how to maka a telescope turn with high precision?

I would have gone with an equatorial mount.

From the picture he is putting some serious torque on the elevation motors.

DAB

I just read up on the German equatorial mount. A scientist in the first half of the 19th century made a mount that follows an object, the motion is driven by a counterweight.

Nice. No Arduino needed.

I always use an equatorial mount for astronomy.

Especially if I want to do photography. You need a fairly good mount and alignment, but the results are worth it.

DAB

thanks for the replies but I need a way to motorize it. anyone an idea?

If you google “diy motorized telescope mount” or something similar you will find lots of examples.  Also check astronomy forums.  In my opinion, the motor is the easy part.  The mount and mechanical parts, especially for a large telescope can be challenging.

I have stepper motors with worm gears on my telescope with a german equitorial mount.  I also made a “barn door” mount once for my camera that was driven by a stepper.  This is a very easy mount to make and It is relatively easy to maintain one degree precision over an extended period with such a setup.  Google...

BTW, It isn’t clear to me whether you are trying to find a spot in the sky (slew) with one degree precision or track.  Tracking only requires one motor for one degree precision over moderate timeframes with an equitorial mount and finding requires two.

I'm experimenting with telescope tracking at the moment. I've used a NEMA17 stepper motor with a 5:1 gearbox and used a DRV8825 driver controlled by Arduino. In theory you can make stepper motors more smooth using microstepping but in practice I've found it difficult to get the speed consistent. It surges for some reason. Perhaps I can improve it with a better driver or a higher gear ratio. You can get stepper motors with 100:1 gearboxes online.

Regarding precision the moon is about 1/2 degree or 30 arcminutes. Venus at it's largest is about 1 arcminute. I would suggest for accurate tracking for astrophotography you need to aim for around 1 arcsecond. I.e. one step of the stepper motor is usually 1.8 degree which is 1.8 x 3600 = 6480 arcseconds. If you gear it down by a 1:100 gearbox you get 64.8 arcseconds. That should reduce further by the ratio of the output of your gearbox to the gear it is driving which depends on your design but let's say it 10:1 which gives you 6.48 arcseconds. That's not bad but would probably still be noticeable. It's roughly the separation of the double stars in Alpha Centauri. With 4x or 8x microstepping you would just make it if you could get your microstepping to be smooth.

The precision of the equatorial axis is most important as it is the one that does the tracking. The declination is less so once you're on the object this axis doesn't move. If you don't have an equatorial mount you can track by moving both motors at the right speed (which is a little complicated) but even with perfect tracking the image slowly rotates which is a problem for astrophotography.

I personally think that a motor to drive focus is more important than the declination axis. Whenever you try to change the focus manually you bump the telescope and have to wait for it to settle before you can see the results of your focusing unless it's a very stable telescope. If people with different eyesight are looking through it, each person needs to focus it for their own eye. Having said that I know motorised focusers exist but they're not common.

I am not sure why you would need to mess with the focus, I thought with the stars so far away it is focused to infinity or there abouts.

regarding the motors, it sounds a bit like you have a lack of torque. Don't try to micro step too much, over 8 only makes movement sound smoother but adds no accuracy. (A common stepper is only 5% accurate on its primary step and you cant change that, add a heavy load like a telescope and it can easily ignore many of the micro-steps as they have no were near enough torque to move the stepper until they get to near a full step (4:1 or even 2:1)

What power supply are you using ?, and what motors

Examine the technology used to move satellite dishes to track birds in orbit or even solar panel arrays to follow the sun to explore some ideas.

I have difficultly transferring physical movement with mechanical movement. Mechanical movement left to right can result in physical movement of an object up and down. I find it hard to wrap my head around it a lot of the time.

I found these two practical technologies have developed products to accomplish the simple movement. The other thing is, that the materials are relatively inexpensive if you are experimenting.

A kit that is great for seeing is believing is the sparkfun pan tilt kit for raspberry pi. https://www.digikey.ca/en/videos/s/sparkfun/pi-zero-w-pan-tilt-camera-kit

I have assembled it and found I was exposed to concepts I wasn't able to visualize. It is not to pricey and rather cool to show friends especially if you complete the project and run the camera through a web page.

If you are interested, drop me an email and I can share some additional resources. I was compensated by a magazine publishers for providing a installation and review so I am unable to post those details in a public forum. I would bend the rules and share them privately if they are use.

Sean

I'm using Nema17 stepper motors and a 12 Volt battery and a poorly soldered circuit just containing the arduino and the stepper motor drivers. The voltage gets pulled down to 10 or 11 volts when I connect the arduino nano which I think is supposed to accept a 12 Volt input. So all in all a pretty lousy setup. I have ordered a variety of driver chips to try out and will be improving my power supply circuit. The TMC2130 'ultra silent' chip will be interesting as the DRV8825 can be quite noisy when attached to the telescope. Is a square wave from the arduino the best signal to drive the driver chip with?

Another issue I'm curious about is how to stop back-current from the motors from destroying the driver chip. If someone pushes the telescope manually the stepper motor creates quite a bit of back current and I'm pretty sure I've blown up chips by doing that in the past.

As you say the focal plane doesn't change when you are looking at distant objects but being able to control the focus without touching the telescope is desirable when you set focus in the first place, when you change eyepieces or when short-sighted people like myself take their glasses off and refocus to their eye. Also the thermal expansion of the telescope can affect the focus.

There's a lot to be said for good tracking on a camera. With the wide field of view of a camera with average optical zoom you could get some good shots that are too wide for most telescopes e.g. Andromeda.