#diy #skywatcher #250p Dobsonian Skywatcher 250p goto project #diy #skywatcher #250p


Arnaud V
 

Hello everybody,
i m new here with the project of convert my dobsonian skywatcher 250p to goto with onstep.I read almost all of the wiki but i m a bit lost with all of the board and stepper motor. my first idea was mks board l 2.1 +TMC 2209 + wemod d1 mini pro but no idea for motor (i see everywhere nema 17) because i m total noob with motor and gear ratio. my second idea was esp32 + cnc to have wifi & bluetooth direclty on the main board.can anyone help me for a choie :D.and an another question is must i have a shc to move the scope or can i handly move the scope when all is not powered?
thank you in advance

nb : capable skill -->soldering,arduino,3d print


Khalid Baheyeldin
 

On Thu, Jul 8, 2021 at 12:13 PM, Arnaud V wrote:
i m new here with the project of convert my dobsonian skywatcher 250p to goto with onstep.I read almost all of the wiki but i m a bit lost with all of the board and stepper motor. my first idea was mks board l 2.1 +TMC 2209 + wemod d1 mini pro
The MKS Gen-L V2.1 is a cheap board with very little soldering required.
But its microcontroller is very slow, and you may be limited in slewing speeds (but other factors are at play, such as gear reduction, ...etc).
One way to speed up the Gen-L V2.1 is to use SPI drivers: i.e. TMC2130 or TMC5160
That allows a feature called MICROSTEPS_GOTO which can speed up slewing speed.

but no idea for motor (i see everywhere nema 17) because i m total noob with motor and gear ratio.
Best source of info on this is the Dobsonian section of the Showcase page on the Wiki.
There, you will find links to builds, and get idea on what gear reduction ratios are used, and how motion is transferred from the motors to the mount axes.

my second idea was esp32 + cnc to have wifi & bluetooth direclty on the main board.
The ESP32/CNC combination does NOT provide WiFi.
It does provide only Bluetooth.
Although the ESP32 does have WiFi hardware, there is no support in OnStep, because of technical reasons too long to explain here.

If WiFi is needed, then this board is not a good fit.

another question is must i have a shc to move the scope
An SHC is convenient because when you are centering an object in the eyepiece, you don't need to take your eye off the eyepiece to see which button you are pressing. You can use an Android device to do that, but you don't get tactile feedback, so you have to look on the phone's screen to know which 'button' you are pressing. But some people (like me prefer not to have wires around and stick with the phone and Android app. The SHC also has full catalogs of popular catalogs
or can i handly move the scope when all is not powered?
When you have a scope with OnStep controlling it, then all movement should be from OnStep, not manually. Otherwise OnStep will lose track of where it is pointing. But a small number of users add encoders that tell OnStep (via the Wemos WiFi module) where the scope is pointing.


Drew 🔭📷🚴‍♂️
 

On Thu, Jul 8, 2021 at 12:32 PM, Khalid Baheyeldin wrote:
The ESP32/CNC combination does NOT provide WiFi.
It does provide only Bluetooth.
Although the ESP32 does have WiFi hardware, there is no support in OnStep, because of technical reasons too long to explain here.

If WiFi is needed, then this board is not a good fit.
Not exactly true. Like all of the ESP32 based versions a Wemos mini (with the SWS firmware) can be attached to the SerialB (Serial2) port pins (designated TX2, IO5 and RX2, IO13). Then you would have both Bluetooth and WiFi.


Mike Ahner
 

On Thu, Jul 8, 2021 at 11:32 AM, Khalid Baheyeldin wrote:
or can i handly move the scope when all is not powered?
When you have a scope with OnStep controlling it, then all movement should be from OnStep, not manually. Otherwise OnStep will lose track of where it is pointing. But a small number of users add encoders that tell OnStep (via the Wemos WiFi module) where the scope is pointing.
Arnaud, I think you mean when you don't power the telescope, can it be moved by hand. In that case, the answer is yes, maybe. Because you will have motors and gears connected to the telescope with belts, you will find it harder to move the telescope by hand unless you disconnect the motors. You can do that with a clutch system or just remove the belts. Then the telescope will move with your hands, just as it does now.

-Mike


Arnaud V
 

thank you for all the informations i see all a bit better now


George Cushing
 

Roman Hujer's ESP32 shield has provision for the ESP-01 WiFi module and simplifies the entire process of building a controller with most features supported by OnStep. 



Arnaud V
 

ok now i see what i want to build for my onstep

with esp32 what is the best for onstep :
wemos r32 esp32 + cnc shield v3 +TMC 2130 + wemos d1 mini pro for wifi
 or
esp32 nodemcu + cnc shield v4 + TMC 2130 + wemos d1 mini pro for wifi
?
for stepper motor i'll take 2 nema 17 planetary 100:1

is that good enough for begin with onstep with basic feature only for goto?


Khalid Baheyeldin
 

Do not use the Wemos D1 Mini Pro, because many users have reported issues
with it. Use the regular Wemos D1 Mini. It works as long as your case is not
made of metal.

In your case, because the R32 + CNC v3 are so cheap, I recommend that you
start with it, now that it has a dedicated serial port for a WiFi module.

As for the gearbox, it depends on what other motion transfer you have and
what are the ratios. As a guideline, the overall GR1 X GR2 should be between
360 and ~ 1600 if you are using 400 step motors. Usually geared steppers
are only 200 step, so that makes the range of GR1 x GR2 between 720 and
3200.


Arnaud V
 

Thanks you.i'll use 2 pulleys for alt and AZ with 320 teeth and a stepper pulleys with 40 teeth.i'm total noob with motor what is gr1 & gr2??


Khalid Baheyeldin
 

GR1 is "Gear Reduction first stage" (connected to motor shaft) and GR2 is the second stage.

These are the values in the spreadsheet that you have to download and fill to make sure nothing is out of reasonable limits, and that you get adequate precision as well as reasonable slewing speed.

http://www.stellarjourney.com/assets/downloads/OnStep-Calculations.xls


Arnaud V
 

So if i understand gr1 is motor pulley so 40 for Me and gr2 is alt/AZ pulley so 320.is that right?


Khalid Baheyeldin
 

No. The spreadsheet uses ratios, not teeth numbers.

For example, Let us say someone has a 200 step motor with a gearbox that is 10:1.
That makes GR1 = 10
Then there are two pulleys, 20 teeth with a belt to a 100 teeth (hypothetical examples)
In that case, it is 100/20 = 5
So GR2 = 5.

You get the idea.


Arnaud V
 

Ok understand thank you very much for explanation


Arnaud V
 

Hello everydone,
after more than 1 month my dobsonian skywatcher is up and running onstep basicly for now.i would say thanks for all informations and all of this awesome project.
My project was :
*Make a new base with wood to stay my original clean.
*Print all part of this--|>https://www.thingiverse.com/thing:3942813
*Use a lazy susan between the 2 circles of the base for more fluidity

For onstep i use :
-wemos r32
-cnc v3
-wemos d1 mini
-2x TMC 2130
-2x nema 17 planetary 100:1
-2 gt2 9mm belts
-shc board with all component

and now all is running fine
ps : i use https://www.thingiverse.com/thing:4853768 for my case and the 2 motors are now connected with 2 jx12 connector in the back


Chad Gray
 

Great Project!


On Thu, Aug 19, 2021 at 2:57 PM Arnaud V <arno.aka.vdb@...> wrote:
Hello everydone,
after more than 1 month my dobsonian skywatcher is up and running onstep basicly for now.i would say thanks for all informations and all of this awesome project.
My project was :
*Make a new base with wood to stay my original clean.
*Print all part of this--|>https://www.thingiverse.com/thing:3942813
*Use a lazy susan between the 2 circles of the base for more fluidity

For onstep i use :
-wemos r32
-cnc v3
-wemos d1 mini
-2x TMC 2130
-2x nema 17 planetary 100:1
-2 gt2 9mm belts
-shc board with all component

and now all is running fine
ps : i use https://www.thingiverse.com/thing:4853768 for my case and the 2 motors are now connected with 2 jx12 connector in the back

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