CGE Gets New Cables

I have been plagued with connection problems in the RA and DEC cables on the CGE since the second day after I received it.  Typically, run-away slews as the controller is unable to receive encoder pulses to detect mount movement.  My first instance of this problem was in the middle of the New Mexico desert on my first field-trip with the new mount over a year ago.   I wasted the entire evening under magnificent skies debugging the mount with a multimeter.  The problem is that the RJ-45 connectors do not make very secure connections, especially since Celestron chose to run a 9th signal wire through the connector shield.  You got to be kidding!

I finally bought one of Gary Bennett's CGE cable kits. This completely replaces the cables and the crappy RJ-45 sockets with beefy screw-on 8-pin connectors.  These are very well designed kits and require no irreversible changes to the mount.

In the image below, note the connector block on the left side of the pier.  This is were the RA and DEC cables plug in.  The connector circuit board under the plate is also replaced.  Shadowed behind the orange knob, you can see where the other end of the RA cable plugs in.  Again, Gary has provided a single-block aluminium piece that, along with another circuit board replaces the original RJ-45 socket.

Full view of the new CGE Cable Kit from Gary Bennett.

Update September 2012 - Cables have been going for a year and a half.  Not motor runaways since I replaced the cables.  Best money I ever spent on this mount.

Thanksgiving Family Star Party

This Thanksgiving holiday, we went back to visit family in Las Cruces, NM.  While there, I setup an impromptu star party in my father's backyard.   The city street lights did not make for great deep-sky observation but we all had a peek at a few interesting objects including Jupiter and Orion.

While observing Jupiter, I noticed that a moon shadow was transiting the surface.  After everyone had seen it visually, I plugged in a webcam and was able to get a nice sequence of not only the moon shadow but also the moon itself passing beyond the limb of Jupiter.  Later looked it up to determine it was Io.

Comet 103P/Hartley

This evening, I imaged a periodic comet, 103P/Hartley from the backyard observatory.  Per the Wikipedia article, the Deep Impact spacecraft approach within 700km of this comet and imaged it close up, showing an asymmetrical dumbbell shape about 1.5km in diameter. It made its recent perihelion approach on October 28 and is on its way back out through the solar-system.

I imaged the comet with a TMB-130SS 5" refractor and a QSI-540ws cooled CCD.  I stacked 7 frames, each a 30s exposure.  I processed the stars and comet core separately.  In the first pass, I aligned on the stars and subtracted out the comet.  In the second pass, I aligned on the comet core and let the median filter remove the stars.  The two images were then stacked for the final result.  The coma shows up very clearly and the stars remain sharp.   The comet has a hint of a tail pointing to the left.  

North American Nebula in Narrowband

After two weeks of collecting narrow-band data, I put together an image of the North American Nebula in Cygnus (NGC-7000).  The image is focused around the "gulf of mexico" region of the nebula, though to me it looks more like the head of a galloping horse at that field of view.

The image was taken from Georgetown with my TMB-130SS refractor with a QSI-540 camera and Astronomik narrow-band filters.  Individual exposures were 30min.  Total times were 9hr in SII (Red), 5hr Ha (Green), and 14hr OIII (Blue).

Imaging at Canyon of Eagles

The Austin Astronomical Society, of which we are members, has its dark site at the Eagle Eye Observatory, located in the Canyon of Eagles park.  Once a month on a Saturday, the club has a members-only night which is ideal for imaging. The portable setup I am currently using includes a Celestron CGE mount, a TMB-130SS refractor with Orion 80mm guidescope, a QSI-540ws CCD, and a dedicated PC.

Many thanks to Todd Hargis, member of AAS, for taking this photo of my setup.  You can see the zodiacal lights in parallel with the OTA and some city lights behind my head. Todd used the trick of "painting" me in with a red-light.  In the star field, Orion and the Pleiades are recognizable. I am posting this after the fact, so I am not certain which Saturday in March 2010 was the member's night.

Observatory Gets Automated Dome

After completion of my backyard observatory project based on the ExploraDome, I began to build the automation system to allow the dome to rotate and follow the movements of the telescope mount.  

Based on cost, I chose to use the semi-do-it-yourself controller called LesveDome  provided by Pierre de Ponthiere.  With this system, you purchase a software license for the ASCOM compliant dome control software from Pierre and you build the actual hardware from a combination of off-the-shelf relay boards and a USB IO controller board.  I highly recommend this system.

Track and Motor - The motor and track assembly in the observatory are provided by ExploraDome as an added purchase.  The first step was to install that hardware.  I removed the support bracket used to hold together the seams of the wheel track.  This bracket is replaced with alternate version that does not have the extra lip.  I had 4 of these left over, not sure if they were pre-planned for this.  Finally, I attach the drive track which now braces the seam.

Once the drive track is in, the 12V DC motor and "acorn drive wheel" are installed.  This is part of the kit from ExploraDome.  The fastening plate is a spring loaded barn-door hinge that keeps the drive gear in contact with the track.  As the dome rumbles around, the whole assembly moved around quite a bit.  Note that due to the extent of the motor housing, I was only able to choose the octagonal corners as locations for the motor.  Here I have it placed just West of due North.

Due to slight deviation from roundness, the gear will sometimes skip a hole when turning dome CCW.  In that direction, the gear is able to "climb" out of its holes.  This happened at a spot where the track was rececess back the most.  I shimmed the track out with some duct tape and increased the spring tension on the motor retaining bolt.  Limiting the rotation speed also helped.

Once the motor is installed, the dome can be rotated by applying either positive or negative 12V across the motor leads.  Initially, I just used a momentary SPCO switch, i.e., (on) - off - (on),  to manually control the dome until the automation system was completed.  I also integrated that switch into the automation circuit to provide manual override or to rotate the dome without starting the computer.

Rotation Encoder - Based on the instructions from Lesvedome, I fitted the azimuth rotation motor with a rotation encoder.  I fabricated a plastic commutator wheel with 3/8" holes every 15 deg and  mounted on top of the acorn gear.  A pair of IR/LED sensors generate a Gray Code to determine rate and direction of rotation.  It is critical that the sensor, wheel, and motor/gear all be part of one non-flexible assembly.  The motor and gear bump around quite a bit as the dome turns; fixing the sensor bracket to the building itself would not work.  I built my version by clamping around the bottom of the motor with a pair of hardwood blocks.  This holds the "C" bracket in place to position the sensors to read the holes in the wheel. 

The rotation encoder is constructed from a pair of EE-SX1042 optical encoders glued together and onto a plastic jig.  The small circuit board contains a resistor and diode and connections to the control board as described on the LesveDome website.  I can losen the jig and reposition the sensors slightly.  This view also shows how I mounted the commutator wheel on three spacers screwed into the plastic part of the gear thus avoiding having to figure out how to redo the main motor shaft.

Home-Position Sensor - The home sensor started out as a magnetic reed sensor.  The hard part was figuring out where to mount it.  I loosened the gear track at a joint in order to be able to screw the movable part of the sensor underneath the track.  I then fashioned another plastic jig to hold the stationary part as shown.  When I tried to simply attach the stationary part with screws vertical into the rotation-ring base, I could not get the switch to close.  By rotating as shown, it worked.  Obviously the ideal would be to mount it vertically directly under the movable part but there is not enough clearance.

It was not long before the magnetic reed sensors were giving me problems.  I found that there was too much hysteresis in the swiching points.  I changed to a new mechanical sensor.  From a piece of spare oak, I fabricated a curved section that is screwed to the bottom of the the drive track.  Again, I did this near a track joint so I could loosen just a bit of the track.  A roller/lever switch is mounted and adjusted so that it just closes at the apex of the curved section.  The broad curve is critical when the dome rotates CW to prevent catching and jamming the end of the switch.  My first attempt self-destructed several time until I figured this out.

The body of the roller/lever switch can pivot for adjustment by loosening the nearest screw on top.  This pivot point allowed my to adjust the dead-band range of the switch.  Once everything was fixed, additional tweaks were possible by bending the lever very slightly.

Controller Hardware - The next step was to build the LesveDome control system.  At its heart is a Velleman 8055 USB IO Control board which I built from a kit.  The LesveDome driver software is written to work with this generic experimenter's board.   The board is connected to several different relay boards to drive the rotation motor and optionally the dome-shutter control motors.  I only constructed the dome-rotation since I did not really have a need for remote control of the dome shutter doors.

A suggested circuit by Charles Harrow is published by the Lesvedome project and various modifications are given by other users.   I based my circuit on "ELK" relay boards as others have done but made a few modifications to address some of the problems I was having.  Here is my variation on the standard circuit:

My main modifications were the inclusion of a motor-speed control board and to alter which triggering mode to use on the ELK boards since some forum users were having problems with the ELK924 triggering all of the time.  Here is a post I put on the LesveDome Yahoo group regarding the triggering problem

The root problem is that the ELK board in "sensitive mode", triggers on a very small current injection into (T-), small enough that the pull-up circuitry in the input section of the 8055 can source this current. Note that the relay boards are powered at 12V and the input of 8055 is only pulled up to 5V. I reasoned that from the ELK ckt point of view, the 5V pull-up actually look "low" enough to to act like the input to the relay board has been pulled down and negatively triggered. ... There are 2 alternative solutions:

(1) Force the relay board to act as a voltage switched device - This was my approach. Ensure that the 8055-Output2 has to pull the boards negative power rail down to GND along with the trigger input. Minor current flowing into 8055-input logic will do nothing because the circuitry in the ELK board is not "grounded".

(2) Shut down the inappropriate current path - This was Joe's approach. The diode between Out2 and In4 only allows current to flow FROM In4 TO Out2. Thus, if Out2 is pulled to 0V, current can flow from In4 to Out2 and be detected by the 8055 as an input signal. However, If Out2 is not enable, the diode prevents current from exiting the 12V circuit of ELK input, into In4, through the pullup resistor, to the 5V level.

In my circuit diagram, I chose to trigger ELK924 in "insensitive" mode.  The reverse-current protection diode D0 prevents the Dig In 4 circuit from triggering ELK924 all the time.  If Out2 is pulled to 0V, current can flow from In4 to Out2 and be detected by the 8055 as an input signal. However, If Out2 is not enable, the diode prevents current from exiting the 12V circuit of ELK input, into In4, through the pull-up resistor, to the 5V level. 

I also included a motor speed control board MX033.  This allows the rotation speed to be lowered.  This was critical since I have problems with the drive wheel on the motor "popping out" of the drive track, especially when rotating the dome counter-clockwise.

I posted another comment to the Lesvedome Yahoo group regarding the function of diode D14:

The windings in the DC motor ( or the windings of any inductor such as the energized coil of a relay ) resist changes to current flowing through the winding. When the supply voltage to the motor is disconnected, current previously flowing through the motor cannot stop instantaneously. The purpose of the diode is to given the current somewhere to flow after the switch disconnects the motor from the power source. Without the diode, a large voltage spike is created across the windings and can cause various problems in the rest of the circuit. The diode needs a current rating at least as large as the largest current that you expect to flow through the motor... that current is much larger if the motor is stalling. 

Further complication ... in the circuit in question, you can't simply place the diode across the motor windings because the current in the motor could be flowing in either direction ... which way would you orient the diode? Instead it has to be placed between the on-off switch and the direction-changing switches at a location where the voltage is always of the same polarity.  Technically, D14 bleeds off the motor current when K1A-A is switched off. On the other hand, it does address brief condition where K2A-A and K2-B are switching and neither is closed for a moment.

Another note, this motor-current-keeps-flowing problem is why, when the lesvedome driver software changes dome direction, it pauses in the off state for a moment. This allows the original current to bleed off through D14 down to zero before trying to switch in to a configuration where the current starts flowing in the other direction. Without this pause, you can damage the power-supply or trip voltage protection circuitry.

Here is a picture of the ELK relay boards, the USB control board, and the motor speed control board mounted on acrylic sheet.

Next is a view of the control board with all of the connections in place.   External connection wire cables go to: 12V Power Supply, USB to Computer, Home Sensor, DC Motor, Rotation Encoder, and Manual Rotation Switch.  Relay boards on the right are for future use for shutter control if I ever include that. In the middle is the motor-speed control used to reduce the rotation speed of the stock ExploraDome motor.  

I then mounted this board in an in-the-wall electronics housing and included a power-supply.   A front panel covers the assembly.

Controller Software Configuration - Once the hardware was completed I needed to configure the driver software.  Here are the key settings for the dome size and encoder wheel that I am using

Here are the mount geometry settings for my CGE mounted on the central dome pier with a TMB-130SS refractor and guide scope:

And finally, the ASCOM Celestron driver parameters for the mount:

With all this completed, I use POTH to perform the dome slaving calculations.  I first tried to do the slaving in MaximDL but had better results using POTH. 

The project is finally completed and working as desired.  The LesveDome solution seems to work very well.  My on-going frustration is still the "roundness" of the ExploraDome track system. I have never been able to get the dome to rotate smoothly all the way around.   

Update September 2012 - I understand that ExploraDome now supplies a rigid aluminium track assembly to address the roundness problem.

Here is the dome in action tracking the mount during an imaging session ... now if I could just automate away the local light pollution ... 

Astro-Camping at Caprock State Park

We have gone camping at Caprock State Park in the Texas panhandle a number of times.  It is one of our favorite destinations because it has a dark sky, flat terrain in the campground, and wonderful hiking in the daytime. This trip was our second time lugging a truck full of telescopes. We stopped for a week on our way to Las Cruces for the holidays.

The state park is near the small town of Quitaque, which I have yet to figure out how to pronounce.

The hiking trails at Caprock are wonderful.  The geology is similar to those at Palo Duro SP but the setting is more intimate.

There are several trails that hike up onto the mesa tops giving a great view of the canyons:

We have camped at the same site, number 27, each time we have come to Caprock. We have plenty of space to setup our telescopes and the low bushes protect us from neighbors. On this trip however, no neighbors, no white lights .... ahhhhh.

My setup includes a Celstron CGE mount, a TMB-130SS refractor, a Canon 450D DSLR and an Orion ST-80 with a Starshoot Auto Guider. The small Windows computer on the tripod table controls the mount and cameras. This time, I brought a monitor and a lit keyboard.

Its pretty cold in the winter time, so I setup a laptop inside the trailer connected to a wireless router.  I am able to monitor the outside computer via VNC.

This is one of the images I took on the last day of the trip.  It is the galaxy NGC-2403.  This is a cropped image from  36x15min @ ISO 800 with a Canon 450D DSLR through a TMB-130SS refractor.

This image of the PacMan Nebula (NGC-281) was taken with the same equipment but 8x30min @ ISO 800.

Dramatic Storm Cloud

As I was driving back from Cedar Park to Georgetown,  I stopped on the side of the road to take a picture of this storm cloud.

Possum Lands on Roof

Interesting encounter with nature while driving home in a heavy evening rain. As we stopped at a stop sign we heard a loud thump on the roof of the minivan.  I got out to see what had happened and found a juvenile possum on the roof.  Apparently, it had slipped out of the tree under which we had parked.  I got a picture of it before it dropped off of the car and disappeared in the dark.

T-Thread Imaging Train for TMB130SS

After much futzing, I have put together a set of adapters that allow me to connect my QSI-540 CCD to the FT-3035 focuser of my TMB-130SS refractor through an all T-Thread imaging train.  I can optionally insert my Vixen flip-mirror as well using the T2 Quck connects.

This image shows all of the adaptors needed to make this work.  A bit of a Rube-Goldberg assembly, but it is solid an has no clamp fittings on the main imaging train. The Baader T2 quick change couplers are as solid and free of flex as a threaded connection.  Adaptors E and F were the ones I had a hard time finding.

When everything is threaded together, I get three parts. The flip-mirror assembly at center is optional and the camera at right can be switched easily to other telescopes.  When assembling these in the field, no threads have to be undone, only the solid T2 quick connects.

Here is everything put together.

Camera and flip-mirror system mounted on the telescope.  With this configuration, focus reached with focuser extended out 45mm.

Update 2012.09.01 - When using the new AP focal reducer, this assembly no longer works.