astronomy7

March 2019, I acquired a 16" Ritchey-Chretien (RC) by GSO (Taiwan, makers of TPO & Astro-tech). HighPoint Scientific of New Jersey had a sale I couldn't ignore and so I advanced my plans by two years. It arrived extremely out of colimation, and since I didn't have a functional mount, it will take some time before I collimate and test. I will greatly improve the design of both from the lessons learned over two decades. Do I look happy?

I've progressed much on the fork mount - it is surprisingly large as compared to what it looked on paper! Supports my weight without tipping, despite not bolted to the ground. Will be fitting the 16" on it soon. I used the 3D mill to work these parts, and used gas shielded welding (MIG) myself for the first time.

I was always wanting to use direct drive brushless motors, but the cost for components is prohibitive, so I fell back onto the tried and true worm gear for the RA drive through a Byer's 10". However, I am testing out a belt on the Dec. The 3 turret drives I lathed and welded and was inspired by 3D printers for the top slit drive, whereas the door is a standard electric piston. Thank you eBay!

Lessons learned over 30+ years?

No electronics or battery on the turret
Simple turret actuators which are powered only at the turret park position
Three turret motors for rotation as is the minimum for support and ensures equal traction, mitigating stalls
Tin sheeting instead of wood because it leads to far faster cooling
Fork mount; easy balancing, no pier flip, less space in motion, no counterweight to knock you out

Faced with 250$ for a second OpalKelly fpga PCB for reading the encoders as I had on the other telescope, I decided to use a Teensy 4.0 as it had a 600 MHz ARM,surmising I'd have better than 100 steps of granularity per bit of the 2.5 Mbs serial stream from the Tamagawa SmartAbs encoder. First time using a Teensy + Arduino IDE, one afternoon, voila! Didn't waste time making circuits, also got an RS485 to digital converter, and a 3.3V to 5V level shifter. Snap easy nowadays! 35$ in all.

And finally at right, she's mostly done, and has her large format CMOS camera with 7 filters 2" diameter each. Will take a few weeks to adjust the scope and test out the optics , camera and software. The electronics and Windows 10 mini PC are shown with the doors open, access is remote so the keyboard, mouse and touch screen are only for troubleshooting.

The declination belt drive is surprisingly good. However the Byer's drive has an unexpected and dramatic lurch over a single worm cycle, might prove difficult to correct. Otherwise the scope, dome, camera, software, PC are working very smoothly, far better than the larger much older dome next door.

The GSO 3" focuser isn't known for carrying much weight - the focus apparatus is housed in plastic parts. One end had no centering bushing, so the shaft would no longer run true at high weight. I added a bushing and it solved the problem. I also made a 3D conforming part and gears to allow a hobby servo to turn the focus knob. A USDigital 0.0005" per step plunger encoder provides focus position feedback. Nice! ...then I scrapped that and replaced the 10:1 focusing with a linear actuator so that it could support a heavy image train - arguably the only such design on the web! The GSO focuser can now handle 6kg of image train with no significant flexing.

I chose a 21" pier with a 9" hollow. To reduce cost, I built a casing out of roof tin and used a rolled grid for armouring I had found on a rock pile. 34 bags of 30 kg mixed concrete in all for the footing and pier. The lower dome sits on three concrete posts, and have cantilevered joices. Galvanized tin wraps around the building. The same tractor that moved the first dome 30 kms was used again to lift the turret onto the buiding. The car hauler was used to both build the turret and deliver it to the site as it was the only flat surface on the farm!