How reliable is the power consumption data in the logs?

cbk · December 31, 2022, 8:44am

Dear folks,

I’ve been lately working on modeling the energy consumption of my private label S500 variant drone. I test horizontal velocity, relative altitude, and payload as model parameters while trying to isolate others and environmental conditions.

What I primarily control is the “discharged_mah” and “voltage_filtered_v” parameters from the logs to calculate the energy consumption for a specified period. But, I encountered several inconsistencies there, like carrying a heavier payload resulting in less energy consumption at the same speed, altitude, and headwind; or flying slower causing more energy consumption.

So my questions are: (i) how is this discharge measured, and (ii) how reliable is the data available in the logs?

Many thanks, and a happy new year to everyone!

cbk · January 11, 2023, 1:05pm

Sorry for bumping up the topic, but the question is vital for an ongoing scientific research, so I’m quite impatient about it.

Cheers!

saengphet · January 11, 2023, 3:34pm

question (i) You can research deep into the source code how the discharge capacity works.
For general power module

github.com

PX4/PX4-Autopilot/blob/main/src/lib/battery/battery.cpp#L185


      
          		_battery_status_pub.publish(battery_status);
          	}
          }
          
          
void Battery::updateAndPublishBatteryStatus(const hrt_abstime &timestamp)
          {
          	updateBatteryStatus(timestamp);
          	publishBatteryStatus(getBatteryStatus());
          }
          
          
void Battery::sumDischarged(const hrt_abstime &timestamp, float current_a)
          {
          	// Not a valid measurement
          	if (current_a < 0.f) {
          		// Because the measurement was invalid we need to stop integration
          		// and re-initialize with the next valid measurement
          		_last_timestamp = 0;
          		return;
          	}
          
          
	// Ignore first update because we don't know dt.

For CAN power module

github.com

PX4/PX4-Autopilot/blob/main/src/drivers/uavcan/sensors/battery.cpp#L195


      
          	_battery_status[instance].is_powering_off = msg.is_powering_off;
          
          
	for (uint8_t i = 0; i < _battery_status[instance].cell_count; i++) {
          		_battery_status[instance].voltage_cell_v[i] = msg.voltage_cell[i];
          	}
          
          
	publish(msg.getSrcNodeID().get(), &_battery_status[instance]);
          }
          
          
void
          UavcanBatteryBridge::sumDischarged(hrt_abstime timestamp, float current_a)
          {
          	// Not a valid measurement
          	if (current_a < 0.f) {
          		// Because the measurement was invalid we need to stop integration
          		// and re-initialize with the next valid measurement
          		_last_timestamp = 0;
          		return;
          	}
          
          
	// Ignore first update because we don't know dt.

question (ii) I’m not sure about your power module specs. In my case, I use the CAN PMU (CUAV) and obtain an accurate result.

Bilal_Mubdir · March 2, 2024, 3:04pm

I’m working on the same topic, do you mind if we can talk privately and cooperate about this?