies, using total power consumption (Watts) is most appropriate. Note when using USB power the USB port on my PC was measured to be 4.5V rather than the 5V standard.
The above chart uses a full (GPS, compass, radio, safety switch) setup. The “min” and “max” refer to the power draw with the main LED of the Pixhawk off and on respectively.
The Pixhawk does use more power when connected via battery. I put this down to the various LED’s (and possibly a few IC’s) using more power as they would be operating at a higher voltage (5V clean power vs the 4.5V USB power).
The difference between the power consumption via the Power Module and via the ESC would be likely due to a lower efficiency 5V regulator in the ESC. However, the gap (~0.3W) seems a little wide to account for all of it. Some of it may be due to the way power is routed through the protection diodes in the Pixhawk.
Next is a comparison with the old APM2. The APM2 uses a far less powerful processor (both in terms of power usage and data processing capacity) and has fewer sensors on-board. So it would be expected to use less power:
The APM2 uses roughly 1/3 as much power as the Pixhawk (not including external components). The APM2 is remarkably efficient with its power usage – a maximum of 0.5W!
Putting this together with the appropriate external components and a standard Lipo battery gives us an expected operational time:
Once the GPS, radios, etc. are included, the gap between the Pixhawk and APM2 narrows. Using a standard 3-cell 2000 mAH battery gives in excess of 8 hours operating time for a Pixhawk and over 10 hours for the APM2, which allows for some very long-duration flights.
In conclusion, for a standard Pixhawk setup, allow 2 to 2.5W power consumption. If this is an issue, look at disabling the main LED and removing non-essential external components.
If power consumption is truly important, it would be worth going back to an APM2, which only uses 0.5W by itself.
How do you disable the bright LED. Is there a parameter, or does it require some custom programming?
hello,Stephen Dade.I am starting with 3DR project.now,I have some problomes with building 3DR ground station. can I ask you for help? Thank you.
Bill Bonney: That's an interesting one! It couldn't be any of the sensors/cpu's browning out, as we would've seen the APM software crashing or resetting.
My best guess is that it's one of the 5 -> 3.3V power regulators being more efficient at a lower voltage?
I did some tests. If the voltgae drops below 4.8V i.e. @4.7V it draws 280mA, but at 4.8V+ it draws nearer 480mA (ie.at 5V)
Using the Power Module suppled at 12V its 180mA, and 16V its 140mA.
I wonder what cuts out below the 47V threshold that consumes 200mA?
Your conclusion that Pixhawk needs about 2-2.5W seems correct, as that is the standard for USB2.0 port see https://en.wikipedia.org/wiki/USB#Power, and some users have USB issues as their computers USB ports struggle to supply that.
2.5W @5V is 500mA (At 4.5v you need 555mA), but you only measured 280mA, and on my lab PSU current meter I usually see 500-600mA with a Pixhawk plugged in (this is a powered USB hub powered by a the Lab PSU). I'll verify this evening when I am home.
The APM was about ~300-350mA with Telem
Disabling status LEDs would save only a milliamps at most, but I would be curious to know if the Pixhawk takes advantage of the CPU's Intelligent Energy Management - a feature that allows for dynamic clock frequency variation and voltage scaling to reduce power consumption.
Disabling the LEDs on the FC and button would change nothing. Their power consumption is literally negligible. You probably couldn't even notice it on most meters.
I wonder - wether it is possible to disable ALL LED's in flight. It may save an occasional watt, especially given the fact, that in an airplane, the flight controller unit is encased in an airframe and is not visible.
I did some measurments on the radio (433MHz version) for the power consumption - and found, that it may be possible to optimize power consumption of the radio, as in some cases the full power output is not needed, and can safely be lowered on the airborn side
I have a LIDAR Lite, RFD900 at 26db, and dual GPS as well.
I wonder how many watts i'm pulling. Probably double those numbers!
My motors-off power consumption is about 12 watts. On a 4S battery, that's about 800mah. That includes:
- Flight Controller (Pixhawk with single GPS/Compass and all usual attachments)
- Communications (Telemetry radio and UHF RC Receiver)
- Video System (Video transmitter, gimbal, and mobius power)
- Lighting (LED position and strobe lights)
If I shut off the lighting and video, it comes down to about 500mah.