EQM35: Low-Cost Belt Mod

[JeromeW]

Jim,

Here are two pictures to give you a vague idea of what I have in mind. The timing pulleys and stepper motor/gearbox are not accurately depicted or to scale.

I'm not actually sure how good of an idea it is to have a timing belt system driving the DEC shaft, I'm not sure it will be strong enough. One of the advantages of the worm gear is that it locks when not powered. Also, this mod will not be cheap, I'm wondering if I should just cut my losses and buy a better mount. I should have bought a Maxvision/Bresser/Explore Scientific/heq5 EXOS-2, at least it has bearings. I'm very disappointed with my EQM-35 mount.

Thank you for all your help.

Jerome

 

https://www.aliexpress.us/item/3256803789062102.html?src=google&src=google&albch=shopping&acnt=708-803-3821&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=19235666539&albag=&trgt=&crea=en3256803789062102&netw=x&device=c&albpg=&albpd=en3256803789062102&gad_source=1&gclid=EAIaIQobChMIh6mmhZbAgwMVJRKtBh1eVwzREAQYBCABEgJL-_D_BwE&gclsrc=aw.ds&aff_fcid=c01b5bdb058b445c9e3881cd0adaafd1-1704251428811-02517-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=c01b5bdb058b445c9e3881cd0adaafd1-1704251428811-02517-UneMJZVf&terminal_id=7cd7b1fba57c4a9ab8bf294d9f0d0a13&afSmartRedirect=y&gatewayAdapt=glo2usa

https://astraeusoptics.com/products/fl-exos-2-goto-eq-mount

 

[jif001]

The holding torque on the motor is pretty good and if you balance your scope it should not challenge that, so it may work in that respect, but the torque necessary to rotate the shaft might be the limiting factor. Turning a worm is a lot easier. 

[JeromeW]

 The torque coming off a 100:1 planetary gearmotor ought to be pretty good. I was worried that the timing belt might snap during setup if I didn't have the rig balanced. Also, my design doesn't have a clutch. Harmonic mounts don't have clutches eighter. I think I could make it work, but I would have to be more careful. I was also considering a Cycloidal drive for my mount. I believe I will proceed with my design, right now my mount is not giving me what I want. They say the EQM-35 is a cheap mount, but $1000 is not cheap when it comes out of your pocket.

[AstroEtcetera]

On 30/12/2023 at 21:55, JeromeW said:

I now have both Axis converted to belt drive.

Hi @JeromeW Would you mind uploading your RA motor mount STL. I'd like to print it and try it out. 

 

Thanks again. 

 

Mark

[JeromeW]

Jim,

Here is what I have, I'm not yet finished. I plan on adding the tabs to secure the original cover. The included tab is a 'glue-on'. I will post the finished bracket soon.

Jerome

RA Motor Bkt cover tab.stl RA Motor Bkt cover tab.AD_PRT RA Motor Bracket.stl RA Motor Bracket.AD_PRT

[jif001]

Hey it wasn’t my request but thanks anyway - like I said, any improvement is welcome! 😊👍🏻

Edited January 5 by jif001

[JeromeW]

Opps, I meant Mark,

This is more complete.

Jerome

RA Motor Bracket v2.stl RA Motor Bracket v2.AD_PRT

[AstroEtcetera]

20 hours ago, JeromeW said:

Opps, I meant Mark,

This is more complete.

Jerome

RA Motor Bracket v2.stl 11.22 MB · 1 download RA Motor Bracket v2.AD_PRT 647 kB · 1 download

Thanks Jerome, 

I have jif001's brackets on my mount already but wanted to try your version of the RA bracket to see if I like the motor mounted better off of the weight bar. 

I didn't print your version of the DEC bracket, but I have noticed that on the one I did print that with the 200mm belt tightened that the DEC bracket will hit the RA clutch if I try to lay the scope horizontal to the West which I often do when checking the balance. @jif001 I'm not sure if you noticed that on your mount with your DEC bracket or not. I was thinking about trying to make the bracket slightly narrower to help with that. What applications are you guys using to do your designs? I don't have my own printer yet, (I use a local service to get the STL's printed), so I haven't had the need to do any designs but I would like to give it a try.

 

Thanks again for everyone's input on these improvements.  I would like to get this mount working as best as it can. At least until I can convince my wife to let me upgrade   

 

Mark

[jif001]

Mark

As you can see in the picture, I engineered some clearance so that the axis could turn fully without clashing, so maybe you need to make some small adjustments to avoid contact (or, as you say, modify the bracket).

I used Fusion 360 for the design. There's a bit of a learning curve to it, but there are hundreds of tutorial videos on YouTube. Fusion 360 is very powerful and is used by professionals. For private use it is fully-functional (apart from some bits you will never need anyway), the only real restriction being that you can only have 10 editable projects at one time. I've never found that to be a problem - you can have as many projects as you want as long as only 10 (any 10) are in edit mode. I started out using Tinkercad (also free), which is easy to learn but creating complex designs is  tricky. It might be a good place to start though.

Jim 

[JeromeW]

Mark,

The current version of the DEC bracket that I uploaded does clear the RA Clutch Lever. It took me 3 iterations to get it right.

The DEC timing pulley did, however, touch the DEC Clutch Lever at a certain position. I chose to grind the DEC Clutch Lever rather than rotate the DEC timing pulley, because I didn't want the pulleys any further away from the body as necessary.

The RA Bracket I just uploaded is my 5th iteration. This iteration adds more pad surface area for more stability and rigidity.

I am currently using Alibre Atom3D. I like it a lot because it is easy to use and it is powerful enough. Their hobbyist version sells for about $150. However, I am switching to the Community Version of Solid Edge. It is a free download, and it supports STEPs and SATs. It is also an awesome STL editor, tricky, but it can be done. On the downside, it’s more difficult and incumbering. I started learning Fusion 360, but in the USA from time to time they change their licensing, so currently it’s not free for me.

Jerome

RA Motor Bracket v2.stl RA Motor Bracket v2.AD_PRT

[AstroEtcetera]

Thanks for all of the great information guys!  We haven't had a clear night here in over 6 weeks so I'm very anxious to try these mods out. 

[JeromeW]

This is what I have so far. It looks like the PLA plastic is going to be strong enough. The telescope is now balanceable. 

[jif001]

@JeromeW: I don’t want to divert this thread, but I have a quick question … what do you make of the Askar V? I’m considering buying one, but wondered in particular if it can achieve a flat field across all of its configurations. I know there is a flattener, but do the reducer and the extender flatten the field independently?

Edited January 23 by jif001

[JeromeW]

Since I live in Light Polluted LA, California my imaging is very limited, and I am still in 'learning' mode, so I am definitely not an authority of the Askar V. In regard to astronomy, I am very much a nubee. However, I am very happy with the Askar V. Since my targets are limited I have only been using the REDUCER. However, I will include a recent image. The Askar V is heavier than I expected, too heavy for my EMQ-35 mount, that's why I built a new DEC Axis for it, see below. I am considering the purchase of the ZWO AM3 if my wife will let me. This picture was taken with the DEC not guiding at all. Does it look flattened to you?

[JeromeW]

WOW!! I can't believe it actually works!! I'm using a NEMA 17 .9 motor with a 100:1 Planetary gear reducer. If anyone is interested I can post my 3D Models and BOM.

Many thanks to jif001!!

[JeromeW]

I took my rig outside tonight.

Well, back to the drawing board, I have to rotate the DEC motor, my telescope went the wrong direction. At least it moved.

[jif001]

You may not need to go back to the drawing board - you may be able to just alter the wiring to the motor. See the extract below from this article.

Also, see here (scroll way down the page) - nicely illustrated. 

 

Edited January 24 by jif001

[jif001]

Assuming your M42 image is not cropped, there is a small amount of aberration in the left-hand corners but it’s not bad at all and the field looks reasonably flat. The stars are a bit out of focus, which is affecting the image more. I don’t know what’s going on down the left edge - a light leak?

Edited January 24 by jif001

[jif001]

10 hours ago, JeromeW said:

If anyone is interested I can post my 3D Models and BOM.

Oh yes please!

Edited January 24 by jif001

[JeromeW]

In the above image of the Great Orion Nebula is not cropped. The white band to the left is caused by the DEC not tracking. In other images where the DEC does track, I don't get the white band.

I am posting an image of the M2, where the DEC was guiding. Also using the reducer.

[JeromeW]

I am posting the STLs of my DEC axis. I will notify you if I update any models.Vixen Saddle Adapter.stlVixen Saddle Adapter.stlVixen Saddle Adapter.stlNut Barrle.stl

Bearing Bushing.stl Counterweight Rod Adapter.stl DEC Body ver 2.stl Motor-Gear Spacer.stl Nut Barrle.stl Shaft collar.stl 162 tooth pulley v2.stl

[JeromeW]

jif001, thank you very much for sharing the articles with me. I'll let you know how it turns out.

[jif001]

Thanks for the files. 
 

The image looks good apart from the lack of calibration, which is easily corrected with darks and flats, and some aberration that indicates the camera is too close to the flattener/reducer. If you look closely, right in the corners, the stars look very slightly elongated in the direction of the image centre (see the image below, which exaggerates the effect). To fix it, you could 3d-print some thin spacers to put between the camera and the flattener/reducer. 

Edited January 25 by jif001

[JeromeW]

jif001, I switched the wires, and the DEC motor seems to be rotating the correct direction. But the DEC motor seems to be falling short of its target by about 60°. When I hit 'Home' it then over-shoots by about 60°. I'm wondering if my gear ratio is wrong.

I'm using a 100:1 planetary gearbox, a 45 tooth pulley on the motor, and a 162 tooth pulley on the DEC Axis. Also, the axis seems to be rotating slower than the RA axis. I'm wondering if maybe the planetary gearbox has too much internal friction, because I can't rotate it by hand.

I'm wondering if you have any ideas?

 

[jif001]

I compared your transmission with mine and the original, see attached image, but can see nothing obviously wrong there. Our numbers match (360 motor turns equating to 1 turn of the axis) and differ from the original numbers (720:1) only because we are using 0.9° motors and different gearing (original Skywatcher is a 1.8° motor, resulting in a factor of 2 difference).

The fact that you can’t turn the gearbox by hand doesn’t mean there is anything wrong with it - I can’t turn my focus motor by hand, but it’s fine. I’m just at the wrong end of the gear train to apply enough torque to it.

What exactly happens? What’s the target if it’s falling 60° short, e.g. are you aiming for 90° and it stops at 30°?

 

Edited January 27 by jif001