Help getting started on Telescope focuser idea..

Using Arduino Motors, Mechanics, Power and CNC
1

Hello all,

I am very new to the Arduino and also these pages. I have not done any programming before so I am diving in feet first and am hoping some of you may be able to help.

I have not bought an Arduino board yet but plan to on advice from you guys..

My project idea is, I hope, a simple idea but I do need help on getting started. I plan on using an Ardrino board and a Linistepper v2 board to drive a 6 wire unipolar stepper motor to drive a telescope focuser. I may be pointing in the wrong direction but, this is the way I see it working.

What I would like to see is having two momentary push buttons for inward and outward movement of the focuser, or as it would be, the forward and reverse directions of the motor. I would also like to see some way of changing from slow speed few steps per second to fast. with full forward and backward movements.

I think from reading, I can use the +5v line on the Arduino board to drive the linistepper by connecting it to pin 9 on the board, but also use an external supply for the steppers, I think I used 12v on my last linistepper project. I think I would need to connect the direction and step lines to pins 1 and 2 of the digital side of the Arduino, is this correct so far? With the speed changing this could be a single push button or on off switch to select between fast and slow, but not sure how I could connect this to the board.

From here I am at a blank as I do not know enough about the arduino (I am still reading up on it) I still have to work on a sketch to control the motor from the arduino (which I am hoping someone has already one the hard work and has some code I could use as a foundation for the project) I also need to know which Arduino to use, from what I see there are several different packages available. I was basing my ideas on the Arduino UNO R3. Would this be suitable?

I hope I have made this idea clear enough, I think the first thing would be for me to get the Arduino board and play around with it? So should I got for the UNO or is there something else out there which is more suitable. I would like to continue to use the linistepper since I do know it works, and it works well.

Anyway thanks for reading this long winded thought, I look forward to your responses.

Regards,
Andrew
South Australia.

2

for motors always use an external supply

variable speed: the longer you press a key the faster the speed could be. (remember the start of the key press)
You could make a ZERO position by pressing both buttons simultaneously.

(Not on Arduino UNO)
If you use a CCD you could use a python script using the PIL library to search for focus automatically.

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Which motor are you thinking of? For unipolar its usually easiest to drive
from a simple ULN2003 or ULN2803 if the current demand isn't too large,
and the Stepper library will sequence it for you.

4

Thanks for the input guys.

Mark, the stepper is a unipolar Nema17 type motor, quite small rated at 900mA from memory (I don't have it in front of me) I was trying to avoid using another component and had the driver here along with the motor, I know they work together well. I was thinking of using the idea from this page... jonandnine: Stepper motor control using Arduino and L293 which uses a L293D but instead of this I was hoping to control the step and direction function of the Linistepper. In the linistepper documentation it talks about the change in direction by having one pin either High, or Low. (not exactly what this means, but I am assuming one has +5v or pulled to ground and the other is open?) The linistepper doc is here... LiniStepper, lini, stepper, linear, 6th microstep, linear microstepping stepper motor driver, constant current linear driver, circuit Linistepper boards, LiniStepper kit, hobby stepper, robot stepper driver kit, CNC stepper driver kit

So from this I am able to press one button to pull the direction High, and the other to Pull it low, to select forward and reverse. I like the idea of the Potentiometer also for speed control.

I bought a book by Simon Monk called "Programming Arduino" to help me along with the programming side of it, but as you can probably guess, I am very much a novice.

I appreciate your replies.

5

Hi Andrew,
Sounds like a cool project! I've only been tinkering with stepper motors for a few weeks, but I've been an ATM for many years and have been using Arduino boards for various projects for the past 4 or 5 years.

Here are some things I think you should consider.

It's easiest to start with an UNO board and it's easy to prototype with a lower power cheap stepper powered through a USB port.
You can get a 28BYJ-48 stepper motor with a controller board very cheaply (<5 US$). It has a gear reduction of a little less than 1:64, and you will find a number of threads on it in this forum. It sources ~300mA, and has a surprising amount of torque due to the gear reduction. You might find it does what you need for your project, but if it doesn't, you haven't wasted much cash. It's significantly smaller and lighter than a NEMA 17 motor. The NEMA 17 and an UNO will make for a bulky focusing system.
After you've prototyped your motor system with an UNO board, you might look into a pro mini board for your final project.
It's easy to use a nonstandard Arduino/Freeduino board once you've become familiar with the UNO, but I wouldn't recommend starting with one.

One thing you want to consider is whether a given stepper motor and drive train will give a small enough increment to give a good focus. If you're trying to focus an F4 Newtonian optical system you need to be more precise than if you have an F15 refractor!

I'm thinking about using a stepper motor to build an equatorial platorm for a 10" Dobsonian telescope. I bought some of the 28BYJ 5V motors because they were cheap/low power so I could teach myself about how steppers work. I learned a lot and am now planning to use one for a barn-door camera mount( a much simpler project!). If you decide to try one, there are a few tricks that are good to know up front:

  1. The controller board has control inputs labeled 1-4, but the motor itself has two wires switched so that the correct pulse sequence to drive the motor is 1-3-2-4. This can cause more than a little confusion because the motor still works at low speeds if you connect it 1-2-3-4, but with poor performance and it won't work at all at higher speeds!
  2. The standard Arduino stepper library works with this motor but not very well. There are several other libraries, example codes you can find in the various 28BYJ threads that work much better.
  3. The exact gear ratio is not quite 1:64 - l don't have my notes with me now, but look around and you will find the actual ratio.

I look forward to hearing how your project progresses!
andy

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Hi Andy, all.

Thanks for all that information, now thats an interesting little stepper, I had not seen that before. So the 28BYJ runs directly off the Arduino board via the ULN2003 board? this may be a better option.. as MarkT previously had said. As you say the NEMA17 is quite bulky, and I had it here so I thought about only using that. I will check out the 28BYJ motor and some sketches and see if I can find something that will work or modify to make it work, will let you know how it goes. Still have yet to get the UNO board, which once I have that, it may help since I can see whats actually changing in the code then. I saw those motors and board for about $4AUD on ebay, so cheap it worth just getting it to try out..

Thanks again.