Pololu DRV8825 and Arduino

Hello everyone, complete and total newbie here, so please be kind to my ignorance.

I really know next to nothing about Arduino, but I am very keen to learn, but I also have very limited time to complete this quick project.

[u]Overview:[/u]

I've got a ye'olde Vixen Polaris telescope mount that I've inherited from my grand dad, still in very good condition, and I want to motorize the RA-axis to be able to take some wide-field shots of the night sky when I go to a remote part of the Drakensberg in South Africa in a week's time.

I've done all the math and leg-work, but now comes the execution, which is the tricky part for me. I've found this thread that is quite helpful so far: http://forum.arduino.cc/index.php?topic=197943.0, but not really, as I don't know what I'm doing.

[u]Equipment:[/u]

Arduino UNO Pololu DRV8825 Stepper Motor Driver Wantai Stepper Motor 57BYGH420-4

[u]What I need it to do:[/u]

The telescope mount makes six rotations per hour of travel, thus I need the stepper motor to do the same, as smoothly as possible. The stepper makes 200 steps per revolution (1.8 degree steps), thus I need 1200 steps per hour, 20 steps per minute, 0.333 steps per second, and finally, one step every three seconds. Obviously I would like to improve that by using the microstep functionality to get more frequent steps. That's the rotation sorted out.

Then I need three buttons as well:

1) Stop/Start at the determined step speed to compensate for the earth's rotation (eg. Six/Hour) 2) Reverse (Is it possible to program it, that if it's pressed down, it starts slowly, then accelerates up to a certain fast speed?) 2) Forward (Is it possible to program it, that if it's pressed down, it starts slowly, then accelerates up to a certain fast speed?)

I think that's about it. Obviously I need to learn on my own, but I don't want to stuff something up and waste time and money, as I really need to finish this asap so that it can go through a test run as well, and I still need to sort out the remote power supply as well and do some fabrication for my camera mount.

Thanks everyone!

That stepper driver is a bit marginal for a 2 amp motor but your application may not need all possible torque so maybe it would work fine if you limit the current to 1.5amps or so.

Your first step (forgive the pun) should be to get a solderless breadboard and set up the motor and the Arduino so you can learn how to make the motor move. It should only require a short sketch to do that. I suggest you set your initial step pulse width to 1000 microseconds and a gap between pulses of 1000 microseconds and then you can experiment with shorter and longer gaps depending on how fast you want the motor to move.

You could control the number of microsteps with the Arduino but it is probably easier just to hardwire it with some jumpers as you probably won't want to change it once you have figured out a suitable arrangement.

...R

Hi Robin,

Yeah it's not a high torque application, I wanted a smaller motor as I didn't realise how powerful this one was, but unfortunately I couldn't get a smaller one with the correct shaft width, or a coupling that would match the smaller motor to the scope mount. None-the-less, the seller said I shouldn't have any problems.

I have got a breadboard as well to work with, I just need to go buy some accessories from the local electronics shop so that I can make a quick connect for the motor.

I'll have to do some reading and playing around with writing the sketches, but a mate of mine is keen to help out which is good.

Thanks for the tips!

You can try running the motor on a lower current than its rated for then, that will waste less power and reduce motor-hearing.