FAN: Kick start fan when the increase is more than 50% (Klipper3d#2085)

Large increases in fan speed can suffer from acceleration lag, so this
change kick starts the fan for a change of 50% or more in the same way
that starting the fan from 0% does.

Signed-off-by: Justin Schuh <code@justinschuh.com>

config/example.cfg

@@ -253,8 +253,9 @@ pin: ar9
 # constrained by the implementation and may be significantly
 # different than the requested cycle_time. The default is False.
 #kick_start_time: 0.100
-# Time (in seconds) to run the fan at full speed when first enabling
-# it (helps get the fan spinning). The default is 0.100 seconds.
+# Time (in seconds) to run the fan at full speed when either first
+# enabling or increasing it by more than 50% (helps get the fan spinning).
+# The default is 0.100 seconds.
 #off_below: 0.0
 # The minimum input speed which will power the fan (expressed as a
 # value from 0.0 to 1.0). When a speed lower than off_below is

klippy/extras/fan.py

@@ -42,8 +42,8 @@ def set_speed(self, print_time, value):
  if value == self.last_fan_value:
  return
  print_time = max(self.last_fan_time + FAN_MIN_TIME, print_time)
- if (value and value < self.max_power
- and not self.last_fan_value and self.kick_start_time):
+ if (value and value < self.max_power and self.kick_start_time
+ and (not self.last_fan_value or value - self.last_fan_value > .5)):
  # Run fan at full speed for specified kick_start_time
  self.mcu_fan.set_pwm(print_time, self.max_power)
  print_time += self.kick_start_time