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Is anyone using OnStep as their goto system?


dazzystar
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Hi All,

I'm in the final stages of trying to fit an OnStep goto system to my EQ3 Synscan mount, doing away with the stock control box and motors. Has anyone done something similar?

Cheers
Daz

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I have, multiple times!

First was converting an LX200 classic to Onstep. Second was replacing and AWR drive system on an old mount.

How's your build going?

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Hi @yuklop

Mine's going very slow. I've built the MaxPCB version and it works surprisingly, I've had a lot of help from George Cushing in getting the firmware right (I think).

I've printed a couple of stepper mounts and attached them to the EQ3. I now need to work out how long the belts need to be. I'm awaiting an email from George on the correct way of measuring for this. Where did you get your belts from by the way?

Once I've got them fitted I can then test it all out before going to work on redesigning the stepper mounts to neaten everything up.

Cheers
Daz

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Hi Daz,

Belt length calculator here:

https://www.technobotsonline.com/timing-pulley-distance-between-centres-calculator.html

Assuming you are using GT2 belts, which work well, ebay is a place to get the pulleys and belts. They are pretty cheap, just take care its a UK supplier if you don't want the long lead time.

Printing stepper mounts is a good effort. I used MaxESP for all my builds. It is probably a perverse choice, as its is one of the trickier ones, by all accounts but it was the more powerful option when I started. There is the FYSTEC option  now, which looks really simple to implement, but hardware is pricey in the UK. I also got a lot of help with my first build, but it is a good helpful community, so got there in the end. Build 2 was a doddle vs build 1.

Dan

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@yuklop thanks.

Would love to see some of your OnStep builds. Going to measure and order the GT2 belts today or tomorrow. The attached image shows a tight fit for the belt and no idea how I'm going to get a measure in there!!!!

IMG_4886.JPG

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This one details the build:

It is also in more gory detail on the Onstep Showcase page.

You don't need to be really precise, as I found it really hard to get exactly the right length belt. Usually a little spacer is required to get the right tension. I have used washers around the mount screws before, or had a bracket I could slide up and down. You can also use belt tensioning pulleys, but that is a bit fancy pants!

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Oh, you can measure the edge of the motor there to the edge of the shaft pretty accurately. Then you know the motor width and the shaft diameter, so you can calculate the centres. Probably how it should be done. I'd just get a caliper and measure roughly centre to centre. To be fair I have had to rebuy the odd belt... so now I usually go one tooth over and space, rather than one tooth under and find its too tight

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So the approx distance between centres is 42mm. The bore diameters of both pulleys is 5mm so would the belt length be 84mm + (5 + 5 /2) = 89mm? Or as close as I can to that? I do have a little play in adjustment. Here's an image of the DEC axis (I hope I've got that right and it's not the RA axis!) motor which has a centre to centre distance also of 42mm but the bores are 6mm and 5mm so (6 + 5 /2) so 89.5mm belt length?

 

 

IMG_4888.JPG

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Thanks @fozzybear for the images. It's the belt lengths which I can't figure out how to calculate. I have (according to George Cushing) the following pulleys:-

Dec 12T motor, 48T worm, 4:1 ratio. 
RA 20T motor 48T worm, 2.4 ratio. 

 

 

 

 

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My pulleys are 40 and 15 with 1x61 and 1x64 teeth belts with a 6.35mm width you could measure the belt length with maybe a simple piece of string around both pulleys and then lookup on the chart on beltingonline

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1 minute ago, dazzystar said:

No problem. I thought they'd be some technical calculator for the belt length?

it all depends on the placement of the steppers as you have a custom mount not relative to the pulley configuration. 

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No I meant if you know the distance between centres and you know the specs on the two pulleys I thought you'd be able to enter that into a calculator. Think the string is the best thing for now though.

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This is going to be a potential PITA I think. I've measured the RA axis with string and it's around 155mm. I have some movement to play with but not on the DEC axis (which I've not measure yet but will be shorter due to the 12T pulley). 

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4 minutes ago, dazzystar said:

This is going to be a potential PITA I think. I've measured the RA axis with string and it's around 155mm. I have some movement to play with but not on the DEC axis (which I've not measure yet but will be shorter due to the 12T pulley). 

like mine one is longer than the other so don't worry

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For the 12T - 48T Dec the length is 147

image.png.82aced8015b2a03ad58867c9d6a6fb01.png

 

For the 20T - 48T RA the length is 154mm

image.png.e8e519fecbccf9c2c580273edc799be5.png

 

But it is often hard to find the exact belt length you need, so some fettling is often required. The calculations are form the link I posted earlier.

 

Dan

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The 158mm fits perfectly. I've ordered a 150mm belt off of ebay and hopefully will get it tomorrow. We'll see if it fits ok but there's virtually no movement on the bracket for the DEC axis.

Edited by dazzystar
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The 150mm belt arrived this morning but I've had to raise the DEC bracket up to get it tighter. Here's a couple of pictures. Even with the bracket raised up by this amount the belt is still a little loose so think I'll have to modify the bracket.

 

 

IMG_4891.JPG

IMG_4890.JPG

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