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Consider the throttle load for battery voltage calculation #1211

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merged 14 commits into from
Jul 21, 2014
Merged

Consider the throttle load for battery voltage calculation #1211

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3a0fc36
Consider the throttle load for battery voltage calculation
LorenzMeier Jul 19, 2014
3db78a4
commander: Warn at 18 and 9% battery remaining instead of 25 and 10% …
LorenzMeier Jul 19, 2014
5d24898
Fix low voltage warning threshold to 9%, not 90%
LorenzMeier Jul 19, 2014
e21cb64
Merge branch 'master' of github.com:PX4/Firmware into battload
LorenzMeier Jul 20, 2014
3935540
Set full voltage correctly to ensure percentage range fits. Force all…
LorenzMeier Jul 20, 2014
264fe88
Fixed load voltage calculation
LorenzMeier Jul 20, 2014
c95de36
commander: Add missing parameter definition
LorenzMeier Jul 20, 2014
25d1cc3
Final value for battery load param default
LorenzMeier Jul 21, 2014
afff123
Add PX4IO voltage dataset and linear fit
LorenzMeier Jul 21, 2014
956c084
Fit IO voltage estimation using a new dataset, cross-validated with a…
LorenzMeier Jul 21, 2014
0fc73a1
Fix comment, missing brace in comment
LorenzMeier Jul 21, 2014
331623b
Fix missing line endings
LorenzMeier Jul 21, 2014
178b0f7
Cross-check with nominal values from divider
LorenzMeier Jul 21, 2014
07d1158
Rely on theoretical value, as the closed-loop test with multimeter su…
LorenzMeier Jul 21, 2014
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11 changes: 10 additions & 1 deletion src/modules/commander/commander.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -918,6 +918,11 @@ int commander_thread_main(int argc, char *argv[])
struct system_power_s system_power;
memset(&system_power, 0, sizeof(system_power));

/* Subscribe to actuator controls (outputs) */
int actuator_controls_sub = orb_subscribe(ORB_ID_VEHICLE_ATTITUDE_CONTROLS);
struct actuator_controls_s actuator_controls;
memset(&actuator_controls, 0, sizeof(actuator_controls));

control_status_leds(&status, &armed, true);

/* now initialized */
Expand Down Expand Up @@ -1199,13 +1204,17 @@ int commander_thread_main(int argc, char *argv[])

if (updated) {
orb_copy(ORB_ID(battery_status), battery_sub, &battery);
orb_copy(ORB_ID_VEHICLE_ATTITUDE_CONTROLS, actuator_controls_sub, &actuator_controls);

/* only consider battery voltage if system has been running 2s and battery voltage is valid */
if (hrt_absolute_time() > start_time + 2000000 && battery.voltage_filtered_v > 0.0f) {
status.battery_voltage = battery.voltage_filtered_v;
status.battery_current = battery.current_a;
status.condition_battery_voltage_valid = true;
status.battery_remaining = battery_remaining_estimate_voltage(battery.voltage_filtered_v, battery.discharged_mah);

/* get throttle (if armed), as we only care about energy negative throttle also counts */
float throttle = (armed.armed) ? fabsf(actuator_controls.control[3]) : 0.0f;
status.battery_remaining = battery_remaining_estimate_voltage(battery.voltage_filtered_v, battery.discharged_mah, throttle);
}
}

Expand Down
10 changes: 7 additions & 3 deletions src/modules/commander/commander_helper.cpp
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Expand Up @@ -281,15 +281,17 @@ void rgbled_set_pattern(rgbled_pattern_t *pattern)
}
}

float battery_remaining_estimate_voltage(float voltage, float discharged)
float battery_remaining_estimate_voltage(float voltage, float discharged, float throttle_normalized)
{
float ret = 0;
static param_t bat_v_empty_h;
static param_t bat_v_full_h;
static param_t bat_n_cells_h;
static param_t bat_capacity_h;
static param_t bat_v_load_drop_h;
static float bat_v_empty = 3.2f;
static float bat_v_full = 4.0f;
static float bat_v_load_drop = 0.1f;
static int bat_n_cells = 3;
static float bat_capacity = -1.0f;
static bool initialized = false;
Expand All @@ -300,20 +302,22 @@ float battery_remaining_estimate_voltage(float voltage, float discharged)
bat_v_full_h = param_find("BAT_V_FULL");
bat_n_cells_h = param_find("BAT_N_CELLS");
bat_capacity_h = param_find("BAT_CAPACITY");
bat_v_load_drop_h = param_find("BAT_V_LOAD_DROP");
initialized = true;
}

if (counter % 100 == 0) {
param_get(bat_v_empty_h, &bat_v_empty);
param_get(bat_v_full_h, &bat_v_full);
param_get(bat_v_load_drop_h, &bat_v_load_drop);
param_get(bat_n_cells_h, &bat_n_cells);
param_get(bat_capacity_h, &bat_capacity);
}

counter++;

/* remaining charge estimate based on voltage */
float remaining_voltage = (voltage - bat_n_cells * bat_v_empty) / (bat_n_cells * (bat_v_full - bat_v_empty));
/* remaining charge estimate based on voltage and internal resistance (drop under load) */
float remaining_voltage = (voltage - bat_n_cells * (bat_v_empty - (bat_v_load_drop * throttle_normalized)) / (bat_n_cells * (bat_v_full - bat_v_empty));

if (bat_capacity > 0.0f) {
/* if battery capacity is known, use discharged current for estimate, but don't show more than voltage estimate */
Expand Down
3 changes: 2 additions & 1 deletion src/modules/commander/commander_helper.h
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Expand Up @@ -80,8 +80,9 @@ void rgbled_set_pattern(rgbled_pattern_t *pattern);
*
* @param voltage the current battery voltage
* @param discharged the discharged capacity
* @param throttle_normalized the normalized throttle magnitude from 0 to 1. Negative throttle should be converted to this range as well, as it consumes energy.
* @return the estimated remaining capacity in 0..1
*/
float battery_remaining_estimate_voltage(float voltage, float discharged);
float battery_remaining_estimate_voltage(float voltage, float discharged, float throttle_normalized);

#endif /* COMMANDER_HELPER_H_ */
4 changes: 2 additions & 2 deletions src/modules/commander/commander_params.c
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Expand Up @@ -56,7 +56,7 @@ PARAM_DEFINE_FLOAT(TRIM_YAW, 0.0f);
*
* @group Battery Calibration
*/
PARAM_DEFINE_FLOAT(BAT_V_EMPTY, 3.4f);
PARAM_DEFINE_FLOAT(BAT_V_EMPTY, 3.3f);
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3.4V was definitely too high. 3.3V is better, but might still be a bit high. We could consider going to 3.25 or 3.2 (note that with default params under load empty == 3.2 - 0.1V then).

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After 3.4V voltage drops much faster and deep discharge (3.2 is deep enough!) is very bad for battery health. Default parameters should be tuned for safe flight. With 3.2V copter may crash after 3 seconds after first warning if user forgot to charge battery, it may be not enough to land.

Of course it depends on battery model, but I would like to stay on safe side with 3.4V. If user wants to kill the battery, he can change parameter.

The problem with voltage drops on high thrust should be solved by internal resistance compensation I think, that you are already trying to do.

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Ok, convinced - I'll change this back.


/**
* Full cell voltage.
Expand All @@ -65,7 +65,7 @@ PARAM_DEFINE_FLOAT(BAT_V_EMPTY, 3.4f);
*
* @group Battery Calibration
*/
PARAM_DEFINE_FLOAT(BAT_V_FULL, 3.9f);
PARAM_DEFINE_FLOAT(BAT_V_FULL, 4.15f);

/**
* Number of cells.
Expand Down