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Pump control - Uni or Bi polar stepper motor? Answered

I am working on a robot that includes several annular gear pumps. We are using the MZR 2521,

manual: (please see section 5.5)

product page:

In the description they say that you can run the pump as if it were a stepper motor. This seems like it could be done perfectly with an Arduino, but I was not sure whether to treat it like a Unipolar or Bipolar stepper motor as the setup for each is quite different. Does anyone have any thoughts as to which it might be? Thanks so much.



5 years ago

The main difference in this context is that a bipolar motor is more 
volume efficient ( smaller machine ) because the coils are 100% used .

However the bipolar drive electronics is more complex then
the unipolar motors.

Remember the stepper motor has more torque at low speed,
So you must plan a ramp-up acceleration and ramp-down deceleration
before hand or risk loosing steps count in a dead reckoning system.

A positive displacement pump unlike an impeller pump does not
match the stepper as well as your PDF portends it does.

Never the less any stepper is a good choice in a pump metering application.


Hi iceng,
Thanks for your advice. We need these pumps to be extremely precise in the amount of solution pumped (<1ml). Also do you think that this would provide enough current?


Their stepper operated at 0.25A per phase.

If your stepper is similar in torque and efficiency to the described pump motor.
Then the 1A per driver of the 754410  H-bridge should be adequate for a 50% variation
of motor design latitude.

Remember to follow the heat sinking in your PCB design.
Take care how hot you make your stepper run, you don't want to singe the
motor wire winding insulation.
And give some thought to Steve's constant current suggestion in opposition
to the series resistor.

....and ramping is VITAL on heavy loads like these.

You don't get a choice how to treat it, its a bipolar motor. That driver is Ok, but smarter drivers have integral current limits, and you can bang the current on harder and faster with a constant current driver.

What a pretty pump. How much are they each ?