rotary_delta: Initial support for rotary delta kinematics

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 73 insertions, 0 deletions

diff --git a/klippy/chelper/kin_rotary_delta.c b/klippy/chelper/kin_rotary_delta.c
new file mode 100644
index 00000000..7859f6fc
--- /dev/null
+++ b/klippy/chelper/kin_rotary_delta.c
@@ -0,0 +1,73 @@
+// Rotary delta kinematics stepper pulse time generation
+//
+// Copyright (C) 2019  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include <math.h> // sqrt
+#include <stddef.h> // offsetof
+#include <stdlib.h> // malloc
+#include <string.h> // memset
+#include "compiler.h" // __visible
+#include "itersolve.h" // struct stepper_kinematics
+#include "trapq.h" // move_get_coord
+
+// The arm angle calculation is based on the following two formulas:
+//   elbow_x**2 + elbow_y**2 = upper_arm**2
+//   (effector_x - elbow_x)**2 + (effector_y - elbow_y)**2 = lower_arm**2
+
+// Calculate upper arm angle given xy position of effector joint
+// (relative to shoulder joint), upper arm length, and lower arm length.
+static inline double
+rotary_two_arm_calc(double dx, double dy, double upper_arm2, double lower_arm2)
+{
+    // Determine constants such that: elbow_y = c1 - c2*elbow_x
+    double inv_dy = 1. / dy;
+    double c1 = .5 * inv_dy * (dx*dx + dy*dy + upper_arm2 - lower_arm2);
+    double c2 = dx * inv_dy;
+    // Calculate scaled elbow coordinates via quadratic equation.
+    double scale = c2*c2 + 1.0;
+    double scaled_elbow_x = c1*c2 + sqrt(scale*upper_arm2 - c1*c1);
+    double scaled_elbow_y = c1*scale - c2*scaled_elbow_x;
+    // Calculate angle in radians
+    return atan2(scaled_elbow_y, scaled_elbow_x);
+}
+
+struct rotary_stepper {
+    struct stepper_kinematics sk;
+    double cos, sin, shoulder_radius, shoulder_height;
+    double upper_arm2, lower_arm2;
+};
+
+static double
+rotary_stepper_calc_position(struct stepper_kinematics *sk, struct move *m
+                             , double move_time)
+{
+    struct rotary_stepper *rs = container_of(sk, struct rotary_stepper, sk);
+    struct coord c = move_get_coord(m, move_time);
+    // Rotate and shift axes to an origin at shoulder joint with upper
+    // arm constrained to xy plane and x aligned to shoulder platform.
+    double sjz = c.y * rs->cos - c.x * rs->sin;
+    double sjx = c.x * rs->cos + c.y * rs->sin - rs->shoulder_radius;
+    double sjy = c.z - rs->shoulder_height;
+    // Calculate angle in radians
+    return rotary_two_arm_calc(sjx, sjy, rs->upper_arm2
+                               , rs->lower_arm2 - sjz*sjz);
+}
+
+struct stepper_kinematics * __visible
+rotary_delta_stepper_alloc(double shoulder_radius, double shoulder_height
+                           , double angle, double upper_arm, double lower_arm)
+{
+    struct rotary_stepper *rs = malloc(sizeof(*rs));
+    memset(rs, 0, sizeof(*rs));
+    rs->cos = cos(angle);
+    rs->sin = sin(angle);
+    rs->shoulder_radius = shoulder_radius;
+    rs->shoulder_height = shoulder_height;
+    rs->upper_arm2 = upper_arm * upper_arm;
+    rs->lower_arm2 = lower_arm * lower_arm;
+    rs->sk.calc_position_cb = rotary_stepper_calc_position;
+    rs->sk.active_flags = AF_X | AF_Y | AF_Z;
+    return &rs->sk;
+}