[motor mixing] add simple python script to calc motor mixing coeffs

sw/tools/motor_mixing.py

@@ -0,0 +1,89 @@
+#!/usr/bin/env python
+
+from __future__ import print_function, division
+
+import numpy as np
+import string
+
+
+class MotorMixing(object):
+    """Calculate motor mixing coefficients from a rotor configuration"""
+
+    # ClockWise and CounterClockWise rotation directions
+    CW = -0.1
+    CCW = 0.1
+
+    def __init__(self):
+        self.rotors = []
+
+    def add_rotor(self, x, y, r):
+        """Add a rotor with x and y coordinates (body frame) and rotation direction"""
+        self.rotors.append([x, y, r])
+
+    def calc_rotor_matrix(self, rotors):
+        """ convert a list of rotors to input matrix for coefficient calculation
+
+        arguments:
+        rotors -- list of rotors, each rotor as [x,y,r]
+
+        Rotor positions in body frame (x forward, y right) with rotation direction r (negative is CW, positive CCW)
+
+        """
+        m = np.asarray(rotors)
+        # "convert" positions to moments around axis
+        m[:, [0, 1, 2]] = m[:, [1, 0, 2]]
+        m[:, 0] *= -1
+        return m.T
+
+    def calc_coeffs(self, input_matrix=None, scale=None):
+        if input_matrix is None:
+            input_matrix = self.calc_rotor_matrix(self.rotors)
+        # Moore-Penrose pseudoinverse of input matrix (A)
+        B = np.linalg.pinv(np.asarray(input_matrix))
+        # normalize roll/pitch to the largest of both
+        # normalize yaw to 0.5
+        # and transpose
+        rp_max = np.fabs(B[:, 0:2]).max()
+        y_max = 2 * np.fabs(B[:, 2]).max()
+        n = np.array([rp_max, rp_max, y_max])
+        B_nt = (B / n).T
+        if scale is None:
+            return B_nt
+        elif isinstance(scale, int):
+            return np.around(scale * B_nt).astype(int)
+        else:
+            return np.around(scale * B_nt, 3)
+
+    def print_xml(self, coeffs=None, scale=256):
+        """calculate and print defines with mixing coefficients ready to paste to the airframe file"""
+        if coeffs is None:
+            coeffs = self.calc_coeffs(scale=scale)
+
+        def fmt(x):
+            if isinstance(x, int):
+                return '{:>4d}'.format(x)
+            else:
+                return '{:>4f}'.format(x)
+
+        print('<section name="MIXING" prefix="MOTOR_MIXING_">')
+        print('  <define name="NB_MOTOR"    value="{}"/>'.format(coeffs.shape[1]))
+        print('  <define name="SCALE"       value="{}"/>'.format(scale))
+        rows = ['ROLL_COEF"   ', 'PITCH_COEF"  ', 'YAW_COEF"    ']
+        for i, r in enumerate(rows):
+            print('  <define name="' + r + 'value="{' + string.join([fmt(c) for c in coeffs[i]], ', ') + '}"/>')
+        print('  <define name="THRUST_COEF" value="{' + string.join([fmt(scale)] * coeffs.shape[1], ', ') + '}"/>')
+        print('</section>')
+
+
+if __name__ == '__main__':
+    """Example for hexa in X configuration"""
+    mm = MotorMixing()
+    mm.add_rotor(0.87, -0.5, mm.CW)
+    mm.add_rotor(0.87, 0.5, mm.CCW)
+    mm.add_rotor(0, 1, mm.CW)
+    mm.add_rotor(-0.87, 0.5, mm.CCW)
+    mm.add_rotor(-0.87, -0.5, mm.CW)
+    mm.add_rotor(0, -1, mm.CCW)
+
+    print("Example for hexa in X configuration:\n")
+    mm.print_xml()