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


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.

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