delta: Initial support for linear delta kinematics

This adds support for delta based robots.

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

8 files changed, 507 insertions, 5 deletions

diff --git a/config/example-delta.cfg b/config/example-delta.cfg
new file mode 100644
index 00000000..777f7dc2
--- /dev/null
+++ b/config/example-delta.cfg
@@ -0,0 +1,94 @@
+# This file serves as documentation for config parameters of delta
+# style printers. One may copy and edit this file to configure a new
+# delta printer. Only parameters unique to delta printers are
+# described here - see the "example.cfg" file for description of
+# common config parameters.
+
+# DO NOT COPY THIS FILE WITHOUT CAREFULLY READING AND UPDATING IT
+# FIRST. Incorrectly configured parameters may cause damage.
+
+# The stepper_a section describes the stepper controlling the front
+# left tower (at 210 degrees). This section also controls the homing
+# parameters (homing_speed, homing_retract_dist) and maximum tower
+# length (position_max) for all towers.
+[stepper_a]
+step_pin: ar54
+dir_pin: ar55
+enable_pin: !ar38
+step_distance: .01
+max_velocity: 200
+max_accel: 3000
+endstop_pin: ^ar2
+homing_speed: 50.0
+position_endstop: 297.05
+position_max: 297.55
+
+# The stepper_b section describes the stepper controlling the front
+# right tower (at 330 degrees)
+[stepper_b]
+step_pin: ar60
+dir_pin: ar61
+enable_pin: !ar56
+step_distance: .01
+max_velocity: 200
+max_accel: 3000
+endstop_pin: ^ar15
+position_endstop: 297.05
+
+# The stepper_c section describes the stepper controlling the rear
+# tower (at 90 degrees)
+[stepper_c]
+step_pin: ar46
+dir_pin: ar48
+enable_pin: !ar62
+step_distance: .01
+max_velocity: 200
+max_accel: 3000
+endstop_pin: ^ar19
+position_endstop: 297.05
+
+[extruder]
+step_pin: ar26
+dir_pin: ar28
+enable_pin: !ar24
+step_distance: .0022
+max_velocity: 200
+max_accel: 3000
+heater_pin: ar10
+thermistor_pin: analog13
+thermistor_type: ATC Semitec 104GT-2
+control: pid
+pid_Kp: 22.2
+pid_Ki: 1.08
+pid_Kd: 114
+min_temp: 0
+max_temp: 250
+
+[heater_bed]
+heater_pin: ar8
+thermistor_pin: analog14
+thermistor_type: EPCOS 100K B57560G104F
+control: watermark
+min_temp: 0
+max_temp: 130
+
+# Extruder print fan (omit section if fan not present)
+#[fan]
+#pin: ar9
+#hard_pwm: 1
+
+[mcu]
+serial: /dev/ttyACM0
+baud: 250000
+pin_map: arduino
+
+[printer]
+kinematics: delta
+#   This option must be "delta" for linear delta printers
+delta_arm_length: 333.0
+#   Length (in mm) of the diagonal rods that connect the linear axes
+#   to the print head
+delta_radius: 174.75
+#   Radius (in mm) of the horizontal circle formed by the three linear
+#   axis towers. This parameter may also be calculated as:
+#    delta_radius = smooth_rod_offset - effector_offset - carriage_offset
diff --git a/config/example.cfg b/config/example.cfg
index a8f7aee4..1bc1dd59 100644
--- a/config/example.cfg
+++ b/config/example.cfg
@@ -1,5 +1,6 @@
 # This file serves as documentation for config parameters. One may
-# copy and edit this file to configure a new printer.
+# copy and edit this file to configure a new cartesian style
+# printer. For delta style printers, see the "example-delta.cfg" file.
 
 # DO NOT COPY THIS FILE WITHOUT CAREFULLY READING AND UPDATING IT
 # FIRST. Incorrectly configured parameters may cause damage.
@@ -189,7 +190,7 @@ custom:
 # The printer section controls high level printer settings
 [printer]
 kinematics: cartesian
-#   This option must currently always be "cartesian"
+#   This option must be "cartesian" for cartesian printers
 motor_off_time: 60
 #   Time (in seconds) of idle time before the printer will try to
 #   disable active motors.
diff --git a/docs/Todo.md b/docs/Todo.md
index 0f454d4c..530104d8 100644
--- a/docs/Todo.md
+++ b/docs/Todo.md
@@ -126,7 +126,7 @@ Hardware features
  * Smoothieboard / NXP LPC1769 (ARM cortex-M3)
  * Unix based scheduling; Unix based real-time scheduling
 
-* Support for additional kinematics: delta, scara, corexy, etc.
+* Support for additional kinematics: scara, corexy, etc.
 
 * Support shared motor enable GPIO lines.
 
diff --git a/klippy/chelper.py b/klippy/chelper.py
index a3ce4a95..d12946be 100644
--- a/klippy/chelper.py
+++ b/klippy/chelper.py
@@ -23,6 +23,14 @@ defs_stepcompress = """
     int32_t stepcompress_push_sqrt(struct stepcompress *sc
         , double steps, double step_offset
         , double clock_offset, double sqrt_offset, double factor);
+    int32_t stepcompress_push_delta_const(
+        struct stepcompress *sc, double clock_offset, double dist
+        , double step_dist, double start_pos, double closest_height2
+        , double height, double movez_r, double inv_velocity);
+    int32_t stepcompress_push_delta_accel(
+        struct stepcompress *sc, double clock_offset, double dist
+        , double step_dist, double start_pos, double closest_height2
+        , double height, double movez_r, double accel_multiplier);
     void stepcompress_reset(struct stepcompress *sc, uint64_t last_step_clock);
     void stepcompress_queue_msg(struct stepcompress *sc
         , uint32_t *data, int len);
diff --git a/klippy/delta.py b/klippy/delta.py
new file mode 100644
index 00000000..0fa8caf2
--- /dev/null
+++ b/klippy/delta.py
@@ -0,0 +1,310 @@
+# Code for handling the kinematics of linear delta robots
+#
+# Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+import math, logging
+import stepper, homing
+
+StepList = (0, 1, 2)
+
+class DeltaKinematics:
+    def __init__(self, printer, config):
+        steppers = ['stepper_a', 'stepper_b', 'stepper_c']
+        self.steppers = [stepper.PrinterStepper(printer, config.getsection(n))
+                         for n in steppers]
+        radius = config.getfloat('delta_radius')
+        arm_length = config.getfloat('delta_arm_length')
+        self.arm_length2 = arm_length**2
+        self.max_xy2 = min(radius, arm_length - radius)**2
+        self.limit_xy2 = -1.
+        tower_height_at_zeros = math.sqrt(self.arm_length2 - radius**2)
+        self.max_z = self.steppers[0].position_max
+        self.limit_z = self.max_z - (arm_length - tower_height_at_zeros)
+        sin = lambda angle: math.sin(math.radians(angle))
+        cos = lambda angle: math.cos(math.radians(angle))
+        self.towers = [
+            (cos(210.)*radius, sin(210.)*radius),
+            (cos(330.)*radius, sin(330.)*radius),
+            (cos(90.)*radius, sin(90.)*radius)]
+        self.stepper_pos = self.cartesian_to_actuator([0., 0., 0.])
+    def build_config(self):
+        for stepper in self.steppers:
+            stepper.set_max_jerk(0.005 * stepper.max_accel) # XXX
+        for stepper in self.steppers:
+            stepper.build_config()
+    def get_max_speed(self):
+        # XXX - this returns conservative values
+        max_xy_speed = min(s.max_velocity for s in self.steppers)
+        max_xy_accel = min(s.max_accel for s in self.steppers)
+        return max_xy_speed, max_xy_accel
+    def cartesian_to_actuator(self, coord):
+        return [int((math.sqrt(self.arm_length2
+                               - (self.towers[i][0] - coord[0])**2
+                               - (self.towers[i][1] - coord[1])**2) + coord[2])
+                    * self.steppers[i].inv_step_dist + 0.5)
+                for i in StepList]
+    def actuator_to_cartesian(self, pos):
+        # Based on code from Smoothieware
+        tower1 = list(self.towers[0]) + [pos[0]]
+        tower2 = list(self.towers[1]) + [pos[1]]
+        tower3 = list(self.towers[2]) + [pos[2]]
+
+        s12 = matrix_sub(tower1, tower2)
+        s23 = matrix_sub(tower2, tower3)
+        s13 = matrix_sub(tower1, tower3)
+
+        normal = matrix_cross(s12, s23)
+
+        magsq_s12 = matrix_magsq(s12)
+        magsq_s23 = matrix_magsq(s23)
+        magsq_s13 = matrix_magsq(s13)
+
+        inv_nmag_sq = 1.0 / matrix_magsq(normal)
+        q = 0.5 * inv_nmag_sq
+
+        a = q * magsq_s23 * matrix_dot(s12, s13)
+        b = -q * magsq_s13 * matrix_dot(s12, s23) # negate because we use s12 instead of s21
+        c = q * magsq_s12 * matrix_dot(s13, s23)
+
+        circumcenter = [tower1[0] * a + tower2[0] * b + tower3[0] * c,
+                        tower1[1] * a + tower2[1] * b + tower3[1] * c,
+                        tower1[2] * a + tower2[2] * b + tower3[2] * c]
+
+        r_sq = 0.5 * q * magsq_s12 * magsq_s23 * magsq_s13
+        dist = math.sqrt(inv_nmag_sq * (self.arm_length2 - r_sq))
+
+        return matrix_sub(circumcenter, matrix_mul(normal, dist))
+    def set_position(self, newpos):
+        self.stepper_pos = self.cartesian_to_actuator(newpos)
+    def get_homed_position(self):
+        pos = [(self.stepper_pos[i] + self.steppers[i].get_homed_offset())
+               * self.steppers[i].step_dist
+               for i in StepList]
+        return self.actuator_to_cartesian(pos)
+    def home(self, toolhead, axes):
+        # All axes are homed simultaneously
+        homing_state = homing.Homing(toolhead, [0, 1, 2])
+        s = self.steppers[0] # Assume homing parameters same for all steppers
+        self.limit_xy2 = self.max_xy2
+        # Initial homing
+        homepos = [0., 0., s.position_endstop, None]
+        coord = list(homepos)
+        coord[2] -= 1.5*(s.position_endstop)
+        homing_state.plan_home(list(coord), homepos, self.steppers
+                               , s.homing_speed)
+        # Retract
+        coord[2] = homepos[2] - s.homing_retract_dist
+        homing_state.plan_move(list(coord), s.homing_speed)
+        # Home again
+        coord[2] -= s.homing_retract_dist
+        homing_state.plan_home(list(coord), homepos, self.steppers
+                               , s.homing_speed/2.0)
+        return homing_state
+    def motor_off(self, move_time):
+        self.limit_xy2 = -1.
+        for stepper in self.steppers:
+            stepper.motor_enable(move_time, 0)
+    def query_endstops(self, move_time):
+        return homing.QueryEndstops(["a", "b", "c"], self.steppers)
+    def check_move(self, move):
+        end_pos = move.end_pos
+        xy2 = end_pos[0]**2 + end_pos[1]**2
+        if xy2 > self.limit_xy2 or end_pos[2] < 0.:
+            if self.limit_xy2 < 0.:
+                raise homing.EndstopError(end_pos, "Must home first")
+            raise homing.EndstopError(end_pos)
+        if end_pos[2] > self.limit_z:
+            if end_pos[2] > self.max_z or xy2 > (self.max_z - end_pos[2])**2:
+                raise homing.EndstopError(end_pos)
+    def move_z(self, move_time, move):
+        if not move.axes_d[2]:
+            return
+        inv_accel = 1. / move.accel
+        inv_cruise_v = 1. / move.cruise_v
+        for i in StepList:
+            towerx_d = self.towers[i][0] - move.start_pos[0]
+            towery_d = self.towers[i][1] - move.start_pos[1]
+            tower_d2 = towerx_d**2 + towery_d**2
+            height = math.sqrt(self.arm_length2 - tower_d2) + move.start_pos[2]
+
+            mcu_time, so = self.steppers[i].prep_move(move_time)
+            inv_step_dist = self.steppers[i].inv_step_dist
+            step_dist = self.steppers[i].step_dist
+            steps = move.axes_d[2] * inv_step_dist
+
+            step_pos = self.stepper_pos[i]
+            step_offset = step_pos - height * inv_step_dist
+
+            # Acceleration steps
+            accel_multiplier = 2.0 * step_dist * inv_accel
+            if move.accel_r:
+                #t = sqrt(2*pos/accel + (start_v/accel)**2) - start_v/accel
+                accel_time_offset = move.start_v * inv_accel
+                accel_sqrt_offset = accel_time_offset**2
+                accel_steps = move.accel_r * steps
+                count = so.step_sqrt(
+                    mcu_time - accel_time_offset, accel_steps, step_offset
+                    , accel_sqrt_offset, accel_multiplier)
+                step_pos += count
+                step_offset += count - accel_steps
+                mcu_time += move.accel_t
+            # Cruising steps
+            if move.cruise_r:
+                #t = pos/cruise_v
+                cruise_multiplier = step_dist * inv_cruise_v
+                cruise_steps = move.cruise_r * steps
+                count = so.step_factor(
+                    mcu_time, cruise_steps, step_offset, cruise_multiplier)
+                step_pos += count
+                step_offset += count - cruise_steps
+                mcu_time += move.cruise_t
+            # Deceleration steps
+            if move.decel_r:
+                #t = cruise_v/accel - sqrt((cruise_v/accel)**2 - 2*pos/accel)
+                decel_time_offset = move.cruise_v * inv_accel
+                decel_sqrt_offset = decel_time_offset**2
+                decel_steps = move.decel_r * steps
+                count = so.step_sqrt(
+                    mcu_time + decel_time_offset, decel_steps, step_offset
+                    , decel_sqrt_offset, -accel_multiplier)
+                step_pos += count
+            self.stepper_pos[i] = step_pos
+    def move(self, move_time, move):
+        axes_d = move.axes_d
+        if not axes_d[0] and not axes_d[1]:
+            self.move_z(move_time, move)
+            return
+        move_d = move.move_d
+        movez_r = 0.
+        inv_movexy_d = 1. / move_d
+        inv_movexy_r = 1.
+        if axes_d[2]:
+            movez_r = axes_d[2] * inv_movexy_d
+            inv_movexy_d = 1. / math.sqrt(axes_d[0]**2 + axes_d[1]**2)
+            inv_movexy_r = move_d * inv_movexy_d
+
+        origx, origy, origz = move.start_pos[:3]
+
+        accel_t = move.accel_t
+        cruise_end_t = accel_t + move.cruise_t
+        accel_d = move.accel_r * move_d
+        cruise_end_d = accel_d + move.cruise_r * move_d
+
+        inv_cruise_v = 1. / move.cruise_v
+        inv_accel = 1. / move.accel
+        accel_time_offset = move.start_v * inv_accel
+        accel_multiplier = 2.0 * inv_accel
+        accel_offset = move.start_v**2 * 0.5 * inv_accel
+        decel_time_offset = move.cruise_v * inv_accel + cruise_end_t
+        decel_offset = move.cruise_v**2 * 0.5 * inv_accel + cruise_end_d
+
+        for i in StepList:
+            # Find point on line of movement closest to tower
+            towerx_d = self.towers[i][0] - origx
+            towery_d = self.towers[i][1] - origy
+            closestxy_d = (towerx_d*axes_d[0] + towery_d*axes_d[1])*inv_movexy_d
+            tangentxy_d2 = towerx_d**2 + towery_d**2 - closestxy_d**2
+            closest_height2 = self.arm_length2 - tangentxy_d2
+            closest_height = math.sqrt(closest_height2)
+            closest_d = closestxy_d * inv_movexy_r
+            closestz = origz + closest_d*movez_r
+
+            # Calculate accel/cruise/decel portions of move
+            reverse_d = closest_d + closest_height*movez_r*inv_movexy_r
+            accel_up_d = cruise_up_d = decel_up_d = 0.
+            accel_down_d = cruise_down_d = decel_down_d = 0.
+            if reverse_d <= 0.:
+                accel_down_d = accel_d
+                cruise_down_d = cruise_end_d
+                decel_down_d = move_d
+            elif reverse_d >= move_d:
+                accel_up_d = accel_d
+                cruise_up_d = cruise_end_d
+                decel_up_d = move_d
+            elif reverse_d < accel_d:
+                accel_up_d = reverse_d
+                accel_down_d = accel_d
+                cruise_down_d = cruise_end_d
+                decel_down_d = move_d
+            elif reverse_d < cruise_end_d:
+                accel_up_d = accel_d
+                cruise_up_d = reverse_d
+                cruise_down_d = cruise_end_d
+                decel_down_d = move_d
+            else:
+                accel_up_d = accel_d
+                cruise_up_d = cruise_end_d
+                decel_up_d = reverse_d
+                decel_down_d = move_d
+
+            # Generate steps
+            inv_step_dist = self.steppers[i].inv_step_dist
+            step_dist = self.steppers[i].step_dist
+            step_pos = self.stepper_pos[i]
+            height = step_pos*step_dist - closestz
+            mcu_time, so = self.steppers[i].prep_move(move_time)
+            if accel_up_d > 0.:
+                count = so.step_delta_accel(
+                    mcu_time - accel_time_offset, closest_d - accel_up_d,
+                    step_dist, closest_d + accel_offset,
+                    closest_height2, height, movez_r, accel_multiplier)
+                step_pos += count
+                height += count * step_dist
+            if cruise_up_d > 0.:
+                count = so.step_delta_const(
+                    mcu_time + accel_t, closest_d - cruise_up_d,
+                    step_dist, closest_d - accel_d,
+                    closest_height2, height, movez_r, inv_cruise_v)
+                step_pos += count
+                height += count * step_dist
+            if decel_up_d > 0.:
+                count = so.step_delta_accel(
+                    mcu_time + decel_time_offset, closest_d - decel_up_d,
+                    step_dist, closest_d - decel_offset,
+                    closest_height2, height, movez_r, -accel_multiplier)
+                step_pos += count
+                height += count * step_dist
+            if accel_down_d > 0.:
+                count = so.step_delta_accel(
+                    mcu_time - accel_time_offset, closest_d - accel_down_d,
+                    -step_dist, closest_d + accel_offset,
+                    closest_height2, height, movez_r, accel_multiplier)
+                step_pos += count
+                height += count * step_dist
+            if cruise_down_d > 0.:
+                count = so.step_delta_const(
+                    mcu_time + accel_t, closest_d - cruise_down_d,
+                    -step_dist, closest_d - accel_d,
+                    closest_height2, height, movez_r, inv_cruise_v)
+                step_pos += count
+                height += count * step_dist
+            if decel_down_d > 0.:
+                count = so.step_delta_accel(
+                    mcu_time + decel_time_offset, closest_d - decel_down_d,
+                    -step_dist, closest_d - decel_offset,
+                    closest_height2, height, movez_r, -accel_multiplier)
+                step_pos += count
+            self.stepper_pos[i] = step_pos
+
+
+######################################################################
+# Matrix helper functions for 3x1 matrices
+######################################################################
+
+def matrix_cross(m1, m2):
+    return [m1[1] * m2[2] - m1[2] * m2[1],
+            m1[2] * m2[0] - m1[0] * m2[2],
+            m1[0] * m2[1] - m1[1] * m2[0]]
+
+def matrix_dot(m1, m2):
+    return m1[0] * m2[0] + m1[1] * m2[1] + m1[2] * m2[2]
+
+def matrix_magsq(m1):
+    return m1[0]**2 + m1[1]**2 + m1[2]**2
+
+def matrix_sub(m1, m2):
+    return [m1[0] - m2[0], m1[1] - m2[1], m1[2] - m2[2]]
+
+def matrix_mul(m1, s):
+    return [m1[0]*s, m1[1]*s, m1[2]*s]
diff --git a/klippy/mcu.py b/klippy/mcu.py
index 79537ed6..2c1e518b 100644
--- a/klippy/mcu.py
+++ b/klippy/mcu.py
@@ -69,6 +69,19 @@ class MCU_stepper:
         clock = mcu_time * self._mcu_freq
         return self.ffi_lib.stepcompress_push_factor(
             self._stepqueue, steps, step_offset, clock, factor * self._mcu_freq)
+    def step_delta_const(self, mcu_time, dist, step_dist, start_pos
+                         , closest_height2, height, movez_r, inv_velocity):
+        clock = mcu_time * self._mcu_freq
+        return self.ffi_lib.stepcompress_push_delta_const(
+            self._stepqueue, clock, dist, step_dist, start_pos
+            , closest_height2, height, movez_r, inv_velocity * self._mcu_freq)
+    def step_delta_accel(self, mcu_time, dist, step_dist, start_pos
+                         , closest_height2, height, movez_r, accel_multiplier):
+        clock = mcu_time * self._mcu_freq
+        mcu_freq2 = self._mcu_freq**2
+        return self.ffi_lib.stepcompress_push_delta_accel(
+            self._stepqueue, clock, dist, step_dist, start_pos
+            , closest_height2, height, movez_r, accel_multiplier * mcu_freq2)
     def get_errors(self):
         return self.ffi_lib.stepcompress_get_errors(self._stepqueue)
 
diff --git a/klippy/stepcompress.c b/klippy/stepcompress.c
index c3f06761..992155d2 100644
--- a/klippy/stepcompress.c
+++ b/klippy/stepcompress.c
@@ -428,6 +428,79 @@ stepcompress_push_sqrt(struct stepcompress *sc, double steps, double step_offset
     return sdir ? count : -count;
 }
 
+// Schedule 'count' number of steps using the delta kinematic const speed
+int32_t
+stepcompress_push_delta_const(
+    struct stepcompress *sc, double clock_offset, double dist, double step_dist
+    , double start_pos, double closest_height2, double height, double movez_r
+    , double inv_velocity)
+{
+    // Calculate number of steps to take
+    double zdist = dist * movez_r;
+    int count = (safe_sqrt(closest_height2 - dist*dist + zdist*zdist)
+                 - height - zdist) / step_dist + .5;
+    if (count <= 0 || count > 1000000) {
+        if (count)
+            fprintf(stderr, "ERROR: push_delta_const invalid count"
+                    " %d %d %f %f %f %f %f %f %f %f\n"
+                    , sc->oid, count, clock_offset, dist, step_dist, start_pos
+                    , closest_height2, height, movez_r, inv_velocity);
+        return 0;
+    }
+    check_expand(sc, step_dist > 0., count);
+
+    // Calculate each step time
+    uint64_t *qn = sc->queue_next, *end = &qn[count];
+    clock_offset += 0.5;
+    height += .5 * step_dist;
+    while (qn < end) {
+        double zh = height*movez_r;
+        double v = safe_sqrt(closest_height2 - height*height + zh*zh);
+        double pos = start_pos + zh + (step_dist > 0. ? -v : v);
+        *qn++ = clock_offset + pos * inv_velocity;
+        height += step_dist;
+    }
+    sc->queue_next = qn;
+    return step_dist > 0. ? count : -count;
+}
+
+// Schedule 'count' number of steps using delta kinematic acceleration
+int32_t
+stepcompress_push_delta_accel(
+    struct stepcompress *sc, double clock_offset, double dist, double step_dist
+    , double start_pos, double closest_height2, double height, double movez_r
+    , double accel_multiplier)
+{
+    // Calculate number of steps to take
+    double zdist = dist * movez_r;
+    int count = (safe_sqrt(closest_height2 - dist*dist + zdist*zdist)
+                 - height - zdist) / step_dist + .5;
+    if (count <= 0 || count > 1000000) {
+        if (count)
+            fprintf(stderr, "ERROR: push_delta_accel invalid count"
+                    " %d %d %f %f %f %f %f %f %f %f\n"
+                    , sc->oid, count, clock_offset, dist, step_dist, start_pos
+                    , closest_height2, height, movez_r, accel_multiplier);
+        return 0;
+    }
+    check_expand(sc, step_dist > 0., count);
+
+    // Calculate each step time
+    uint64_t *qn = sc->queue_next, *end = &qn[count];
+    clock_offset += 0.5;
+    height += .5 * step_dist;
+    while (qn < end) {
+        double zh = height*movez_r;
+        double v = safe_sqrt(closest_height2 - height*height + zh*zh);
+        double pos = start_pos + zh + (step_dist > 0. ? -v : v);
+        v = safe_sqrt(pos * accel_multiplier);
+        *qn++ = clock_offset + (accel_multiplier >= 0. ? v : -v);
+        height += step_dist;
+    }
+    sc->queue_next = qn;
+    return step_dist > 0. ? count : -count;
+}
+
 // Reset the internal state of the stepcompress object
 void
 stepcompress_reset(struct stepcompress *sc, uint64_t last_step_clock)
diff --git a/klippy/toolhead.py b/klippy/toolhead.py
index d57a22e5..91843805 100644
--- a/klippy/toolhead.py
+++ b/klippy/toolhead.py
@@ -4,7 +4,7 @@
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
 import math, logging, time
-import cartesian
+import cartesian, delta
 
 EXTRUDE_DIFF_IGNORE = 1.02
 
@@ -159,7 +159,10 @@ class ToolHead:
         self.printer = printer
         self.reactor = printer.reactor
         self.extruder = printer.objects.get('extruder')
-        self.kin = cartesian.CartKinematics(printer, config)
+        kintypes = {'cartesian': cartesian.CartKinematics,
+                    'delta': delta.DeltaKinematics}
+        kin = config.get('kinematics', 'cartesian')
+        self.kin = kintypes[kin](printer, config)
         self.max_speed, self.max_accel = self.kin.get_max_speed()
         self.junction_deviation = config.getfloat('junction_deviation', 0.02)
         self.move_queue = MoveQueue()