What's OnStep Today?

OnStep is an open source automated motion control system designed to operate the mountings under telescopes and other astronomical instruments. Its emphasis is on astronomy and astrophotography. 

Also second not insignificant aspect of OnStep is cost. On commercial automated telescope mounts the electronic control systems add 50 to 70% to the price of an unautomated system. In my experience, too many of these systems have proven to be short lived and unreliable, repair parts are often unavailable or horribly overpriced. Repair when available, is equably expensive, often less than competent and requires shipping heavy equipment thousand of miles or for folks in other markets across oceans. Other mounts, names like, Byers, Takahashi, Astro Physics, Losmandy, etc. can retain their mechanical soundness well beyond that of their limited control systems and are due for an update. And of course nothing sadder than a expensive mount that is now a doorstop due a failed system.

There is nothing magic about the design of the systems. Anyone with basic hand skills can work with them. The magic is in the operating software. Developed as freeware by Howard Dutton and constantly improved by members of the Google OnStep group over the last decade it has been adopted as a commercial product by unrelated enmities in Asia. Yet it remains mainly a user directed and designed project. Do-it yourself is generally the least expensive path to converting or adapting OnStep to your project. An I encourage those interested in OnStep to take that approach.

I see my part as administering a group buy to save on the cost of parts for building the controllers. However, being too wise or lazy to administer group buys, I front the money to inventory the parts for commonly built controllers and recover the costs when kits are shipped. I use Paypal, they keep the books and assume performance on my part. 

The economies of buying part in units of up to 1,000 is considerable. Much of the cost of individuals trying to source enough parts for one controller is in the shipping expense. Pretty much everything for a controller is manufacture or assembled in Asia and shipped by air. This usually entailed a lengthy wait for shipments. I usually have most of the parts on hand, so it's just a mater of how slow I am and at least you can complain to me personally about that.

The OnStep Wiki has much of the information you need to accomplish your project. 

Answer to a recent inquiry:

Currently you are using a controller built around the Arduino Mega MCU. as the size of your controller causes no restraints on your choice. You are not trying to fit it neatly into the mount's casting. There are only three MCUs to consider; the Espressif ESP32-S, Teensy 4.1 or the STM32407ZTG6.

ESP32-S controllers:

FYSETC E4* https://onstep.groups.io/g/main/wiki/32747

R1-D32/Hujer Shield OnStepShieldESP32 - EasyEDA open source hardware lab

MiniESP3* 

MaxESP3*

MaxESP4*

Teensy 4.1-MaxPCB4*

*Up to 4 motors controlled

STM32F407ZTG6-BIGTREETECH SKR PRO V1.2 32 Bit, up to 6 motors controlled.

All controllers except the FYSETC E4 require purchase of motor drivers separately. The ESP32S controllers are pretty much arranged by price lowest to highest. The FYSETC E4 is currently $23 on AliExpress. The partially populated MaxESP4 is available from sales@graydigitalarts.com in various states of assembly from $12 to 110. These controllers are intended to be used with OnStepX, which is almost out of Beta. 

The Max and Mini ESP3 controllers are the same design with the Mini supporting 2 drives and a somewhat smaller footprint. The Mini comes assembled and tested for $45. The Max kit is $35 less drivers. $75 assembled and tested. The advantages the Max has over the FYSETC E4 are that it runs OnStep 4.24, is modular making repair and replacement of major components possible.

The D1-R32/Hujer is a simple to assemble Arduino format shield that plugs on to the WeMOS D1-R32 development board. A kit including the D1-R32 is $20. It has a RTC and WiFi and a guider/HBX port. It's basically the same functionality as the Mini in a smaller package. 

See Kits Available for what I have available.