polar: Experimental support for polar kinematics

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

config/example-polar.cfg

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+# This file serves as documentation for config parameters of "polar"
+# style printers. One may copy and edit this file to configure a new
+# polar printer.
+
+# POLAR KINEMATICS ARE A WORK IN PROGRESS. Moves around the 0,0
+# position are known to not work properly. Moves to a negative Y
+# coordinate from a positive Y coordinate (and vice-versa) when the
+# head is at a negative X coordinate also do not work properly.
+
+# Only parameters unique to polar printers are described here - see
+# the "example.cfg" file for description of common config parameters.
+
+# The stepper_bed section is used to describe the stepper controlling
+# the bed.
+[stepper_bed]
+step_pin: ar54
+dir_pin: ar55
+enable_pin: !ar38
+step_distance: 0.000981748
+#   On a polar printer the step_distance is the amount each step pulse
+#   moves the bed in radians (for example, a 1.8 degree stepper with
+#   16 micro-steps would be 1.8 / 360 * pi / 16 == 0.000981748). This
+#   parameter must be provided.
+
+# The stepper_arm section is used to describe the stepper controlling
+# the carriage on the arm.
+[stepper_arm]
+step_pin: ar60
+dir_pin: ar61
+enable_pin: !ar56
+step_distance: .01
+endstop_pin: ^ar14
+position_endstop: 300
+position_max: 300
+homing_speed: 50
+
+# The stepper_z section is used to describe the stepper controlling
+# the Z axis.
+[stepper_z]
+step_pin: ar46
+dir_pin: ar48
+enable_pin: !ar62
+step_distance: .0025
+endstop_pin: ^ar18
+position_endstop: 0.5
+position_max: 200
+
+[extruder]
+step_pin: ar26
+dir_pin: ar28
+enable_pin: !ar24
+step_distance: .0022
+nozzle_diameter: 0.400
+filament_diameter: 1.750
+heater_pin: ar10
+sensor_type: ATC Semitec 104GT-2
+sensor_pin: analog13
+control: pid
+pid_Kp: 22.2
+pid_Ki: 1.08
+pid_Kd: 114
+min_temp: 0
+max_temp: 250
+
+[heater_bed]
+heater_pin: ar8
+sensor_type: EPCOS 100K B57560G104F
+sensor_pin: analog14
+control: watermark
+min_temp: 0
+max_temp: 130
+
+[fan]
+pin: ar9
+
+[mcu]
+serial: /dev/ttyACM0
+pin_map: arduino
+
+[printer]
+kinematics: polar
+#   This option must be "polar" for polar printers.
+max_velocity: 300
+max_accel: 3000
+max_z_velocity: 25
+max_z_accel: 30