cartesian: Fix min_stop_interval calculation error

It is possible to have an acceleration greater than max_z_accel on
XY+Z moves.  That needs to be taken into account when calculating the
min_stop_interval.  This prevents spurious "No next step" MCU errors.

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

4 files changed, 14 insertions, 13 deletions

diff --git a/klippy/cartesian.py b/klippy/cartesian.py
index 1786c63f..f0d2e258 100644
--- a/klippy/cartesian.py
+++ b/klippy/cartesian.py
@@ -21,11 +21,11 @@ class CartKinematics:
         self.need_motor_enable = True
         self.limits = [(1.0, -1.0)] * 3
         # Setup stepper max halt velocity
-        max_xy_halt_velocity = toolhead.get_max_axis_halt(max_accel)
-        self.steppers[0].set_max_jerk(max_xy_halt_velocity, max_accel)
-        self.steppers[1].set_max_jerk(max_xy_halt_velocity, max_accel)
-        max_z_halt_velocity = toolhead.get_max_axis_halt(self.max_z_accel)
-        self.steppers[2].set_max_jerk(max_z_halt_velocity, self.max_z_accel)
+        max_halt_velocity = toolhead.get_max_axis_halt()
+        self.steppers[0].set_max_jerk(max_halt_velocity, max_accel)
+        self.steppers[1].set_max_jerk(max_halt_velocity, max_accel)
+        self.steppers[2].set_max_jerk(
+            min(max_halt_velocity, self.max_z_velocity), max_accel)
     def set_position(self, newpos):
         for i in StepList:
             self.steppers[i].mcu_stepper.set_position(newpos[i])
diff --git a/klippy/corexy.py b/klippy/corexy.py
index a730e933..286811d9 100644
--- a/klippy/corexy.py
+++ b/klippy/corexy.py
@@ -23,12 +23,12 @@ class CoreXYKinematics:
         self.need_motor_enable = True
         self.limits = [(1.0, -1.0)] * 3
         # Setup stepper max halt velocity
-        max_xy_halt_velocity = toolhead.get_max_axis_halt(max_accel)
-        max_xy_halt_velocity *= math.sqrt(2.)
+        max_halt_velocity = toolhead.get_max_axis_halt()
+        max_xy_halt_velocity = max_halt_velocity * math.sqrt(2.)
         self.steppers[0].set_max_jerk(max_xy_halt_velocity, max_accel)
         self.steppers[1].set_max_jerk(max_xy_halt_velocity, max_accel)
-        max_z_halt_velocity = toolhead.get_max_axis_halt(self.max_z_accel)
-        self.steppers[2].set_max_jerk(max_z_halt_velocity, self.max_z_accel)
+        self.steppers[2].set_max_jerk(
+            min(max_halt_velocity, self.max_z_velocity), self.max_z_accel)
     def set_position(self, newpos):
         pos = (newpos[0] + newpos[1], newpos[0] - newpos[1], newpos[2])
         for i in StepList:
diff --git a/klippy/delta.py b/klippy/delta.py
index e3ec0123..8eddc3c9 100644
--- a/klippy/delta.py
+++ b/klippy/delta.py
@@ -32,9 +32,9 @@ class DeltaKinematics:
         self.max_z_velocity = config.getfloat(
             'max_z_velocity', self.max_velocity,
             above=0., maxval=self.max_velocity)
-        max_xy_halt_velocity = toolhead.get_max_axis_halt(self.max_accel)
+        max_halt_velocity = toolhead.get_max_axis_halt()
         for s in self.steppers:
-            s.set_max_jerk(max_xy_halt_velocity, self.max_accel)
+            s.set_max_jerk(max_halt_velocity, self.max_accel)
         # Determine tower locations in cartesian space
         angles = [config.getsection('stepper_a').getfloat('angle', 210.),
                   config.getsection('stepper_b').getfloat('angle', 330.),
diff --git a/klippy/toolhead.py b/klippy/toolhead.py
index 6ed6099e..6df5e17f 100644
--- a/klippy/toolhead.py
+++ b/klippy/toolhead.py
@@ -381,11 +381,12 @@ class ToolHead:
             logging.exception("Exception in force_shutdown")
     def get_max_velocity(self):
         return self.max_velocity, self.max_accel
-    def get_max_axis_halt(self, max_accel):
+    def get_max_axis_halt(self):
         # Determine the maximum velocity a cartesian axis could halt
         # at due to the junction_deviation setting.  The 8.0 was
         # determined experimentally.
-        return math.sqrt(8. * self.junction_deviation * max_accel)
+        return min(self.max_velocity,
+                   math.sqrt(8. * self.junction_deviation * self.max_accel))
 
 def add_printer_objects(printer, config):
     printer.add_object('toolhead', ToolHead(printer, config))