am i right if i believe that i have a real stable rpm when i use a stepper motor with a certain amount of ticks per minute? what happens when the torch on the axle is higher than the power of the actual coil? a sudden still-standing? or does the motor a slowing down, depending on the relationship between motor power/force on the axle?
i have got an orangutan SVP-1284. would i need an any additional hardware for controlling the motor?
With a stepper motor, you control exactly when it takes a step (and the step size is fixed by the geometry of the stepper motor itself), so you have total control over motor speed and position. As long as your step commands are sent at a steady pace, the motor speed will be steady, unless the load is too high for the speed you are trying to achieve.
As torque is applied to the stepper motor at some point that torque will cause the stepper motor to start missing steps. When the torque gets high enough the stepper motor will stop or even move backwards. Keep in mind that the torque that a stepper motor can deliver goes down as the step rate goes up; at some point, the stepper motor will not be able to keep up, even with no load (at this point it will generally just abruptly stop turning entirely).
You should be able to control the motor with the SVP-1284 since all you really need to drive a bipolar stepper motor are two H-bridges, but it would probably be easier to use one of our stepper motor drivers (these also allow for better performance). Which driver you choose will depend on the stepper motors characteristics.
thanks, sounds great in general. may i ask you something about the specifications?
what i need is a speed around 80-100 rpm with a relatively high torque. is that speed possible with the most powerful stepper of the pololu-program?
and what would be the maximum force at this speed? can i apply more than 4v to this motor (i have got a 12V transformer). or should i look for an other stepper motor?
You can get a good idea of the torque you can expect as a function of speed on the “Pull Out Torque” graph on the stepper motor pages.
You can supply more than the rated voltage if you use a driver that actively limits the current; you can find out more about that here.