What type of stepper motor should I use in my project and how do I control them?

Question

I'm building a video camera pan and tilt head. Here's what I'm getting at:

I'll need one motor to control the horizontal rotation of the camera, and one for the vertical. The horizontal motor shouldn't meet much resistance, as I'll be using bearings to carry the weight.

The vertical motor on the other hand, will have to move the camera to a position and hold it there. The camera might be anything up to 5kgs. I'm designing it to obviously be as balanced as possible minimising strain on the motor, but there may still be a fair amount.

I'm using stepper motors because I need to be able to do repeatable movements, as well as extremely slow movements, e.g. move 2 steps, wait 10 seconds, move 2 steps again.

I've been looking at the SparkFun stepper motors, but I've been recommended Farnell and have been completely overwhelmed by choice.

So what kind of stepper motors would you recommend? I'd even been thinking of using two different types of motors, given the different stresses they'll be under. For instance, using this for pan and this for tilt. I'd tried calculating the holding torque from the 125 oz.in figure, but haven't come up with anything meaningful.

And finally, as I'm going to be controlling this from an Arduino, what is the best way to connect up the two stepper motors to the Arduino? The SparkFun stepper motor driver doesn't seem very cost-effective, given I'd be using two of them at $16 each. What would you recommend?

Just to be clear, I don't mean this to be a shopping-list type post. I'm asking whether the motors I mentioned are suitable or not, and if not what kind of things I should be looking for.

Answer 1

One important factor when working with stepper motors is hold torque. You can do some simple calculations based on your camera weight and platform radius to determine the torque due to gravity, and your hold torque should be a fair about larger than that or the motor will slip. You'll also need stepper motor drivers in order to control the motors and provide enough current as well as the proper signal to control the motor. I've had experience with the Pololu A4988 I'm conjunction with Arduino; it's simple to use and only used 2 digital IO pins (at minimum). You can also spare more pins and control things like the driver enable, etc. As for actually choosing a motor, that can be tough. I'd pick a price range and form factor that you'd like to be within and use that to narrow it down. I'd also stay away from the spark fun motors as they are usually on the more expensive end and not the best bang for the buck.