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First time configuration

It's a good idea to configure some settings to tailor OnStep's behavior to your mount.  These settings are available in the Android App, website, or the ASCOM driver unless otherwise noted.

Limits

During tracking and gotos if a limit is broken motion is stopped by canceling any goto and turning tracking off.  Keep in mind that up to DegreesForRapidStop (Config.xxx.h) distance should be allowed for to stop the motors/mount once the limit is detected.  Limits are not adhered to during guide commands since *guiding is used to move the mount back within limits to restore operation (allowing you to re-enable tracking and continue operation.)

  • Overhead:
    • Eq and Alt-Az modes.
    • Runtime setting (ASCOM, website, etc.)
    • Range: 60 to 90 degrees.
    • Default 80.
    • Maximum Altitude.  A setting of 90 disables.
  • Horizon:
    • Eq and Alt-Az modes.
    • Runtime setting.
    • Range: -30 to 30 degrees.
    • Default: -10.
    • Minimum Altitude.  A setting of 0 is right at the Horizon, can be negative (below the Horizon.)
  • Meridian East:
    • Eq mode only.
    • Runtime or Config.xxx.h setting.
    • Range: -45 to 45 degrees (Config.xxx.h uses minutes of RA.)
    • Default: 7 (=30 minutes.)
    • How far past the Meridian (+) when telescope is East of the pier (triggers a Meridian Flip.) 
    • Note: Remove MinutesPastMeridianE from Config.xxx.h to enable full run-time support.
  • Meridian West:
    • Eq mode only.
    • Runtime or Config.xxx.h setting.
    • Range: -45 to 45 degrees (Config.xxx.h uses minutes of RA.)
    • Default: 7 (=30 minutes.)
    • How far past the Meridian (+) when telescope is West of the pier (triggers a Meridian Flip or stops Tracking.)
    • Note: Remove MinutesPastMeridianW from Config.xxx.h to enable full run-time support.
  • MinDec/MaxDec:
    • Eq mode only.
    • Config.xxx.h setting.
    • Range: MinDec 0 to -91 degrees.  MaxDec 0 to 91 degrees.
    • Default: MinDec -91.  MaxDec 91.
    • For English Yoke Equatorial mounts (physically can't point near celestial pole NCP/SCP.)
  • UnderPoleLimit:
    • Eq mode only.
    • Config.xxx.h setting.
    • Range: 10 to 12 hours.
    • Default: 12.
    • Maximum hour angle (+/-) near the celestial pole (triggers a Meridian Flip or stops Tracking.)
  • MaxAzm:
    • Alt/Az mode only.
    • Config.xxx.h setting.
    • Range: 180 to 360 degrees.
    • Default: 180.
    • Maximum Azimuth (+/-) which allows coordinate wrap to help avoid frequent long slews in Azimuth.
  • LIMIT_SENSE_ON:
    • All modes.
    • Config.xxx.h setting.
    • Range: N/A.
    • Default: _OFF.
    • Optional physical switch input (see Config.xxx.h for the pin #.)  Normally HIGH.  Pull the pin LOW (ground) to signal that a limit has been broken.  Wire in parallel for multiple switches if needed.  Sometimes used to connect a "Panic Button" for manual emergency stop.

* = Guiding can hang and continue indefinitely in certain situations (comms failure) due to the design of LX200 commands.  OnStep has a Config.xxx.h parameter GUIDE_TIME_LIMIT that allows you to specify a guide timeout period to guard against this.

Backlash

Backlash compensation is used to improve pointing accuracy and (in some cases) guiding responsiveness by allowing for the slack (or space) between teeth in the gear train.  Values for RA/Dec (Alt/Az) can be entered. 

OnStep by default enables backlash compensation during guiding, even at low rates (<= 1X) typically used for auto-guiding.  The option below, if enabled, causes any low rate guide (ST4, pulse-guide, normal guide) on Axis1 or Axis2 to disable backlash compensation on both axes.  It will then remain disabled until the guiding session ends by a guide > 1X, a goto, a reset home, etc.

  • GUIDES_DISABLE_BACKLASH_ON:
    • Config.xxx.h setting.
    • Range: N/A.
    • Default: _OFF.

Note that there is also a setting that controls the rate at which the stepper motors move (relative to the sidereal rate) during backlash compensation.  This usually doesn't need to be changed:

  • BacklashTakeupRate:
    • Config.xxx.h setting.
    • Recommended Range: 4 to 50 times sidereal.
    • Default: 25.

Max. Goto Rate

Goto rates are adjustable at runtime from half (0.5X) to double (2X) the normal speed as established by MaxRate (see below.)  This adjustment can be made in the Android App, website, or Sky Planetarium.

  • MaxRate:
    • Config.xxx.h setting.
    • Recommended Range: depends on processor/hardware limitations.
    • Default: 96.
    • This is the default (but still run-time adjustable) fastest micro-seconds per step during a goto or slew.
    • OnStep will issue warnings or refuse to compile if the MaxRate you set is likely to cause MCU instability.
    • Use the configuration spreadsheet to help pick a reasonable value for your hardware resulting in a low (1°/s) goto speed to start with then test and adjust for final setting range.