Project Phyllix - An EQ mount
Hey guys, I am a student at Nossal High School, currently in Year 11, and seeing as this is the first year we have had the subject Systems Engineering, Ive decided to create an equatorial mount for my Year 12 Systems Engineering project(2015) that we do for the whole year. I realise its a big undertaking but I think the finished product is going to be worth it and if it works well, should rack up some nice marks for the subject, and be a sweet mount to put in an observatory that I plan to build soon.
The primary design goals of this mount are
- Stability
- Accuracy
- Ease of Setup
- Fit for Observatory Use for years to come
- ASCOM friendly
- Friendly Go-To Control Interface - If I have time, I may develop a hand controller.
Now, seeing as a friend of mine owns a machining company and I can get stuff machined cheaper than normal rates, I've decided to go for a 'fancy' telescope mount, and not simply 2 shafts held in with a plate and pillow blocks. Ill keep the design of the mount open source so if anyone wants to hop in and refine the design with their wisdom they can and/or make one themselves
So far I have gone through about 6 revisions of the design where i've just started from scratch again, and I think I'm getting close to a functional design. Having not actually seen or operated a Go-To equatorial mount physically (I have a small CG-3..), I have based most of my design off the White Swan 180, and WS 240, along with the Astro-Physics mount range.
At this stage, It is designed to be 100% made out of Aluminium T6-6061 except for the worm wheels and worm gear. Right now, the latest design is missing its base, DEC shaft and saddle, But as soon as I finish designing it, I shall post an image of it and the cross section.
In the meantime, here's a render I just did of
Rev 4, Its missing a lot of things, But generally what it will look like.. Dont mind the Base, It was a trial and error thing that didnt work out. Currently its at 25kg, 12kg on RA and 13kg on DEC so its pretty beefy for a high load capacity. The mount is able to be disassembled into 2 parts by removing 4 bolts ( or 3 if you take off the base)
**Why dont the image tags work on the thread but show in the preview??
4 Bearings Each Axis
- 1x AXK130170 on RA Gear, 2x HJ 324120 Needle Roller Bearings on Axis shafts, 1x NTA-3244 on Clutch knob side
- 1x AXK120155 on DEC Gear, 2x HJ 324120 Needle Roller Bearings on Axis shafts, 1x NTA-3244 on Clutch knob side
Current Drive Idea
- Arduino Mega2560 - To be replaced later on with a custom board with Atmega2560 chip
- Nema17 steppers with either 14:1 planetary gearbox or 5:1 timing pulley drive
- DRV8825 1/32 micro-stepping capable stepper motor driver
- Worm Drives - DEC 173mm 270 teeth, RA 190mm 297 teeth
I have ordered an Arduino, and as soon as I get it, will start coding the control system.
I don't know whether I should include encoders in the design or not. Opinions would be nice. If I was to employ encoders in this mount I would either use the
CUR AMT203 encoder - Binary (Absolute), Quadrature with Index (Incremental) - Although im not sure if they truly are absolute,
or the
CUR AMT103 encoder - Quadrature with Index (Incremental).
Something tells me that the Absolute encoders are probably a better idea, but they do cost twice the price of each AMT103. The absolute encoders also need me to play around with SPI, which I havent done before, while the AMT103 would be easier to implement, just simply connecting up to the interrupts of the Arduino and counting from there.
I'm guessing the optimal placement of the encoders would be on the worm itself(seeing as on axis encoders are expensive$$$$) to also overcome inaccuracies in the motor gearbox or timing pulley drive.
Most of this year is just planning and designing - Im trying to get a head start on this project so that next year my workload would be reduced.
Some Questions:
1. What should the telescope control system need to do separate from the hand-controller or PC.
eg. Should it have a way to correct for refraction, have its own alignment system, etc..
2. Are encoders on the worm worth it, or just count the number of steps in software.
3. Will encoders on the worm help with reducing PE by a lot?
4. Should the CoG of the telescope mount be over the centre of the base or does the weight of the telescope and CW change the position of the CoG?
5. Losmandy Style Clutch or like the ones on the Astrophysics mounts?
This is a project that is going to keep going as long as I have the mount, so I'll still be working on it after High School.
Any suggestions, help, and tips are more than welcome.