Mixed corexy and hybrid-corexy kinematic for single toolhead

My random ideal when playing with Hybrid-corexy based idex. What if we only use 1 toolhead instead 2. The inner belt path(AB) is traditional corexy, and the outer belt path(Y1,Y2) are driven by 2 motors in cartesian mode.
This kind of setup will help alot with large size machines since the heavy gantry is taken care by 2y motors with short belt path. We also have double the torque for X axis.

I’m working on the code to make it work, but still not sure about the bellow points

  • Should it be a new kinematic or just a new mode for the Hybrid-corexy or corexy kinematic? I called it extended_corexy for now.
  • Endstop logic are done. But by default I have to define endstop for both B and Y rails. Since they are control the same Y axis, we only use one rail to home, so only one of them need endstop.

Bellow is my current modify based on corexy kinematic code. Seem to work well on my machine with 50 hours+ of printing.

# Code for handling the kinematics of extended corexy robots
# Copyright (C) 2022  John Smith <chip@snakeoildev.com>
# This file may be distributed under the terms of the GNU GPLv3 license.
import logging, math
import stepper

class ExtendedCoreXYKinematics:
    def __init__(self, toolhead, config):
        # Setup axis rails
        self.rails = [stepper.LookupMultiRail(config.getsection('stepper_' + n))
                      for n in 'abzc']

        # rail[0](a)
        for s in self.rails[1].get_steppers():
        # rail[1](b)
        for s in self.rails[0].get_steppers():
        for s in self.rails[3].get_steppers():
        # rail[3](c)
        for s in self.rails[0].get_steppers():
        for s in self.rails[1].get_steppers():

        self.rails[0].setup_itersolve('corexy_stepper_alloc', b'+')
        self.rails[1].setup_itersolve('corexy_stepper_alloc', b'-')
        self.rails[2].setup_itersolve('cartesian_stepper_alloc', b'z')
        self.rails[3].setup_itersolve('cartesian_stepper_alloc', b'y')

        for s in self.get_steppers():
        # Setup boundary checks
        max_velocity, max_accel = toolhead.get_max_velocity()
        self.max_z_velocity = config.getfloat(
            'max_z_velocity', max_velocity, above=0., maxval=max_velocity)
        self.max_z_accel = config.getfloat(
            'max_z_accel', max_accel, above=0., maxval=max_accel)
        self.limits = [(1.0, -1.0)] * 3

        # check ranges and endstop positions of B and Y motors
        if self.rails[1].get_range() != self.rails[3].get_range():
            raise config.error("B and C motors must have the same position_min and position_max")
        if self.rails[1].position_endstop != self.rails[3].position_endstop:
            raise config.error("B and C motors must have the same position_endstop")

        # get ranges : X from rail 0(A), Y from rail 1(B), Z from rail 2(Z)
        ranges = [self.rails[0].get_range(),self.rails[1].get_range(),self.rails[2].get_range()]
        self.axes_min = toolhead.Coord(*[r[0] for r in ranges], e=0.)
        self.axes_max = toolhead.Coord(*[r[1] for r in ranges], e=0.)

        # what rail wil be used to home y axis
        self.home_y_axis_with_b_rail = config.getboolean(
            'home_y_axis_with_b_rail', False)
    def get_steppers(self):
        return [s for rail in self.rails for s in rail.get_steppers()]
    def calc_position(self, stepper_positions):
        pos = [stepper_positions[rail.get_name()] for rail in self.rails]
        return [0.5 * (pos[0] + pos[1]), 0.5 * (pos[0] - pos[1]), pos[2]]
    def set_position(self, newpos, homing_axes):
        for i, rail in enumerate(self.rails):
            if i in homing_axes:
                self.limits[i] = rail.get_range()
    def note_z_not_homed(self):
        # Helper for Safe Z Home
        self.limits[2] = (1.0, -1.0)
    def home(self, homing_state):
        # Each axis is homed independently and in order
        for axis in homing_state.get_axes():
            rail_number_to_home = axis
            # Decide to use rail 1(B) or rail 3(C) to home Y axis
            if axis == 1 and not self.home_y_axis_with_b_rail:
                rail_number_to_home = 3
            rail = self.rails[rail_number_to_home]

            # Determine movement
            position_min, position_max = rail.get_range()
            hi = rail.get_homing_info()
            homepos = [None, None, None, None]
            homepos[axis] = hi.position_endstop
            forcepos = list(homepos)
            if hi.positive_dir:
                forcepos[axis] -= 1.5 * (hi.position_endstop - position_min)
                forcepos[axis] += 1.5 * (position_max - hi.position_endstop)
            # Perform homing
            homing_state.home_rails([rail], forcepos, homepos)
    def _motor_off(self, print_time):
        self.limits = [(1.0, -1.0)] * 3
    def _check_endstops(self, move):
        end_pos = move.end_pos
        for i in (0, 1, 2):
            if (move.axes_d[i]
                and (end_pos[i] < self.limits[i][0]
                     or end_pos[i] > self.limits[i][1])):
                if self.limits[i][0] > self.limits[i][1]:
                    raise move.move_error("Must home axis first")
                raise move.move_error()
    def check_move(self, move):
        limits = self.limits
        xpos, ypos = move.end_pos[:2]
        if (xpos < limits[0][0] or xpos > limits[0][1]
            or ypos < limits[1][0] or ypos > limits[1][1]):
        if not move.axes_d[2]:
            # Normal XY move - use defaults
        # Move with Z - update velocity and accel for slower Z axis
        z_ratio = move.move_d / abs(move.axes_d[2])
            self.max_z_velocity * z_ratio, self.max_z_accel * z_ratio)
    def get_status(self, eventtime):
        axes = [a for a, (l, h) in zip("xyz", self.limits) if l <= h]
        return {
            'homed_axes': "".join(axes),
            'axis_minimum': self.axes_min,
            'axis_maximum': self.axes_max,

def load_kinematics(toolhead, config):
    return ExtendedCoreXYKinematics(toolhead, config)

Thank in advance!
Sorry for my bad English!