diff --git a/libraries/AP_Motors/AP_MotorsHeli.cpp b/libraries/AP_Motors/AP_MotorsHeli.cpp
index faf432c669..405069f826 100644
--- a/libraries/AP_Motors/AP_MotorsHeli.cpp
+++ b/libraries/AP_Motors/AP_MotorsHeli.cpp
@@ -198,10 +198,12 @@ void AP_MotorsHeli::set_update_rate( uint16_t speed_hz )
     _speed_hz = speed_hz;
 
     // setup fast channels
-    hal.rcout->set_freq(_motor_to_channel_map[AP_MOTORS_MOT_1], _speed_hz);
-    hal.rcout->set_freq(_motor_to_channel_map[AP_MOTORS_MOT_2], _speed_hz);
-    hal.rcout->set_freq(_motor_to_channel_map[AP_MOTORS_MOT_3], _speed_hz);
-    hal.rcout->set_freq(_motor_to_channel_map[AP_MOTORS_MOT_4], _speed_hz);
+    uint32_t mask = 
+	    1U << _motor_to_channel_map[AP_MOTORS_MOT_1] |
+	    1U << _motor_to_channel_map[AP_MOTORS_MOT_2] |
+	    1U << _motor_to_channel_map[AP_MOTORS_MOT_3] |
+	    1U << _motor_to_channel_map[AP_MOTORS_MOT_4];
+    hal.rcout->set_freq(mask, _speed_hz);
 }
 
 // enable - starts allowing signals to be sent to motors
diff --git a/libraries/AP_Motors/AP_MotorsMatrix.cpp b/libraries/AP_Motors/AP_MotorsMatrix.cpp
index 726a8d11d0..f7215b651c 100644
--- a/libraries/AP_Motors/AP_MotorsMatrix.cpp
+++ b/libraries/AP_Motors/AP_MotorsMatrix.cpp
@@ -34,11 +34,13 @@ void AP_MotorsMatrix::set_update_rate( uint16_t speed_hz )
     _speed_hz = speed_hz;
 
     // check each enabled motor
+    uint32_t mask = 0;
     for( i=0; i<AP_MOTORS_MAX_NUM_MOTORS; i++ ) {
         if( motor_enabled[i] ) {
-            hal.rcout->set_freq( _motor_to_channel_map[i], _speed_hz );
+		mask |= 1U << _motor_to_channel_map[i];
         }
     }
+    hal.rcout->set_freq( mask, _speed_hz );
 }
 
 // set frame orientation (normally + or X)
diff --git a/libraries/AP_Motors/AP_MotorsTri.cpp b/libraries/AP_Motors/AP_MotorsTri.cpp
index 7be68e54d1..44f78eb253 100644
--- a/libraries/AP_Motors/AP_MotorsTri.cpp
+++ b/libraries/AP_Motors/AP_MotorsTri.cpp
@@ -30,9 +30,11 @@ void AP_MotorsTri::set_update_rate( uint16_t speed_hz )
     _speed_hz = speed_hz;
 
     // set update rate for the 3 motors (but not the servo on channel 7)
-    hal.rcout->set_freq(_motor_to_channel_map[AP_MOTORS_MOT_1], _speed_hz);
-    hal.rcout->set_freq(_motor_to_channel_map[AP_MOTORS_MOT_2], _speed_hz);
-    hal.rcout->set_freq(_motor_to_channel_map[AP_MOTORS_MOT_4], _speed_hz);
+    uint32_t mask = 
+	    1U << _motor_to_channel_map[AP_MOTORS_MOT_1] |
+	    1U << _motor_to_channel_map[AP_MOTORS_MOT_2] |
+	    1U << _motor_to_channel_map[AP_MOTORS_MOT_4];
+    hal.rcout->set_freq(mask, _speed_hz);
 }
 
 // enable - starts allowing signals to be sent to motors