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Observatory Construction

ED-1 Lower Shutter Door RetroFit - April 2013


The original design for the ED-1 automated lower shutter had one limit switch placed at the bottom of the right actuator. I found that this design did not close the door reliably.  Bfehner published a revised design for the door on the Yahoo Exploradome users group.  My first (partial) implementation still did not work. This page changes a couple of parts of Barbara's design, but retains the key features.  The modification consists of three parts.

  1. Two sensors are used instead of one.  These are placed at the top of the door instead of at the actuator.
  2. The limit point of the actuator has to be carefully set.
  3. The bracket at the bottom requires bracing so it does not flex. I did not do this in my first attempt.  Barbara was correct that flexing would change the point where the limit switch on the top triggers.
  4. The top shutter needs flashing so it rides on top of the lower shutter instead of sticking.

Upper Limit Switches

Barbara's design uses two switches instead of one.  Power is maintained to the actuators until both switches trigger.  My design works the same way, but I used a different switch.  The switch I chose was an SAIA XGH6-88-S21Z Mini Snap Switch

SAIA XGH6-88-S21Z switch

I selected this switch because it only requires 0.79 oz to activate.  This will prevent the switch from forcing the door open.  If you plan to use this switch here is a drawing to help you drill the holes. The holes in the switch are 3.1 mm (.122").  I used 3 mm screws, but American #4 screws are only .006 " smaller.

I mounted the switch using a bracket made of 2x2 1/8" channel.  I cut all but about 1/2" from one side so the channel would fit into the "U" that forms the door track. Note on this side I had to cut a notch due to a bolt in the dome.

right limit switch bracket

Installing the switches is straightforward.

Left Limit Switch
          Installed

All of the parts were painted black before final installation, but since that would give a "black cow at night" appearance I am showing the brackets unpainted. The gray is rubber flashing I use to plug the gap between the shutters.

Adjusting the Actuator

One point that I did not spend enough time on the first time I tried this was setting the trigger point of the actuator correctly.  With Barbara's design the actuator motion stops in one of two ways

The head of the actuator screws out to adjust its length; however, for this design to work correctly the actuator needs to trigger its switch before it reaches its limit.  Since both sides may not trigger at the same instant it is important that the actuator does not move too far past the triggering its side or the door may be damaged.

Figuring out how to set up the actuator was easy once I understood these points.

Bottom Brace

Barbara correctly argued that it was important to reinforce the bottom bracket so it does not flex.  When I first tried her design I did not do this and my implementation did not work.  This time I decided to take her advice.  She placed her reinforcement at the bottom of the bracket.  I was concerned that this might interfere with the shutter.  I instead decided to reinforce higher on the bracket which would apply more leverage to the actuator bracket and not interfere with the shutter. Again the parts use 1/8" channel.  One part is from 2" and the others are 1". Note the bend in the 2".  I will discuss this below.

Right Brace

brace installed

There are two parts of this design that are tricky.  The first is that you must be careful that the screws on the brace do not interfere with the actuator.  When I finally installed the brace I placed the head of the screw inside the brace.  My shutter also contains a modification so it does not fully open since doing so would just give me a better view of the nearby house and its lights.  If you want to have the shutters fully open you may have to place the screws differently.  This is definitely a case of "measure twice..."

The 2" piece of channel needs to be bent at greater than 90.  I cold bent one bracket.  I found that heating the channel with a MAP torch made bending the second far easier.

Top Shutter Flashing

This is something I got from Exploradome and may be standard on new installations.  It is basically 1/16" channel bent to about 120 and then attached to the bottom of the upper shutter.  The flashing allows the upper shutter to move over the lower shutter.

Flashing on Upper Shutter of Exploradome ED-1