diff --git a/libraries/AP_HAL_PX4/RCOutput.cpp b/libraries/AP_HAL_PX4/RCOutput.cpp
index ec978112f3..cb448bf918 100644
--- a/libraries/AP_HAL_PX4/RCOutput.cpp
+++ b/libraries/AP_HAL_PX4/RCOutput.cpp
@@ -26,23 +26,96 @@ void PX4RCOutput::init(void* unused)
     if (ioctl(_pwm_fd, PWM_SERVO_ARM, 0) != 0) {
         hal.console->printf("RCOutput: Unable to setup IO arming\n");
     }
+    _rate_mask = 0;
+    _alt_fd = -1;    
+    _servo_count = 0;
+    _alt_servo_count = 0;
+
+    if (ioctl(_pwm_fd, PWM_SERVO_GET_COUNT, (unsigned long)&_servo_count) != 0) {
+        hal.console->printf("RCOutput: Unable to get servo count\n");        
+        return;
+    }
+
+    /* if we have 8 servos, then we are attached to PX4IO. In that
+     * case, we want to open the PX4FMU driver for the 4 additional
+     * channels
+     */
+    if (_servo_count <= 4) {
+        return;
+    }
+    _alt_fd = open("/dev/px4fmu", O_RDWR);
+    if (_alt_fd == -1) {
+        hal.console->printf("RCOutput: failed to open /dev/px4fmu");
+        return;
+    }
+    if (ioctl(_alt_fd, PWM_SERVO_ARM, 0) != 0) {
+        hal.console->printf("RCOutput: Unable to setup alt IO arming\n");
+    }
+    if (ioctl(_alt_fd, PWM_SERVO_GET_COUNT, (unsigned long)&_alt_servo_count) != 0) {
+        hal.console->printf("RCOutput: Unable to get servo count\n");        
+        return;
+    }
 }
 
 void PX4RCOutput::set_freq(uint32_t chmask, uint16_t freq_hz) 
 {
-    if (freq_hz == _freq_hz) {
-        // avoid the ioctl() if possible
-        return;
-    }
     // we can't set this per channel yet
-    if (ioctl(_pwm_fd, PWM_SERVO_SET_UPDATE_RATE, (unsigned long)freq_hz) == 0) {
+    if (freq_hz > 50) {
+        // we're being asked to set the alt rate
+        if (ioctl(_pwm_fd, PWM_SERVO_SET_UPDATE_RATE, (unsigned long)freq_hz) != 0) {
+            hal.console->printf("RCOutput: Unable to set alt rate to %uHz\n", (unsigned)freq_hz);
+            return;
+        }
         _freq_hz = freq_hz;
     }
+
+    /* work out the new rate mask. The PX4IO board has 3 groups of servos. 
+
+       Group 0: channels 0 1
+       Group 1: channels 4 5 6 7
+       Group 2: channels 2 3
+
+       Channels within a group must be set to the same rate.
+
+       For the moment we never set the channels above 8 to more than
+       50Hz
+     */
+    if (freq_hz > 50) {
+        // we are setting high rates on the given channels
+        _rate_mask |= chmask & 0xFF;
+        if (_rate_mask & 0x3) {
+            _rate_mask |= 0x3;
+        }
+        if (_rate_mask & 0xc) {
+            _rate_mask |= 0xc;
+        }
+        if (_rate_mask & 0xF0) {
+            _rate_mask |= 0xF0;
+        }
+    } else {
+        // we are setting low rates on the given channels
+        if (chmask & 0x3) {
+            _rate_mask &= ~0x3;
+        }
+        if (chmask & 0xc) {
+            _rate_mask &= ~0xc;
+        }
+        if (chmask & 0xf0) {
+            _rate_mask &= ~0xf0;
+        }
+    }
+
+    if (ioctl(_pwm_fd, PWM_SERVO_SELECT_UPDATE_RATE, _rate_mask) != 0) {
+        hal.console->printf("RCOutput: Unable to set alt rate mask to 0x%x\n", (unsigned)_rate_mask);
+    }
 }
 
 uint16_t PX4RCOutput::get_freq(uint8_t ch) 
 {
-	return _freq_hz;
+    if (_rate_mask & (1<<ch)) {
+        return _freq_hz;
+    }
+    return 50;
 }
 
 void PX4RCOutput::enable_ch(uint8_t ch)
@@ -67,7 +140,7 @@ void PX4RCOutput::disable_mask(uint32_t chmask)
 
 void PX4RCOutput::write(uint8_t ch, uint16_t period_us)
 {
-    if (ch >= PX4_NUM_OUTPUT_CHANNELS) {
+    if (ch >= _servo_count + _alt_servo_count) {
         return;
     }
     if (ch >= _max_channel) {
@@ -114,7 +187,19 @@ void PX4RCOutput::_timer_tick(void)
     if (_need_update && _pwm_fd != -1) {
         _need_update = false;
         perf_begin(_perf_rcout);
-        ::write(_pwm_fd, _period, _max_channel*sizeof(_period[0]));
+        if (_max_channel <= _servo_count) {
+            ::write(_pwm_fd, _period, _max_channel*sizeof(_period[0]));
+        } else {
+            // we're using both sets of outputs
+            ::write(_pwm_fd, _period, _servo_count*sizeof(_period[0]));
+            if (_alt_fd != -1 && _alt_servo_count > 0) {
+                uint8_t n = _max_channel - _servo_count;
+                if (n > _alt_servo_count) {
+                    n = _alt_servo_count;
+                }
+                ::write(_alt_fd, &_period[_servo_count], n*sizeof(_period[0]));
+            }
+        }
         perf_end(_perf_rcout);
         _last_output = now;
     }
diff --git a/libraries/AP_HAL_PX4/RCOutput.h b/libraries/AP_HAL_PX4/RCOutput.h
index 78850aafd5..bb92d7192d 100644
--- a/libraries/AP_HAL_PX4/RCOutput.h
+++ b/libraries/AP_HAL_PX4/RCOutput.h
@@ -26,12 +26,16 @@ public:
 
 private:
     int _pwm_fd;
+    int _alt_fd;
     uint16_t _freq_hz;
     uint16_t _period[PX4_NUM_OUTPUT_CHANNELS];
     volatile uint8_t _max_channel;
     volatile bool _need_update;
     perf_counter_t  _perf_rcout;
     uint32_t _last_output;
+    unsigned _servo_count;
+    unsigned _alt_servo_count;
+    uint32_t _rate_mask;
 };
 
 #endif // __AP_HAL_PX4_RCOUTPUT_H__