Some questions about stepper motors

Voltage motors
Currently I use unipolar motors in my robot and just one ULN2803 as stage of power. To save power and improve torque, I decided use bipolar motors.

Pololu offers a variety of stepper motors and stepper motors controllers. The feed motor varies a lot, from 2.7V to 10V.

What after all is really the difference in voltage? How voltage affects motor performance? I have seen motors with all possible combinations of voltage, consumption and torque.

In my beginner’s opinion, it would be better to have motors with low voltage because it would allow use a lighter, compact and cheaper batteries. That´s true?

Pololu has some bipolar control drives, but all they report a relatively high minimum voltage:

From A4988 Stepper Motor Driver Carrier:

So, this driver can not be used with less than 8 volts motor? Or I miss something?

To make the motion smoother, currently I use the time between pulses as a way to accelerate and brake the robot. For example, the movement always starts with 40ms pulses and gradually decreases until it reaches cruising speed with 6 or 7 ms. To stop is the same thing, but in reverse.

I was wondering if I could have the same effect keeping the time between pulses constant and varying the step size. Then the movement initiate with the maximum microstepping and would ranging gradually until reaching the full-step, that would be the cruising speed. It’s work?




Your first two questions are answered by the first FAQ on our stepper motor driver pages:

Please let me know if you still have questions after reading this.

Regarding your microstepping question, changing the microstepping resolution is probably not a good way to gradually accelerate or decelerate a stepper motor because it will change the speed (assuming you keep the pulse rate on the STEP pin constant) by a factor of two.

- Ben

Hi Ben, and thanks for answer.

I was hoping to stop using 12 volt batteries and use 6-volt batteries. It’s easy to find 6 volt batteries with high amperage (like 5000 mAh) and they are much smaller, lighter and cheaper than 12 volts batteries. But if I use the Pololu drives then I will be forced to continue using 12-volt batteries, even if my motors use less than 6 volts. I do not see this as an advantage, unless the voltage really make a lot difference in motor performance.

As I understand it, a higher voltage allows faster pulses. Whereas two motors with different rated voltages, each one operating at its nominal voltage, the motor with higher voltage will achieve faster pulses than the other. So motors of 2.7 volts are slow, 12-volt motors are faster. Is this true?

Perotti, a stepper motor rated as a “2.7v” motor will have a lower inductance than one rated at “12v.” This means if they are the same size, and same type, you will be able to step the 2.7v ones faster.

In the case of DC motors, a “6v” rating might mean you don’t want to run it much higher than 6V. But in the case of stepper motors, the voltage rating is really just describing the impedance of the windings. In some cases, it makes sense to get a higher voltage stepper motor, but for most hobbyist applications you want a lower voltage motor.

As an example of the problems with higher voltage stepper motors: Right now I am using NEMA14s that are “12v” rated. I’m having a hell of a time running them above 800steps/seconds when powering with 32v. I’ve been forced to spend $100 to upgrade my system to 40V in a desperate attempt to spin the motors faster with sufficient current (I’ve measured to determine that the problem is I’m not getting enough current into the motors.)

You should carefully read the links that the pololu guy offered. I believe they have answered all of your questions.

Remember, a 12v 25000mAh battery has as much energy as a 6v 5000mAh battery. You’re better off supplying ample voltage to a stepper motor system. It’s best to leave yourself leeway.

Hi Tomek, thanks for the reply, was quite enlightening. Actually this question about motors voltage was explained much better for you than the indicated link, especially because I have no training in electronics, my knowledge is pretty basic.

Thank you again.

Good luck! :). There might be a lot of background to read, but we’re alive right now in a time with an abundance of resources for learning electronics. It’s there, on the internet, but it might take some time to gather all the pieces.