new global default max jerk is 1e9 bigger will throw off the calculations

Author: Luca Toniolo

configs/sim/axis/axis_9axis_scurve.ini

@@ -7,10 +7,14 @@
 # acceleration profiles that can reduce machine vibration and
 # improve surface finish.
 #
-# IMPORTANT: S-curve planning is OPTIONAL and DISABLED by default.
+# IMPORTANT: S-curve planning is OPTIONAL.
 # Traditional trapezoidal acceleration is used when:
 #   - PLANNER_TYPE = 0, OR
-#   - MAX_LINEAR_JERK = 0 (or not specified)
+#   - MAX_LINEAR_JERK = 0
+#
+# NOTE: If MAX_LINEAR_JERK is not specified, it defaults to 1e9 (1 billion),
+# which effectively disables jerk limiting while still using S-curve calculations.
+# This produces motion similar to trapezoidal but not identical.
 #
 # ========================================================
 [EMC]
@@ -64,6 +68,8 @@ PLANNER_TYPE = 1
 # Units: machine-units/second^3 (e.g., mm/s^3 or inch/s^3)
 #
 # Setting this to 0 disables S-curve planning regardless of PLANNER_TYPE
+# If not specified, defaults to 1e9 (effectively no jerk limiting)
+# Maximum allowed value is 1e9 (values above are automatically clamped)
 #
 # Recommended starting values (adjust based on your machine):
 #   - Light/rigid machines: 1000-10000

configs/sim/axis/axis_mm_scurve.ini

@@ -7,10 +7,14 @@
 # acceleration profiles that can reduce machine vibration and
 # improve surface finish.
 #
-# IMPORTANT: S-curve planning is OPTIONAL and DISABLED by default.
+# IMPORTANT: S-curve planning is OPTIONAL.
 # Traditional trapezoidal acceleration is used when:
 #   - PLANNER_TYPE = 0, OR
-#   - MAX_LINEAR_JERK = 0 (or not specified)
+#   - MAX_LINEAR_JERK = 0
+#
+# NOTE: If MAX_LINEAR_JERK is not specified, it defaults to 1e9 (1 billion),
+# which effectively disables jerk limiting while still using S-curve calculations.
+# This produces motion similar to trapezoidal but not identical.
 #
 # ========================================================
 [EMC]
@@ -64,6 +68,8 @@ PLANNER_TYPE = 1
 # Units: machine-units/second^3 (e.g., mm/s^3 or inch/s^3)
 #
 # Setting this to 0 disables S-curve planning regardless of PLANNER_TYPE
+# If not specified, defaults to 1e9 (effectively no jerk limiting)
+# Maximum allowed value is 1e9 (values above are automatically clamped)
 #
 # Recommended starting values (adjust based on your machine):
 #   - Light/rigid machines: 1000-10000

docs/src/config/ini-config.adoc

@@ -863,8 +863,10 @@ Finally, no amount of tweaking will speed up a tool path with lots of small, tig
 * `PLANNER_TYPE = 0` - (((PLANNER TYPE))) Selects the trajectory planner type: 0 = trapezoidal (default), 1 = S-curve with jerk limiting.
   S-curve planning is only active when `PLANNER_TYPE = 1` AND `MAX_LINEAR_JERK > 0`.
 * `MAX_LINEAR_JERK = 10000.0` - (((MAX JERK))) The maximum jerk (rate of change of acceleration) for coordinated moves, in 'machine units' per second cubed.
-  Default is 10000.0.
+  Default is 1e9 (1 billion) if not specified, which effectively disables jerk limiting while avoiding numerical instability.
+  Values are clamped to a maximum of 1e9 to prevent numerical issues in S-curve calculations.
   When `PLANNER_TYPE = 1`, this enables S-curve trajectory planning.
+  Note: Not specifying MAX_LINEAR_JERK (defaulting to 1e9) produces motion similar to trapezoidal planning (PLANNER_TYPE = 0) but not identical, as extremely high jerk still uses S-curve calculations.
 * `POSITION_FILE =` _position.txt_ - If set to a non-empty value, the joint positions are stored between runs in this file.
   This allows the machine to start with the same coordinates it had on shutdown.
   This assumes there was no movement of the machine while powered off.

docs/src/config/integrator-concepts.adoc

@@ -279,6 +279,8 @@ MAX_JERK = 1000.0
 
 S-curve planning is only active when `PLANNER_TYPE = 1` and `MAX_LINEAR_JERK > 0`.
 
+NOTE: If `MAX_LINEAR_JERK` is not specified, it defaults to 1e9 (1 billion), which effectively disables jerk limiting while maintaining S-curve calculations. This produces motion similar to trapezoidal planning but not identical. The maximum allowed value is 1e9 to prevent numerical instability.
+
 === Tuning
 
 Start with a conservative jerk value and increase gradually:
@@ -293,6 +295,8 @@ Typical values: 100-100,000 units/s^3^ depending on machine rigidity and units
 Increase `MAX_LINEAR_JERK` until motion becomes sluggish or following errors
 increase, then reduce slightly. Test with coordinated moves and arcs.
 
+Values above 1e9 are automatically clamped to 1e9 to avoid numerical issues in the S-curve trajectory calculations.
+
 == RTAI
 
 The Real Time Application Interface (RTAI) is used to provide the best

src/emc/ini/initraj.cc

@@ -203,8 +203,8 @@ static int loadTraj(EmcIniFile *trajInifile)
         }
         old_inihal_data.traj_max_acceleration = acc;
 
-        // Set max jerk (default to 10000 if not specified in INI)
-        jerk = 10000.0;
+        // Set max jerk (default to 1e9 if not specified in INI)
+        jerk = 1e9;
         trajInifile->Find(&jerk, "MAX_LINEAR_JERK", "TRAJ");
         if (0 != emcTrajSetMaxJerk(jerk)) {
             if (emc_debug & EMC_DEBUG_CONFIG) {

src/emc/task/taskintf.cc

@@ -1228,6 +1228,9 @@ int emcTrajSetMaxJerk(double jerk)
 {
     if (jerk < 0.0) {
 	jerk = 0.0;
+    } else if (jerk > 1e9) {
+	// Clamp to 1e9 to prevent numerical instability in S-curve calculations
+	jerk = 1e9;
     }
 
     TrajConfig.MaxJerk = jerk;

tests/interp/m98m99/12-M99-endless-main-program/expected.motion-logger

@@ -3,7 +3,7 @@ SET_NUM_SPINDLES 1
 SET_VEL vel=0, ini_maxvel=1.2
 SET_VEL_LIMIT vel=4
 SET_ACC acc=1e+99
-SET_JERK jerk=10000
+SET_JERK jerk=1e+09
 SET_PLANNER_TYPE planner_type=0
 SETUP_ARC_BLENDS
 SET_MAX_FEED_OVERRIDE 1

tests/motion-logger/basic/expected.builtin-startup.in

@@ -3,7 +3,7 @@ SET_NUM_SPINDLES 1
 SET_VEL vel=0, ini_maxvel=1.2
 SET_VEL_LIMIT vel=4
 SET_ACC acc=1e+99
-SET_JERK jerk=10000
+SET_JERK jerk=1e+09
 SET_PLANNER_TYPE planner_type=0
 SETUP_ARC_BLENDS
 SET_MAX_FEED_OVERRIDE 1

tests/motion-logger/mountaindew/expected.motion-logger

@@ -3,7 +3,7 @@ SET_NUM_SPINDLES 1
 SET_VEL vel=0, ini_maxvel=120
 SET_VEL_LIMIT vel=400
 SET_ACC acc=1e+99
-SET_JERK jerk=10000
+SET_JERK jerk=1e+09
 SET_PLANNER_TYPE planner_type=0
 SETUP_ARC_BLENDS
 SET_MAX_FEED_OVERRIDE 1

tests/motion-logger/startup-gcode-abort/expected.motion-logger.in

@@ -8,7 +8,7 @@ SET_NUM_SPINDLES 1
 SET_VEL vel=0, ini_maxvel=1.2
 SET_VEL_LIMIT vel=4
 SET_ACC acc=1e+99
-SET_JERK jerk=10000
+SET_JERK jerk=1e+09
 SET_PLANNER_TYPE planner_type=0
 SETUP_ARC_BLENDS
 SET_MAX_FEED_OVERRIDE 1