stepper motor
I am interested in using one of these cheap stepper motors for one of my projects, but need a step angle of ~2°. I came across the 28BYJ-48 and noticed that it has a "stride angle" of 5.625°/64. What exactly does this mean? I doubt it will give me the 2° accuracy which I desire, so maybe I could use a gear system to reduce that step angle further.
But in general, what is that stride angle referring to?
The maximum rate you can move a stepper motor is based on the shaft torque and coil current. Attempting to move too fast against too high a torque will cause the motor to become desynchronized with the step impulses and move unpredictably/uncontrollably.
Here's a generalized graph:
The whole curve shifts up and down with current.
Most drivers' speed will be orders of magnitude faster than any motor, the few exceptions are things with a bunch of protection/intelligence (of which the Darlington driver you linked has neither)
You'll need to consider how much current the motor takes, and compare it to the microcontroller's datasheet, which will state the maximum current draw on any pin.
Whatever you do, you'll also need to add a flyback diodes. When the MCU or driver attempts to change the current suddenly, the coil will generate back EMF (a possibly large voltage). Since you will be using current in both directions, you'll need 4 diodes.
My advice though would be to use an H-Bridge chip.
Best Answer
5.625 = 360 / 64, ie, there are 64 steps per revolution.
However, the actual number of steps can be some multiple of that, depending on how you energize the windings. 2 to 4 times that number is easily achieved, and microstepping drivers can provide substantially finer interpolated resolution.
Your specification is not very clear - you seem to say both 2 degree steps, and 2 degree accuracy. Probably you want 2 degree steps with an accuracy of some fraction of that.
64 steps is relatively course - 200 step motors are widely available.
If you are looking at mechanical reduction, consider toothed timing belts and sprockets instead of gears. They are have less critical needs for mechanical alignment, and run quieter. If your system must operate in both directions without slop, the fact that timing belts suffer minimal backlash when the direction of torque is reversed makes them strongly preferable versus gears.