New Project

I have a new brainstorm project that I would like to develop that involves stepper motors and possibly some optic tracking device and maybe some solenoids. Is there anyone out there willing to take me under their wing and give me an education on what i need and how to go about doing it? I have computer knowledge but not much knowledge of stepper motors and whats required to make them run and how to program and interface them.

Thanks,
Steve

Stepper motors need a driver to run them. Steppers have different control methods or interfaces with logic circuitry, but most used one is with step/dir/en. These are 3 wires between your arduino and your stepper driver, that are digital logic, e.g. can be zero (zero volts) or logic 1 (5v). En is a logic input that has two states, when is 5v, the driver cuts off current to the motor (driver outputs are disabled), and when is 0 then outputs are enabled. Or, en can be exactly the other way around, exact way should be read from stepper ic datasheet, for example tb6560 are the other way than allegro chips. Dir can also be 0 or 1, so when its 5v motor moves one direction, when its 0v moves the opposite. And step is a square wave with certain characteristics also from datasheet, specifically how small the plateau of 5v can be to still be intrepreted as a command. Each square from the square wave is a command for driver to execute one move. This move can be a full step or a microstep, which is a jumper setting. If the motor is in full step mode its a move of 1.8 degree if that is motor specification 200 steps per revolution, or 0.9degrees for motors that are 400 steps/rev. If its half step mode (1/2) then a step pulse commands half of a full step angle, if its 1/4 or 1/8 or 1/16 then the move is accordingly. So to interface the stepper driver you need an arduino board, and you either write your own firmware or borrow one existing firmware. From the said arduino put 3 wires for step/dir/en to the stepper driver and you can control your motor.

Reprap uses bipolar motors, which means the voltage is to be reversed along entire coil length. You need a bipolar motor (4 wire) or a unipolar motor (6 wire) to which you will ignore the middle coil taps, practically using it also as a 4 wire bipolar. But for example a 5 wire motor is no-go. The stepper has a label with usually with V and A and from that you can deduct coil resistance. This coil resistance needs to be as low as possible, for example maximum about 3-4 ohm but would be much better if lower. E.g. if it would approach 1ohm would be even better. Dont think the voltage on the label is the voltage intended for the motors supply, its just a rating from ohms law, for example you will run a 3v labeled motor at 12v supply, and thats not an error, its how it should be. Stepper driver beside doing coil current reversal also controls and limits the current in the coil, and it has a potentiometer setting to set max (peak) coil current. So if you think of a dc motor, that draws the current it wants to draw, so the voltage from ohm law is in fact the voltage intended to be supplied with. But the stepper motor is poor and only gets the current the driver lets him have, and the ohms law voltage means the real life voltage better be many times multiple, because if the switching frequency is fast the current level may not have time reach its intended value in due time. Sort of the voltage across the coil builds the flux to which the current is proportional, and if current is low than flux was not enough. Also the driver limiting the current has the power effect. For example you have a 12W motor and you will run it at 12V and 1A that does give 12W indeed, but if you set the current at 0.5A, it will have only 6W.

I'm sry my pedagogical skills are lacking, but if you spend like 1-2 hours reading this forum i think you will get the hang of it. Enjoy the read and good luck!

With a modern micro stepping driver, the current in the coils is a constant frequency sine wave when the motor speed is constant. As you change the speed the drive is still a sine wave, it's just the frequency that changes. That's not really surprising since you are using the stepper as a multi pole synchronous AC motor. If you run the motor slowly, then ohm's law does indeed apply. It's only at high speed that the inductance of the rotor has any real impact.

Each time the voltage is applied to the coil, the voltage starts to builds the flux, and current is proportional to said flux. And what is significance of ohms law, it sets the current final value for rising edge formula. But it never reaches that value coz driver limits it before reaching it, but nonetheless the natural rising edge does aim at that final value. If ohms law gets to apply more than this afterwards, it means the coil resistance is way too big, and the current setting in the driver becomes irrelevant because simply never reaches it. Other ways saying the driver doesnt get to limit the current wave because the currrent wave is smaller than the driver limiting setting. Which should not happen if the motor and driver make a good pair.

Like for example pairing a 12v psu with a 24ohms coil and setting the driver current to 1A peak, it will never actually reach 1A because the theoretical max is 12v/24r=0.5A, this is dc value even ignoring s*L impedance which would make it much lower at high frequencies. Basically this is what ppls posting here should avoid, and this is why it matters to make a good match between driver and motor.

Generally speaking there are 2 types of steppers, and there is some correlation between some of the characteristics on the labels. For example for higher voltage motors, like 12v or higher, its very likely that they are higher voltage labeled coz they also have high coil resistance. And because its same form-factor (nema number is the size of the motor), so in same space, high coil resistance means thinner wire with more turns, so this situation more or less it ends up in being more inductance. And vice-versa.

Its not always good to generalize things and it can even be dangerous sometimes. But as for me being a generalizing twat we will say types are more or less something like this (values given for exemplification, not classification of sorts) :

1) higher voltage (12+ volts), low current (0.5a or less), higher coil resistance (6-12ohms and higher) , higher impedance;
This type 1) is really not that good of a match neither for reprap drivers nor the 12v psu. These are probably best run with much higher voltage than 12v. Its not to be said these steppers wont rotate with our drivers and 12v, they will rotate, but probably have power lower than rated and somewhat poor performance, even worse at speeds.

2) low voltage (3-4 volts and lower), higher current (1.2a and higher), low coil resistance (3-4 ohms or lower, ideally aiming at ~1-1.5ohms), and low impedance;
This type 2) is best match for reprap usual drivers with 12v psu.

The point is that there is already current flowing in the coil in a normal micro stepping setup. You very much do *not* start and stop the current with each step. The motor is moving at a constant velocity. The change in current is very small with each step.