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

Joe Zeglinski


... Think about a "proximity sensor" - like StarTreky force fields.

If you could measure the change in capacitance of a fibre coated metal
pier, as an object like the OTA approaches, you can use the PC to determine
the rate of approach, and by voltage sensors determine which section of the
pier is targetted by the errant scope. This is something like our early days
experiments in first year electrical engineering, with electrostatic fields
plotted using Telideltos (sp.?) Paper. The pier could be considered covered in
such similar material.

Rather than waiting for the OTA to "strike" the pier to close a
microswitch, we need to get ahead of the collision, and treat the pier as a
giant, electrostatic field sensing, wand.


----- Original Message -----
From: "Rick Wiggins" <rickwiggins@...>
To: <ap-gto@...>
Sent: Tuesday, July 10, 2007 6:20 PM
Subject: [ap-gto] Re: Anyone designed a limit switch or similar to prvent pier

Hi Roland,
The timer idea certainly works well for manual imaging where the
operator is available to set the timer once a target is dialed in.
That is basically what I used to do before I started automated
imaging with automated meridian flips and multiple targets. This
solution will not work at all for automated imaging. In automated
imaging, the mount can be sent at any time to a target that may be
very near or 6 hours away from a required flip. In order to set the
timer, there would need to be a program that determines how far away
from the flip that the target is when the mount is sent to this
target. The target call could be a a given time, or after some
preprogrammed sequence, therefore, it is not simple to calculate the
time before the required flip. This is possible by programming some
software to read the automated imaging program, then determine the
proper timeout, and then setting a programmable timer. There are
some of us pursuing this type of trap; however, since this requires
much of the software to be operational, we would use the trap to
send a signal to the mount to park rather than simply turn off power.

The type of error that one is protecting is when the computer or
software gets stuck and the mount keeps on tracking. That is why a
physical limit is preferred although having both is even better.

I haven't seen such a mounting (that allows all mount positions and
tracks through meridian without interference) unless you are
referring to a fork mount (and even these usually have stay out
zones). A standard straight "pipe like" pier runs around $700 and up
for the AP 1200 and I expect this unique pier would be quite a bit
more, but that is simply my speculation.

I am continuing to pursue both a mechanical and a software solution
and am very open to suggestions.
Thanks, Rick

--- In ap-gto@..., chris1011@... wrote:

One of our local astrophotographers uses a simple alarm clock
which has a
built-in 110 volt outlet. he plugs the power supply into the alarm
clock, sets
the time for the alarm to go off and goes to bed. When the preset
alarm goes
off, the scope simply turns off and cannot hit the pier.

Of course, then there's the time honored astrographic mounting,
where the
pier is made in a bent configuration, allowing the scope to clear
underneath at
all declination settings. It would not be that difficult to make
such a pier
for a permanent observatory.


In a message dated 7/9/2007 3:29:03 PM Central Daylight Time,
rickwiggins@... writes:

Hi Roland,
I have a few items to post here:
1. I would love to see an option to add a microswitch shutoff
capability to the AP mounts (see below).

2. A software version would also be nice, but of course these
on computers for remote applications. A version for the
handcontroller would be nice for single session portable imaging.

3. My current design: I designed and built a relay box to shut
power to my mount (or anything) when it receives an input from a
microswitch. It requires a microswitch and a trip block to be
installed on the mount. One of the devices can be attached to
stationary section of the mount and one must be attached to the
moving portion of the mount (most likely, I will mount the block
the moving section). When the block hits the switch, it triggers
relay to shut down power. I designed the system such that I can
off the switch to allow resetting of the system or simply defeat
system. I have not determined a best method of mounting the
and would love to get ideas from you or the group. So far, I
considered using strong double sided tape, epoxy, or silicone to
attach the devices to the mount. Obviously, this design does not
easily accomodate adjustment, but works fine for a permanent,
automated observatory. I can make a section of the trip block to
removable to accomodate tracking past the meridian when desired.
you were to build in this type of feature (adding adjustability
the position is even better) into the AP mounts, I believe it
be very useful. The reason that I like a hardware stop is that
it is
not dependent on the computer or any software.

Thanks, Rick

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