how to maka a telescope turn with high precision?

Stepper motor will be best... Nema17 is standard low cost stepper motor mostly you find in 3d printers...

Further for automatic telescope you need 3 stepper motors for azimuth angle, elevation angle and one for change focus..

For control stepper motors you can use arduino uno or Arduino mega with stepper motor driver shield based on A4988 or other drivers from allegro.

Also you will need magnetometer hmc5883l for get reference of azimuth respect to North...

You can use some online tool to get azimuth elevation angle of known starts with reference to geographic location of telescope...

In continuation with previous reply... You can write java, python or c software to calculate and pass azimuth elevation angle from host computer to arduino via usb...

Or make Android app that do similar thing via Bluetooth and arduino with hc05 bluetooth module

Ohh as you have posted your question in raspberry pi group... Another solution is use raspberry pi itself as standalone host computer and stepper motor controller.. with onboard WiFi and Bluetooth on raspberry pi ... It will be true automatic internet connected IoT based telescope which you can control from anywhere in the world and get feed of video of image in realtime

Hi Simon,

You can greatly multiply the precision if you put a worm gear on the stepper and use it to drive a large gear.

John

Hi Simon,

For the Azmuth a clock motor would be better than a stepper as you will see a quantized step with the stepper and the clock motor would be able to track smoothly.

John

Can you provide a link to a "clock motor"?  I haven't explored those.

-Sean

I would think that having a stepper control the focus would be unnecessary. It depends a bit on what you're looking at, but when stars are far away, planets (other than earth) are not close enough to require a change-of-focus.

Even when you gear things down, the steps from a stepper will be noticeable if you're going to try track the stars. I would recommend the strategy: Point the telescope at the area you're interested in and take a series of pictures. Combine the series of pictures using software. This should give you better results than trying to keep sub-pixel accuracy in pointing the scope. The software to do that was described on Hackaday. Not sure if it is already on github.

Here is a link to the wikipedia page on hysteresis synchronous motors. These motors are commonly used in clock mechanisms and timers that use mains voltage for power. I have seen similar type motors used in azimuth drives on telescopes so that they can track contra the rotation of the Earth. I called it a clock motor as it will  have to be precise enough to to maintain telescope position against the rotation of the Earth particularly if timed photos are to be taken.

https://en.wikipedia.org/wiki/Synchronous_motor

John

There are many examples of automated telescopes with open source designs and software available with a websearch.

Depending upon what you are doing, you will need much better than 1 degree accuracy.

The stepper motor approach is probably the cleanest, though you might want to add a star tracker camera to get smooth tracking on star targets.

You will also need to account for sun, moon, planet and comet tracking.

For Asteroids you usually need time exposures, so you use the star trackers.

The timing issues are fairly straight forward depending upon your telescope mount.

Are you using an Azimuth/elevation or equatorial mount?

DAB

Maybe ask my pal thecurrensource?