diff --git a/libraries/AP_Motors/AP_MotorsTri.cpp b/libraries/AP_Motors/AP_MotorsTri.cpp
index 14163bee80..0528a7f5bc 100644
--- a/libraries/AP_Motors/AP_MotorsTri.cpp
+++ b/libraries/AP_Motors/AP_MotorsTri.cpp
@@ -80,6 +80,14 @@ void AP_MotorsTri::output_min()
     hal.rcout->write(pgm_read_byte(&_motor_to_channel_map[AP_MOTORS_CH_TRI_YAW]), _rc_yaw.radio_trim);
 }
 
+// get_motor_mask - returns a bitmask of which outputs are being used for motors or servos (1 means being used)
+//  this can be used to ensure other pwm outputs (i.e. for servos) do not conflict
+uint16_t AP_MotorsTri::get_motor_mask()
+{
+    // tri copter uses channels 1,2,4 and 7
+    return (1U << 0 | 1U << 1 | 1U << 3 | 1U << AP_MOTORS_CH_TRI_YAW);
+}
+
 // output_armed - sends commands to the motors
 void AP_MotorsTri::output_armed()
 {
diff --git a/libraries/AP_Motors/AP_MotorsTri.h b/libraries/AP_Motors/AP_MotorsTri.h
index c7522d6751..f457069a9e 100644
--- a/libraries/AP_Motors/AP_MotorsTri.h
+++ b/libraries/AP_Motors/AP_MotorsTri.h
@@ -41,6 +41,10 @@ public:
     // output_min - sends minimum values out to the motors
     virtual void        output_min();
 
+    // get_motor_mask - returns a bitmask of which outputs are being used for motors or servos (1 means being used)
+    //  this can be used to ensure other pwm outputs (i.e. for servos) do not conflict
+    virtual uint16_t    get_motor_mask();
+
 protected:
     // output - sends commands to the motors
     virtual void        output_armed();