Stepper or DC motor? Syringe Pump

Hi All. I am wanting to make a syringe pump using a linear screw slider and Adafruit motor shield v2, but not sure whether to use a Stepper motor or a DC motor. I have test with the Nema 17, but it seems too jerky (nature of stepper).Is a DC motor the way to go? Any suggestions on which DC motor?


Depends on the mechanical setup and purpose for the pump. Do you have an example link or a sketch?

If you need precision displacement/fluid delivery definitely a stepper. If your goal is flow fo a Dc motor. If you’re after pressure you might want a different or multi stage design.

Thanks Oliver. I’ll be doing drop/drip count from the syringe, so yes precision is needed. I haven’t tried microstep yet on the stepper. My rig is far from being assembled, so just thinking ahead.
Thanks for your input.

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Hey Peter,

Steppers are almost certainly the way to go if you’re looking for precision, the problem with other motors is coasting, because they don’t have a fixed endpoint when power is removed. The other option is to use a pressurized container at a fixed pressure, and then turn on and off a solenoid to get the drips you need to eliminate the issue entirely. Although it’d require some clever design work in order to stop as soon as the solenoid is closed.

You can improve the jerkiness by:
. Using microstepping. You lose some torque, however, so whether or not it works depends on your rig.
. Using a stepper with more steps per revolution (less travel per step).
. Using gearing so you drive the stepper multiple steps for each drip.
Using gearing with microstepping solves the torque issue and gives more preciser control over the flow.


Good idea Jeff :slight_smile:

One thing to watch out for if using a gearbox and going for accuracty is backlash - not an issue if you’re only driving in one direction but something you need to account for if driving in both directions.

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They will stop if you arrange a low value resistor or diode to be switched across the motor in the off position. The resistor or diode have to be quite large as even a fairly small motor can generate quite large currents (usually equals the stall current of the motor).
Cheers Bob

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Exactly, although it’d still likely not be the most optimal solution to use one of these motors as you can’t get any kind of feedback the motor will adjust to if there were changes in the power supply or connections to it that cause it to rotate at a different speed. It’s minor, and you can certainly get away with using them if you’ve got a mod such as that which Bob has described. However, if you’re looking for a more reliable system to use, either a solenoid based setup or stepper motor (as an extension linear actuator) would be your best option.

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Can get a bit messy but the technique mostly used in limit switch situations. NC contact cuts power to a motor and NO contact connects large diode across motor to stop it dead. There is often a very large amount of rotating inertia in this situation and overrun has the potential to cause much mechanical damage.
I have used the resistor solution to assist a mechanical brake on a coil winding machine where the mechanical brake had difficulty stopping a motor where it was supposed to stop.
Cheers Bob