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Cheap EQ Goto SimpleDream Onstep


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Posted (edited)

Hi, I am picking up a cheap eq3-2 tomorrow and am considering cheap goto upgrade options.

Does anyone have any experience of using SimpleDreamEQ3?

Primary usage would be for EEVA and some light imaging. 

Thanks

Edited by Gmx76
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Thanks for that.  Must say I emailed astro-tech to see if it supports plate solving late last night and had an email back within a few hours saying yes.  So that's promising.  Just got my eq3 but maybe next month I can buy this.  Trying to do AP as cheap as possible!

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Hi Greg,

I'm sure you're aware that the maximum slewing speed of the Simple Dream is 60x siderial which is much too slow to be practical for long slews. ( Typical Goto systems slew at 600x to 800x or more. At 60x a meridian flip would take about 15 minutes ! )

So you would have to loosen the clutches and push the scope close to your target before engaging the Simple Dream "micro Goto"  and a planetarium app to zero in.

If you are handy & want a full-speed Goto you could build an OnStep Goto system using Nema 17 motors for around £100.

https://onstep.groups.io/g/main/wiki/3860

Good luck.

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Thanks @lenscap. Not too confident with the DIY thing but appreciate it's a good cheap way to go. Do you know if anyone sells pre-built versions of these? 

As for micro goto I realise its more push then goto.  I do have a az-gti in eq mode.  Would you happen to know what the x60 compares to on the 1-9 scale in synscan? 

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@Gmx76 I did managed to find some pre built version of Onstep for EQ3-2 mounts in a China second hand market, should cost around 100 USD. Maybe if you can find some agent in your country that could help you get those stuffs? Planning to get one for myself too (be getting an EQ3-2 mount soon!) :)

Edited by Tan Zhi Qi
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I should think that a GoTo that slews at 60x siderial would be fairly useless.   And if you de-clutch it you will have lost the GoTo alignment.

If you don't want to invest £300+ in the Skywatcher Synscan upgrade, a more sensible option on a low budget might be not to have GoTo at all, but to motorise the RA and Dec axes.  You can do planetary imaging perfectly well with a RA motor drive, and you don't need GoTo for guided imaging, though admittedly the performance of guided GoTo mounts is said to be better.  And you should be able to do EVAA without GoTo provided you can actually find the objects, for which I recommend a good RACI finder + a red-dot finder.

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On 09/07/2021 at 18:56, lenscap said:

Hi Greg,

I'm sure you're aware that the maximum slewing speed of the Simple Dream is 60x siderial which is much too slow to be practical for long slews. ( Typical Goto systems slew at 600x to 800x or more. At 60x a meridian flip would take about 15 minutes ! )

So you would have to loosen the clutches and push the scope close to your target before engaging the Simple Dream "micro Goto"  and a planetarium app to zero in.

If you are handy & want a full-speed Goto you could build an OnStep Goto system using Nema 17 motors for around £100.

https://onstep.groups.io/g/main/wiki/3860

Good luck.

Hi @lenscap I saw in another post that you have built your own onstep for eq3. I'm not that handy but now thinking about it, one of my friends teaches electronics, so could get some help. Would you mind sharing how you did your onstep please? 

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On 10/07/2021 at 22:59, Gmx76 said:

Hi @lenscap I saw in another post that you have built your own onstep for eq3. I'm not that handy but now thinking about it, one of my friends teaches electronics, so could get some help. Would you mind sharing how you did your onstep please? 

All the info you need to build an Onstep Goto is in the Wiki, which can be confusing because there are at least 10 microcontroller boards to choose from, ranging from  custom designed pcb's to which you solder each component, to off-the-shelf modules that require little or no soldering.

I built my first Onstep for my EQ3-2 a few years ago using the Arduino Mega 2560/Ramps 1.5 board. This works fine but better boards are now available. I've recently finished an Onstep for my EQ5 using the WeMos D1 R32/CNC V3 board. This is the controller before I put it in a case.

WemosD1R32CNCv3power.thumb.jpg.8e091937a916ef2ebc9a9ae3dd890df2.jpg

The lower board (that the power jack plugs into) is the WeMos D1 R32 microcontroller board which runs the Onstep software.

The CNC V3 shield (with all the yellow headers) just plugs into it. It has sockets for the stepper drivers, and pins to which you can connect various optional bells & whistles.

The two stepper drivers, (I used LV8729's, with the blue heatsinks) plug into the CNC V3 without the need for any wiring.

Just configure & upload the Onstep software to the WeMos, connect the  power &  the motors & you have a basic functional Onstep controller that can be directed by the Onstep app and/or Skysafari via Bluetooth from your phone, or by Stellarium/CdC/Kstars etc by USB from your laptop.

https://www.ebay.co.uk/itm/152975590787

https://wiki.keyestudio.com/Ks0160_keyestudio_CNC_Shield_V3

https://wiki.fysetc.com/LV8729_V1.0/

I'll post some notes on the mechanical side of the build tomorrow.

 

 

 

 

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Drive Trains for an EQ3-2 Onstep conversion.

I suggest NEMA 17, 400 step , bipolar steppers using 32 microsteps with 3:1 belt drives. Each motor needs at least 50 ounce.inches of torque.The RA worm ratio on the EQ3-2 is 130:1 so the tracking resolution will be 0.26 arc sec which is similar to a Synscan system.

(360 x 3600) / (130 x 3 x 400 x 32)  = 0.26

The Dec worm ratio is 65:1 so if you are guiding you could use 64 microsteps on the Dec for symmetry if you wish.

Motors;  https://www.omc-stepperonline.com/nema-17-stepper-motor/nema-17-bipolar-0-9deg-44ncm-62-3oz-in-1-68a-2-8v-42x42x47mm-4-wires.html

Pulleys;  16 tooth & 48 tooth GT2 pulleys will give you a 3:1 ratio. 6mm wide belts will be adequate. Select bores to suit the motors (5mm) and the worm shafts (6mm).

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2499334.m570.l1311&_nkw=gt2+timing+pulley&_sacat=0

You could use these brackets. One of them will mount the Dec motor.

You could use 2 of them in a "U" or "Z" arrangement to mount the RA motor. There are other options. I used 1 angle bracket & a diy hardwood block for the RA on my EQ3-2. (see pic) . Or search for EQ3 on thingiverse for 3D printed brackets. Angle Brackets

Dec

EQ32DecFront.jpg.bdfbaafa8a2a60a0d6e385b9e30f7683.jpg

Dec

EQ32DecSide.jpg.000172d799d16c4d6d012fc00941bb9d.jpg

RA

EQ32RAFront.jpg.f997482c56ce297c991a06515a258c8d.jpg

RA

EQ32RASide.jpg.d94cb45e1ba2829b7a54c15b74d29848.jpg

Those are the main items. If you go ahead with the build post as many questions as you like.

Hope this is enough to get you started.

 

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I emailed AG yesterday asking about the slew rate on the EQStarPro EQ3 for my CG-4, which admittedly is twice the cost of the Simple Dream, but it works with Stellarium and several other PC-based software packages.  I was unsure if the go-to speed was reasonably fast or not.  The product info does not list that info, whereas the simple dream does (60x).  If I'm correct in my figures, even at 60x you're only covering .4 degrees / sec.  Well...last night he emailed me back:  

--------------------------------------------

Hello,

GoTo speed (rotation speed of the mount when searching for objects) for the EQStarEQ3 is 600x. GoTo speed for SimpleDreamEQ3 is 60x. Therefore EQStarEQ3 is better than SimpleDreamEQ3.

Best Regards,
Alexander.
www.astro-gadget.com 

---------------------------------------------

$279 seems pretty reasonable, doesn't it?  For smartphone or PC control...guiding compatibility...?

Erks me too...because I just bought the Celestron motors a month ago. 

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Looks very affordable.  And I hear good things.  I'm going to try the onstep route though as it seems not too hard and much cheaper.

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hi @Lens capi'm going to start buying up stuff based on your recommendations above, just have a couple of questions.

Is any soldering needed?

Also, what do you use to power your onstep?

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3 hours ago, Gmx76 said:

Also, what do you use to power your onstep?

The controller uses less than 500 mA when tracking and a maximum of about 1A  ( at a nominal 12V DC ) when slewing  both axes together with an 8" Newt on board.

Any reliable source of 12V DC that can supply say, 3A or more will do.  I generally use a 12V, 7Ah,  scooter battery which runs for 5 or 6 hours between charges. If I did all-nighters I would use a 17Ah battery.

3 hours ago, Gmx76 said:

Is any soldering needed?

Referring to the photo of the WeMos R32/CNC V3 in my previous post,  the only soldered joints are the 2 that connect the power cables to the crocodile clips. I suppose you could use screw terminals. Some of the optional features that you may decide to add, require some soldering, but there's nothing too challenging.

I've just noticed that the WeMos R32/CNC V3 section of the Wiki has been updated. It's much improved - well worth a look

.https://onstep.groups.io/g/main/wiki/19670

Good luck with your Onstep journey.

 

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On the EQ3-2 the RA driven pulley will foul the RA clutch lever unless you do something to avoid it. I cut away part of the lever which you can just see in the bottom left this pic.

EQ32RASide.jpg.d94cb45e1ba2829b7a54c15b74d29848.jpg

This works but if I was repeating the build I would use a shaft extension something like this to move the driven pulley outboard to clear the lever.

https://www.ebay.co.uk/itm/143565881640?epid=1974551016&hash=item216d318128:g:pU8AAOSwMNxXaROM

Maybe you could find a 6mm rigid coupling plus a short length of 6mm D shaft a bit cheaper.

You can adjust your RA motor mounting bracket(s) to maintain pulley alignment.

Once you have mounted the motors & pulleys you can measure the shaft spacings and calculate the  belt lengths.

Onward & upward!

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Might be a dumb question but why use pulleys and belts and not connect the motors direct?  I have a RA motor which just connects directly. 

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17 hours ago, Gmx76 said:

I have a RA motor which just connects directly.

Is that a tracking motor? I think you'll find it has an internal gearbox which is needed to achieve the tracking resolution necessary for long exposure photography.

Driving the RA direct with an ungeared stepper would give a calculated resolution of about 0.8", so maybe 1.5" in practice. I did this on my EQ3-2 for a while. The resolution was fine for visual. Would  it good enough for your EEVA plans? I don't know. You would also lose the 3:1 torque magnification. My direct driven EQ3-2 could handle a 6" Newt but struggled with an 8" (not surprising since it was about 100% overloaded 😀) so I went to belt driven.

Geared steppers have been used for Onstep, mostly for Dobs where they may be the only way of achieving the required overall gear ratio. Excessive backlash in the internal gearbox has been a problem. The vast majority of EQ builds use belt drives which have little backlash & tend to be quieter than gear sets.

HTH

 

 

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  • Gmx76 changed the title to Cheap EQ Goto SimpleDream Onstep

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