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i just bought a hobby telescope, it works well for being nothing much than a toy, the very problem is that the gesrs that should keep it stable are all plastic and very hard to tighten while keeping it steady.

So I thought to let the gears wide open and move it with arduino: you point the object manually then with 4 buttons move it by small steps.

I've tried to use a couple of servos i had at home, mg90s 2kg 180°; while 180° is enough for the purpose, first i don't think 2kg is enough for the X axis motor, second one is not very precise (using the default library). I know I can achieve better results calibrating the pulse manually, but maybe is better if I use better motors.

What motors (and why) would you reccomand? Servo or stepper?

Being for a hobby the budget is low, so very max 50$?

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  • It's really not an easy task to build a stable mount control on an unstable platform. There are good reasons why reasonable quality telescope mounts are in the $500+ price range. Will you be using it for astonomical objects (i.e. tracking)? – StarCat Feb 17 at 11:52
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I wouldn't use a servo for this. You don't have very fine control over the angle with a servo. Also with a typical telescope the focus is more on rather slow and precise movements, instead of fast ones.

Instead I would use a stepper motor. Depending on your exact requirements, these can be rather cheap to rather expensive.

Here also the mechanics come into play. The motor should not be attached directly to the axis, but instead through some gears (the axis of the telescope having the larger gear). That will allow for smaller, more precise movements and also lower the needed torque for the motor. Of course this depends on your actual telescope hardware, meaning if you can put a gear right to the axis. If not, you could limit the motor driven movement a bit and install a level, which then could be pushed or pulled by a nut on a threaded rod, which gets driven by the servo motor. This would be rather easy to implement, though you may need to correct for the different rotation behavior, when you get to the outer sides of the movement (for the actuator being linear, while the resulting movement is circular), by some mathematics in your code.

Since you want to keep your costs very low, you might wanna use the 28BYJ-48 stepper motor (including the fitting driver). In terms of stepper motors they are rather bad, but they are really really cheap and - depending on the gear ratio/level length/thread pitch - it might not matter that much for you. You could always update to a better stepper motor in the future.

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  • I agree with using a stepper motor. Some commercial telescope mounts use a normal gear motor with feedback from an opical encoder. – StarCat Feb 17 at 11:46
  • Thank for your reply. The main idea is to build something with a rotating plate (this way can be paired with some lights and become a quick tool to take pictures of small items, for example), and since here no problem i could use the cheapest motor with a gear and a belt, easy to do and to keep stable. For the up/down movement, considering that has to lift the weight of the telescope, I'll try your suggestion. I need to make some prototypes with the structure becouse would be nice to have a full 160° rotation. – Strae Feb 17 at 21:28
  • For the vertical motion a stepper motor would also be better than a servo. It ca give you more torque. Also: When you are using a gear or threaded rod with nut on it, the actual force is also multiplied. The mentioned stepper motors have a bit of slack, but I used them for a self build laser engraver and had OK results. Make sure, that you provide enough power to the motors, or you will have less torque – chrisl Feb 17 at 22:34

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