EQASCOM Mount Limits

EQASCOM Mount Limits

Mount Limits provide a way to restrict mount movement perhaps to correspond to a physical horizon or to help protect equipment from possible pier collisions. It is important to understand that limit detection is performed within the EQASCOM driver and not by the mount motor controller itself. In common with all other PC based mount control applications, if you intend to leave the mount unattended you should carefully consider the potential risks to your equipment that may be caused by Windows crashes, restarts, or failures to applications and/or hardware failures.

Limit detection is optional and can be enabled/disabled via the associated check box. EQASCOM provides detection of limit conditions for both the meridian and horizon. The meridian limits dictate how far the mount is allowed to track past the meridian and it is recommended that Meridian limits are always defined when horizon detection is desired.

Operations that are subject to limit detection are:

  • Tracking
  • Gotos

Operations to which limits not applied are:

  • Park
  • Unpark & Goto (*new feature)
  • Manual slews initiated by the EQASCOM direction pad or external gamepad

When a limit condition is detected the following actions are performed

  • Both RA and DEC motors are stopped
  • Tracking is stopped.
  • The Mount position display will alternately flash “LIMIT” and the current coords.

  • If desired the mount can be automatically moved to a park position on limit detection.

These actions are continually re-applied until such time as the limit condition no longer applies. To remove the mount from the “limited” state use the direction pad or gamepad to slew the scope away from the limit point or execute a Park operation.

Limits Configuration

Meridian Limits.

These limits apply when the scope has moved past the meridian (usually through tracking) and has been a part of EQASCOM since V1 .07. By default the limit is set to trigger when the RA axis is horizontal but most folks will want to allow some degree of tracking past the meridian. To set the limits simply slew the scope to the limit position and click the “add” button. You will need to do this for both East and West sides of the pier.

As these limits use encoder positions they can only be applied properly if the mount is parked and unparked. On start-up the default ‛horizontal' limits are applied and on unparking any user specified limits are restored.

The default ‛horizontal' limit can be restored by pressing the [defaults] button. Meridian limits can be removed altogether by pressing the [delete] button.

Horizon Limits.

This detects when the mount is pointing below a specified horizon profile. By default a horizon is applied of Alt= 0 degrees.

There are three ways to create a horizon profile.

  1. Slew the scope along your horizon using the “add” button to add points.
  2. Manually enter points, either in Az/Alt or HA/DEC (i.e. useful if reading setting circles).
  3. Edit a text file with your horizon points (in Alt/Az)

The horizon profile is stored in a text file that is the same format as CDC's horizon file. This allows both applications to share the same file if you wish.

EQASCOM provides a plot of the current profile and the mounts current position is marked with a cross. Points can be individually deleted if required. The [defaults] button removes all points restoring the Alt=0 horizon.

Adding a single point will give a 360 degree horizon at the associated Altitude

As you add more points the horizon profile is built.

There are two algorithms that determine how EQASCOM uses the points list to calculate an Altitude limit.

Using Interpolated mode EQASCOM calculates a straight line between the two points and then establishing the point on the line that corresponds to the current Azimuth.

Using “Greatest Alt” mode EQACOM finds the two points on either side of the scopes current Azimuth and uses the one that has the greatest Altitude.

Limits File Load/Save & Startup

On startup EQASCOM will attempt to reload the last opened horizon definition file (the filename was stored in the EQMOD.ini file). To make any changes permanent then you must save the file otherwise they will apply only for the current EQASCOM session.

Time to Horizon

The time it will take the scope to reach the current horizon is display. If the mount is at a position such that it will never “set” then –:–:– is displayed.


If “Park on Limit” is checked the mount will automatically Park (using the currently selected park mode) when a limit is reached.

If “Apply Limits to Gotos” is checked the Limit detection is active during a goto slew. This may be inconvenient if your slew path crosses a visual obstruction when moving from one above horizon point to another as shown below.

However if the horizon file represents physical mount movement obstructions you will want to ensure this option is checked.

Limits Park and Unpark.

As mentioned previously Park operations are excluded from limit detection so the Park position can be below the horizon limits. A new Unpark mode has been added, “Unpark to defined position” which allows the scope to be moved to a predefined above horizon start position on unpark .

/home/welshdra/public_html/eqmod/data/pages/setting_mount_limits.txt · Last modified: 2010/02/04 01:09 (external edit)
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