Newbie questions about Stepper Motors

Hello, I know absolutely nothing about mechanics, I just bought an Arduino and was able to set it up to get a stepper motor spinning. I want to build a moving camera mount with it, then later a robot. But I'm having some very stupid problems I'm not sure how to best solve.

1) How do I physically connect the motor to other parts? I'm using a 28BYJ-48 5V Stepper Motor, it has this shaft that spins, but I don't know how to screw a plastic platform to the shaft. On every tutorial that I've seen, either it was a complete kit with motor + legs/wheels that already fit in it, or the gears to fit the motor were 3d printed. But I was wondering if maybe these things have a standard format so I can just buy some nuts or something on any hardware store that would let me screw it to something else? Is that how it works? So far I have just duct-taped it to other stuff, but I suppose that are better ways :S If I find an arbitrary motor on ebay, how to I search for some other parts to screw it to the rest of my machine?

2) From what I understand, the stepper motor offers no feedback to the Arduino about its current position, right? How do you guys deal with this? What if I need to know the position of the motor on my code? If I just store an estimate on a variable, that will be off when the system is turned off. I read somewhere people use "endstops" for this, I'm not sure how. Does that mean, that every time the whole thing boots up, you just try to move the stepper in direction of the endstop, when it stops, you now know it's at that position. Is this really the best way? This sounds like waaaay too much trouble for just getting the position of the motor.

3) When looking at datasheets of motors. What is the "speed ratio" and "reduction ratio"? Some robotics tutorials suggests I look for a motor with 120:1 ratio, but I have no idea what does that mean? Is that the same as "reduction ratio" or is it something else?

Thanks ^^

Stepper motors use shaft couplers and drive pulleys and special drive belts that are non-slip. You hva to count STEPS like Hanzel and Gretta and the bread crumbs to get back to your starting position

Most stepper systems don't need endstops because they have Opto+interrupter Home flags they use to Home on powerup. They immediately start moving towrard home (which is always in the same direction because the S/W neber allows the motor past the home flag by more than 5 - 10 microsteps and then it is forced to reverse 20 microsteps , meaniing it is always "South" of Home.

I like the idea of the opto sensor, I'll look up into it. Thanks :)

Does that mean, that every time the whole thing boots up, you just try to move the stepper in direction of the endstop, when it stops, you now know it's at that position. Is this really the best way? This sounds like waaaay too much trouble for just getting the position of the motor.

It might sound like hassle but that is what you have to do to find an absoloute position.

A reduction ratio of 120:1 means that for every 120 revolutions of the input shaft the output shaft turns round once. Less speed but more torque.

Think about it. If that is "way too much trouble " to get the motor position , then just pay "way more money" for an absolute encoder. End of story. If your cheap, don't complain.

You mean a "rotary encoder"? I had no idea what that was before you mentioned it, I just looked it up and looks exactly like what I need. Thanks a lot for the help!

There’s more than one type. The top of the line is called ABSOLUTE encoder because the position is readable without power to the motor. You can turn the shaft with your fingers and watch it change. The less expensive kind are called incremental and there’s also quadtrature encoders.

A hall effect absoloute rotory encoder is less that $10 so it is not that much although optical ones will be in excess of $200.

Grumpy_Mike:
A hall effect absoloute rotory encoder is less that $10 so it is not that much although optical ones will be in excess of $200.

Interesting page here about lots of encoder technologies:
http://machinedesign.com/sensors/basics-rotary-encoders-overview-and-new-technologies-0

The top of the line is called ABSOLUTE encoder

This comment is a reference to the optical absolute encoders Mike is referring to.