AP_Motors: added new MOT_PWM_TYPE=8 for PWM range

this allows multirotors to set individual PWM ranges per motor. This
is needed for heliquads flying as multirotors

libraries/AP_Motors/AP_MotorsMulticopter.cpp

@@ -78,7 +78,7 @@ const AP_Param::GroupInfo AP_MotorsMulticopter::var_info[] = {
     // @Param: PWM_TYPE
     // @DisplayName: Output PWM type
     // @Description: This selects the output PWM type, allowing for normal PWM continuous output, OneShot, brushed or DShot motor output
-    // @Values: 0:Normal,1:OneShot,2:OneShot125,3:Brushed,4:DShot150,5:DShot300,6:DShot600,7:DShot1200
+    // @Values: 0:Normal,1:OneShot,2:OneShot125,3:Brushed,4:DShot150,5:DShot300,6:DShot600,7:DShot1200,8:PWMRange
     // @User: Advanced
     // @RebootRequired: True
     AP_GROUPINFO("PWM_TYPE", 15, AP_MotorsMulticopter, _pwm_type, PWM_TYPE_NORMAL),
@@ -512,8 +512,9 @@ void AP_MotorsMulticopter::set_throttle_range(int16_t radio_min, int16_t radio_m
     _throttle_radio_min = radio_min;
     _throttle_radio_max = radio_max;
 
-    // if all outputs are digital adjust the range
-    if (SRV_Channels::have_digital_outputs(get_motor_mask())) {
+    // if all outputs are digital adjust the range. We also do this for type PWM_RANGE, as those use the
+    // scaled output, which is then mapped to PWM via the SRV_Channel library
+    if (SRV_Channels::have_digital_outputs(get_motor_mask()) || (_pwm_type == PWM_TYPE_PWM_RANGE)) {
         _pwm_min = 1000;
         _pwm_max = 2000;
     }

libraries/AP_Motors/AP_Motors_Class.cpp

@@ -92,7 +92,12 @@ void AP_Motors::set_radio_passthrough(float roll_input, float pitch_input, float
 void AP_Motors::rc_write(uint8_t chan, uint16_t pwm)
 {
     SRV_Channel::Aux_servo_function_t function = SRV_Channels::get_motor_function(chan);
-    SRV_Channels::set_output_pwm(function, pwm);
+    if ((1U<<chan) & _motor_pwm_range_mask) {
+        // note that PWM_MIN/MAX has been forced to 1000/2000
+        SRV_Channels::set_output_scaled(function, pwm - 1000);
+    } else {
+        SRV_Channels::set_output_pwm(function, pwm);
+    }
 }
 
 /*
@@ -142,6 +147,19 @@ void AP_Motors::rc_set_freq(uint32_t mask, uint16_t freq_hz)
     case PWM_TYPE_DSHOT1200:
         hal.rcout->set_output_mode(mask, AP_HAL::RCOutput::MODE_PWM_DSHOT1200);
         break;
+    case PWM_TYPE_PWM_RANGE:
+        /*
+          this is a motor output type for multirotors which honours
+          the SERVOn_MIN/MAX values per channel
+         */
+        _motor_pwm_range_mask |= mask;
+        for (uint8_t i=0; i<16; i++) {
+            if ((1U<<i) & mask) {
+                SRV_Channels::set_range(SRV_Channels::get_motor_function(i), 1000);
+            }
+        }
+        hal.rcout->set_output_mode(mask, AP_HAL::RCOutput::MODE_PWM_NORMAL);
+        break;
     default:
         hal.rcout->set_output_mode(mask, AP_HAL::RCOutput::MODE_PWM_NORMAL);
         break;

libraries/AP_Motors/AP_Motors_Class.h

@@ -220,7 +220,8 @@ public:
                     PWM_TYPE_DSHOT150   = 4,
                     PWM_TYPE_DSHOT300   = 5,
                     PWM_TYPE_DSHOT600   = 6,
-                    PWM_TYPE_DSHOT1200  = 7};
+                    PWM_TYPE_DSHOT1200  = 7,
+                    PWM_TYPE_PWM_RANGE  = 8 };
     pwm_type            get_pwm_type(void) const { return (pwm_type)_pwm_type.get(); }
 
     MAV_TYPE get_frame_mav_type() const { return _mav_type; }
@@ -273,6 +274,9 @@ protected:
     // mask of what channels need fast output
     uint16_t            _motor_fast_mask;
 
+    // mask of what channels need to use SERVOn_MIN/MAX for output mapping
+    uint16_t            _motor_pwm_range_mask;
+    
     // pass through variables
     float _roll_radio_passthrough;     // roll input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed
     float _pitch_radio_passthrough;    // pitch input from pilot in -1 ~ +1 range.  used for setup and providing servo feedback while landed