Re: Anyone designed a limit switch or similar to prvent pier col...

Mark Squicquero


Good point, but I was thinking only in terms of tracking during long
exposures etc. where the only concern would be the RA drive. I
believe the example given previously was if the mount was left on
inadvertantly or left tracking too long and unatended. If trying to
protect the equipment during slews then your approach would make more
sense. But just off the top of my head, wouldn't reversing the RA
motor prevent any contact regardless of which axis was moving? On
the other hand, would guider input have any effect during a slew? If
an all encompassing approach is the desired outcome then it gets back
to using a logic device of some sort to issue a "stop" command
or ":Q#" through one of the serial ports. I may be wrong (wouldn't
be the first time ;-) ) but it seems like such a device would be
nothing more than a modem capable of replaying keystrokes on command
over an rs232 serial line.


--- In, "Joseph Zeglinski" <J.Zeglinski@...>


Just one question though. How will you figure out, automatically,
which axis
caused the collision with the pier?

You can't reverse both motors, since if the RA caused the hit,
example, reversing the DEC which was in a good position, might get
into more
collisions. If the AP was slewing with both motors, perhaps it's
best to stop,
issue the alarms, and let the human figure out how to untangle the
mess. Stopping means another relay/breaker, to cut off all DC power
to the
mount. Drastic, but better than putting a ding in the pier :-(

Actually, I faced this same quandary, when I designed my
variation of the
Mel Bartels stepper tracking system (Scope.exe). However, my
circuit version
knew which axis signals were sending stepper pulses to each motor,
so it was
simple to reverse individual motors, while activating (optional)
user selected
alarm devices. In your approach, you only know that the some part
of the scope
has started to strike the pier, so figuring out which way to
reverse, is
difficult. It will handle pier detection during tracking - one axis
reversal -
but I don't see how it can handle two axis slewing with reversal.
Best to stop
the mount altogether, in that situation.


----- Original Message -----
From: "Mark Squicquero" <docsquic@...>
To: <>
Sent: Friday, July 13, 2007 12:41 PM
Subject: [ap-gto] Re: Anyone designed a limit switch or similar to
prvent pier


That's a great idea! Very simple and easy to implement, cheap
Just close the circuit on the proper lead of the autoguider port
the mount reverses direction until the pressure is off the mat.
mount would go into a harmless loop. I suppose some type of time
delay relay could be used to increase the length of time the mount
reverses upon activation so that the mount wouldn't be "shifting
gears" too quickly. The idea of an led and an alarm is good also.
Elagantly simple.

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