__pdata int16_t ao_ground_pres; /* startup pressure */
__pdata int16_t ao_ground_accel; /* startup acceleration */
__pdata int16_t ao_min_pres; /* minimum recorded pressure */
-__pdata uint16_t ao_launch_time; /* time of launch detect */
+__pdata uint16_t ao_launch_tick; /* time of launch detect */
__pdata int16_t ao_main_pres; /* pressure to eject main */
/*
__pdata int16_t ao_interval_max_pres;
__data uint8_t ao_flight_adc;
-__xdata int16_t ao_accel, ao_prev_accel, ao_pres;
-
-#define AO_INTERVAL_TICKS AO_SEC_TO_TICKS(5)
+__pdata int16_t ao_raw_accel, ao_raw_accel_prev, ao_raw_pres;
/* Accelerometer calibration
*
*
* 26.67 mV/g * 32767/3300 counts/mV = 264.8 counts/g
*
- * Zero g was measured at 16000 (we would expect 16384)
+ * Zero g was measured at 16000 (we would expect 16384).
+ * Note that this value is only require to tell if the
+ * rocket is standing upright. Once that is determined,
+ * the value of the accelerometer is averaged for 100 samples
+ * to find the resting accelerometer value, which is used
+ * for all further flight computations
*/
#define ACCEL_G 265
#define ACCEL_ZERO_G 16000
#define ACCEL_NOSE_UP (ACCEL_ZERO_G - ACCEL_G * 2 /3)
-#define ACCEL_BOOST (ACCEL_NOSE_UP - ACCEL_G * 2)
+#define ACCEL_BOOST ACCEL_G * 2
#define ACCEL_LAND (ACCEL_G / 10)
/*
* Pressure range: 15-115 kPa
* Voltage at 115kPa: 2.82
* Output scale: 27mV/kPa
- *
+ *
* If we want to detect launch with the barometer, we need
* a large enough bump to not be fooled by noise. At typical
* launch elevations (0-2000m), a 200Pa pressure change cooresponds
*/
#define BARO_kPa 268
-#define BARO_LAUNCH (BARO_kPa / 5) /* .2kPa */
-#define BARO_APOGEE (BARO_kPa / 10) /* .1kPa */
-#define BARO_MAIN (BARO_kPa) /* 1kPa */
-#define BARO_LAND (BARO_kPa / 20) /* .05kPa */
+#define BARO_LAUNCH (BARO_kPa / 5) /* .2kPa, or about 20m */
+#define BARO_APOGEE (BARO_kPa / 10) /* .1kPa, or about 10m */
+#define BARO_COAST (BARO_kPa * 5) /* 5kpa, or about 500m */
+#define BARO_MAIN (BARO_kPa) /* 1kPa, or about 100m */
+#define BARO_LAND (BARO_kPa / 20) /* .05kPa, or about 5m */
/* We also have a clock, which can be used to sanity check things in
* case of other failures
* it's scaled by 100
*/
__data int32_t ao_flight_vel;
+__xdata int32_t ao_raw_accel_sum, ao_raw_pres_sum;
+#define GRAVITY 9.80665
/* convert m/s to velocity count */
-#define VEL_MPS_TO_COUNT(mps) ((int32_t) ((int32_t) (mps) * (int32_t) 100 / (int32_t) ACCEL_G))
+#define VEL_MPS_TO_COUNT(mps) ((int32_t) (((mps) / GRAVITY) * ACCEL_G * 100))
+
+/* Landing is detected by getting constant readings from both pressure and accelerometer
+ * for a fairly long time (AO_INTERVAL_TICKS)
+ */
+#define AO_INTERVAL_TICKS AO_SEC_TO_TICKS(10)
void
ao_flight(void)
{
__pdata static uint8_t nsamples = 0;
-
+
ao_flight_adc = ao_adc_head;
- ao_prev_accel = 0;
- ao_accel = 0;
- ao_pres = 0;
+ ao_raw_accel_prev = 0;
+ ao_raw_accel = 0;
+ ao_raw_pres = 0;
+ ao_interval_cur_min_pres = 0x7fff;
+ ao_interval_cur_max_pres = -0x7fff;
+ ao_interval_cur_min_accel = 0x7fff;
+ ao_interval_cur_max_accel = -0x7fff;
for (;;) {
ao_sleep(&ao_adc_ring);
while (ao_flight_adc != ao_adc_head) {
- ao_accel = ao_adc_ring[ao_flight_adc].accel;
- ao_pres = ao_adc_ring[ao_flight_adc].pres;
+ ao_raw_accel = ao_adc_ring[ao_flight_adc].accel;
+ ao_raw_pres = ao_adc_ring[ao_flight_adc].pres;
ao_flight_tick = ao_adc_ring[ao_flight_adc].tick;
- ao_flight_vel += (int32_t) (((ao_accel + ao_prev_accel) >> 4) - (ao_ground_accel << 1));
- ao_prev_accel = ao_accel;
+ /* all of our accelerations are negative, so subtract instead of add to get speed */
+ ao_flight_vel -= (int32_t) (((ao_raw_accel + ao_raw_accel_prev) >> 1) - ao_ground_accel);
+ ao_raw_accel_prev = ao_raw_accel;
ao_flight_adc = ao_adc_ring_next(ao_flight_adc);
}
ao_flight_accel -= ao_flight_accel >> 4;
- ao_flight_accel += ao_accel >> 4;
+ ao_flight_accel += ao_raw_accel >> 4;
ao_flight_pres -= ao_flight_pres >> 4;
- ao_flight_pres += ao_pres >> 4;
-
+ ao_flight_pres += ao_raw_pres >> 4;
+
if (ao_flight_pres < ao_min_pres)
ao_min_pres = ao_flight_pres;
+ if (ao_flight_pres < ao_interval_cur_min_pres)
+ ao_interval_cur_min_pres = ao_flight_pres;
+ if (ao_flight_pres > ao_interval_cur_max_pres)
+ ao_interval_cur_max_pres = ao_flight_pres;
+ if (ao_flight_accel < ao_interval_cur_min_accel)
+ ao_interval_cur_min_accel = ao_flight_accel;
+ if (ao_flight_accel > ao_interval_cur_max_accel)
+ ao_interval_cur_max_accel = ao_flight_accel;
+
if ((int16_t) (ao_flight_tick - ao_interval_end) >= 0) {
ao_interval_max_pres = ao_interval_cur_max_pres;
ao_interval_min_pres = ao_interval_cur_min_pres;
ao_interval_max_accel = ao_interval_cur_max_accel;
ao_interval_min_accel = ao_interval_cur_min_accel;
ao_interval_end = ao_flight_tick + AO_INTERVAL_TICKS;
+ ao_interval_cur_min_pres = ao_interval_cur_max_pres = ao_flight_pres;
+ ao_interval_cur_min_accel = ao_interval_cur_max_accel = ao_flight_accel;
}
-
+
switch (ao_flight_state) {
case ao_flight_startup:
+
+ /* startup state:
+ *
+ * Collect 100 samples of acceleration and pressure
+ * data and average them to find the resting values
+ */
if (nsamples < 100) {
+ ao_raw_accel_sum += ao_raw_accel;
+ ao_raw_pres_sum += ao_raw_pres;
++nsamples;
continue;
}
- ao_ground_accel = ao_flight_accel;
- ao_ground_pres = ao_flight_pres;
- ao_min_pres = ao_flight_pres;
+ ao_ground_accel = (ao_raw_accel_sum / nsamples);
+ ao_ground_pres = (ao_raw_pres_sum / nsamples);
+ ao_min_pres = ao_ground_pres;
ao_main_pres = ao_ground_pres - BARO_MAIN;
ao_flight_vel = 0;
-
+
ao_interval_end = ao_flight_tick;
-
+
/* Go to launchpad state if the nose is pointing up */
if (ao_flight_accel < ACCEL_NOSE_UP) {
ao_flight_state = ao_flight_launchpad;
ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
} else {
ao_flight_state = ao_flight_idle;
-
+
/* Turn on the Green LED in idle mode
- * This also happens to bring the USB up for the TI board
*/
ao_led_on(AO_LED_GREEN);
ao_timer_set_adc_interval(100);
/* pad to boost:
*
* accelerometer: > 2g
+ * OR
* barometer: > 20m vertical motion
+ *
+ * The accelerometer should always detect motion before
+ * the barometer, but we use both to make sure this
+ * transition is detected
*/
- if (ao_flight_accel < ACCEL_BOOST ||
- ao_flight_pres + BARO_LAUNCH < ao_ground_pres)
+ if (ao_flight_accel < ao_ground_accel - ACCEL_BOOST ||
+ ao_flight_pres < ao_ground_pres - BARO_LAUNCH)
{
ao_flight_state = ao_flight_boost;
+ ao_launch_tick = ao_flight_tick;
ao_log_start();
ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
break;
/* boost to coast:
*
* accelerometer: start to fall at > 1/4 G
+ * OR
* time: boost for more than 15 seconds
+ *
+ * Detects motor burn out by the switch from acceleration to
+ * deceleration, or by waiting until the maximum burn duration
+ * (15 seconds) has past.
*/
if (ao_flight_accel > ao_ground_accel + (ACCEL_G >> 2) ||
- (int16_t) (ao_flight_tick - ao_launch_time) > BOOST_TICKS_MAX)
+ (int16_t) (ao_flight_tick - ao_launch_tick) > BOOST_TICKS_MAX)
{
ao_flight_state = ao_flight_coast;
ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
break;
}
- break;
+ /* fall through ... */
case ao_flight_coast:
-
- /* coast to apogee detect:
- *
+
+ /* boost/coast to apogee detect:
+ *
* accelerometer: integrated velocity < 200 m/s
+ * OR
* barometer: fall at least 500m from max altitude
+ *
+ * This extra state is required to avoid mis-detecting
+ * apogee due to mach transitions. For slow flights (<200m/s)
+ * we expect to transition right through this stage to
+ * apogee detect.
*/
if (ao_flight_vel < VEL_MPS_TO_COUNT(200) ||
- ao_flight_pres - (5 * BARO_kPa) > ao_min_pres)
+ ao_flight_pres > ao_min_pres + BARO_COAST)
{
ao_flight_state = ao_flight_apogee;
ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
/* apogee to drogue deploy:
*
* accelerometer: integrated velocity < 10m/s
+ * OR
* barometer: fall at least 10m
+ *
+ * If the barometer saturates because the flight
+ * goes over its measuring range (about 53k'),
+ * requiring a 10m fall will avoid prematurely
+ * detecting apogee; the accelerometer will take
+ * over in that case and the integrated velocity
+ * measurement should suffice to find apogee
*/
if (ao_flight_vel < VEL_MPS_TO_COUNT(-10) ||
ao_flight_pres - BARO_APOGEE > ao_min_pres)
ao_flight_state = ao_flight_drogue;
ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
}
- break;
+ break;
case ao_flight_drogue:
-
+
/* drogue to main deploy:
*
* accelerometer: abs(velocity) > 50m/s
+ * OR
* barometer: reach main deploy altitude
*/
if (ao_flight_vel < VEL_MPS_TO_COUNT(-50) ||
/* drogue/main to land:
*
* accelerometer: value stable
+ * AND
* barometer: altitude stable
*/
- if ((ao_interval_max_accel - ao_interval_min_accel) < ACCEL_LAND ||
+ if ((ao_interval_max_accel - ao_interval_min_accel) < ACCEL_LAND &&
(ao_interval_max_pres - ao_interval_min_pres) < BARO_LAND)
{
ao_flight_state = ao_flight_landed;
projects / fw / altos / blobdiff