CGEM Onstep conversion #celestron


KPK
 

Dear all,

I've read and studied the Onstep wiki, and found this Onstep groups. So, now I'm trying to find my way in it.
I have a Celestron CGEM mount, which I want to convert to Onstep. I want to use it for astrophotography.

I've already found the projects of Chris Vaughan and Francois Jr Bouchard, and read their project thoroughly. 

I've already hyper tuned my CGEM mount, but... I think it still can be improved. So, I started with buying the hardware, ie the stepper motors as suggested by Chris Vaughn and decided to go for the 4:1 reduction with the 15/60T combination. 
Thanks to their work and efforts, the data on reduction etc. are already known. 

Now I have to decide which drivers and other electronics I'm going to use. And to be honest, the choice and possibilities are a bit overwhelming.
I want to use the mount for astrophotography, and I. plan to use an Asiair pro or a mini PC with Nina with this mount (I use both on my other EQ6R non-onstep mount).

I can solder, but I wouldn't miss it if not needed. I like puzzling, but, to be honest, I think starting simple is the best option.
So, I don't need a wifi connection, prefer a wired connection to my computer/asiair to start with. And I love goto functionality. 

What would be a wise choice...?

Thanks in advance for your time to help me starting this project!

Regards, KP


Khalid Baheyeldin
 

On Sat, Jun 26, 2021 at 03:00 PM, KPK wrote:
Now I have to decide which drivers and other electronics I'm going to use. And to be honest, the choice and possibilities are a bit overwhelming.
They are.
Tell us about the motors. What are their specs?
Which board do you plan to use? Or have you not decided on that yet?


Derek Regan
 

I'm going to follow this as I'm more or less in the same boat as KP but the board part worries me slightly, I'm not computer savvy, and I've no idea what most of the things you all talk about actually is.. long time lurker here.. 


KPK
 

Dear Khalid,
i have stepperonline 17HM19-2004S1, 0,9 degrees, 46nm 2A steppermotors

from Chris I understood that the minipcb v1 would fit into the cgem housing, but to me, anything which works is ok…

I have a 3D printer, so making housings won’t be a problem


Khalid Baheyeldin
 

For those motors, the current settings will be around 1.4A

2.0A X 1.41 X 0.5 = 1.4A

That current is not suitable for two of the most popular StepStick drivers (LV8729 and TMC2130).
This means your remaining options are limited to the TMC5160, and you need a board that supports SPI.

The MiniPCB does support SPI, which requires soldering.
Other options are the Blue Pill with the RobotDyn F303CC (requires soldering), and the FYSETC S6 (least soldering option).


Chris Vaughan
 

KPK

Those motors are full on. I'm only using 17HM19-2004S with TMC2209 drivers running at ~50-60% of max current.
Good enough for faux-narrowband running 10min subs. See my last image on astrobin.

Chris


KPK
 

That’s an awesome picture!!!


Brian Davis
 

I loaded up a MKS GEN-L V2.1 first, and it worked well, but the board is very slow, and very limited on memory.  I upgraded to the FYSETC S6 (which takes a couple of weeks to arrive), and am happy with it so far.  It has more than enough power to handle anything Onstep is likely to throw at it in the near future.  I used/followed the same motors Chris did, and they work very well with TMC2130's.. The Minipcb controller makes a very clean install, but I built mine into a 50cal ammo can, to give me lots of room for addons like cooling fans, RPi's, etc etc.


On Sat, Jun 26, 2021 at 11:56 PM KPK <flyingdockp@...> wrote:
That’s an awesome picture!!!


 

On Sun, Jun 27, 2021 at 08:06 AM, Brian Davis wrote:
I loaded up a MKS GEN-L V2.1 first, and it worked well, but the board is very slow, and very limited on memory.  
Also used the MKS V 2.0 on my first Onstep build.  No soldering except for the pins on the Wemos module.  The Mks is on the slow slide, but I am quite happy with it.  Even with the non-SPI TMC2209 drivers, I get a decent slew rate at 32 microsteps with a 24v power supply.

I also recently built the basic hand controller which works very nicely with the MKS.  No need to solder pullup resistors, though the controller requires a bit of soldering to assemble.


KPK
 

That makes the choice a lot easier!!!
I will take a good look at the fysetc s6


Khalid Baheyeldin
 

The FYSETC S6 is a good option. I use it myself.

But here are some points to consider:

You will not be using everything that it offers, such as an additional focuser,
a rotator, dew heaters (since you already have that), weather sensors, and so on.

Note that wiring tends to be complicated if you want to have the full set of features
(many wires coming out of the board and going to the components).

It also has a large foot print and may not fit inside a CGEM.


KPK
 

I can always put it outside in a dedicated box…

that’s the easiest part of this project I guess!

most important part is that it’s going to work

in an external box it’s even easier to upgrade it with new functions if needed 

now to find the components!

so if I understood it correctly, with this FYSETC S6 I don’t need a mini pcb board, so I can route the wires from the steppermotors directly to the FYSETC S6 board(at least, that’s how it looked in your YouTube vid)


KPK
 

Damn! What a possibilities with this board!!!

I guess it’s sensible to add a gps sensor

wifi… if I want to connect this to the Asiair or a mini pc with Nina, I guess it’s only handy but not essential?

do you use the st4? Thusfar, I haven’t needed it…
phd2 and the Asiair work fine with usb to control a mount

I think the cgem has a limit switch built in. Is that suitable for use?

the PEC sensor, is that a photoelectric sensor or a sensor for the periodic error correction? I guess thi last one.

Anyway I think I’ll limit myself to gps for this moment 


Khalid Baheyeldin
 

On Sun, Jun 27, 2021 at 01:24 PM, KPK wrote:
most important part is that it’s going to work
The S6 should work. Several people are using it, including me.

so if I understood it correctly, with this FYSETC S6 I don’t need a mini pcb board,
No, you don't need the Mini PCB board if you use any other OnStep board (S6 included).

so I can route the wires from the steppermotors directly to the FYSETC S6 board(at least, that’s how it looked in your YouTube vid)
Yes.
I have 3D printer motor cables from the board to an RJ45 breakout board with an RJ45 female socket.
Then I use regular Ethernet cables from the box to the motors.



Khalid Baheyeldin
 

On Sun, Jun 27, 2021 at 01:44 PM, KPK wrote:
Damn! What a possibilities with this board!!!
Yeah, but be careful before you go overboard. Those who went for the full kitchen sink option did not enjoy all the wiring that ends up in a cramped space. Makes troubleshooting harder too.

I guess it’s sensible to add a gps sensor
It is actually required, and must have a PPS pin, since it calibrates the relatively inaccurate clock of the S6.
Unless you are autoguiding, which corrects for that.

wifi… if I want to connect this to the Asiair or a mini pc with Nina, I guess it’s only handy but not essential?
If you have an Android phone or tablet, then I highly recommend a WeMos D1 Mini, because you now have the OnStep Android app, which is very very useful for many tasks.

do you use the st4? Thusfar, I haven’t needed it…
No.

phd2 and the Asiair work fine with usb to control a mount
Yes.

I think the cgem has a limit switch built in. Is that suitable for use?
I don't have one, but it should work.

the PEC sensor, is that a photoelectric sensor or a sensor for the periodic error correction? I guess thi last one.
It is any sensor that closes on the worm gear's period (i.e. once per rotation).
I used a Hall Effect sensor and a magnet initially, but ever since getting autoguiding going, I have not bothered to connect it at all. That would be true for any mount with a relatively low periodic error (mine is +/- 2" or 4", can't remember).

Don't bother initially. See how things go, and evaluate after having tested it for a month or so.


KPK
 

I will follow your advice! Sounds logical 

thanks a lot for all your tips!


KPK
 

So… it will be a 

Fysetc s6 

AGM336H GPS module
TMC 2109
WeMos D1 Mini 

IRF520 MOSFET

stepperonline 17HM19-2004S1
60t-15t 


Khalid Baheyeldin
 

No objections to the AGM336H or the WeMos.

The TMC2209 has some limitations: a limited set of microstepping allowed, and no SPI, so you cannot speed gotos if you need to. The TMC5160 is the recommended driver in your case, if you have the 2A motors. It has none of those limitations, and also runs cool enough, so no fan needed (hopefully).

The IRF520 is not needed. The AGM336H does not have the same limitation as the NEO 7M (prevents DFU mode). The IRF520 workaround would be useful in a remote observatory setting so you can upload the firmware remotely.
If you don't have that use case, then just attach a switch and two wires to Boot0 and you are done, like I have in my video.


KPK
 

Thanks!
I thought of the tmc 2209 due to the experiences from Chris and others
but I will follow your advice for the 5160

i must have misread the wiki concerning the mosfet😬
I will use a switch 


Khalid Baheyeldin
 

On Sun, Jun 27, 2021 at 03:40 PM, KPK wrote:
I thought of the tmc 2209 due to the experiences from Chris and others
but I will follow your advice for the 5160
The TMC2209 works fine (for tracking), and it is cheaper.
But there are reports that it heats up, and it is not SPI.
So it cannot switch microstepping dynamically (when slewing).
So if you need faster slewing, you cannot get it.

Before you buy either, fill in the spreadsheet and see what you get.