diff --git a/libraries/AP_RPM/AP_RPM.cpp b/libraries/AP_RPM/AP_RPM.cpp
new file mode 100644
index 0000000000..3d17826c7f
--- /dev/null
+++ b/libraries/AP_RPM/AP_RPM.cpp
@@ -0,0 +1,119 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "AP_RPM.h"
+#include "RPM_PX4_PWM.h"
+
+extern const AP_HAL::HAL& hal;
+
+// table of user settable parameters
+const AP_Param::GroupInfo AP_RPM::var_info[] PROGMEM = {
+    // @Param: _TYPE
+    // @DisplayName: RPM type
+    // @Description: What type of RPM sensor is connected
+    // @Values: 0:None,1:PX4-PWM
+    AP_GROUPINFO("_TYPE",    0, AP_RPM, _type[0], 0),
+
+    // @Param: _SCALING
+    // @DisplayName: RPM scaling
+    // @Description: Scaling factor between sensor reading and RPM.
+    // @Increment: 0.001
+    AP_GROUPINFO("_SCALING", 1, AP_RPM, _scaling[0], 1.0f),
+
+#if RPM_MAX_INSTANCES > 1
+    // @Param: 2_TYPE
+    // @DisplayName: Second RPM type
+    // @Description: What type of RPM sensor is connected
+    // @Values: 0:None,1:PX4-PWM
+    AP_GROUPINFO("2_TYPE",    10, AP_RPM, _type[1], 0),
+
+    // @Param: 2_SCALING
+    // @DisplayName: RPM scaling
+    // @Description: Scaling factor between sensor reading and RPM.
+    // @Increment: 0.001
+    AP_GROUPINFO("2_SCALING", 11, AP_RPM, _scaling[1], 1.0f),
+#endif
+
+    AP_GROUPEND
+};
+
+AP_RPM::AP_RPM(void) :
+    num_instances(0)
+{
+    AP_Param::setup_object_defaults(this, var_info);
+
+    // init state and drivers
+    memset(state,0,sizeof(state));
+    memset(drivers,0,sizeof(drivers));
+}
+
+/*
+  initialise the AP_RPM class. 
+ */
+void AP_RPM::init(void)
+{
+    if (num_instances != 0) {
+        // init called a 2nd time?
+        return;
+    }
+    for (uint8_t i=0; i<RPM_MAX_INSTANCES; i++) {
+#if CONFIG_HAL_BOARD == HAL_BOARD_PX4  || CONFIG_HAL_BOARD == HAL_BOARD_VRBRAIN
+        uint8_t type = _type[num_instances];
+        uint8_t instance = num_instances;
+
+        if (type == RPM_TYPE_PX4_PWM) {
+            state[instance].instance = instance;
+            drivers[instance] = new AP_RPM_PX4_PWM(*this, instance, state[instance]);
+        }
+#endif
+        if (drivers[i] != NULL) {
+            // we loaded a driver for this instance, so it must be
+            // present (although it may not be healthy)
+            num_instances = i+1;
+        }
+    }
+}
+
+/*
+  update RPM state for all instances. This should be called by main loop
+ */
+void AP_RPM::update(void)
+{
+    for (uint8_t i=0; i<num_instances; i++) {
+        if (drivers[i] != NULL) {
+            if (_type[i] == RPM_TYPE_NONE) {
+                // allow user to disable a RPM sensor at runtime
+                continue;
+            }
+            drivers[i]->update();
+        }
+    }
+}
+    
+/*
+  check if an instance is healthy
+ */
+bool AP_RPM::healthy(uint8_t instance) const
+{
+    if (instance >= num_instances) {
+        return false;
+    }
+    // assume we get readings at at least 1Hz
+    if (hal.scheduler->millis() - state[instance].last_reading_ms > 1000) {
+        return false;
+    }
+    return true;
+}
diff --git a/libraries/AP_RPM/AP_RPM.h b/libraries/AP_RPM/AP_RPM.h
new file mode 100644
index 0000000000..cbfebb7ec9
--- /dev/null
+++ b/libraries/AP_RPM/AP_RPM.h
@@ -0,0 +1,87 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __RPM_H__
+#define __RPM_H__
+
+#include <AP_Common/AP_Common.h>
+#include <AP_HAL/AP_HAL.h>
+#include <AP_Param/AP_Param.h>
+#include <AP_Math/AP_Math.h>
+
+// Maximum number of RPM measurement instances available on this platform
+#define RPM_MAX_INSTANCES 2
+
+class AP_RPM_Backend; 
+ 
+class AP_RPM
+{
+public:
+    friend class AP_RPM_Backend;
+
+    AP_RPM(void);
+
+    // RPM driver types
+    enum RPM_Type {
+        RPM_TYPE_NONE    = 0,
+        RPM_TYPE_PX4_PWM = 1
+    };
+
+    // The RPM_State structure is filled in by the backend driver
+    struct RPM_State {
+        uint8_t                instance;        // the instance number of this RPM
+        float                  rate_rpm;        // measured rate in revs per minute
+        uint32_t               last_reading_ms; // time of last reading
+    };
+
+    // parameters for each instance
+    AP_Int8  _type[RPM_MAX_INSTANCES];
+    AP_Float _scaling[RPM_MAX_INSTANCES];
+
+    static const struct AP_Param::GroupInfo var_info[];
+    
+    // Return the number of rpm sensor instances
+    uint8_t num_sensors(void) const {
+        return num_instances;
+    }
+
+    // detect and initialise any available rpm sensors
+    void init(void);
+
+    // update state of all rpm sensors. Should be called from main loop
+    void update(void);
+
+    /*
+      return RPM for a sensor. Return -1 if not healthy
+     */
+    float get_rpm(uint8_t instance) const {
+        if (!healthy(instance)) {
+            return -1;
+        }
+        return state[instance].rate_rpm;
+    }
+
+    bool healthy(uint8_t instance) const;
+
+private:
+    RPM_State state[RPM_MAX_INSTANCES];
+    AP_RPM_Backend *drivers[RPM_MAX_INSTANCES];
+    uint8_t num_instances:2;
+
+    void detect_instance(uint8_t instance);
+    void update_instance(uint8_t instance);  
+};
+#endif // __RPM_H__
diff --git a/libraries/AP_RPM/RPM_Backend.cpp b/libraries/AP_RPM/RPM_Backend.cpp
new file mode 100644
index 0000000000..cec72b74cf
--- /dev/null
+++ b/libraries/AP_RPM/RPM_Backend.cpp
@@ -0,0 +1,29 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <AP_Common.h>
+#include <AP_HAL.h>
+#include "AP_RPM.h"
+#include "RPM_Backend.h"
+
+/*
+  base class constructor. 
+*/
+AP_RPM_Backend::AP_RPM_Backend(AP_RPM &_ap_rpm, uint8_t instance, AP_RPM::RPM_State &_state) :
+        ap_rpm(_ap_rpm),
+        state(_state) 
+{
+}
diff --git a/libraries/AP_RPM/RPM_Backend.h b/libraries/AP_RPM/RPM_Backend.h
new file mode 100644
index 0000000000..57241bfa44
--- /dev/null
+++ b/libraries/AP_RPM/RPM_Backend.h
@@ -0,0 +1,42 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __AP_RPM_BACKEND_H__
+#define __AP_RPM_BACKEND_H__
+
+#include <AP_Common.h>
+#include <AP_HAL.h>
+#include "AP_RPM.h"
+
+class AP_RPM_Backend
+{
+public:
+    // constructor. This incorporates initialisation as well.
+	AP_RPM_Backend(AP_RPM &_ap_rpm, uint8_t instance, AP_RPM::RPM_State &_state);
+
+    // we declare a virtual destructor so that RPM drivers can
+    // override with a custom destructor if need be
+    virtual ~AP_RPM_Backend(void) {}
+
+    // update the state structure. All backends must implement this.
+    virtual void update() = 0;
+
+protected:
+
+    AP_RPM &ap_rpm;
+    AP_RPM::RPM_State &state;
+};
+#endif // __AP_RPM_BACKEND_H__
diff --git a/libraries/AP_RPM/RPM_PX4_PWM.cpp b/libraries/AP_RPM/RPM_PX4_PWM.cpp
new file mode 100644
index 0000000000..4ee145eef8
--- /dev/null
+++ b/libraries/AP_RPM/RPM_PX4_PWM.cpp
@@ -0,0 +1,94 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <AP_HAL.h>
+
+#if CONFIG_HAL_BOARD == HAL_BOARD_PX4 || CONFIG_HAL_BOARD == HAL_BOARD_VRBRAIN
+#include "RPM_PX4_PWM.h"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <drivers/drv_pwm_input.h>
+#include <drivers/drv_hrt.h>
+#include <drivers/drv_sensor.h>
+#include <uORB/topics/pwm_input.h>
+#include <stdio.h>
+#include <errno.h>
+#include <math.h>
+
+extern const AP_HAL::HAL& hal;
+
+/* 
+   open the sensor in constructor
+*/
+AP_RPM_PX4_PWM::AP_RPM_PX4_PWM(AP_RPM &_ap_rpm, uint8_t instance, AP_RPM::RPM_State &_state) :
+	AP_RPM_Backend(_ap_rpm, instance, _state)
+{
+    _fd = open(PWMIN0_DEVICE_PATH, O_RDONLY);
+    if (_fd == -1) {
+        hal.console->printf("Unable to open %s\n", PWMIN0_DEVICE_PATH);
+        return;
+    }
+
+    // keep a queue of 5 samples to reduce noise by averaging
+    if (ioctl(_fd, SENSORIOCSQUEUEDEPTH, 5) != 0) {
+        hal.console->printf("Failed to setup RPM queue\n");
+        close(_fd);
+        _fd = -1;
+        return;
+    }
+}
+
+/* 
+   close the file descriptor
+*/
+AP_RPM_PX4_PWM::~AP_RPM_PX4_PWM()
+{
+    if (_fd != -1) {
+        close(_fd);
+        _fd = -1;
+    }
+}
+
+void AP_RPM_PX4_PWM::update(void)
+{
+    if (_fd == -1) {
+        return;
+    }
+
+    struct pwm_input_s pwm;
+    uint16_t count = 0;
+    const float scaling = ap_rpm._scaling[state.instance];
+    float sum = 0;
+
+    while (::read(_fd, &pwm, sizeof(pwm)) == sizeof(pwm)) {
+        // the px4 pwm_input driver reports the period in microseconds
+        if (pwm.period > 0) {
+            sum += (1.0e6f * 60) / pwm.period;
+            count++;
+        }
+    }
+
+    if (count != 0) {
+        state.rate_rpm = scaling * sum / count;
+        state.last_reading_ms = hal.scheduler->millis();
+    }
+}
+
+#endif // CONFIG_HAL_BOARD
diff --git a/libraries/AP_RPM/RPM_PX4_PWM.h b/libraries/AP_RPM/RPM_PX4_PWM.h
new file mode 100644
index 0000000000..87d9446047
--- /dev/null
+++ b/libraries/AP_RPM/RPM_PX4_PWM.h
@@ -0,0 +1,40 @@
+// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+ 
+#ifndef AP_RPM_PX4_PWM_H
+#define AP_RPM_PX4_PWM_H
+
+#include "AP_RPM.h"
+#include "RPM_Backend.h"
+
+class AP_RPM_PX4_PWM : public AP_RPM_Backend
+{
+public:
+    // constructor
+    AP_RPM_PX4_PWM(AP_RPM &ranger, uint8_t instance, AP_RPM::RPM_State &_state);
+
+    // destructor
+    ~AP_RPM_PX4_PWM(void);
+    
+    // update state
+    void update(void);
+
+private:
+    int _fd = -1;
+    uint64_t _last_timestamp = 0;
+};
+
+#endif // AP_RPM_PX4_PWM_H