A little tune up for the EQ6...

...also known as "My EQ6 mount improvement - Part 3." When I received my mount back from Astro Motion Technologies it was immediately apparent that something was amiss in the operation of the mount's internal motors. The DEC axis would not move at all with a strange noise coming from the motor, and the RA axis would move less than halfway before stopping with the same noise. Here's a little video of the DEC axis trying to move:



As you can see and hear there's no movement and the sound is very much NOT the typical whine of the motors that I am used to. Being an electrical engineer I was dreading the thought of troubleshooting something mechanical. I searched around the Internet and read everything I could about taking apart the EQ6. Then, with a little nervousness I began removing the DEC axis. It was really quite easy and well documented on other websites. Inside the DEC housing you can see all the major parts: the big brass-colored ring gear, the steel worm gear, the small brass-colored spur gear, and the tiny little set screws that become very important later.



Those little set screws adjust the position of the worm gear relative to the larger ring gear. They actually move the entire housing, and since the worm gear is fixed to the housing you are moving the worm gear too. Below you can see what the housing sits on. There's a little metal block for one of the set screws to push against and the other set screw pushes against the metal lip around the large DEC axis shaft hole. You can also see the top of the gearbox which is driven by a stepper motor.



At this point it's a good time to scrape away all that black paint on the mating surfaces of the housing and mount. A flat razor blade and some sort of mild solvent will quickly remove this paint. I used decal remover. Removing the paint ensures that you have a tight fit and accurate tolerances. Now that I had the DEC axis apart I checked all parts and could find no problem. A bit puzzled, I put it back together. Another check of the motors revealed nothing new - still no movement. I then checked to make sure the stepper motor gearbox was making good contact with the spur gear. This can be done be removing a small screw under the end cap of the worm gear and looking in where the gears meet, as seen below:



Everything looked good there, so it was back to the worm gear housing. By this time I had done a little more research, gotten some help from Tom at Astro Motion Technologies, and discovered the secret to the little set screws shown in the above pictures. To adjust, you first loosen the four 5mm bolts that secure the housing to the mount, but only very slightly:



The set screw shown above loosens gear mesh when tightened. The set screw on the other side tightens gear mesh when tightened, and is shown below:



The best way to know when you are pretty close to having the right gear mesh is to remove the stepper motor for the axis you are adjusting and spin the spur gear with your finger. To accomplish this the electronics board of the mount is removed and disconnected. The stepper motors are behind this board, and easily removed with two screws. Below you can see the motor compartment with the DEC motor removed. The edge of the spur gear is just visible near the top of the compartment:



The spur gear should feel a little firm but not tight, and not very loose. Adjust the set screws until the spur gear is very hard to spin, then back off a little. Now you can put the motor back and check the gear alignment by peering into the hole shown previously. Then tighten the four 5mm housing bolts in a criss-cross pattern just like putting a tire on your car. Once I got to this point the motor still did not turn the DEC axis, which meant a little more adjustment of the set screws was necessary. The object here is to find the sweet spot between backlash and motor stall (what you saw in the video above). Backlash is "play" in the gears which you can feel by trying to rotate the axis with your hands while it is locked. If it wiggles back and forth - that's backlash. There's only a tiny spot between no backlash and motor stall, and it takes time to find. The gears must be checked across the full range of motion. They may seem fine at one point, then the motor might stall as you slew the axis around. Each time the set screws are tweaked, the adjustments are very tiny - just 1/8 of a turn or less. It turned out that I never needed to take apart the mount to make these adjustments, but I am glad I did. I really learned a lot in the process and am no longer afraid to dig into my EQ6. The RA axis is nearly identical as far as adjustments are concerned. Here you can see the first pair of 5mm bolts to be loosened just behind the RA setting circle, as well as the housing adjust set screw:



The other 5mm bolts and the other set screw are located down below the RA setting circle as shown below:



One other thing to check is the spanner nut at the end of each worm gear. These are behind caps located on the same side of the mount as the electronics board. The nut should be snug, but not too tight and not too loose. This is another source of play in the mount. The DEC axis spanner nut is shown below:



It took a couple of hours to get my EQ6 tweaked properly. Now I have no play in either axis and no motor stall either. With the WS2 coating I am even able to adjust beyond zero backlash. This means getting the backlash adjusted out, then tightening the gear mesh just a little more. This preloads the bearings and increases the contact area between the gears. I should get more payload capacity and better periodic error as a result.
Thanks to Tom at Astro Motion Technologies for guiding me through all the adjustments and patiently explaining the reasons behind them. His help has given me a much better understanding of the mechanics inside my mount. We both now realize that all the electronics and hand control are needed for the WS2 modification. I didn't send my hand controller or electronics board with my mount, thus Tom could not operate the motors. He got the gears pretty darn close though! Now my mount is running smooth as silk. If these fierce winds ever die down I might actually be able to get out and test out the improvement.
In case you want to hear what the mount should sound like, check out this video:

More on the focus control project

Last weekend I put together a couple of different stepper motor control kits to see how they each perform. The first was the CK1405 kit from Carl's Electronics. My assembled kit in it's testing configuration is shown below:

I really wanted the CK1404 kit but they do not carry it any more due to the UCN5804B chip being discontinued. But, I also ordered another kit from Alltronics. Their kit did not have much of a description but I took a chance on it anyway. As luck would have it, their kit included the UCN5804B stepper motor IC and much more versatility in features. Back to the original kit - I tested it out and just could not get satisfactory operation of the motor. It was very "choppy" and did not have much speed adjustment range. I put that one aside and moved on to the Alltronics kit, as shown below:

This kit worked very well. Motor operation was very smooth and there was a wide range of speed adjustment. Plus, this kit offers a low-speed mode, single-step function, half step mode, and a selectable full wave/2-phase drive. I decided to use the Alltronics kit for my design, which required some changes. Originally I intended to put everything in the hand-held case shown in my previous project post. But the Alltronics kit is too large to fit in that case. So the motor control kit will be mounted in a separate box at the mount. The hand-held case will just house the control switches and display.
This design got me thinking - can I control three different motors with one control board? Why not? I have three focusers, so it sure would be nice to control them all. What I am planning is a relay switching circuit that only switches on one motor at a time. There's no reason to ever control two focusers at the same time, so this should work. My hand control just needs three more switches, each one to enable one motor. Below is my basic schematic of the motor control circuit, without all the hand controls and display:

Also, over the weekend I built the display board, but have not yet tested it out:

It's getting closer! My mount comes back tomorrow, so the focus control project will probably be sidelined for a while until we have some cloudy weather.

My EQ6 mount improvement - Part 2

Last time we were at the stage where the gears came out of the ultrasonic cleaner all nice an shiny. The next step is to take very precise measurements of the gears. One type of measurement performed is to measure the "run out" of the gear. This is done on a machine scale as shown below:

My gears averaged out less than 0.001" overall deviation. Pretty darn good! Next, the gears are checked on an optical comparator:

This device allows a very exact measurement so that the right amount of WS2 can be applied. Here's a view of the worm gear before treatment showing the roughness and machining marks:

After treatment you can see that everything looks much nicer:

After coating, a close-up inspection of the gear shows the WS2 coating as a light-colored edge on the teeth of the gears:

And here's a picture of the gears after coating. The WS2 is the darker area on the surfaces of the gears:

That's it for now. My mount is almost ready and should be back next week. Just in time for more cloudy weather!

My EQ6 mount improvement - Part 1

This is the first part of I don't how many to describe the improvements being done to my EQ6 mount right now. The mount is currently getting worked on and I hope to have it back in the next week or so. In the meantime I have some pictures of the process that were sent to me by Tom at Astro Motion Technologies. This process is currently in beta test mode and I am one of the lucky beta testers.
The point of this process is to even out all the inaccuracies in the mounts internal gears and make them all mesh together much better. This will reduce periodic error and increase the load bearing ability of the gears. The secret of the process is the application of WS2, also known as Tungsten Disulphide. This is a compound developed by NASA as a lubricant for spacecraft. WS2 forms a molecular bond with whatever it is coating, but does not stick to itself so it won't build up where you don't want it. It has a very low coefficient of friction and can withstand pressures of over 300,000 psi. The coating is applied with high-velocity and is very thin - about 0.5 microns thick.

My EQ6, like other mounts of this type, move and track objects in two axis - right ascension (RA) and declination (DEC). Each axis has a worm gear, as shown in the worm block above. Each worm gear drives a larger gear along the axis of motion. The worm gears are driven by stepper motors controlled by the mounts internal electronics. The larger shaft gear, shown to the right of the mount, and the worm gear are the surfaces to be coated with WS2. The shaft gear has bearings inside that are friction-fit. They are pressed out using a hand press with even pressure, as shown below.

Once the gears and bearings have been completely removed, they are given a good cleaning in an ultrasonic cleaner. Thankfully Synta has stopped using the super-thick black grease that has always caused sticky operation in cold weather. They put that thick grease in there to make up for less-than-accurate gear tolerances. Back to the process - the gears come out of the ultrasonic cleaner all nice and shiny:

The worm gear is then measured on a machine gauge to check run out, radial run out, and gear tooth spacing. My gears checked out pretty good, with accuracies down to around a thousandth of an inch variance. Looks like Synta is doing pretty good with their gears. After the gears are measured, they are closely inspected on an optical comparator. But, more on that next time.

A new project...

Things are kind of slow around here while my mount is still away (I promise to post lots about this soon!). So, it's time for a little indoor project that I have been thinking about for a while now. I wanted a "hands-off" focus control for my telescope, something I wouldn't have to touch which causes vibrations. I also wanted a way to return to a known point of focus, which is important whenever you change cameras or add a reducer or barlow. Every time you change something the focuser must be moved to reach focus again. This becomes more of an issue with a Schmidt-Cassegrain telescope because the focus knob, which moves the primary mirror, can be turned about a million times without any indication of where you are (or more correctly - where the mirror is at). My other focusers don't move so much, and have a scale engraved on them which helps me find the right focus. (NOTE: my Celestron C8 has a built-in focuser - the one I am talking about now - but I also have an additional Crayford focuser on the C8 for fine focusing, as well as a similar Crayford focuser on my ZS80FD) Touching any of the focusers causes vibrations in the entire rig, not to mention the fact I have to get up out of my chair. After researching around the Internet, I decided that a stepper motor with electronic control was easy enough for me to build, and affordable. I got most of my inspiration from this site. The stepper motor kit shown on that site is no longer available, so I found another kit here. It's not quite the same, so we will see how it works out.

Above are the parts I have purchased so far, mostly from Mouser Electronics. The display/counter kit was purchased from Ozitronics down in Australia. If you contact Frank there, he will program the circuit for no debounce, which is important for the operation of the focus control system.

Here's the schematics of the stepper driver kit, and counter/display kit. I chose kits instead of building from scratch because it saves loads of time. I am still trying to figure out the best way to interface these two circuits, but it shouldn't be too hard.

Here's a couple view of the stepper motor. It's a 12VDC motor with 100 steps per revolution. I actually bought two just in case (they are cheap!). To attach the motor to the focuser, I'll use a mechanical coupler like this:

Beyond that, a bracket will need to be fabricated to secure the motor assembly to the focuser. I still haven't figured that out yet. I hope to get started on this project soon. If this works well I will put stepper motors on everything for the ultimate lazy-man's setup. Later I will take it another step by making everything computer-controlled. My ultimate goal is to eventually control everything remotely from inside. Or am I getting too lazy? Hmmm...

Chasing Iridium Flares

While my mount is away getting worked on (more on that later) I am looking for other things to image. Iridium flares are something I try to catch visually when I can, but I haven't tried to catch one with the DSLR. What are Iridium flares? They are reflections of sunlight off one of the 66 or so Iridium communications satellites orbiting all over the earth. They have large antenna arrays made of aluminum treated with silver-coated Teflon. Thus, they are highly reflective. The satellites are maintained at a fixed vertical position relative to the earth as they orbit, so if we know the position in orbit, we can use software to predict when and where we'll see the glint of sunlight off the antenna panels. You can check the next times for flares at the Heavens Above website. They require some careful planning to catch with a camera, so use a planetarium program to see where the satellite will be at the time of the flare. Even then you don't always get it right, as you can see by my image. I was a little low with the camera. Fortunately there's always another Iridium flare in the near future.

The Lunar Eclipse

Saturday night was the first total lunar eclipse in 2-1/2 years. Unfortunately for us the moon was rising well past the beginning of totality. That's the phase where the earth's shadow completely covers the moon and the moon turns a blood-red color. In this case the totality phase began at 5:44PM, but the moon wasn't going to rise until 6:21PM at my location. With the hills and trees on my eastern horizon, I would have to wait much later to even see anything. Totality ended at 6:58PM, at which time the moon was still hidden behind the trees. That's when I could see the bright crescent as the earth's shadow began moving off the moon. I sat with my telescope ready, positioned just above the tree line. The high clouds that were around all day were breaking up, but still making the view of the moon pretty fuzzy. Once the moon cleared the trees, I snapped a few shots but they were all fuzzy. The above image is my favorite of the bunch. Too bad we didn't have a good view of the entire eclipse. I haven't had good weather to see that since May of 2003, when I took the sequence of images below. At that time I didn't have a telescope, but the awesome lens on my old Sony DSC-F505V provided some great images. I'll be looking forward to nearly a year from now when we have our next total lunar eclipse on February 21, 2008.