diff options
| author | Vegard Storheil Eriksen <zyp@jvnv.net> | 2011-04-11 05:46:10 +0200 |
|---|---|---|
| committer | Vegard Storheil Eriksen <zyp@jvnv.net> | 2011-04-11 05:46:10 +0200 |
| commit | 82ffa82cc0423ed83ab94def6d3295f424a7c03c (patch) | |
| tree | 3f95ee11a3c3d68371c33856bd5124eefe3c276b /IMU.cpp | |
| parent | c6ac90fc731d8411380f582be3b91ce4e93f61fc (diff) | |
Test IMU filter.
Diffstat (limited to 'IMU.cpp')
| -rwxr-xr-x | IMU.cpp | 92 |
1 files changed, 92 insertions, 0 deletions
@@ -0,0 +1,92 @@ +//=====================================================================================================
+// IMU.c
+// S.O.H. Madgwick
+// 25th September 2010
+//=====================================================================================================
+// Description:
+//
+// Quaternion implementation of the 'DCM filter' [Mayhony et al].
+//
+// User must define 'halfT' as the (sample period / 2), and the filter gains 'Kp' and 'Ki'.
+//
+// Global variables 'q0', 'q1', 'q2', 'q3' are the quaternion elements representing the estimated
+// orientation. See my report for an overview of the use of quaternions in this application.
+//
+// User must call 'IMUupdate()' every sample period and parse calibrated gyroscope ('gx', 'gy', 'gz')
+// and accelerometer ('ax', 'ay', 'ay') data. Gyroscope units are radians/second, accelerometer
+// units are irrelevant as the vector is normalised.
+//
+//=====================================================================================================
+
+//----------------------------------------------------------------------------------------------------
+// Header files
+
+#include "IMU.h"
+#include <math.h>
+#include <ch.h>
+
+//----------------------------------------------------------------------------------------------------
+// Definitions
+
+#define Kp 2.0f // proportional gain governs rate of convergence to accelerometer/magnetometer
+#define Ki 0.005f // integral gain governs rate of convergence of gyroscope biases
+#define halfT (0.5f / 100) // half the sample period
+
+//---------------------------------------------------------------------------------------------------
+// Variable definitions
+
+float q0 = 1, q1 = 0, q2 = 0, q3 = 0; // quaternion elements representing the estimated orientation
+float exInt = 0, eyInt = 0, ezInt = 0; // scaled integral error
+
+//====================================================================================================
+// Function
+//====================================================================================================
+
+void IMUupdate(float gx, float gy, float gz, float ax, float ay, float az) {
+ float norm;
+ float vx, vy, vz;
+ float ex, ey, ez;
+
+ // normalise the measurements
+ norm = sqrt(ax*ax + ay*ay + az*az);
+ ax = ax / norm;
+ ay = ay / norm;
+ az = az / norm;
+
+ // estimated direction of gravity
+ vx = 2*(q1*q3 - q0*q2);
+ vy = 2*(q0*q1 + q2*q3);
+ vz = q0*q0 - q1*q1 - q2*q2 + q3*q3;
+
+ // error is sum of cross product between reference direction of field and direction measured by sensor
+ ex = (ay*vz - az*vy);
+ ey = (az*vx - ax*vz);
+ ez = (ax*vy - ay*vx);
+
+ // integral error scaled integral gain
+ exInt = exInt + ex*Ki;
+ eyInt = eyInt + ey*Ki;
+ ezInt = ezInt + ez*Ki;
+
+ // adjusted gyroscope measurements
+ gx = gx + Kp*ex + exInt;
+ gy = gy + Kp*ey + eyInt;
+ gz = gz + Kp*ez + ezInt;
+
+ // integrate quaternion rate and normalise
+ q0 = q0 + (-q1*gx - q2*gy - q3*gz)*halfT;
+ q1 = q1 + (q0*gx + q2*gz - q3*gy)*halfT;
+ q2 = q2 + (q0*gy - q1*gz + q3*gx)*halfT;
+ q3 = q3 + (q0*gz + q1*gy - q2*gx)*halfT;
+
+ // normalise quaternion
+ norm = sqrt(q0*q0 + q1*q1 + q2*q2 + q3*q3);
+ q0 = q0 / norm;
+ q1 = q1 / norm;
+ q2 = q2 / norm;
+ q3 = q3 / norm;
+}
+
+//====================================================================================================
+// END OF CODE
+//====================================================================================================
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