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Clarification regarding the What-If Spreadsheet

Sam
 

Hi, forgive me for coming here empty handed. I was hoping to begin my calculations for what I need and I can't seem to wrap my head around the required values on the spreadsheet. I am sorry as this might be a required common knowledge but can someone tell me what the values are for?
Well I have a Vixen GPE mount and all I know is that it has a gear ratio of 1:144. I place the value of 1 under StepsPerDegreeAxis1 / GR1 and the value of 144 under StepsPerDegreeAxis1 / GR2. I don't even know if I am correct with those values. I don't know what the values for my Dec are or if it is also 1:144. I hope someone could help.

Howard Dutton
 

Both axes appear to be 144:1 according to this:
http://www.company7.com/vixen/mounts/gpegem.html

Looks like an EQ5 class mount, there are plenty of examples of similar conversions:
https://onstep.groups.io/g/main/wiki/Showcase%3A-What-Users-Built-With-OnStep

Most go with NEMA17 size 400 step (0.9 degree) motors driving the worms through timing belts/pulleys for an additional reduction of about 3:1.

Sam
 

Hi, thank you for the reply! I can see on the spreadsheet that the value of GR1 is 3, is this due to the timing belts (i.e. 3:1:144)? And the DesiredBaseSlewRate is that something that I arbitrarily create or is there a recommendation/formula?

fetoma
 

On Fri, Jan 10, 2020 at 01:13 PM, Sam wrote:
I can see on the spreadsheet that the value of GR1 is 3, is this due to the timing belts (i.e. 3:1:144)?
3:1 pulleys like a 12 tooth and 36 tooth pair

Sam
 

Where does the GR1 value come from though?

fetoma
 

On Fri, Jan 10, 2020 at 01:37 PM, Sam wrote:
Where does the GR1 value come from though?
It's the ratio between your pulleys. 3 = 3:1
If you had 12 tooth and 48 tooth pulleys it would be 4:1, so the GR1 value would be 4.

Khalid Baheyeldin
 

On Fri, Jan 10, 2020 at 05:08 PM, fetoma wrote:
On Fri, Jan 10, 2020 at 01:37 PM, Sam wrote:
Where does the GR1 value come from though?
It's the ratio between your pulleys. 3 = 3:1
If you had 12 tooth and 48 tooth pulleys it would be 4:1, so the GR1 value would be 4.
GR1 is something that you do yourself, usually using pulleys, because they do the job
without the backlash inherent in doing the same with gears.

The main challenge with many mounts is whether room is available to attach the larger
pulley to the worm gear without hitting other parts of the mount in certain positions.

If you can do 4:1, it is better than 3:1, because of finer resolution, and better torque.

So you have to buy two pulleys, and a belt to go between them. The length of the
belt will depend on the distance between the two axles after you attach a motor to
the mount.

Sam
 

I see, everything is clearer now. Thank you very much for everyone.

Khalid Baheyeldin
 

You should also carefully read the showcase page on the wiki, since it contains
a lot of examples of conversions of EQ5 mounts, like yours. These are actual
projects by many people, and the links there should contain lots of important
information that will help you.

George Cushing
 

I haven't found any 12T pulleys for 6mm wide belts and the 12T pulleys for 3mm belts are all 3mm bore. So they'd have to be re-bored on a lathe.

Thus you're practically limited to 16T for your motor output. So 40T:16T = 2.5:1, 48T:16T = 3:1 and 60T:16T = 3.75:1 are your practical options. Several EQ-5 types seem to be able to use a 60T pulley. 

fetoma
 

On Sat, Jan 11, 2020 at 06:48 AM, George Cushing wrote:
I haven't found any 12T pulleys for 6mm wide belts
Got mine here:

https://www.aliexpress.com/item/32871142006.html?spm=a2g0s.9042311.0.0.7e1d4c4d2BVAZR

Khalid Baheyeldin
 

On Sat, Jan 11, 2020 at 09:48 AM, George Cushing wrote:
Thus you're practically limited to 16T for your motor output. So 40T:16T = 2.5:1, 48T:16T = 3:1 and 60T:16T = 3.75:1 are your practical options. Several EQ-5 types seem to be able to use a 60T pulley. 
There are 15T 5mm bore pulleys available.
He can pair it with a 45T pulley, for a 3:1 reduction. Try also the 60T one.
But first you have to check if its dimensions will fit your mount, in various pointing positions.

Pete
 
Edited

I too have a CG-5 and here is how I did the stepper motors and the GR1 gearing https://photos.app.goo.gl/BiYvj42BbgtfHvjn6  I used 20T pulleys https://www.amazon.com/gp/product/B077GNZK3J/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 on the 400 step Nema 17 motors and 60T pulleys https://www.aliexpress.com/item/32733860048.html?spm=a2g0s.9042311.0.0.41cb4c4dLVaMNp on the worm gears.  This makes GR1 = 3, just like yours. All the parts came from Aliexpress and Amazon.  Please make sure you read the comments at the side of each image.  It gives an explanation of what I did and why. This may help.

The belts I used are RA = 160T and DEC = 168T.  It works.

The CG-5 and its cousins a\leave the factory with the most amazingly sticky grease all over the worms gears.  The general consensus in the amateur astronomy world is that the mount will work much better without this and a really good cleanup is worth  doing.  I did mine and it has paid off. the mount is much smoother and is easier to move.  Look at http://www.astronomyboy.com/cg5/preparation.shtml and https://twitter.com/wcoastsands/status/1113815732763025408 as well as on Cloudynights.com.  There is even a company that will do this for you https://www.deepspaceproducts.com/hypertune-service-for-the-celestron-cg-5-mount_8_4226_8659.html.  I replaced the worm bearings with ceramic ones.  I bought them here https://www.aliexpress.com/item/32953885580.html?spm=a2g0s.9042311.0.0.41cb4c4dLVaMNp