Observatory Dome

The Observatory Dome was built and installed by AshDome. Richard Olson, President of AshDome, is very helpful in answering questions and helping one track down replacement parts. AshDome's phone number is: (815) 436-9403. Their website is:

Upper Dome Slit

There is a manual control box for the upper dome slit on the north wall of the 1-meter enclosure. To operate the slit manually, put the dome into "Manual" mode with the upper switch then use the raise/lower switch as appropriate. There is a limit switch next to the motor at the top of the dome that automatically shuts the shutter power off when the dome is all the way open or closed.

Procedure to follow in the event that the upper shutter fails to close: If the 1-meter dome does not close, immediate inspection of the dome and its control systems are required. The following is a point-by-point list detailing the steps and order that should be followed in the event that the dome does not close.

We had continuing problems with the original relays for the upper dome slit. These dome relays were Icron MY4 relays, 110/120 VAC (Mfg part MY4-AC110/120(S). They can be purchased from a variety of sources, e.g. Twenty were ordered in February 2006 of the MY4N variety (with indicator light) for about $8.00 each.

In late 2007, Mark Klaene and Dave Woods redid the upper (and lower) slit control to use more robust relays. These appear to work much more reliably, although we have still had some failures that resulted in blown fuses.

The dome box has two fuses, with spots for two spares; these are 6A slow blow fuses.

Dome Home Switch

There is a dome azimuth home switch located just south of east, mounted to the slip-ring contactor post. There are spares for this switch in the big red tool box on the south side of the 1-meter enclosure.

Lower Dome Dropout

Automated lower dome dropout operation was designed and built in-house by David Summers. Electrical drawings are in the Yellow Observatory folders and there are copies stored in the master control box inside the 1-meter enclosure itself on the South wall. To achieve lower dome automation, a Bodine AC motor was simply attached to the winch that raises and lowers the dropout.

The winch is a Fulton K2550 Work winch; this was purchased to replace the original K1550 winch which has a lower gear ratio. The winch was purchased from Grainger. The higher gear ratio winch was obtained so the the dome would not ``bounce'' on the limit switch, which happened with the lower gear ratio; the downside of the higher gear ratio is that the lower dome slit takes about 3 minutes to open or close. These winches are ratcheted for pulling the load in; the load is let out using a slip clutch, so the ratchet is not disengaged when the dome is lowered.

The shaft is 2.5" from the mounting surface, and the shaft has a 0.5" (??) diameter. There is a relay box for motor control on the dome it's the hinged small box to the right of the upper dome slit relay box.

To lower the dropout using the master box on the south wall of the enclosure, flip the lower red switch into the "Lower" position and flip the upper red switch into the "Power On" position. It is important to perform this operation in the correct order. Once the dropout has powered itself off at the limit switch, move both of the red switches to the power off or automatic positions.

To raise the dropout using the master box on the south wall of the enclosure, flip the lower red switch into the "Raise" position and flip the upper red switch into the "Power On" position. Once the dropout has powered itself off at the limit switch, move both of the red switches to the power off or automatic positions.

If the motor or power fails, the dropout may be closed by grabbing the blue clutch between the motor and the winch and turning by hand (or use a wrench on the nut) until the shutter is closed.

Sometimes the lower dome gets closed too tight (mostly with the old winch) and the dome clutch does not slip to let it open again. If this happens, simply take a wrench and turn the nuts on the dome side of the blue clutch in the opening direction (relieving tension on the cable); the dome should start to open.

Lower dome closed limit switch: white goes to common, yellow to norm closed.

In late 2007, Mark Klaene and Dave Woods redid the lower dome slit system to use more robust switches (and relays?).

Rotation and Motor Adjustment

The dome's rotation motor is located on the north side of the dome just above the dome control box. The rotation motor gear engages track that goes around the circumference of the dome. Good engagement of the gear and rail are critical for accurate positioning of the dome. The dome motor is on a hinged base. Engagement of the gear and rail is maintained by a single piece of threaded rod that comes up from the motor mount and through the motor base. There is a nut on the the threaded rod. If the nut works loose, the motor can be allowed to "bounce" on the rail instead of driving the dome. When this happens, a rather distinctive bumping noise can be heard. To fix this, the hinged piece needs to be tightened. However, the bolt which currently runs through the bottom plate was poorly designed so there is nothing apart from friction to keep it from turning when the nut is tightened. As a result, it takes some care to tighten down the motor. Until a better design can be implemented, the preferred strategy is to use a C-clamp to tighten down the hinged plate until the motor engages fully, then the nut can be tightened without having the bolt rotate; do not use pliers to try to hold the bolt at the threads will likely become damaged. Tighten the clamp and then the nut so that there is good engagement between the motor gear and the rail.

The dome motor gear seems to come disengaged first when the dome slit is either over the motor or opposite the motor (Dome azimuth of 0 or 180 degrees.) To check that the dome is well-engaged, put the dome into manual mode and rotate until the slit is over the motor. Run the motor in short bursts. It should start and stop smoothly. If there is a loud banging or clanking as the motor starts and stops, it's time to adjust the motor. Repeat this test with the dome 180 degrees from the first test position.

Periodically, the rollers around the circumference of the dome should be greased so that the dome operates quietly with minimal wear. There is a spray can of open gear lube located on the brown table against the south wall of the enclosure. However, Jon Davis recommends using a dry lube because of our dust exposure. He likes Dow Corning Silicone Lubricant 557, but unfortunately this comes in an aerosol can and it is not recommended to use an aerosol near optics. Instead, John recommends spraying some in a squirt bottle outside the dome, waiting for it to warm up, then squirting it from the bottle. There is a can of the lubricant in the APO machine shop, in a green aerosol can.

However, Norm Blythe recommends using a grease on the sprockets, and another lubricant on the rollers.

Dome rollers were relubed 2014 May 30 with a 3in1 Garage Door Lube.

Dome encoder

The dome encoder is coupled to the shaft at the motor. The encoder is a BEI Motion Systems (1-800-350-2727) Optical Encoder E206-1000-3G. It was originally read by the Tech 80 card in the telescope computer, but in July 2005 this stopped functioning (not positive which element failed), and we switched over to using the CP4016 card instead. The latter only reads 16-bits, so some code modification was necessary to count encoder wraps (this only functions properly when dome is moved under computer control!). The cable connections are different for the two cards, so we made a converter cable to work with CP4016. The CP4016 also only has inputs for the 3 poles, while the Tech 80 had the 3 poles plus their inverses (a support person at COP said it was OK to just hook up the 3 poles).

A new encoder was ordered and installed in November 2006. At this time, it was still left hooked to the CP4016. The dome was having some serious positioning problem, unclear if this was due to the encoder, the coupler with the dome motor, or the dome motor to dome interface. A new, longer coupler was installed with the new encoder.

Dome control

The dome is controlled through the Autoscope OCS box. This box takes input from an OMS PC34 card in the telescope computer. The OCS box itself contains Opto-22 relays to switch things on and off. This box controls: rotation power, rotation direction, shutter power, shutter directory, dome home switch sense, watchdog and watchdog reset, and LN2 fill system through an auxiliary port.

A description (probably not fully accurate) of the system can be found in the Autoscope documentation, along with some schematics.

Some information is also available about the OMS PC34 card.