AZ-GTi Equatorial Mode at Low Latitude Problem Solved

Just a few weeks ago, I decided to get back into my old hobby, amateur astronomy. I spoke to old astronomy friends to get some tips in buying an ultra-portable telescope and mount. This led me to Skywatcher's AZ-GTI mount and a 127cm Maksutov Cassegrain telescope. I bought a kit online which arrived in just a couple of days. I knew this mount is an alt-az mount but then my friend told me this can be converted to an equatorial mount, and be used for some basic astrophotography. I looked up online and found that, indeed, some people are using this mount in equatorial mode by putting it on a wedge and changing the firmware. I bought the wedge and the counterweight after watching this youtube video.

The wedge and the mount arrived in a week and this is when I found the problem. The whole setup looks cool and very compact. But the problems is, I can't configure it to my location's latitude. I am in a city that is only 1.4 degrees north of the equator. The mount hits the base of the wedge starting at 7 degrees. But I needed 1.4 degrees.

The review videos I watched online was done by people living in Canada or the USA which is far up in the northern hemisphere. So they do not have this problem.

Though I found people talking about the exact same problem, I never really found a real solution. I guess there is not a lot of people in the low latitude countries who bought this mount and wedge. So I decided to fix this myself. As an Agile practitioner, I solve problems iteratively.

Iteration 1

In the first iteration, I tried flipping the pinion gear of the wedge so that the dovetail is facing the opposite side. It somehow fixed the original problem. But it also created a new one. Some bolts are in an odd position and difficult to access, like the altitude adjuster. Also, the centre of gravity is now too far off the centre. It could actually tip the tripod over and could break your precious telescope.

 

Iteration 2

In the second iteration, I designed and 3d printed a wedge that will replace the Skywatcher wedge. The objective is to test the feasibility first and see if the plastic can hold the weight. I designed a very simple L bracket pre-configured angle of 91.4 degrees. This will give me a fixed altitude of 1.4 degrees.

I printed it at 40% honeycomb infill at a slightly higher temperature and higher extrusion rate for stronger layer adhesion. The printing process took 34 hours.

Although it looks cool, and it shows that it can handle the load, there are some problems with the design.

Problems / Lessons learned

•  The main problem was that this 40% semi-hollow plastic shell flexes when there is a load. And when it does, that 1.44 degrees of altitude is lost and sometimes points below the horizon depending on the position of the telescope.
• The second problem was that you cannot adjust the azimuth so it's very difficult to polar-align especially when you cannot see Polaris.
• And lastly, the power adapter port is no longer accessible at a certain Right-Ascension angle. I forgot to take this into account while designing.
  

Iteration 3

Based on what I learned from the second iteration, this Iteration was a complete pivot from the second. I decided to reuse the Skywatcher's wedge instead of replacing it so that I still have an azimuth adjuster. The objective this time was not to replace the wedge with a 3d printed one but to help that wedge alleviate the stress of very low latitude configuration. So I designed an extension of that wedge. This extension will tilt the wedge at 12 degrees angle and also move the wedge's mount point off centre, just enough to give room for the counterweight before hitting the tripod legs. This will give a better centre of gravity. And because of the 12 degrees offset, to achieve a 1.4 degrees altitude, the mount will just have to be configured at 13.4 degrees position, which is above the 7 degrees limit.

I printed this solid (100% infill) with a yellow PLA plastic that I already have. The printing process took almost 20 hours to complete. The result is amazing! It's very strong and heavy. It weighs almost a kilogram.

Problems / Lessons Learned

Although this iteration has proven that the new design works and the result is amazing and almost perfect, there are still very minor issues that need fixing.

• The colour is Yellow, does not fit with the Skywatcher's colour palette. This just because that's the only available filament I had at the time of printing.
  
• The thumbscrews at the bottom are quite difficult to tighten with your thumb. Because the gap between the thumb screw knobs and the base of the wedge extension is too tight as shown in the following image.
  
  
  

With these minor problems, I decided to do another iteration with more experimentation.

 

Iteration 4

In this iteration, apart from fixing the Iteration 3 issues, I also experimented with a different material, ABS, an oil-based plastic. This is a slightly stronger material than what I usually use in 3d printing. This material also does not decompose. I have not tried printing with this material before. And, to be able to print with this material, I had to modify my printer by adding a heater at the print bed. This is required to print this material. So as extra work in this iteration, I hacked my 3d printer. I stuck a silicon heater to the glass print bed, installed a relay module and updated the firmware.

But this has led to a failed print. The material has warped significantly even though the bed is heated. It seems that the bed temperature settings were not set correctly. 

In this iteration, I also tweaked the printing configuration, changed the nozzle temperature, increased the print bed temperature to 110 degrees Celsius and picked a slower printing speed. The print has less warping but after just 2 hours of printing, strange issues came up. There were layer shifting issues, and about 3 hours into the process, the printer crashed. The motherboard overheated and went into thermal shutdown and resets itself leaving me with unfinished print. The layer shifting can also be explained by overheating.

This iteration is a failure but it surfaced an issue with my 3d printer. I changed the design of the print bed of my 3d printer so that it leaves a gap where hot air can escape from the bottom of the print bed where the motherboard is. 

The design change worked well. The printer no longer overheats. I tried a couple of huge prints without overheating issues. So I'm ready to try again.

Iteration 5 

In this iteration, since the printer design is fixed, I tried again printing in ABS. There is less warping but there are layer adhesion problems. There are cracks in the print. I think I was still printing too fast. Or perhaps I should have enclosed the printer to give a uniform temperature across the layers.

The resulting print was indeed super strong, but with ugly looks and many cracks all over.

Iteration 6

I decided I had enough of ABS printing. So I bought a white PLA filament instead. I adjusted the design to fix the thumb screws gap. Added an embossed branding. Printed with a little over extrusion to make sure it doesn't leave any gaps between layers and ensures a stronger layer bond.

And here's the final result with the wedge and the AZ-GTI mount attached to it.

I'm happy with the final result and decided that this is the final version. Overall, I spent around $40 on filaments, few hours of CAD design, about a total of 40 hours of overnight printing. But the result is worth it. All problems are now solved. It looks cool and blends in very well with the Skywatcher colours. The only thing that worries me now is that in the next few years, PLA, the material I used, will start to degrade and eventually decompose especially when exposed outdoors. But I guess will deal with that in the next few years.

For anyone who has the same problem with AZ-GTi mounts in equatorial mode at low latitudes, feel free to download the 3d model STL file and print it yourself. Save yourself of the troubles I had.

You can get the STL file here --> https://github.com/rossbrigoli/az-gti-low-lat-adapter

Here are my print settings.

• Filament  - 3d-aura PLA Extreme (super strong PLA)
• Nozzle diameter  -  0.4mm
• Layer height - 0.2mm
• Infill - 100% solid
  
• Printed support  -  Yes
  
• Bed temperature - 70 deg C
• Nozzle temperature  - 210 deg C
• The print speed at 120mm per second
• Printing orientation for maximum tension strength as per below:
  
  
  
  
  

Happy 3d printing!

DIY Delta 3D Printer Rebuild

 

About 5 years ago, I built a Delta 3d printer from a kit I bought from AliExpress. You will find the details in this post. In that same year, I have been exploring 3D printing and building a 3D-printed electronic drum kit. The 3D models are opensource and are available on Github. The drum kit has been working very well, and I have used it to produce songs that you can now find on Youtube and Spotify. That's my other hobby.

Old Printer

5 years have passed, the 3D printed PLA plastic (Poly Lactic Acid) parts of my old 3d printer has degraded and started to become weak and brittle. Each part started to crumble and break apart one by one. PLA plastic is biodegradable; I guess it has reached the PLA's limited life span. Unfortunately, I have not printed reserved parts of the printer, and even if I did, it would have also degraded at the same time and would render unusable Today. The images below show the broken parts and have rendered the printer unusable.

Just before the year-end holidays, I decided to rebuild the printer and make it more robust. I wanted to replace most of the plastic parts with aluminium, but I can no longer find the exact spare parts. So I had to improvise and fit non-standard parts in it. The results were surprisingly amazing!

Spare Parts Sourcing

I can no longer find a supplier of the exact same parts, so I decided to find other parts and fit them in the printer. I got new aluminium extruder parts from Creality; this was originally designed to work with Creality 3D printers. I bought generic carriage/rollers, effector plate, hot end and nozzle from somewhere else and put them all together. Later on, I also replaced the cheap, mechanically unstable push rod with a better one. With these parts, this printer is never going to look the same.

Using some nylon spacers, I managed to attach the carriage to the roller with minimum impact on the printer's geometry. The dimension is about 0.3 mm off from the original. But this is OK as I can compensate for this in the firmware. I assembled a version 6 J-head hot-end made in brass and the classic hammock effector plate.

The aluminium extruder from Creality looks beautiful. I also bought an aluminium version of the delta frames. It was originally made of injection-moulded orange plastic.

Knocking the Old Printer Down

Knocking this printer down is a kind of a test of my memory. I had to remember how I assembled this to make the disassembly smoother. I assembled this printer 5 years ago without any assembly instructions. Now it's time to knock it down to the last bolts/screws.

Dismantling was fun. It took less than an hour to disconnect every electronic part and take every bolt and nut. Disconnect all peripherals from the motherboard and remove disassemble the effector.

 

Building the New Version

Starting at the bottom triangle frame using the new aluminium version of the corner frame, attaching the motors and building up to the top frame was the sequence I followed. During the assembly process, I made few mistakes. I had to redo some parts of the build. At this point, I realized that I may be wiser than my younger self, but I am definitely not smarter than my 5-year younger self. Nevertheless, I managed to assemble the frame with the motors in it and the timing belts installed, well greases bearings, etc..., in less than a couple of hours. 

Mechanical

The image below shows the complete mechanical assembly—no more orange plastic parts. The only remaining plastic part is the new effector plate which is made of injection-moulded nylon. I liked the hammock auto-levelling design of the effector plate, but I could not find an aluminium version of it. The pushrods were not replaced and still made of carbon fibre. The rest are now made of aluminium painted in black (not anodized).

 

Electronics

Assembling the electronics was quite fast except for one part. I realized that the Z-axis's mechanical lever limit switch for automatic bed levelling cannot be attached to this type of effector plate. The holes do not match.

Connected everything to the Arduino board

Loaded the Marlin firmware

 

After reading about this version 6 design of the hammock effector plate, I learned that it was designed to use a particular Industrial Automation optical sensor. The optical sensor is Omron SX-671. I found it on AliExpress and just ordered it right away.

SX-671 Optical Sensor

 

I knew this order will take at least three weeks. But I want to use the printer immediately to start printing some of the remaining parts of the printer. I made a crude plastic frame that allows me to mount the mechanical lever limit switch. It worked and should last long enough to print the remaining parts.

The plastic assembly bolted to support the lever limit switch.

 

Crude lever Z-axis limit switch assembly just so I can print the other parts while waiting for the optical sensor.

After the electronics are complete, I flashed the modified firmware. The firmware configuration was modified according to the new geometry of the printer. The Z-axis height is slightly bigger because of the shorter hot-end and a better end stop positioning.  After flashing the firmware to the existing MKS Mini Arduino board, it just worked right away. With just a minor adjustment on the Z height, the printer was then ready to print its own LCD panel housing + plus other parts.

Printing its own LCD panel housing + motherboard chassis

I have also designed a cover for the carriage rollers. This part becomes important now that I have a kid that could stick her fingers between those rollers. Putting a cover makes sure nothing gets in between the rollers and adds a better look to the entire build.

To test the reliability of the machine I just built and to break-in the new bearings, I printed a
"Baby Groot" for my little girl, which took 6.5 hours.

Finally, after two weeks, the optical sensor and the pushrods have arrived. The pushrods are of good quality with zero backlashes. It's built for the FLSUN Q5 printer, but it fits perfectly. After a few test prints, I can see that the print quality has improved with less mechanical errors caused by a worn-out ball and socket joints. And finally, here's the rebuild 3D printer in action. Printing a camera T-ring telescope adapter.

Including waiting for the orders to arrive from China, the project took more than a month. But it only cost around $100 in total. A lot cheaper than buying a new printer. Overall, I am very with how it came out. I like the yellow chrome over all the black metal frame.

I now am a proud owner of a unique 3d printer that no one can buy from anywhere. I hope this inspires someone to build their own 3d printer by leveraging open-source hardware.

Update:

I decided to add a heater to the print bed. The issue was that the motherboard I have, "MKS Mini v1.2", has no support for the heated bed. Therefore there is no port to attach a print bed heater. But the bed temperature sensor exists, and the D8 pin of the MPU is also exposed. D8 pin is used by Marlin firmware to trigger print bed heater on or off. Another issue is that the power supply I am using is only 72 watts, while if some print bed heaters are about 100W. So how did I solve this?

 

I bought a silicon heater which is 220V and 100W. Then I bought a relay module connected it to the D8 pin of the motherboard. This only adds a little bit more current load on the board just to drive the tiny relay. But then the switching of the heater is done in the relay. There is just this mechanical "tick" sound whenever the print bed turns on or off. The bed heats up to the target temperature in just a few seconds.

I also revised the print bed clamp design; I raised the print bed to leave a gap between the frame and the print bed. This allows the air to flow in and out and not accumulate under the print bed, which heats up the motherboard. This is a response to an issue where the motherboard was overheating.

Now, with this revision, the printer can print materials other than PLA. I tried printing with ABS, and it works!