Merge branch 'sphinx' of https://github.com/flash62au/dcc-ex.github.io …

…into sphinx

docs/ex-turntable/configure.rst

@@ -183,7 +183,7 @@ SANITY_STEPS
 
 `Default: 10000 (Disabled)`
 
-`Valid values: 1 to 65535`
+`Valid values: 1 to 32767`
 
 This is the maximum number of steps the stepper motor will move during homing and calibration before flagging a failure.
 
@@ -205,7 +205,7 @@ FULL_STEP_COUNT
 
 `Default: 4096 (Disabled)`
 
-`Valid values: 1 to 65535`
+`Valid values: 1 to 32767`
 
 If for some reason the automatic calibration sequence is not recording the correct number of steps required for a full 360 degree rotation, or if there is some other requirement to override this value, then uncomment this line and define the desired number of steps.
 

docs/ex-turntable/overview.rst

@@ -102,6 +102,29 @@ To control the turntable, the simplest method is using EX-RAIL automation comman
 
 Refer to the :ref:`ex-turntable/test-and-tune:testing, tuning, and control` page for more details on this.
 
+Considerations when using geared steppers, turntables, and/or microsteps
+------------------------------------------------------------------------
+
+In the current implementation of |EX-TT|, the maximum number of steps per rotation it can address is 32767.
+
+If your physical turntable involves gearing, for example a small spur gear on the stepper driving a large gear connected to the turntable, you will need to calculate the resulting gear ratio, and multiply that by the number of steps per rotation of your stepper motor. This would give a resultant steps per rotation that needs to be no more than 32767 steps.
+
+.. code-block:: 
+
+  # large gear teeth / # small gear teeth * stepper steps per rotation
+
+If you have a large gear on the base of a turntable with 200 teeth which is driven by a 20 tooth spur gear, that gives a gear ratio of 10:1 (200 / 20). If you then use the 28BYJ-48 stepper in half step mode with 4096 steps per revolution, this would result in 40960 steps per revolution with this gearing, meaning |EX-TT| will not be able to successfully address a full rotation.
+
+In this scenario, running the 28BYJ-48 in full step mode (2048 steps) would allow this to work, as a full rotation is 20480 steps.
+
+When using stepper drives such as the A4988 or DRV8825, these are able to be configured using microsteps, which again impacts the number of steps per revolution of the stepper.
+
+In the case of a DRV8825, the smallest microstep it can be configured for is 1/32, meaning a NEMA17 stepper with 200 steps per revolution in 1/32 microstep mode equates to 6400 steps per revolution.
+
+While this is well within the limit of the maximum 32767 steps in |EX-TT|, if you then use this in the same gear ratio calculated above, it will result in 64000 steps per revolution, which is well outside |EX-TT|'s limit.
+
+These same considerations apply when using steppers with built-in gearing.
+
 Important! Phase (or polarity) switching
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