EQM35: Low-Cost Belt Mod

[malc-c]

10 hours ago, jif001 said:

It seems to be mentioned a lot in a Green Swamp Server forum. I think the author has a presence there.

Could well be.. Andrew has been known to be behind a lot of  the work on deciphering the workings of these mounts. 

[jif001]

Someone requested the STLs, and the only reason I didn't upload these in the first place is that I was still tinkering with them. I think they are OK now, so here they are...

Five files:

The RA motor bracket attaches the motor to the weight bar. For this you'll need to add two M5 nuts (which fit inside the tube) and two corresponding M5 bolts (I use the thumbscrew type shown here).

RA MOTOR BRACKET:

Note: this is for a NEMA 17 motor and will need amending if you use a NEMA 14

The RA junction box houses the two DIN sockets that you will find attached to a black plastic box marked 'RA IN' and 'Dec OUT' on the mount. Be very careful when removing and refitting these - the soldered joints are not very strong and can break. Take some pictures before removing them so you can record which wires go where, just in case.

The RA junction box back plate is a 'nice-to-have' but is not essential.

RA JUNCTION BOX AND BACK PLATE:

    

The Dec motor housing similarly requires an M5 nut, which fits in a recess (not shown in this picture). The bolt used to mount the existing motor bracket is re-used here. Again,  be very careful with those DIN socket connections, and the back plate is a 'nice-to-have' but is not essential.

DEC MOTOR HOUSING AND BACK PLATE:

Note: this is for a NEMA 17 motor and will need amending if you use a NEMA 14

       

Obviously there are numerous other bolts and washers needed to fit stuff together, plus some self-tapping screws for the Dec motor housing back plate, but they are easy enough to figure out and some existing bolts already on the mount can be re-used.

Here are some pics showing the final assemblies, for reference.

   

   

 

My next project is to replace the DIN sockets with something better. If that works then there will be some redesign work on this lot, so watch this space!

NOTE:

Before printing the components you may need to rotate them in your slicer to minimise the need for supports - they may not be in the best orientation for printing when opened.

RA Motor Bracket.stlRA Junction Box.stlRA Junction Box Back Plate.stl

Dec Motor Housing.stlDec Motor Housing Back Plate.stl

Edited August 30, 2023 by jif001

[GTom]

Following the topic: I want to revive my old EQ3-2. It is in very good shape, sitting on a rock stable steel tripod, I'd be flattered to convert this little mount to an AP workhorse!

[JeromeW]

I'd like to thank jif001 for his help. I did the DEC axis first, I was surprised the NEMA 17 stepper motor didn't burn-up my controller board. 

[jif001]

I’ve been running two NEMA 17 motors for a number of months* and the controller has been fine, so you shouldn’t have any trouble. 
 

* when the weather allowed 🙄 but I think I’m well into double figures with imaging hours since making the mods. 

[JeromeW]

I can't wait for clear sky's so I can test my new DEC motor. If it works out, I'll be upgrading my RA as well.

Edited November 19, 2023 by JeromeW

[JeromeW]

This picture shows the NEMA 17 RA stepper motor with the new connector spliced to it. I didn’t want to snip off the connector from the original stepper motor so I ordered new connectors from eBay: https://www.ebay.com/itm/155403343100?hash=item242ec2d4fc:g:PhQAAOSwoIlarzG3&amdata=enc%3AAQAIAAABAMRVe3AW7%2BrM8cuBQO%2B8KPsCb%2B8zaJ48odDREeX5fVL7g4Ca2dXj10bDPhSfVHTNms0X3wPuqLQHBVvs5k%2FYpSan9M3AiTnLoxy2PrHLEK%2FHeFc2c5O7jT485YC5d6Z3sP9Xv6CyM%2BXQRCgafYMdfTnKU4mXy6J0EtMAOM7SGnAXqABQ%2BnXsd2UxIXdY0S6x7rep7UJOIpBb6Bv2wPRrWiu9qMlhwc%2FatWRxi%2F%2BXFDqeOOJS1QGvx08LVsdm6mgkYdSHLNQa%2Fs4g4PJgdnIBhXXT%2BF8jCWkpy%2FVDCX0m6AG9Es9MSr3vSHoATJLMcoF25lXhK95qqDbiF2SqzWwWs4o%3D%7Ctkp%3ABk9SR7SQ6IGDYw

 

[JeromeW]

The wire color coding between the wire on the original connectors and the new eBay connectors is different.

[JeromeW]

This picture shows the rear end of the DEC stepper motor. The yellow bracket is designed so I can install a longer stepper motor.

[JeromeW]

This side view of the Yellow DEC bracket shows the attaching slot. It is tight fitting to the tang of the DEC Axis.

I will be installing my RA belt upgrade as soon as I get all the other parts.

I would like to thank jif001 for all his help.

[JeromeW]

Attached is my DEC Motor Bracket STL and Alibre Atom3D files. 

I tested my rig last night, and the NEMA 17/Belt upgrade definitely helped. But my real problem is that my Askar V telescope is too heavy for my EQM-35 mount. It doesn't help that balancing is very difficult with such a stiff mount. I may yet have to purchase a better mount for my telescope. My Askar V weighs about 12 pounds with cameras, focuser, etc. I am always open for suggestions.

DEC Motor Bracket.stl DEC Motor Bracket.AD_PRT

[jif001]

On 28/11/2023 at 23:25, JeromeW said:

This picture shows the NEMA 17 RA stepper motor with the new connector spliced to it. I didn’t want to snip off the connector from the original stepper motor so I ordered new connectors from eBay: https://www.ebay.com/itm/155403343100?hash=item242ec2d4fc:g:PhQAAOSwoIlarzG3&amdata=enc%3AAQAIAAABAMRVe3AW7%2BrM8cuBQO%2B8KPsCb%2B8zaJ48odDREeX5fVL7g4Ca2dXj10bDPhSfVHTNms0X3wPuqLQHBVvs5k%2FYpSan9M3AiTnLoxy2PrHLEK%2FHeFc2c5O7jT485YC5d6Z3sP9Xv6CyM%2BXQRCgafYMdfTnKU4mXy6J0EtMAOM7SGnAXqABQ%2BnXsd2UxIXdY0S6x7rep7UJOIpBb6Bv2wPRrWiu9qMlhwc%2FatWRxi%2F%2BXFDqeOOJS1QGvx08LVsdm6mgkYdSHLNQa%2Fs4g4PJgdnIBhXXT%2BF8jCWkpy%2FVDCX0m6AG9Es9MSr3vSHoATJLMcoF25lXhK95qqDbiF2SqzWwWs4o%3D%7Ctkp%3ABk9SR7SQ6IGDYw

 

Yeah - I did the same thing!

[malc-c]

Just a heads up... when posting links  there is no need to include the random characters after the question mark (highlighted in red)..   https://www.ebay.com/itm/155403343100?  

Or you could use the link option (looks like two square circles next to the quotation mark icon) from the formatting options when posting... you can then add text into the post rather then having the hyper-ling displayed

Hope that helps

[AstroEtcetera]

Hi Guys, thanks for all of this great information. @jif001 I've ordered/received all of the parts to do this conversion on my EQM-35 Pro mount but I do have a question about the wiring bit. For the DEC wiring what comes out of my DIN connector at the DEC motor housing is 5 wires and not 4. This then plugs into a 5 pin to 4 pin board mounted on top of the stepper motor then 4 wires out to the motor. Is this what you guys had (I don't see that part in the electrical diagram)?.  If so did you reuse the converter board from the original stepper motor and just put it inside the new housing somehow? Or did you use some other method to go from 5 pin to 4 pin? Here are photos of my mounts DEC stepper motor for reference.

 

 

 

Thanks for the insight and STL's in this post.

Mark

 

Edited December 27, 2023 by AstroEtcetera
edit photo info

[jif001]

This was an issue I had forgotten about. The black wire may be a ground connection, connecting through the board to the motor chassis via those screw holes (see the attached sketch I made at the time), but it doesn’t seem to be essential to the mount operation. I omitted that connection, and the board, in the final configuration and made the connections as shown in the diagram earlier in this thread. The mount has worked fine without it. 
 

The board has no components and is merely a way of connecting the two halves of the circuit. If you want to be sure it’s ok, you could use the black wire as a flying lead and connect it to a convenient piece of metal on the mount. 

[AstroEtcetera]

Great, thanks for the insight. I had assumed that maybe it was a ground but wanted to confirm what you guys had done. I see now, looking closer at JeromeW's photos that he has a black wire coming out of the housing and is attached to one of the screws that hold the motor to the housing. Good to know that you were able to omit that connection without any issue's though. 

 

Cheers!

Mark

[JeromeW]

The black 5th wire is the ground, the the picture below.

[JeromeW]

I'm working on a replacement for my DEC Axis. Yes, it's plastic, but it will have ball bearings. I'm planning on using a double reduction belt drive. The timing pulley on the NEMA 17 .9° stepper motor is 12 tooth. I hate to ask such a stupid question, but does anyone have any idea how many teeth the larger timing pulleys should have?

[jif001]

In this message on the first page of this thread, I explain how I arrived at the original gear ratios. For dec it was 1:11 using a 1.8 degree motor. You need a ratio of 1:5.5 with a 0.9 degree motor and you can simply adapt those numbers until you get the desired result. So:

original figures:

Gear teeth: 12 : 66 : 35 : 70

Simple arithmetic using these numbers (noting that the 66 and 35 are co-axial gears so are 1:1):

70/35 = 2

66/12 = 5.5

5.5 x 2 = 11, hence we achieve the desired ratio of 1:11

However, you need 1:5.5 because you’re using a 0.9 degree motor. So, you can adapt those numbers as you see fit to achieve that. Here’s one possibility:

12 : 33 : 20 : 40

40/20 = 2

33/12 = 2.75

2.75 x 2 = 5.5. 
 

so, using this example you could have 12 teeth on the motor pulley, a second pulley with 33 and 20 teeth, and 40 teeth on the worm pulley. 

Edited December 30, 2023 by jif001

[JeromeW]

Hey, I just finished the belt conversion for my RA!!

Many thanks to JIF001!!!

If I understand correctly, the 40 tooth pulley would attache to the shaft connecting the Vixen Saddle holding the telescope. 

Thank you very much for helping me with the timing pulleys.

[JeromeW]

I now have both Axis converted to belt drive.

Edited December 31, 2023 by JeromeW
confused DEC for RA

[jif001]

Great! Post some info here on how it performs when imaging, in particular how it compares with the original configuration: did you see a worthwhile improvement? 

[AstroEtcetera]

@JeromeW That’s great. I just finished mine as well but haven’t had a chance to try it out yet due to crappy weather where I live in Canada. Would you mind posting your RA motor mount STL. I’d like to print it and see if I like that mounting position any better than on the weight bar.  
 

thanks to all. I really hope this helps with my backlash/guiding issues. 
 

Mark

[JeromeW]

In summary, here in California, we had clear skies tonight!! I was able to test my guiding. My RA axis improved stability. My DEC axis went from not guiding at all, to guiding a little. I feel my real problem is that my new Askar V telescope is too heavy. My mount guided ok with my old telescope which was about 5 pounds lighter.

I am building a new DEC axis with my 3D Printer. Here is what I have so far, it will have ball bearings. The GT2 timing pulley shown is 162 tooth. I plan on driving it with a NEMA 17 stepper motor with a 100:1 planetary gear reducer with a 45 tooth timing gear to drive it. The timing gears will give me a 3.6:1 ratio. I will be using my original counter weight. Also is included is one of tonight's image.

JIF001, does this sound correct to you?

[jif001]

Interesting stuff!

I’m assuming that you have eliminated the original dec worm and gear arrangement and replaced it with the orange pulley in your photograph, to be belt-driven by a NEMA 17 motor (how/where will you mount it?). In principle that seems a great idea because it also eliminates the last major source of dec backlash, between the worm and gear.

Theoretically, dec guiding should not be needed when imaging because you are tracking in RA only, from east to west. However, reality means that there will be some alignment error or other factor creating a north/south drift that needs to be managed by dec guiding. The corrections needed are generally quite small, which is why dec backlash can be a real headache - it is often larger than the guide corrections, and so the mount appears unresponsive until the backlash has cleared, by which time you may see drift in your image. I really hope your idea works as it should because it seems as if dec backlash should be minimal or non-existent, and if it is then I’ll be making that mod myself! Even though my dec guiding is pretty good (better than RA) any improvement is a worthwhile improvement  

I’m not sure how the numbers stack up because I can’t picture the exact configuration - maybe post a sketch or a picture of the assembly - but two things are important in deciding the ratios. Firstly you want the dec axis to be responsive enough to allow your guiding software to control it, but not so sensitive that it overshoots with every guide correction. If you are using PHD2 then there are some parameters you can set that may help optimise that. The second important factor is the maximum slew rate - you want it fast enough to be able to locate your target in a reasonable time. Before I made the belt mod, as a benchmark I measured the time taken by each axis to complete a 360-degree rotation when set at the maximum slew rate (Rate 9 on the hand controller). For each it was 105 seconds. 

For both axes I matched the rates with the original geared configuration.

Jim

 

Edited January 2 by jif001