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Where to put the "resolution"? Pulleys, motors, drivers.. ?


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

With the eq3 almost finish, just waiting for some pieces to add the st4 and put everything together, need to start planning the gc5.
So I need to buy all. Motors, pulleys, boards, etc. Well, I have some 200 steps motors I can use....
To achieve a good "resolution", meaning being able to do photography (yes, I know the mount itself is the biggest factor) I need some minimum value of steps per degree, or better yet, call it an optimal value, whatever that could mean.
To have that value several combinations of pulley, motor steps, driver micro steps can be used, so my questions are:
- is there an "optimal" value for steps per degree?Β 
- what is more important, having more teeth on the pulley, more steps on the motors, or more micro steps on the drivers?
- and for the cg5 is there a recommended combination of the above?

Thanks!


Khalid Baheyeldin
 

On Thu, Apr 1, 2021 at 03:02 PM, Pedro Miguel Barbosa Moutinho Nunes dos Reis wrote:
- is there an "optimal" value for steps per degree?Β 
About 12,800 is the recommended value for astrophotography.
How high can it go? To 61,200 in theory, but you run into other limitations.
Among those limitations: motor RPM maximum, board microcontroller speed, ...etc.

So plan for something above 12,800, but not much higher.

- what is more important, having more teeth on the pulley, more steps on the motors, or more micro steps on the drivers?
Driver microsteps tend to be less accurate as they become finer, compared to mechanical gear reduction.
More steps on the motor (basically 400 vs. 200) is preferred.
More teeth on the pulley is also nice to have, but then if you have too large a pulley, you may have problems fitting it into the space available without hitting something.

- and for the cg5 is there a recommended combination of the above?
400 Step motor
4:1 pulleys, if you can fit them, otherwise 3:1
1/32 microsteps

See the showcase page for actual examples.


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

Understood!
Something like between
AXIS1_STEPS_PER_DEGREE 15360,00000 400 32 3 144
AXIS2_STEPS_PER_DEGREE 15360,00000 400 32 3 144
with 16/48 pulleys
and
AXIS1_STEPS_PER_DEGREE 20480,00000 400 32 4 144
AXIS2_STEPS_PER_DEGREE 20480,00000 400 32 4 144
With 18/72 pulleys
I'll take a look at the gallery for inspiration :)

And off-the-shelf board?
The wemos is acceptable right?


Khalid Baheyeldin
 

I don't think you will find 72T pulleys readily available and cheap enough.
Even if you did, they may be too big for an EQ5.

But you can compensate by making the other pulley smaller, for example: 15T to 60T =4:1.


Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ
 

On Thu, Apr 1, 2021 at 03:34 PM, Khalid Baheyeldin wrote:
But you can compensate by making the other pulley smaller, for example: 15T to 60T =4:1.
Also the 12T pulley will work here (Vixen GP type class). I use the 12T to 48T on my LXD75 without any problems.


Khalid Baheyeldin
 

On Thu, Apr 1, 2021 at 03:47 PM, Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ wrote:
Also the 12T pulley will work here (Vixen GP type class). I use the 12T to 48T on my LXD75 without any problems.
And the advantages of a 12T to 48T is still smaller pulleys, which means more likely to fit the space at hand.


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

On Thu, Apr 1, 2021 at 08:34 PM, Khalid Baheyeldin wrote:
I don't think you will find 72T pulleys readily available and cheap enough.
Even if you did, they may be too big for an EQ5.

But you can compensate by making the other pulley smaller, for example: 15T to 60T =4:1.
IΒ  was looking at my local supplier list


I dont know the price...


Khalid Baheyeldin
 

There is MXL, and there is also GT2.
GT2 is the one used for 3D printers, and most people who use pulleys for OnStep use GT2 without problems.

Whichever type you end up using, make sure that the two pulleys and the belt are all the same type.
Never mix pulley and belts of different types.


Dave Schwartz
 

The 60T was too big to use on my EQ5 so I use 48T (with 16T on the motor) to get 3:1. I also use 64 microsteps to get 30720 steps per degree. I can get away with 64 microsteps tracking because this is on a real OnStep board that does non-SPI-driver mode switching so I get good tracking resolution and decent goto speed at the same time.

On 2021-04-01 3:50 p.m., Khalid Baheyeldin wrote:
On Thu, Apr 1, 2021 at 03:47 PM, Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ wrote:

Also the 12T pulley will work here (Vixen GP type class). I use
the 12T to 48T on my LXD75 without any problems.

And the advantages of a 12T to 48T is still smaller pulleys, which means more likely to fit the space at hand.


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

On Thu, Apr 1, 2021 at 09:07 PM, Khalid Baheyeldin wrote:
There is MXL, and there is also GT2.
GT2 is the one used for 3D printers, and most people who use pulleys for OnStep use GT2 without problems.
Yes. I know. But locally I'm a bit limited. They don't have GT2, at least onlineΒ https://eurocorreias.pt/catalogo/
Also, they have all the belts, etc, if I need some other size, I don't need to wait weeks for it arrives from abroad.
I need to go to the shop and see exactly what they have.


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

In "3 M" type they have it.


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

And in other formats... The wider the better in the belts? Does the smallest belt step is better?Β 


Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ
 

Danger! Those are MXL pulleys. We use GT2 pulleys. You would not be the first to make this mistake(particularly if you mix types). The preferred belt/tooth type is the GT2 6mm wide for the Vixen GP type mounts. There are quite a few reasons for the GT2 type. Zero backlash is the big one. If I can find my good technical article I will post it.

Spend some time and find a GT2 vendor you can source. I get most of mine from China.


andrea tasselli
 

5mm should be about right for that kind of torque. What matter is the number of engaged step, the more the better as any error in groove to groove distance tends to average out. Also, the load applied to each belt step goes down. Still, you don't need to apply a lot of torque as you would need to only overcome static/dynamic friction (in an ideal world, at least). Most of the tension would occur in ramping up and down the speed when performing goto and a 5mm width is more than capable to handle the for the sort of load you are likely to face with the mount of this class.


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

On Thu, Apr 1, 2021 at 09:45 PM, Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ wrote:
Danger! Those are MXL pulleys. We use GT2 pulleys. You would not be the first to make this mistake(particularly if you mix types). The preferred belt/tooth type is the GT2 6mm wide for the Vixen GP type mounts. There are quite a few reasons for the GT2 type. Zero backlash is the big one. If I can find my good technical article I will post it.

Spend some time and find a GT2 vendor you can source. I get most of mine from China.
Damn. ok.. locally I cant source afaik.


Mike Ahner
 

On Thu, Apr 1, 2021 at 03:45 PM, Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ wrote:
Those are MXL pulleys
Drew, why won't a match set of MXL pulleys & belts work? The gear ratio is the same. What I think you refer to is the user who mixed belt-types with different pulleys and so the teeth didn't fit making the diameter wrong.

Others have used pulleys and belts other than GT2, especially on larger telescopes. There is at least one in the showcase.

-Mike


Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ
 

On Thu, Apr 1, 2021 at 05:17 PM, Mike Ahner wrote:
Drew, why won't a match set of MXL pulleys & belts work?
Yes, of course they will work. But, there are reasons the 3D printers and OnStep use the GT2. I am just saying it is worth the effort to find and use them.


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

On Thu, Apr 1, 2021 at 09:45 PM, Drew πŸ”­πŸ“·πŸš΄β€β™‚οΈ wrote:
Spend some time and find a GT2 vendor you can source. I get most of mine from China.

Β 

Β 
Can you share the source?


Khalid Baheyeldin
 

On Thu, Apr 1, 2021 at 06:24 PM, Pedro Miguel Barbosa Moutinho Nunes dos Reis wrote:
On Thu, Apr 1, 2021 at 09:45 PM, Drew wrote:
Spend some time and find a GT2 vendor you can source. I get most of mine from China.
Can you share the source?
Amazon, eBay, AliExpress.

Just search for "GT2 pulley" and "GT2 belt".


Pedro Miguel Barbosa Moutinho Nunes dos Reis
 

so, if my calculations are correct, I need 154mm length belts. Im going to look for the pulleys now, I think I've found a source for the belts locally :)Β