diff --git a/src/drivers/drv_pwm_output.h b/src/drivers/drv_pwm_output.h
index 3d4b7cd7f7..bab063897f 100644
--- a/src/drivers/drv_pwm_output.h
+++ b/src/drivers/drv_pwm_output.h
@@ -114,14 +114,14 @@ __BEGIN_DECLS
 /**
  * Default trim PWM in us
  */
-#define PWM_DEFAULT_TRIM 0
+#define PWM_DEFAULT_TRIM 1500
 
 /**
  * Lowest PWM allowed as the maximum PWM
  */
 #define PWM_LOWEST_MAX 200
 
-#endif // PX4_PWM_ALTERNATE_RANGES
+#endif // not PX4_PWM_ALTERNATE_RANGES
 
 /**
  * Do not output a channel with this value
@@ -222,10 +222,10 @@ struct pwm_output_rc_config {
 /** get the maximum PWM value the output will send */
 #define PWM_SERVO_GET_MAX_PWM	_PX4_IOC(_PWM_SERVO_BASE, 19)
 
-/** set the maximum PWM value the output will send */
+/** set the TRIM value the output will send */
 #define PWM_SERVO_SET_TRIM_PWM	_PX4_IOC(_PWM_SERVO_BASE, 20)
 
-/** get the maximum PWM value the output will send */
+/** get the TRIM value the output will send */
 #define PWM_SERVO_GET_TRIM_PWM	_PX4_IOC(_PWM_SERVO_BASE, 21)
 
 /** set the number of servos in (unsigned)arg - allows change of
diff --git a/src/drivers/px4fmu/fmu.cpp b/src/drivers/px4fmu/fmu.cpp
index a828051b69..0996b8dfb6 100644
--- a/src/drivers/px4fmu/fmu.cpp
+++ b/src/drivers/px4fmu/fmu.cpp
@@ -644,7 +644,7 @@ PX4FMU::set_mode(Mode mode)
 int
 PX4FMU::set_pwm_rate(uint32_t rate_map, unsigned default_rate, unsigned alt_rate)
 {
-	DEVICE_DEBUG("set_pwm_rate %x %u %u", rate_map, default_rate, alt_rate);
+	PX4_DEBUG("set_pwm_rate %x %u %u", rate_map, default_rate, alt_rate);
 
 	for (unsigned pass = 0; pass < 2; pass++) {
 		for (unsigned group = 0; group < _max_actuators; group++) {
@@ -720,12 +720,12 @@ PX4FMU::subscribe()
 
 	for (unsigned i = 0; i < actuator_controls_s::NUM_ACTUATOR_CONTROL_GROUPS; i++) {
 		if (sub_groups & (1 << i)) {
-			DEVICE_DEBUG("subscribe to actuator_controls_%d", i);
+			PX4_DEBUG("subscribe to actuator_controls_%d", i);
 			_control_subs[i] = orb_subscribe(_control_topics[i]);
 		}
 
 		if (unsub_groups & (1 << i)) {
-			DEVICE_DEBUG("unsubscribe from actuator_controls_%d", i);
+			PX4_DEBUG("unsubscribe from actuator_controls_%d", i);
 			::close(_control_subs[i]);
 			_control_subs[i] = -1;
 		}
@@ -761,6 +761,8 @@ PX4FMU::update_pwm_rev_mask()
 void
 PX4FMU::update_pwm_trims()
 {
+	PX4_DEBUG("update_pwm_trims");
+
 	if (_mixers == nullptr) {
 		PX4_WARN("no mixers defined");
 
@@ -779,13 +781,13 @@ PX4FMU::update_pwm_trims()
 			if (param_h != PARAM_INVALID) {
 				param_get(param_h, &ival);
 				values[i] = ival;
-				PX4_INFO("aux trim %d %d", i, values[i]);
+				PX4_DEBUG("%s: %d", pname, values[i]);
 			}
 		}
 
 		/* copy the trim values to the mixer offsets */
 		unsigned n_out = _mixers->set_trims(values, _max_actuators);
-		PX4_INFO("set %d trims", n_out);
+		PX4_DEBUG("set %d trims", n_out);
 	}
 }
 
@@ -1019,7 +1021,7 @@ PX4FMU::cycle()
 			update_rate_in_ms = 100;
 		}
 
-		DEVICE_DEBUG("adjusted actuator update interval to %ums", update_rate_in_ms);
+		PX4_DEBUG("adjusted actuator update interval to %ums", update_rate_in_ms);
 
 		for (unsigned i = 0; i < actuator_controls_s::NUM_ACTUATOR_CONTROL_GROUPS; i++) {
 			if (_control_subs[i] > 0) {
@@ -1159,7 +1161,7 @@ PX4FMU::cycle()
 			/* the PWM limit call takes care of out of band errors, NaN and constrains */
 			// TODO: remove trim_pwm parameter
 			pwm_limit_calc(_throttle_armed, arm_nothrottle(), num_outputs, _reverse_pwm_mask,
-				       _trim_pwm, _disarmed_pwm, _min_pwm, _max_pwm, outputs, pwm_limited, &_pwm_limit);
+				       _disarmed_pwm, _min_pwm, _max_pwm, _trim_pwm, outputs, pwm_limited, &_pwm_limit);
 
 
 			/* overwrite outputs in case of lockdown with disarmed PWM values */
@@ -1664,7 +1666,7 @@ PX4FMU::ioctl(file *filp, int cmd, unsigned long arg)
 		break;
 
 	default:
-		DEVICE_DEBUG("not in a PWM mode");
+		PX4_DEBUG("not in a PWM mode");
 		break;
 	}
 
@@ -1681,6 +1683,8 @@ PX4FMU::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 {
 	int ret = OK;
 
+	PX4_DEBUG("fmu ioctl cmd: %d, arg: %ld", cmd, arg);
+
 	lock();
 
 	switch (cmd) {
@@ -1931,12 +1935,14 @@ PX4FMU::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 
 			/* discard if too many values are sent */
 			if (pwm->channel_count > _max_actuators) {
+				PX4_DEBUG("error: too many trim values: %d", pwm->channel_count);
 				ret = -EINVAL;
 				break;
 			}
 
 			/* copy the trim values to the mixer offsets */
 			_mixers->set_trims(pwm->values, pwm->channel_count);
+			PX4_DEBUG("set_trims: %d, %d, %d, %d", pwm->values[0], pwm->values[1], pwm->values[2], pwm->values[3]);
 
 			break;
 		}
@@ -2292,7 +2298,7 @@ PX4FMU::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 				ret = _mixers->load_from_buf(buf, buflen);
 
 				if (ret != 0) {
-					DEVICE_DEBUG("mixer load failed with %d", ret);
+					PX4_DEBUG("mixer load failed with %d", ret);
 					delete _mixers;
 					_mixers = nullptr;
 					_groups_required = 0;
@@ -2301,7 +2307,7 @@ PX4FMU::pwm_ioctl(file *filp, int cmd, unsigned long arg)
 				} else {
 
 					_mixers->groups_required(_groups_required);
-					PX4_INFO("loaded mixers \n%s\n", buf);
+					PX4_DEBUG("loaded mixers \n%s\n", buf);
 				}
 			}
 
diff --git a/src/modules/systemlib/mixer/mixer_group.cpp b/src/modules/systemlib/mixer/mixer_group.cpp
index 574831bcb3..4f6d14246a 100644
--- a/src/modules/systemlib/mixer/mixer_group.cpp
+++ b/src/modules/systemlib/mixer/mixer_group.cpp
@@ -119,7 +119,13 @@ MixerGroup::set_trims(uint16_t *values, unsigned n)
 	unsigned index = 0;
 
 	while ((mixer != nullptr) && (index < n)) {
-		/* hardwired assumption that PWM output range is [1000, 2000] usec */
+		/*
+		 * hardwired assumption that PWM output range is [1000, 2000] usec
+		 *
+		 * This only works with SimpleMixer::set_trim(float) which always returns the value one,
+		 * but the only other existing implementation is MultirotorMixer, which ignores
+		 * the trim value.
+		 */
 		float offset = ((float)values[index] - 1500) / 500;
 
 		/* to be safe, clamp offset to range of [-100, 100] usec */
@@ -127,6 +133,7 @@ MixerGroup::set_trims(uint16_t *values, unsigned n)
 
 		if (offset >  0.2f) { offset =  0.2f; }
 
+		debug("set trim: %d, offset: %5.3f", values[index], (double)offset);
 		index += mixer->set_trim(offset);
 		mixer = mixer->_next;
 	}
diff --git a/src/modules/systemlib/pwm_limit/pwm_limit.c b/src/modules/systemlib/pwm_limit/pwm_limit.c
index e14934155e..a157e29eed 100644
--- a/src/modules/systemlib/pwm_limit/pwm_limit.c
+++ b/src/modules/systemlib/pwm_limit/pwm_limit.c
@@ -192,6 +192,7 @@ void pwm_limit_calc(const bool armed, const bool pre_armed, const unsigned num_c
 		break;
 
 	case PWM_LIMIT_STATE_ON:
+
 		for (unsigned i = 0; i < num_channels; i++) {
 
 			float control_value = output[i];
@@ -223,6 +224,7 @@ void pwm_limit_calc(const bool armed, const bool pre_armed, const unsigned num_c
 			} else if (effective_pwm[i] > max_pwm[i]) {
 				effective_pwm[i] = max_pwm[i];
 			}
+
 		}
 
 		break;